cas 112926-00-8, Silica gel | Articles data

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The hydration behavior of Ca-P-Si system via mechanochemical treatment
In the present study, the Si-substituted amorphous calcium phosphate (Si-ACP) was prepared via a dry-mechanochemical method, and the hydration behavior of Si-ACP was investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electronic microscopy, and the determination of the setting time and compressive strength. The results showed that the mechanochemical treatment had a great effect on the resolution property of Si-ACP, which induced the different hydration behavior. With the presence of Si, the hydration product of Si-ACP showed better results of cell proliferation and metabolic activity, which were characterized by the methyl thiazolyl tetrazolium assay (MTT) with mesenchymal stem cells. This work was expected to have a guiding effect on the study of calcium phosphate cement.
Yu, Tao,Ye, Jiandong,Zhang, Shujiang
p. 2990 - 2993
(2010)
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KINETIC STUDY ON HYDROLYSIS OF SILICON PHOSPHATE IN AQUEOUS ALKALINE SOLUTIONS.
Kinetic study of the hydrolysis of silicon phosphate, Si//3(PO//4)//4 (hexagonal), was carried out in borax buffer solutions (pH 5-12, temperature 20-50 degree C) to investigate how it acts as a hardener for alkali silicate adhesive. The silicon phosphate was found to be hydrolyzed with a resulting release of orthophosphate ion, soluble silicate ions, and colloidal silica under mild conditions; the decomposition rate increased with decreasing the particle size of the phosphate and with increasing the pH and temperature of the buffer solution.
Saeki,Narita,Naito
p. 1591 - 1595
(1984)
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AFM studies on the difference in wear behavior between Si and SiO2 in KOH solution
Wear behavior between a Si tip and a SiO2 film in KOH solution at various pH values has been examined by using an atomic force microscope. We found that the Si tip removal amount strongly depended on the solution pH value and was at a maximum at pH 10.2-12.5. This result indicates that wear behavior of the Si tip is similar to that of actual chemical mechanical polishing of a Si wafer. It was also found that the Si removal volume in moles was approximately equal to that of SiO2 irrespective of the solution pH value. This equality implies that a Si-O-Si bridge is formed between one Si atom and one SiO2 molecule at the wear interface, followed by the oxidation of the Si tip, and finally the bond rupture by the tip movement and the silica species including the Si-O-Si bridge is dissolved in the KOH solution.
Katsuki, Futoshi,Kamei, Kazuhito,Saguchi, Akihiko,Takahashi, Wataru,Watanabe, Junji
p. 2328 - 2331
(2000)
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Functionalized mesoporous materials for adsorption and release of different drug molecules: A comparative study
The adsorption capacity and release properties of mesoporous materials for drug molecules can be improved by functionalizing their surfaces with judiciously chosen organic groups. Functionalized ordered mesoporous materials containing various types of org
Wang, Gang,Otuonye, Amy N.,Blair, Elizabeth A.,Denton, Kelley,Tao, Zhimin,Asefa, Tewodros
p. 1649 - 1660
(2009)
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Study of Ge bonding and distribution in plasma oxides of Si1-xGex alloys
Secondary ion mass spectroscopy (SIMS) and Fourier transform infrared (FTIR) absorption have been studied in thin oxides of Si1-xGex grown by plasma oxidation. SIMS analysis reveals that Ge can migrate to the oxide film surface leavi
Seck,Devine,Hernandez,Campidelli,Dupuy
p. 2748 - 2750
(1998)
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Effect of Mie resonance on photocatalytic hydrogen evolution over dye-sensitized hollow C-TiO2 nanoshells under visible light irradiation
Light utilization is one of the key factors for the improvement of photocatalytic performance. Herein, we design C-TiO2 hollow nanoshells with strong Mie resonance for enhanced photocatalytic hydrogen evolution in a dye-sensitized system under visible light irradiation (λ ≥ 420 nm). By tuning the inner diameters of hollow nanoshells, the Mie resonance in hollow nanoshells is adjusted for better excitation of dye molecules, which thus greatly enhances the light utilization in visible light region. This work shows the potential of Mie resonance in nanoshells can be an alternative strategy to increase the light utilization for photocatalysis.
Yao, Xiaxi,Hu, Xiuli,Cui, Yingying,Huang, Jialei,Zhang, Wenjun,Wang, Xuhong,Wang, Dawei
p. 750 - 754
(2021)
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Synthesis of magnesium silicate by heat treatment of sols and mechanical activation of solid components
A layered magnesium silicate, an analog to natural talc, was synthesized by mechanical treatment of a mixture of magnesium hydroxide and hydrated silicic acid powders, as well as by heat treatment of aqueous dispersions containing magnesium hydroxide particles and silica sols prepared from different precursors.
Dudkin,Vasyutin
p. 751 - 755
(2011)
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Synthesis of surfactant-templated silica films with orthogonally aligned hexagonal mesophase
Thin silica films with orthogonally aligned hexagonal close-packed cylindrical structure are synthesized by dip coating silica precursors and poly(ethylene oxide)-polyproplyene oxide (PEO-PPO) triblock surfactants (P123) onto modified glass slides. All films cast from this sol display 2D hexagonal pore structures (a a?? 6.2 nm) under transmission electron microscopy (TEM). However, X-ray diffraction (XRD) shows that confining freshly deposited films between two chemically neutral modified slides completely aligns the pores toward the direction orthogonal to the substrate. Equally effective alignment is obtained by using slides modified with either a random PEO-PPO copolymer or P123 itself. The channels in films cast onto unmodified slides, onto modified slides which are exposed to air, or onto modified slides which are exposed to unmodified glass slides align at least partially parallel to the substrate. Parallel mesophase alignment is also observed in a control experiment with a sol containing the nonionic surfactant template decaethelyne glycol hexadecyl ether (Brij-56) sandwiched between copolymer-modified slides because the surfaces are not chemically neutral toward Brij-56. This study confirms that it is possible to use substrate surface chemistry to control the orientation of mesophases in mixtures of reactive silicates and low molecular weight nonionic surfactant templates. ? 2005 American Chemical Society.
Koganti, Venkat R.,Rankin, Stephen E.
p. 3279 - 3283
(2005)
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Self-assembled-monolayer film islands as a self-patterned-mask for SiO2 thickness measurement with atomic force microscopy
A novel method for measuring ultrathin (2-12 nm) SiO2 film thickness is discussed. The process consists of: (1) formation of octadecyltrichlorosilane (OTS) self-assembled-monolayer (SAM) islands on SiO2 of which thickness to be measured, (2) removal of the SiO2 layers not covered by the OTS-SAM islands, and (3) measurement of the height difference between the etched and nonetched areas by atomic-force-microscopy. The OTS film is good resist against HF and its islands can be regarded as self-patterned-mask. Practical usefulness is demonstrated not only by the compatibility of the measured values but also by the short measurement period resulting from the -~-directness of the method.
Komeda,Namba,Nishioka
p. 3398 - 3400
(1997)
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Development of Highly Active Silica-Supported Nickel Phosphide Catalysts for Direct Dehydrogenative Conversion of Methane to Higher Hydrocarbons
The direct dehydrogenative conversion of methane (DCM) to higher hydrocarbons was investigated over silica-supported nickel phosphide catalysts (NixPy/SiO2) over 1023?K. NixPy/SiO2 catalysts were prepared by precipitation method to promote formation of nickel phosphide (Ni2P) as an active phase for the DCM reaction. Characterization studies of the NixPy/SiO2 catalysts with different P/Ni molar ratios were conducted by a X-ray diffraction analysis, a H2-temperature-programmed reduction spectrum, a scanning electron microscopy image, a X-ray absorption spectroscopy and a N2-adsorption measurement. Catalytic activity tests for the DCM reaction were conducted using a conventional fixed-bed reactor. Products of C2H4 (ethylene), C2H6 (ethane), C2H2 (acetylene), C3H6 (propylene), C6H6 (benzene), C7H8 (toluene), C10H8 (naphthalene) and H2 were analyzed by GC-TCD and GC-FID instruments. Different degrees of the Ni2P phase and character were observed for the NixPy/SiO2 catalysts from characterization studies. Data from characterization studies indicated that smaller and dispersed Ni2P particles were obtained by precipitation method as compared to that of impregnation method. NixPy/SiO2 with a molar ratio of P/Ni = 3.0 showed optimum catalytic performance with 3.28% of methane conversion, 1.93% of total product yield, and 60% of selectivity to hydrocarbons. The experimental results of the effects of reaction temperatures on the product distributions and activation energies indicated that the Ni2P phase successfully activated the C–H bond of methane and selectively converted to ethane. Ethane thermally converted to other higher hydrocarbons in the gas phase without the participation of the catalyst. Graphic Abstract: [Figure not available: see fulltext.].
Dipu, Arnoldus Lambertus,Nishikawa, Yuta,Inami, Yuta,Iguchi, Shoji,Yamanaka, Ichiro
p. 199 - 212
(2022)
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Synthesis of ordered porous SiO2 with pores on the border between the micropore and mesopore regions using rosin-based quaternary ammonium salt
A novel, sustainable, rosin-based quaternary ammonium salt, dehydroabietyltrimethyl ammonium bromine, has been applied for the synthesis of ordered hexagonal supermicroporous silica with nanosheet morphology. Unlike the conventional short chain surfactants, rosin-based surfactant possesses a rigid group of a three-ring phenanthrene skeleton. Such a hydrophobic group gives the surfactant a large total volume and small effective headgroup area, which are beneficial for the formation of 2D hexagonal phase. XRD, N2 adsorption-desorption, TEM, and SEM are used to characterize the samples. The results indicate that the molar ratios of mixture of silicate source, template agent and inorganic acid in the synthesis system have great effects on the regularity of the pore structure. The synthesized material possesses large surface area (1229 m2 g-1), high pore volume (0.59 cm3 g-1) and narrow pore size distribution (centered at about 2.03 nm), which is on the borderline between the micropore and mesopore regions. Such a material will be attractive for applications in separations and catalysis because of its potential shape and size selectivities.
Wang, Peng,Chen, Shang-Xing,Zhao, Zhen-Dong,Wang, Zongde,Fan, Guorong
p. 11223 - 11228
(2015)
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Microporous SiO2 with huge electric-double-layer capacitance for low-voltage indium tin oxide thin-film transistors
Electric-double-layer (EDL) effect is observed in microporous SiO 2 dielectric films deposited at room temperature by plasma-enhanced chemical vapor deposition method. Indium tin oxide thin-film transistors gated by such microporous SiO2/
Lu, Aixia,Sun, Jia,Jiang, Jie,Wan, Qing
(2009)
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Porosity effects on properties of mesoporous silica low- k films prepared using tetraethylorthosilicate with different templates
A series of mesoporous silica films with different porosities and different pore sizes were prepared using different templates or different template concentrations in tetraethylorthosilicate colloid solutions. The amphiphilic templates such as cetyltrimethylammonium bromide (C16 TMABr), Brij-56, Tween80, and Pluronic P123 were used. To investigate the effect of self-assembly surfactants on the film properties and to make a comparison, polyethylene glycol (molecular weight = 1450) which is not a surfactant was also used as a template in this research. Various film properties such as porosity, refractive index, dielectric constant, leakage current density, flatband voltage, hardness, and Young's modulus were measured. For the film templated with C16 TMABr, the high leakage current density and positive flatband voltage were attributed to the residual bromide in the framework, which was from bromine in C16 TMABr after the calcination process. Moreover, its abnormally low dielectric constant was mainly due to the high leakage current density. For the films made with nonionic templates, the dielectric constant and the refractive index can be reduced linearly by increasing the film porosities; in other words, they are strongly related to the porosity rather than the pore size or the ordering of pore structure. However, the larger leakage current density and the weaker mechanical strength for more porous films are the drawbacks. According to higher values of flatband voltage, the elevation of leakage current densities are attributed to more silanol groups in the films. It was shown that the films with more ordered structures or thicker pore wall possessed better mechanical strength. Nevertheless, the porosity is the most influential factor upon mechanical strength of the films.
Ting, Chih-Yuan,Sheu, Hwo-Shuenn,Wu, Wen-Fa,Wan, Ben-Zu
p. G1-G5
(2007)
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Preparation of titania/silica composite microspheres by sol-gel process in reverse suspension
Silica gel microspheres were prepared by sol-gel process of silicon tetraethoxide in reverse suspension. Subsequently, titanium tetra-2-propoxide solution was added to the system for producing titania gel. The composite microspheres prepared were analyzed with optical microscopy, electron probe microanalysis, and X-ray diffraction. Lowering the titanium alkoxide concentration in the continuous phase was effective to depress the agglomeration of fine titania particles. When the titanium alkoxide solution was divided into four parts and each aliquot was added separately, the covering state with titania became more uniform. The composite microspheres prepared were suspended in dye solution under ultraviolet irradiation and examined for the possibility of treating wastewater. The dye concentration rapidly decreased more than with a commercial titania powder, due to the effects of both photodegradation and adsorption.
Kimura, Isao,Kase, Takayuki,Taguchi, Yoshinari,Tanaka, Masato
p. 585 - 597
(2003)
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Silicon dioxide deposition by atmospheric pressure and low-temperature CVD using TEOS and ozone
Recently, tetraethoxysilane (TEOS) is again attracting attention as one of the organosilicon materials because of the better film quality. We report characteristics of the film deposited by an atmospheric pressure and low-temperature CVD process using TEO
Fujino,Nishimoto,Tokumasu,Maeda
p. 2883 - 2887
(1990)
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Sol-gel preparation and characterization of uniform core-shell structured LaInO3:Sm3+/Tb3+@SiO2 phosphors
The core-shell structured LaInO3:Ln3+@SiO2 (Ln3+ = Sm3+, Tb3+) phosphors were realized by coating LaInO3:Ln3+ phosphors on the surface of silica microspheres via a modified Pechini sol-gel process. The phase, structure, morphology, and fluorescent properties of the materials were well characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform IR spectroscopy (FT-IR), photoluminescence (PL) spectra, cathodoluminescence (CL) spectra, and the kinetic decays, respectively. The results reveal that the obtained core-shell structured phosphors consist of amorphous silica core and crystalline LaInO3:Ln3+ shell, which keep the uniform spherical morphology of pure silica spheres with narrow size distribution. Upon excitation by ultraviolet (UV) irradiation or electron beam, the phosphors show the characteristic emission lines of Sm3+ (4G 5/2-6H5/2,7/2,9/2, orange) in LaInO 3:Sm3+@SiO2 and characteristic emissions of Tb3+ (5D4-7F6,5,4,3, green) in LaInO3:Tb3+@SiO2, respectively. This kind of phosphors may have potential applications in field emission displays (FEDs) based on their uniform shape, low-cost synthetic route, and diverse luminescent properties.
Shang, Yongchen,Yang, Piaoping,Wang, Wenxin,Wang, Yanli,Niu, Na,Gai, Shili,Lin, Jun
p. 837 - 844
(2011)
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Surface modification of base materials for TEOS/O3 atmospheric pressure chemical vapor deposition
Atmospheric pressure tetraethyloxysilicane (TEOS)/O3 chemically vapor deposited provides excellent step coverage for submicron device structures; however, the properties of the deposited films depend on the surface characteristics of the base materials being used. To illustrate this dependence, the deposition rate of nondoped silicon dioxide obtained on a thermal oxide surface is significantly lower than the deposition rate obtained on a bare silicon surface. A new method to eliminate this base material dependence involving plasma treatment has been investigated. The optimum treatment consists of exposing the base materials to a nitrogen plasma for 1 min while maintaining the base materials at 250°C. Films deposited on thermal oxide base materials which have first been treated by this new method were found to have the same deposition rate, aqueous HF etch rate, and surface morphology as those films deposited on untreated bare silicon. In addition to a nitrogen plasma, oxygen and argon plasmas were studied and found to produce similar results when the base material temperature was raised to 350°C. The elimination of base material dependence through the use of this new plasma treatment technique has resulted in higher integrity TEOS/O3 oxides and has also expanded the range of applications for this unique planarizing technology for very large scale integrated device fabrication.
Fujino,Nishimoto,Tokumasu,Maeda
p. 1690 - 1692
(1992)
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Radiation-induced luminescence and photoluminescence from sol-gel silica glasses and phosphosilicate glasses by 1 MeV H+ irradiations
Radiation-induced luminescence (RIL), photoluminescence (PL) and PL excitation (PLE) spectra have been applied to the study of photon emission from sol-gel silica glasses and phosphosilicate glasses. The photoemissions from oxygen excess-related defects a
Kitazawa, Sin-Iti,Yamamoto, Shunya,Asano, Masaharu,Ishiyama, Shintaro
p. 159 - 165
(2004)
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Strain relaxation mechanism in the Si-SiO2 system and its influence on the interface properties
The results of the investigation of stresses relaxation by strain by means of EPR spectra, IR absorption spectra, SEM and samples deflection are presented. It has been shown that stresses relaxation mechanism depended on the oxidation condition: temperatu
Kropman,Mellikov,?pik,Lott,Volobueva,K?rner,Heinmaa,Laas,Medvid
p. 5153 - 5155
(2009)
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The heat capacity and derived thermodynamic functions of La2Si2O7 and Ce2Si2O7 from 4 to 1000 K
The heat capacities of cerium and lanthanum silicates (Ce2Si2O7 and La2Si2O7) were measured from 4 to 400 K by adiabatic calorimetry. The derived thermodynamic functions, {H°(T) - H°(O}, S°
Bolech,Cordfunke,Van Genderen,Van Der Laan,Janssen,Van Miltenburg
p. 253 - 261
(1996)
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Electrical conduction of buried SiO2 layers analyzed by photon stimulated electron tunneling
The conductivity of buried SiO2 layers produced by implantation of oxygen ions into silicon was compared with the photon stimulated electron tunneling from Si into SiO2. The latter process is found to originate from defects located in interfacial SiO2 layers with an electron energy level 2.8 eV below the oxide conduction band. The dark and photon induced currents show a correlated dependence on the electric field strength in the oxide, and both increase with the Si enrichment of the oxide, thus advancing the isolated defects as the common origin of both currents. The same defects were also observed in thermally grown and deposited oxides, so they appear as intrinsic imperfections related to the excess silicon in SiO2.
Afanas'ev,Stesmans
p. 1260 - 1262
(1997)
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Silica-supported chlorometallate(iii) ionic liquids as recyclable catalysts for Diels-Alder reaction under solventless conditions
A range of Lewis acidic metal chlorides were tested as homogeneous catalysts in a model Diels-Alder reaction; AlCl3and GaCl3performed best in terms of conversion andendo : exoselectivity. Based on this outcome, the corresponding chlorometallate(iii) ionic liquids were tested as homogeneous catalysts, without a decrease in performance compared to the chlorides. Finally, these ionic liquids were heterogenised by covalent tethering of the cation onto a multimodal porous silica support; such supported chlorogallate(iii) ionic liquids are reported for the first time. Supported chlorometallate(iii) ionic liquids were used as recyclable heterogeneous catalysts for the Diels-Alder reaction under solventless conditions. High yields (99%) and highendo-selectivities (95%) were obtained after very short reaction times (5 min) at near-ambient temperature (25 °C).
Chrobok, Anna,Jarz?bski, Andrzej,Latos, Piotr,Markiton, Magdalena,Matuszek, Karolina,Swad?ba-Kwa?ny, Ma?gorzata,Szymańska, Katarzyna
p. 8129 - 8137
(2016)
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Tailoring porous silica films through supercritical carbon dioxide processing of fluorinated surfactant templates
The tailoring of porous silica thin films synthesized using perfluoroalkylpyridinium chloride surfactants as templating agents is achieved as a function of carbon dioxide processing conditions and surfactant tail length and branching. Well-ordered films with 2D hexagonal close-packed pore structure are obtained from sol-gel synthesis using the following cationic fluorinated surfactants as templates: 1-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-octyl) pyridinium chloride (HFOPC), 1-(3,3,4,4,5,5,6,6,7,8,8,8-dodecafluoro-7- trifluoromethyl -octyl)pyridinium chloride (HFDoMePC), and 1-(3,3,4,4,5,5,6,6,7, 7,8,8,9,9,10,10,10-heptadecafluoro-decyl)pyridinium chloride (HFDePC). Processing the sol-gel film with CO2 (69-172 bar, 25 and 45°C) immediately after coating results in significant increases in pore diameter relative to the unprocessed thin films (increasing from 20% to 80% depending on surfactant template and processing conditions). Pore expansion increases with CO2 processing pressure, surfactant tail length, and surfactant branching. The varying degree of CO2 induced expansion is attributed to the solvation of the "CO2-philic" fluorinated tail and is interpreted from interfacial behavior of HFOPC, HFDoMePC, and HFDePC at the CO2-water interface.
Ghosh, Kaustav,Vyas, Sandhya M.,Lehmler, Hans-Joachim,Rankin, Stephen E.,Knutson, Barbara L.
p. 363 - 370
(2007)
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Depth-resolved micro-Raman study of porous silicon at different oxidation states
Photoluminescence (PL) and Raman spectra were measured along a cross section of porous silicon films at different oxidation times after application of anodic current transients. The average crystallite size was determined from the Raman spectra with the standard phonon confinement model Before oxidation, the PL emission energy and crystallite size were found to be independent of the layer depth. Also, the integrated PL emission was larger for the middle layers. The effect of oxidation was a blueshift of the PL band and a decrease in the integrated emission for the outer layers. The crystallite size increases for all layers, particularly the outer ones.
Moreno,Agullo-Rueda,Montoya,Marcos,Gonzalez-Velasco,Guerrero-Lemus,Martinez-Duart
p. 2166 - 2168
(1997)
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Strong blue and violet photoluminescence and electroluminescence from germanium-implanted and silicon-implanted silicon-dioxide layers
The photoluminescence (PL) and electroluminescence (EL) properties of Ge-implanted SiO2 layers thermally grown on a Si substrate were investigated and compared to those of Si-implanted SiO2 films. The PL spectra from Ge-implanted SiO2 were recorded as a function of annealing temperature. It was found that the blue-violet PL from Ge-rich oxide layers reaches a maximum after annealing at 500°C for 30 min, and is substantially more intense than the PL emission from Si-implanted oxides. The neutral oxygen vacancy is believed to be responsible for the observed luminescence. The EL spectrum from the Ge-implanted oxide after annealing at 1000°C correlates very well with the PL one, and shows a linear dependence on the injected current. The EL emission was strong enough to be readily seen with the naked eye and the EL efficiency was assessed to be about 5×10-4.
Rebohle,Von Borany,Yankov,Skorupa,Tyschenko,Froeb,Leo
p. 2809 - 2811
(1997)
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Acidic Property of FSM-16. 2. Generation of Lewis Acid Sites and Catalysis
Catalysis over Lewis acid sites on siliceous mesoporous FSM-16 was confirmed. Acidic property of FSM-16 was studied by pyridine TPD measurements, and catalyses of α-pinene isomerization and methylamine synthesis. FSM-16 possess both Br?nsted and Lewis acid sites, and another Lewis acid site formed on FSM-16 when a catalyst was pretreated above 873 K. α-Pinene isomerization was catalyzed over Br?nsted acid sites, the activity of which is the highest when FSM-16 is pretreated at 673 K. Lewis acid sites on FSM-16 catalyze methylamine synthesis, and the initial rates are enhanced with increasing pretreatment temperature up to 1273 K. The structure of FSM-16 was completely retained throughout a pretreatment at 1273 K and a reaction procedure for methylamine synthesis at 673 K.
Yamamoto, Takashi,Tanaka, Tsunehiro,Inagaki, Shinji,Funabiki, Takuzo,Yoshida, Satohiro
p. 6450 - 6456
(1999)
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Alkali metals extraction reactions with the silicides Li15Si4 and Li3NaSi6: Amorphous Si versus allo -Si
The silicides Li15Si4 and Li3NaSi6 were subjected to chemical extraction of the alkali metal component by liquid ammonia and ethanol, respectively, which after washing yielded black powders of amorphous silicon. The investigated reactions are interesting with respect to both the formation of novel Si modifications and the delithiation process in Si anode materials. The products termed a-Si (from Li15Si4) and a-allo-Si (from Li3NaSi6) were characterized by a combination of methodologies (X-ray diffraction, transmission electron microscopy, differential thermal analysis, Raman, atomic absorption, and energy-dispersive X-ray spectroscopy) which revealed (i) a porous microstructure for a-Si built from spherically shaped particles with sizes around 10 nm, (ii) partial surface oxidation of both materials and (iii) the presence of nanocrystalline Si in both materials. The result of the protic oxidation of Li3NaSi6 is at variance with earlier findings reporting the formation of a crystalline bulk allotrope of silicon (allo-Si) from the topotactic combination of silicon layers present as polyanions in Li3NaSi6. Additionally, quantum chemical calculations show that silicon layers in Li3NaSi6 cannot combine to energetically favorable allotropic forms of Si. This is different from Li7Ge12, where polyanionic germanium layers topotactically convert to the germanium allotrope m-allo-Ge upon oxidation.
Zeilinger, Michael,Jantke, Laura-Alice,Scherf, Lavinia M.,Kiefer, Florian J.,Neubüser, Gero,Kienle, Lorenz,Karttunen, Antti J.,Konar, Sumit,H?ussermann, Ulrich,F?ssler, Thomas F.
p. 6603 - 6612
(2014)
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Ge nanocrystals in SiO2 films
SiO2/Ge nanocrystal/SiO2 structures have been fabricated by deposition of Ge film on a SiO2 layer and subsequent oxidation of the structure at a temperature between 800°C and 1000°C. Secondary ion mass spectrometry results indicate that the Ge precipitates into the bulk SiO2 at a density of 1 × 1012 cm-2. Raman spectra show a sharp peak at 300 cm-1 for the nanocrystallized Ge. The nanocrystal diameter is determined to be 5 nm on average. In the metal-insulator-silicon structure, electron storage occurs in the SiO2/Ge/SiO2 potential well via electron tunneling into the oxide film. Capacitance-voltage measurements indicate that flatband voltage (VFB) shifts to 0.91 V after the electron injection. The VFB shift is attributed to the charge storing for a single electron per potential well.
Kobayashi, Takamitsu,Endoh, Toshiaki,Fukuda, Hisashi,Nomura, Shigeru,Sakai, Akira,Ueda, Yuji
p. 1195 - 1197
(1997)
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Gold aggregates on silica templates and decorated silica arrays for SERS applications
In this work, we report the fabrication and characterization of size controllable gold nanoparticles (NPs) aggregates for their application in surface enhanced Raman scattering (SERS). Aggregates were prepared using two methodologies: (i) by using silica
Castillo,De La Rosa,Pérez
p. 301 - 306
(2011)
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A Cu electroplating solution for porous low-k/Cu damascene interconnects
A Cu electroplating solution applicable to porous silica ultralow- k films (k=2.1) without pore sealing was investigated. A suppressor which causes permeation of Cu electroplating solution was replaced by polyethylene glycol (PEG) with specific molecular weight (Mw). Transmission electron microscopy observation revealed that permeation by the Cu solution into the porous silica layer can be suppressed by decreasing the molecular weight of the PEG suppressor in the electroplating solution. A Cu electroplating solution using PEG with Mw=600 was examined for the low- k porous silica/ Cu single-damascene integration process of 300 mm wafer. The filling characteristics in trenches and the uniformity of Cu film thickness were investigated. Interline leakage current on low- kCu damascene interconnects was successfully reduced by six orders of magnitude using this Cu plating solution compared with the conventional solution.
Shimoyama, Masashi,Chikaki, Shinichi,Yagi, Ryotaro,Kohmura, Kazuo,Tanaka, Hirofumi,Fujii, Nobutoshi,Nakayama, Takahiro,Ono, Tetsuo,Ishikawa, Akira,Matsuo, Hisanori,Kinoshita, Keizo,Kikkawa, Takamaro
p. D692-D696
(2007)
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Synthesis of mesoporous silica with different pore sizes for cellulase immobilization: Pure physical adsorption
To discuss the physical adsorption mechanism of the adsorption process of cellulase, a commercial enzyme cocktail sourced from Acremonium was immobilized in mesoporous silica with various pore sizes by pure physical adsorption in this study. Mesoporous silica materials with 17.6 nm and 3.8 nm pore sizes (hereafter referred to as MS-17.6 nm and MS-3.8 nm, respectively) were synthesized in the manner of a seeded-growth method. Other available mesoporous silica materials denoted as H-32 and diatomite were also used as sorbents. Then, the sorbents were characterized via small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), the Barrett-Emmett-Teller (BET) method and the Barrett-Joyner-Halenda (BJH) method to confirm their mesostructure. Furthermore, the adsorption abilities of different sorbents and enzymatic activities of immobilized cellulase were studied. The adsorption amounts exhibited a clear correlation with the pore size of the sorbents; i.e., the adsorption amount of MS-17.6 nm (410 mg g-1) with the pore size similar to the long axes of cellulase molecules was higher than that of MS-3.8 nm (315 mg g-1) with the pore size approximated to the short axes of cellulase (which was realized at 50 °C). Besides, the adsorption behavior of diatomite (with a pore size of about 200 nm) revealed a periodicity because the pore size was significantly larger than cellulase molecules. Moreover, the pore size was suggested to be a critical factor for the enzymatic activity of cellulase. When the average pore size of MS-3.8 nm just matched the short axes of cellulase molecules, immobilized cellulase preserved the active sites of cellulase intactly and showed the best activity (i.e. 63.3% of free cellulase activity at 50 °C). Consequently, the pore size of the sorbents had a significant influence on cellulase immobilization.
Chen, Baiyi,Qiu, Jianhui,Mo, Haodao,Yu, Yanling,Ito, Kazushi,Sakai, Eiichi,Feng, Huixia
p. 9338 - 9345
(2017)
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CuSiO3: A quasi-one-dimensional S=1/2 antiferromagnetic chain system
CuSiO3, isotypic to the spin-Peierls compound CuGeO3, was discovered recently as a metastable decomposition product of the silicate mineral dioptase, Cu6Si6O18·6H2O. We investigated the physical properties of CuSiO3 using susceptibility, magnetization, and specific heat measurements on powder samples. The magnetic susceptibility X(T) is reproduced very well above T=8 K by theoretical calculations for an S=1/2 antiferromagnetic Heisenberg linear chain without frustration (α= 0) and a nearest-neighbor exchange coupling constant of J/kB=21 K, much weaker than in CuGeO3. Below 8 K the susceptibility exhibits a substantial drop. This feature is identified as a second-order phase transition at T0 = 7.9 K by specific heat measurements. The influence of magnetic fields on T0 is weak, and ac-magnetization measurements give strong evidence for a spin-flop phase at μ0HSF?3 T. The origin of the magnetic phase transition at T0=7.9 K is discussed in the context of long-range antiferromagnetic order (AF) versus spin-Peierls (SP) order. Susceptibility and specific heat results support the AF ordered ground state. Additional temperature dependent 63.65Cu nuclear quadrupole resonance experiments have been carried out to probe the Cu2+ electronic state and the spin dynamics in CuSiO3.
Baenitz,Geibel,Dischner,Sparn,Steglich,Otto,Meibohm,Gippius
p. 12201 - 12205
(2000)
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THIN SILICON DIOXIDE USING THE RAPID THERMAL OXIDATION (RTO) PROCESS FOR TRENCH CAPACITORS.
Growth and electrical characteristics of thin silicon dioxide using the rapid thermal oxidation (RTO) process have been studied for planar and trench capacitors. Growth of silicon dioxide follows the linear-parabolic model. The activation energies of the linear rate constant B/A and the parabolic rate constant B are found to be 1. 98 and 1. 42 ev, respectively. Good electrical characteristics can be achieved by increasing the oxidation temperature from 1000 degree to 1150 degree C. For the trench capacitors oxidized at 1150 degree C, it is found that oxide breakdown occurs dominantly at the fields 10 to approximately 12 mv/cm, the leakage current density is 3 multiplied by 10** minus **1 A/cm**2 and the interface-state density is 3 multiplied by 10**1****1 A/cm**2 and the interface-state density is 3 multiplied by 10**1**0 cm** minus **2. The RTO process is proved to be a promising technique for the fabrication of trench capacitors.
Miyai,Yoneda,Oishi,Uchida,Uchida,Inoue
p. 150 - 155
(1988)
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Large Cage Face-Centered-Cubic Fm3m Mesoporous Silica: Synthesis and Structure
The synthesis and precise structural characterization of highly ordered three-dimensional close-packed cage-type mesoporous silica is reported. The siliceous mesoporous material is proven to be commensurate with the face-centered-cubic Fm3m symmetry in high purity by a combination of experimental and simulated powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. The cage-type calcined samples were additionally characterized by nitrogen physisorption. The aqueous synthesis method to prepare large cage mesoporous silica with cubic Fm3m structure is based on the use of EO105PC70EO106 triblock copolymer (F127) at low HCl concentrations, with no additional salts or organic additives. Here, emphasis is put on the low HCl concentration regime, allowing the facile thermodynamic control of the silica-triblock copolymer mesophase self-assembly. Further, simple application of hydrothermal treatments at various temperatures ranging from 45 to 150 °C enables the tailoring of the mesopore diameters and apertures. The combination of experimental and simulated XRD patterns and TEM images is confirmed to be a very powerful means for the accurate elucidation of the structure of new mesoporous materials.
Kleitz, Freddy,Liu, Dinan,Anilkumar, Gopinathan M.,Park, In-Soo,Solovyov, Leonid A.,Shmakov, Alexandr N.,Ryoo, Ryong
p. 14296 - 14300
(2003)
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Tuning the structure and orientation of hexagonally ordered mesoporous channels in anodic alumina membrane hosts: A 2D small-angle X-ray scattering study
Circular or columnar orientations of mesoporous silica can be selectively prepared by tuning the silica-to-surfactant ratio and the humidity during the synthesis of the mesoporous material within the regular larger channels of anodic alumina membranes. The transmission electron microscopy image shows the circular orientation of these highly ordered hexagonal mesostructures. (Figure Presented).
Platschek, Barbara,Petkov, Nikolay,Bein, Thomas
p. 1134 - 1138
(2006)
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The influence of high-energy electron irradiation and boron implantation on the oxide thickness in the SiO2/Si system
The SiO2/Si system exposed to irradiation with 11-12 MeV electrons was studied by soft-x-ray emission spectroscopy using the variable-exciting-electron-energy, optical ellipsometry, and nuclear reaction techniques. For the SiO2/Si system prepared on an n-substrate, oxidation of Si was observed, and the thickness of the SiO2 layer after electron irradiation was estimated. For the SiO2/Si system prepared on a p-Si substrate, irradiation-induced oxidation was not observed. It was found that preliminary boron implantation in the SiO2/n-Si system blocks oxidation of the n-Si substrate exposed to electron irradiation.
Kurmaev,Shamin,Galakhov,Makhnev,Kirillova,Kurennykh,Vykhodets,Kaschieva
p. 6969 - 6978
(1997)
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SYNTHESES OF NEW LANTHANUM-SILICON-ARSENIC TERNARY COMPOUNDS.
A new ternary compound, the F-type phase, was synthesized from LaAs and silicon in a fused silica ampoule at 900 degree C under controlled arsenic vapor pressures using a temperature-gradient furnace. This compound was orthorhombic with a equals 6. 084(1) A, b equals 5. 986(1) A and c equals 26. 235(3) A. Conditions for the formation of this system were examined by X-ray techniques and the stoichiometric composition of the phase was found to be LaSiAs//3. The F-type phase was formed at 900 degree C under an arsenic pressure in the range 0. 2-15 atm. Above this range, LaAs//2 and SiAs//2 were formed, while below 0. 08 atm LaAs and silicon remained unreacted.
Hayakawa,Suzuki,Ono
p. 235 - 243
(1980)
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Observation and control of Si surface and interface processes for nanostructure formation by scanning reflection electron microscopy
We observe the oxidation process on clean Si surfaces using high-resolution scanning reflection electron microscopy and form nanostructures on them using focused electron-beam-(EB-) induced surface reactions. Si thermal oxidation occurs layer by layer, and the interface between the oxide film (2 film is selectively decomposed from the EB-irradiated area, resulting in the exposure of a clean Si substrate. The typical width of the clean Si 'open windows' is about 10 nm. Using selective reactions during heating after the deposition of Si and Ge films on the patterned samples, Si nanowires and Ge nanoislands with 10 nm size are formed on Si surfaces. Ga-adsorbed Si nanoareas and Ga nanodots are also formed by selective adsorption of Ga on the Si window areas.
Ichikawa, Masakazu
p. 9861 - 9870
(1999)
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A long-lived intermediate product in the oxidation of monosilane and dichlorosilane at low pressures and 293 K
An electron-vibration structure of the UV spectrum of a long-lived intermediate is detected during oxidation of SiH4 and SiH2Cl2. This product is common to both reactions and exhibits the same promoting effect on them. It is shown that the formation of this promoting compound in the course of a branched chain reaction accounts for nonthermal flame propagation in reacting mixtures outside of the self-ignition region.
Rubtsov,Azatyan,Tsvetkov,Chernysh
p. 585 - 588
(2000)
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NEW METHODS TO PREPARE HIGH-PURITY SILICA.
Two methods are described to prepare high-purity silica to be employed as a low-cost starting material for solar-grade silicon production. In the first process, abundantly available quartz sand is purified by fusing it with glass forming oxides to form a melt from which the glass fibers are drawn. Subsequent treatment of the fibers with hot HCl leads to an exchange whereby all non-siliceous oxides are removed from the glass network leaving an insoluble matrix of high-purity silica. The second method employs sodium hexafluosilicate (Na//2SiF//6 ), prepared from fluosilic acid, a by-product of the fertilizer industry. The Na//2SiF//6 is thermally decomposed to yield gaseous SiF//4 which is subsequently hydrolyzed in an ammonia solution. With both methods silica having a purity of greater than 99. 99% was obtained.
Aulich,Eisenrith,Urbach
p. 1710 - 1717
(1984)
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Modifying silica xerogels by fluoride-ion-catalyzed chemical treatment
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Le Strat,Boury,Corriu,Delord
p. 371 - 378
(2001)
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RhNPs supported onN-functionalized mesoporous silica: effect on catalyst stabilization and catalytic activity
Amine and nicotinamide groups grafted on ordered mesoporous silica (OMS) were investigated as stabilizers for RhNPs used as catalysts in the hydrogenation of several substrates, including carbonyl and aryl groups. Supported RhNPs on functionalized OMS were prepared by controlled decomposition of an organometallic precursor of rhodium under dihydrogen pressure. The resulting materials were characterized thoroughly by spectroscopic and physical techniques (FTIR, TGA, BET, SEM, TEM, EDX, XPS) to confirm the formation of spherical rhodium nanoparticles with a narrow size distribution supported on the silica surface. The use of nicotinamide functionalized OMS as a support afforded small RhNPs (2.3 ± 0.3 nm), and their size and shape were maintained after the catalyzed acetophenone hydrogenation. In contrast, amine-functionalized OMS formed RhNP aggregates after the catalytic reaction. The supported RhNPs could selectively reduce alkenyl, carbonyl, aryl and heteroaryl groups and were active in the reductive amination of phenol and morpholine, using a low concentration of the precious metal (0.07-0.18 mol%).
Pulido-Díaz, Israel T.,Serrano-Maldonado, Alejandro,López-Suárez, Carlos César,Méndez-Ocampo, Pedro A.,Portales-Martínez, Benjamín,Gutiérrez-Alejandre, Aída,Salas-Martin, Karla P.,Guerrero-Ríos, Itzel
p. 3289 - 3298
(2021/03/16)

Catalytic hydrogenation of CO2from airviaporous silica-supported Au nanoparticles in aqueous solution
The conversion of the ubiquitous greenhouse gas CO2to valuable organic products is much sought after. Herein, the hydrogenation of CO2to C1 products with an 80% yield in water is reported using a novel catalyst, porous-silica-supported Au nanoparticles (Au/SiO2). In the presence of a Lewis acid, boric acid, the Au/SiO2catalyst enables an efficient conversion of amine-captured CO2to methanol, formate, and formamide. A mechanistic study involving isotopic labelling suggests that methanol production in the catalytic process arises from the direct hydrogenation of formate. Most importantly, this one-pot, two-step process is able to convert CO2in air at ambient pressures to C1 products in the absence of an organic solvent. Furthermore, the catalyst is readily recycled without further purification or reactivation and shows no significant decrease in catalytic activity after four reaction cycles in a reusability test.
Lennox, R. Bruce,Li, Chao-Jun,Ni, Siting,Roy, Ranjan,Zhu, Jun
p. 3740 - 3749
(2021/06/06)

Effects of temperature on the structure of mesoporous silica materials templated with cationic surfactants in a nonhydrothermal short-term synthesis route
This paper reports the influence of synthesis temperature on the structure of mesoporous silica materials templated with ionic surfactant. The results obtained allow for the prediction of optimal temperature value to be used in nonhydrothermal short-term synthesis. The model materials were mesoporous silicates of MCM-41 type. The samples were prepared under alkaline conditions using tetraethyl orthosilicate as a silica source and cetyltrimethylammonium bromide or octadecyltrimethylammonium bromide as templates. An increase in synthesis temperature led to a rougher surface and decrease in the long-range ordering of the materials obtained, while a slight temperature decrease produced additional porosity. The reasons for these structural disturbances were briefly explained. The best material structure was obtained by synthesis at a temperature slightly higher than the Krafft temperature of surfactant of the porosity template.
Borówka, Anna,Skrzypiec, Krzysztof
(2021/05/03)

In situthermosensitive hybrid mesoporous silica: preparation and the catalytic activities for carbonyl compound reduction
In this study, free-radical polymerisation inside MCM-41 mesopores was examined to expose a construction route for a temperature-responsive switchable polymer-silica nanohybrid material with well-defined porosity. Herein, we introduced a vinyl monomer (N-isopropyl acrylamide), a cross-linker, and an AIBN initiator into the palladium nanoparticle incorporated MCM-41 pore channels using the wet-impregnation method followed byin situradical polymerisation. The structural properties of the synthesised PNIPAM-PdNP-MCM-41 catalyst were analysed by various sophisticated analytical techniques. The temperature switchable nanohybrid catalyst was used to reduce carbonyl compounds to their corresponding alcohols. The catalyst showed high catalytic efficiency and robustness in an aqueous medium at 25 °C. Moreover, the system's polymer layer remarkably boosted catalytic selectivity and activity for carbonyl compound reduction as compared to other controlled catalysts. The suggested switchable system can be employed as a temperature-controllable heterogeneous catalyst and highlights a substitute technique to counter the methodical insufficiency in switchable supported molecular catalytic system production.
Ha, Chang-Sik,Mohan, Anandhu,Nagappan, Saravanan,Parambadath, Surendran,Park, Sung Soo,Peter, Jerome,Rout, Lipeeka,Thomas, Anju Maria,Zhang, Wei-Jin
p. 11730 - 11741
(2021/09/06)

Graphene Oxide-Mesoporous Silica-Polyaniline Composite with Intercalated Structures As Supercapacitor Electrode Materials
Abstract: In this work, the graphene oxide/mesoporous silica/polyaniline (GO/mSiO2/PANI) composite was synthesized via in-situ polymerization method. PANI was introduced into the mesoporous channels of mSiO2, followed by dispersion o
Chen, Xiangmeng,Xu, Li,Liu, Guoji
p. 623 - 629
(2021/04/09)

Preparation of ethyl levulinate from wheat stalk over Zr(SO4)2/SiO2
A series of Zr(SO4)2/SiO2solid acid catalysts with different Zr(SO4)2 loadings were prepared by water-soluble-impregnation method at room temperature. Then, the prepared catalysts were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy and energy-dispersive X-ray spectrum, X-ray diffraction, adsorption/desorption of N2, and temperatureprogrammed desorption of NH3. The results showed that the active component Zr(SO4)2 was successfully adhered to the mesoporous SiO2, and the acid amount of Zr(SO4)2/SiO2increased with the increasing of the Zr(SO4)2 loadings. Finally, the wheat stalk was used as raw material and depolymerized over Zr(SO4)2/SiO2to produce ethyl levulinate (EL). The reaction mixture was separated and purified by filtration and vacuum distillation. The kinetic characteristics and the reaction pathway were also studied. A comparative study showed that 20 wt.% Zr(SO4)2/SiO2exhibited higher catalytic activity. When reaction temperature, time, catalyst dosage and Zr(SO4)2 loadings were 190°C, 50 min, 20 wt.% and 30 wt.%, the EL yield reached a maximum of 17.14%. The relative content of EL exceeded 90% after three steps of distillation.
Cui, Ming-Yu,Fu, Shui-Yuan,Guo, Tian-Tian,Li, Wei-Gang,Wang, Ding-Kai,Zhao, Wei
p. 1133 - 1145
(2021/09/04)

Highly active carbon nanotube–promoted Rh-Mn-Li/SiO2 catalysts for the synthesis of C2+ oxygenates from syngas
The effect of carbon nanotubes on the catalytic properties of Rh-Mn-Li/SiO2 catalysts was investigated for CO hydrogenation. The catalysts were comprehensively characterized by means of X-ray power diffraction, N2 sorption, transmission electron microscope, H2–temperature-programmed reduction, CO–temperature-programmed desorption, temperature-programmed surface reaction, and X-ray photoelectron spectroscopy. The results showed that an appropriate amount of carbon nanotubes can be attached to the surface of the SiO2 sphere and can improve the Rh dispersion. Moderate Rh-Mn interaction can be obtained by doping with the appropriate amount of carbon nanotubes, which promotes the formation of strongly adsorbed CO and facilitates the progress of CO insertion, resulting in the increase in the selectivity of C2+ oxygenate synthesis.
Chen, Guoqing,Han, Ying,Mao, Dongsen,Mao, Haifang,Xiao, Xiuzhen,Yu, Jun
p. 436 - 442
(2021/01/11)

Synthetic ferripyrophyllite: Preparation, characterization and catalytic application
Sheet silicates, also known as phyllosilicates, contain parallel sheets of tetrahedral silicate built up by [Si2O5]2- entities connected through intermediate metal-oxygen octahedral layers. The well-known minerals talc and pyrophyllite are belonging to this group based on magnesium and aluminium, respectively. Surprisingly, the ferric analogue rarely occurs in nature and is found in mixtures and conglomerates with other materials only. While partial incorporation of iron into pyrophyllites has been achieved, no synthetic protocol for purely iron-based pyrophyllite has been published yet. Here we report about the first artificial synthesis of ferripyrophyllite under exceptional mild conditions. A similar ultrathin two-dimensional (2D) nanosheet morphology is obtained as in talc or pyrophyllite but with iron(iii) as a central metal. The high surface material exhibits a remarkably high thermostability. It shows some catalytic activity in ammonia synthesis and can serve as catalyst support material for noble metal nanoparticles.
Qiao, Yunxiang,Theyssen, Nils,Spliethoff, Bernd,Folke, Jan,Weidenthaler, Claudia,Schmidt, Wolfgang,Prieto, Gonzalo,Ochoa-Hernández, Cristina,Bill, Eckhard,Ye, Shengfa,Ruland, Holger,Schüth, Ferdi,Leitner, Walter
p. 850 - 857
(2021/02/03)

Polytriptycene@CdS double shell hollow spheres with enhanced interfacial charge transfer for highly efficient photocatalytic hydrogen evolution
A double-shell triptycene covalent polymer@CdS hollow sphere (TCP@CdS HS) composite has been successfully synthesized byin situgrowing a TCP on the surface of CdS@SiO2spheres and then removal of the SiO2templateviaalkali etching. Characterization indicates that an amorphous TCP layer is coated on the thin CdS shellviaan electrostatic self-assembly process, and the TCP layer thickness can be tuned by adjusting TCP loading. The photocatalytic hydrogen generation rate of the optimal TCP@CdS HS composite is up to 9480 μmol h?1g?1under visible-light irradiation, which is 57, 37 and 18 times higher than those of pristine CdS HS, SiO2@CdS HS and SiO2@CdS@SiO2, respectively. Besides, the TCP@CdS HS composite possesses excellent stability, which is superior to that of SiO2@CdS HS and SiO2@CdS@SiO2. An in-depth study of the electron transfer process and the photocatalytic mechanism was performed byin situtransient photovoltage experiments, which indicate that the TCP can facilitate the diffusion of hydrogen and stabilize the photoinduced electrons. This work provides an effective strategy to design novel hollow sphere heterostructures for solar energy conversion.
Liang, Qian,Liu, Lijuan,Wu, Zhenyu,Nie, Haodong,Shi, Hong,Li, Zhongyu,Kang, Zhenhui
p. 9105 - 9112
(2021/04/16)

Microcalorimetric adsorption and infrared spectroscopic studies of supported Pd, Ru and Pd-Ru catalysts for the hydrogenation of aromatic rings with carboxyl groups
The Ru/SiO2, Pd/SiO2 and Pd-Ru/SiO2 catalysts (5% wt) were prepared for the hydrogenation of benzoic acid (BA) and toluene (without and with propionic acid (PA)) to study the effects of -COOH groups on the hydrogenation of aromatic rings. The results showed that PA adsorbed strongly on the catalysts and inhibited the adsorption of toluene and H2 and thus led to the significant decrease in the conversion of aromatic rings. The strong dissociative adsorption of PA might be responsible for the low selectivity to cyclohexanecarboxylic acid (CCA) on the Ru/SiO2. Particularly, the adsorption heat of PA was the lowest while that of H2 was the highest on the Pd-Ru/SiO2 in the catalysts, indicating its special surface chemical properties that allowed it to adsorb toluene and H2 still quite strongly even with the pre-adsorbed PA and thus to be highly active and selective for the hydrogenation of BA to CCA. The FTIR spectra of co-adsorbed toluene and H demonstrated that the weakly adsorbed H was highly active for the hydrogenation of toluene on the Ru/SiO2 even at room temperature, and the higher activity of Ru than Pd for the hydrogenation of aromatic rings might be due to the stronger adsorption of toluene and weaker adsorption of H2 on Ru than on Pd.
Cai, Jingxuan,Hou, Qiumei,Shen, Jianyi,Zhao, Danyang,Zhao, Shiling
p. 3070 - 3083
(2021/05/25)

Assembly of discrete and oligomeric structures of organotin double-decker silsesquioxanes: Inherent stability studies
Double-decker silsesquioxane (DDSQ), a type of incompletely condensed silsesquioxane, has been used as a molecular precursor for synthesizing new organotin discrete and oligomeric compounds. The equimolar reaction between DDSQ tetrasilanol (DDSQ-4OH) and Ph2SnCl2 in the presence of triethylamine leads to obtaining discrete [Ph4Sn2O4(DDSQ)(THF)2] (1). The change of sterically bulky aryl Ph2SnCl2 precursor to linear alkyl nBu2SnCl2 led to the isolation of oligomeric [nBu4Sn2O4(DDSQ)] (2). The structures of compounds 1 and 2 have been demonstrated using single-crystal X-ray diffraction measurements. Indeed, the formation of oligomeric organotin DDSQ compound (2) was determined using GPC and MALDI-TOF mass spectroscopy. In compound 1, the geometry of the tin atom is five-coordinated trigonal bipyramidal by two phenyl groups, two Si-O from DDSQ and one tetrahydrofuran. Compound 2 contains four coordinated two peripheral tin atoms and two five-coordinated central tin atoms, in which, the fifth coordinating oxo groups in the central tin atoms create the bridge between two different DDSQ units that leads to the formation of oligomeric structure. Density functional theory calculations on organotin DDSQs infer that the obtained lattice energy for compound 1 is far higher than for the case of compound 2, which indicates that the crystal of compound 1 is better stabilized in its crystal lattice with stronger close packing via intermolecular interactions between discrete molecules with coordinated THF compared to the crystal of compound 2. The greater stability arises mainly due to the sterically bulkier phenyl groups attached to the tin centers in compound 1, which provide accessibility for accommodating the THF molecule per tin via Sn-THF bonding, while contrarily the smaller n-butyl groups aid the polymerization of the four repeating units of [SnSi4O7] or two Sn2O4(DDSQ) through μ-oxo groups. Both compounds 1 and 2 were chosen to be promising precursors for the synthesis of ceramic tin silicates. The thermolysis of 2 at 1000 °C afforded the mixture of crystalline SnSiO4 and SiO2 but the same mixture was only formed by thermolysis of 1 at relatively higher temperature (1500 °C), which infers that compound 1 is more stable than compound 2 that is in good synergy with theoretical lattice energy.
Bhuvanesh, Nattamai S. P.,David, Ezhumalai,Jeevananthan, Velusamy,Loganathan, Pushparaj,Palanisami, Nallasamy,Pillai, Renjith S.,Shanmugan, Swaminathan
p. 20144 - 20154
(2021/11/22)

High thermal stability of SiO2–ZrO2 aerogels using solvent-thermal aging
The ZrO2–SiO2 aerogels (ZSA) with varied particle size were synthesized by solvent-thermal aging (STA) method. The effects of STA temperature (60, 110, 170 and 210 ?°C) on microstructure and thermal stability of the ZSA were investigated by SEM, TEM, FT-IR and XRD. The ZSA-210 presents the minimum shrinkage (9.3percent), and it has the largest retention values of specific surface area (59.2percent) and pore volume (90.8percent) after 1000 ?°C heat treatment for 1 ?h. Compared with the aerogels prepared by traditional aging, the ZSA prepared by STA can maintain a low thermal conductivity (0.0285–0.0328 ?W ?m?1 ?K?1) while improving the compression strength (~1.28 ?MPa, 10percent strain). STA can restrain viscous flow between ZSA particles by particles growth and skeleton coarsening; and STA can restrain the growth of t-ZrO2 by forming more Si–O–Zr bonds in the system. The work will be meaningful for the design of super thermal insulation materials with high thermal stability and low thermal conductivity.
Ji, Huiming,Li, Xiaolei,Qiao, Yingchen,Su, Dong,Tong, Zongwei,Yang, Zhuchao,Yu, Huijun,Yue, Sheng
(2020/08/21)

Scalable preparation of stable and reusable silica supported palladium nanoparticles as catalysts for N-alkylation of amines with alcohols
The development of nanoparticles-based heterogeneous catalysts continues to be of scientific and industrial interest for the advancement of sustainable chemical processes. Notably, up-scaling the production of catalysts to sustain unique structural features, activities and selectivities is highly important and remains challenging. Herein, we report the expedient synthesis of Pd-nanoparticles as amination catalysts by the reduction of simple palladium salt on commercial silica using molecular hydrogen. The resulting Pd-nanoparticles constitute stable and reusable catalysts for the synthesis of various N-alkyl amines using borrowing hydrogen technology without the use of any base or additive. By applying this Pd-based catalyst, functionalized and structurally diverse N-alkylated amines as well as some selected drug molecules were synthesized in good to excellent yields. Practical and synthetic utility of this Pd-based amination protocol has been demonstrated by upscaling catalyst preparation and amination reactions to several grams-scales as well as recycling of catalyst. Noteworthy, this Pd-catalyst preparation has been up-scaled to kilogram scale and catalysts prepared in both small (1 g) and large-scale (kg) exhibited similar structural features and activity.
Alshammari, Ahmad S.,Natte, Kishore,Kalevaru, Narayana V.,Bagabas, Abdulaziz,Jagadeesh, Rajenahally V.
p. 141 - 149
(2020/01/06)

SiO2?TiO2 Core?Shell Nanoparticles Deposited on 2D-Layered ZnIn2S4 to Form a Ternary Heterostructure for Simultaneous Photocatalytic Hydrogen Production and Organic Pollutant Degradation
It is challenging to design and prepare difunctional photocatalysts for simultaneous photocatalytic wastewater purification and hydrogen (H2) energy production. In this study, a novel ternary heterostructure pholocatalyst, ZnIn2S4?SiO2?TiO2 (ZIS?SiO2?TiO2) was successfully prepared by simple sol-gel and solvothermal methods. The SiO2 nanospheres were used as a support to prevent the aggregation of TiO2 nanoparticles efficiently. The SiO2?TiO2 nanoparticles were uniformly inserted into the 2D-layered flowerlike ZnIn2S4 to form a ternary heterostructure that can efficiently improve the separation and transportation of photoinduced electron-hole pairs. As expected, the 150%-ZIS?SiO2?TiO2 nanocomposite exhibited an excellent rate of H2 production under simulated sunlight (618.3 μmol g-1 h-1), which was 229 and 3.3 times higher than the binary SiO2?TiO2 nanoparticles and pure ZnIn2S4. Furthermore, the degradation efficiency of methylene blue reached 99.7% during the H2 production process. These findings provided possibilities to couple energy conversion with environmental restoration.
Qian, Xuhui,Song, Yali,Wang, Lan,Zhang, Hongzhong,Zhang, Huan,Zhou, Hanghang
p. 2278 - 2287
(2020/03/05)

Ultra-low temperature carbon (di)oxide hydrogenation catalyzed by hybrid ruthenium-nickel nanocatalysts: Towards sustainable methane production
It is a paradox that the excess of carbon dioxide in our atmosphere can endanger lives and even the civilization that has been founded on carbon. Human addiction to carbon is persistent and therefore we need novel chemistry for the efficient conversion of CO2 to harmless or useful products. Accordingly, catalytic CO2 hydrogenation has been widely studied as a potential method for fuel engineering, and methane production in particular. Syngas, a blend of CO with H2 has been observed as an incomplete product of this reaction. Here we report a surprising discovery that syngas to methane conversion can be attained in flow at temperatures starting from -7 °C with a hybrid bimetallic Ru/Ni catalyst. In turn, the ultra-low temperature effect cannot be observed for the Re/Ni and Pd/Ni combinations. To our knowledge, this is the first report showing that such a process can be performed at a temperature lower than the freezing point of water. These ultra-low temperature conditions could potentially lead to sustainable methane production.
Antoniotti, Sylvain,Balin, Katarzyna,Bartczak, Piotr,Kapkowski, Maciej,Polanski, Jaroslaw,Siudyga, Tomasz,Szade, Jacek,Zubko, Maciej
supporting information
p. 5143 - 5150
(2020/08/25)

Synthesis and characterization of mesoporous silica carrier releasing valsartan
The aim of the present study is to synthesize a mesoporous silica MCM-48 and loading it with the poorly soluble drug valsartan. The MCM-48 was characterized by Brauner-Emmett-Teller surface area analyzer, scanning electron microscope, powder X-ray diffraction, thermal gravimetric analysis and Fourier transform infra-red (FTIR). The exact loading capacity was found to be 40.12%. in vitro dissolution studies at physiological conditions demonstrated controlled release of 57.2% valsartan over 240 min. The controlled dissolution was attributed to the incomplete amorphization of crystalline valsartan by MCM-48 as evidenced by PXRD studies. The interactions between the mesoporous silica surface and drug molecules were evidenced by FTIR studies and the diffusion of therapeutic agent molecules through the silica pores. The results of the present study confirmed that the controlled adsorption and liberation of valsartan demonstrated a long-term release, which is important for its antihypertensive activity. Moreover, the structural properties of mesoporous silica assured the feasibility of designing reliable drug delivery systems by appropriate choice of the carrier.
Muhana,Abu-Huwaij,Khalaf,Khalili,Shalan
p. 2927 - 2933
(2020/11/23)

Fabrication and properties of amorphous silica particles by fluorination of zircon using ammonium bifluoride
A method to prepare amorphous silica particles from zircon has been developed using the fluorination method through a three-step process: the fluorination of zircon using ammonium bifluoride at 230 ℃, the sublimation of (NH4)2SiF6 at 300 ℃ and the hydrolysis of (NH4)2SiF6. During above progress, the composition and phases of materials produced during fluorination of zircon were analyzed; the chemical reaction of silica with ammonium bifluoride, the sublimation behavior of (NH4)2SiF6 and its composition were determined; the effect of hydrolysis temperature (30 ℃, 45 ℃ and 60 ℃) on the hydrolysis ratio of Si and the size of silica particles were investigated. The results indicated that (NH4)3ZrF7 and (NH4)2SiF6 formed after the fluorination of zircon at 230 ℃ for 5 h. (NH4)2SiF6 started to sublimate at 175 ℃, but the sublimation dominated at 280 ℃ and ended at 300 ℃. The hydrolysis results indicated that uni-modal silica particles in micrometer size range were produced at 45 ℃, while bi-modal particles in a variety of sizes ranging from nanometer to micrometer were produced at 30 ℃ and 60 ℃. The amorphous silica particles obtained at 45 ℃ exhibited high purity above 99.96 wt.%, narrow size distribution (average: 254 ± 17 nm), high specific surface (136.8 m2/g), high dibutyl phthalate (DBP)-absorption (2.7 cm3/g), low density (0.532 g/cm2) and pH (5.7). Therefore, the amorphous silica obtained has potential application as filler in plastic and rubber compounding. After the hydrolysis process, ammonium bifluoride can be recycled through the evaporation of NH4F solution. Thus, this work provides a novel strategy for processing zircon by ammonium bifluoride to produce amorphous silica particles and recycle of ammonium bifluoride.
Wang, Yongdong,Zhang, Yupeng,Liang, Gang,Zhao, Xia
(2020/02/04)

Zinc Imine Polyhedral Oligomeric Silsesquioxane as a Quattro-Site Catalyst for the Synthesis of Cyclic Carbonates from Epoxides and Low-Pressure CO2
In the present research, the synthesis, spectroscopic characterization, and structural investigations of a unique ZnII complex of imine-functionalized polyhedral oligomeric silsesquioxane (POSS) is designed, and hereby described, as a catalyst for the synthesis of cyclic carbonates from epoxides and CO2. The uncommon features of the designed catalytic system is the elimination of the need for a high pressure of CO2 and the significant shortening of reaction times commonly associated with such difficult transformations like that of styrene oxide to styrene carbonate. Our studies have shown that imine-POSS is able to chelate metal ions like ZnII to form a unique coordination complex. The silsesquioxane core and the hindrance of the side arms (their steric effect) influence the construction process of the homoleptic Zn4@POSS-1 complex. The compound was characterized in solution by NMR (1H, 13C, 29Si), ESI-MS, UV/Vis spectroscopy and in the solid state by thermogravimetric/differential thermal analysis (TG-DTA), elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), cross-polarization magic angle spinning (CP MAS) NMR (13C, 29Si) spectroscopy, and X-ray crystallography.
Janeta, Mateusz,Lis, Tadeusz,Szafert, S?awomir
p. 13686 - 13697
(2020/10/02)

A novel chiral inorganic mesoporous silica used as a stationary phase in GC
Chiral mesoporous silica (CMS) has attracted widespread attention because of some unique properties, such as high surface area, uniformly structured nanoscale cavities, and excellent chemical and thermal stability. In this work, we report the utilization of a CMS as the stationary phase for the separation of racemates in gas chromatography (GC). A CMS-coated capillary column was fabricated by a dynamic coating method. Eighteen racemates belonging to different classes of organic compounds were separated on this column, including chiral alcohols, aldehydes, ketones, organic acids, halohydrocarbons, alkenes, alcohol amines, epoxides, and amino acid derivatives. In addition, linear alkanes, alcohols, and aromatic hydrocarbons have also been resolved.
He, Yu-Yu,Zhang, Jun-Hui,Pu, Qing,Xie, Sheng-Ming,Li, Yan-Xia,Luo, Lan,Chen, Xue-Xian,Yuan, Li-Ming
p. 1053 - 1059
(2019/11/11)

Azamacrocycles and tertiary amines can be used to form size tuneable hollow structures or monodisperse oxide nanoparticles depending on the 'M' source
We show that the azamacrocycle 'cyclam' (1,4,8,11-tetraazacyclodecane) in conjunction with a silicon catecholate ion generates novel hollow tetragonal tube-like crystalline materials [(C6H4O2)3Si][C10H26N4]·H2O, whose dimensions can be tuned according to the pH of the reaction medium. The synthesis approach was successful for both silicon and germanium and we hypothesise that a range of other catecholate precursors of elements such as iron could be used to generate a large array of inorganic materials with interesting morphologies. The synthesis approach can be extended to tertiary diamines with functional group spacing playing an important role in the efficacy of complexation. Of the molecules explored to date, a C2 spacing (N,N,N′,N′-tetramethylethylenediamine (4MEDAE)), leads to the most efficient structure control with hollow hexagonal tube-like structures being formed. In addition, we show that azamacrocycles, in the presence of unbuffered tetramethoxysilane (TMOS) solutions can be used to manipulate silica formation and provide a fast (ca. 10 minutes) synthesis route to particles whose diameter can be tuned from ca. 20 nm to several hundreds of nm under reaction conditions (no extremes of pH) that make the sols suitable for direct use in biotechnological applications.
Tilburey, Graham E.,Blundell, Toby J.,Argent, Stephen P.,Perry, Carole C.
p. 15470 - 15479
(2019/11/03)

Photocatalytic degradation of benzothiophene by a novel photocatalyst, removal of decomposition fragments by MCM-41 sorbent
In this study, a catalyst was synthesized by introduction of ZnO onto the surface of FSM-16 catalyst support (ZnO/FSM-16). Impregnation of catalyst support by ZnO proceeded through reacting of FSM-16 nanoparticles with Zn(CH3COO)2 solution followed by calcination of the product. The synthesized photocatalyst was then identified by different methods, and the optical property of the photocatalyst was studied by the DRS method. The results showed that after deposition of photocatalyst on FSM-16 support, the photocatalyst band gap was shifted to the visible region. The photoluminescence studies revealed lower recombination of electron–holes of the photocatalyst after immobilization on FSM-16. The influence of different variables on the photocatalytic performance of the samples was studied. Under optimized conditions, the high degradation efficiency of 97% was obtained by ZnO/FSM-16. The compounds produced from degradation of benzothiophene were recognized by the GC–MS method, and the products containing sulfur were properly adsorbed by MCM-41 sorbent. The photocatalyst showed high regeneration capability, and its activity was mostly preserved after six regeneration cycles.
Hosseini, Asma,Faghihian, Hossein
p. 2383 - 2401
(2019/01/29)

Nanosized carriers for hydrophobic compounds based on mesoporous silica: synthesis and adsorption properties
MCM-41 type mesoporous silica particles were obtained using a template method in an alkaline medium and cetyltrimethylammonium bromide as a matrix. The structural and adsorption characteristics of the mesoporous material were studied by dynamic light scattering, scanning electron microscopy, low-temperature adsorption—desorption of nitrogen, IR spectroscopy, and simultaneous thermal analysis. It was shown that the obtained mesoporous material possesses high porosity with the specific pore volume in excess of 1 cm3 g?1. It was established that the size of silica particles does not exceed 200 nm, which is a value acceptable for the penetration of drugs through cell membranes. The optimal compositions of aqueous dispersions of MCM-41 with minimal sedimentation processes were determined. A drug (indomethacin) was encapsulated into the silica pores using the precipitation method at various temperatures (40 and 60 °C), the quantitative parameters of loading efficiency were calculated. The infl uence of temperature on the encapsulation ability was demonstrated.
Ibragimova,Gabdrakhmanov,Khamatgalimov,Saifina,Gubaidullin,Egorova,Lamberov,Danilaev,Zakharova, L. Ya.
p. 1358 - 1365
(2019/08/12)

The Influence of Heteroatom Dopants Nitrogen, Boron, Sulfur, and Phosphorus on Carbon Electrocatalysts for the Oxygen Reduction Reaction
A hard templating method, using SBA-15 in combination with glucose solution and different heteroatom precursors, has been employed to investigate the influence of the different heteroatom dopants nitrogen, boron, sulfur, and phosphorus on carbon electrocatalysts for the oxygen reduction reaction. Samples were synthesized under the same conditions and resulted in a similar morphology and surface areas around 1000 m2/g. Incorporating nitrogen into the carbon matrix was found to be easier than for boron or phosphorus, while sulfur doping proved problematic and only yielded 2 at% of sulfur or less. Different dopant concentrations as well as a combination of dopants suggested that nitrogen was the only heteroatom exerting an actual influence on the catalytic activity, resulting in higher electron transfer numbers. The other dopants exhibited a similar performance regardless of the dopant content, though slightly improved when compared to an undoped control sample. These findings indicate that incorporated nitrogen can act as catalytic sites, while boron, sulfur and phosphorus can enhance the catalytic activity by possibly creating defects in the carbon matrix.
Preuss, Kathrin,Siwoniku, Adaeze M.,Bucur, Cristina I.,Titirici, Maria-Magdalena
p. 457 - 464
(2019/04/10)

Highly oxygen deficient, bimodal mesoporous silica based supercapacitor with enhanced charge storage characteristics
The present study elaborates facile approach to generate active sites in cashew nut shaped silica (SiO2). These active sites are attributed to the high concentration of oxygen vacancies and bimodal mesoporosity in silica owing to etching and calcination treatment. In the etched calcined silica (ECS), mesopores act as buffered spaces, whereas, OVs provide high carrier/donor density (3 ×1024cm?3). High density of carriers/donor reduces the distance between active sites (2.5 nm) further enhancing the rate of electron transfer. Consequent to the unique combination of OVs and bimodal mesoporosity, ECS exhibits high electrochemically accessible surface area (3170 m2 g?1) and excellent charge storage in ECS||ECS cell (～337 F g?1 at 1 A g?1). In addition, the symmetric cell (ECS||ECS) delivers maximum energy density of 46.86 Wh Kg?1 at power density of 537.59 W kg?1 with respectable capacitance retention (111% after 10,000 cycles). Remarkably, the solid state flexible device unveiled energy density of 2.16 Wh Kg?1 at 166.05 W kg?1 even under the bent state retaining 165% of its capacitance up till 3000 cycles. This work essentially highlights the synergism between mesoporosity and oxygen vacancies on the charge storage characteristics of silica.
Joshi, Akanksha,Lalwani, Shubra,Singh, Gurmeet,Sharma, Raj Kishore
p. 705 - 714
(2019/01/05)

Sn6SiO8, a Tin(II) Silicate with a Zinc Blende Related Structure and High Thermal Stability
The crystal structure of a novel cubic tin(II) silicate, Sn6SiO8 (space group F4ˉ 3m, a = 10.40708(2) ?, and Z = 4), synthesized by microwave-assisted hydrothermal synthesis has been solved by Rietveld refinement of the powder X-ray diffraction (PXRD) data. The structure, analogous to zinc blende, comprises a face-centered-cubic array of [Sn6O8]4- anions, with Si4+ occupying half of the tetrahedral holes. The tin(II) silicate has been further characterized by variable-temperature PXRD, demonstrating stability of the structure and resistance to SnII oxidation up to ～600 °C, when the compound begins to thermally decompose.
Parsons, Daniel S.,Savva, Savvaki N.,Tang, Wai Chi,Ingram, Andrew,Hriljac, Joseph A.
p. 16313 - 16316
(2019/12/24)

Multiparametric Study of the Synthesis of ThSiO4 under Hydrothermal Conditions
A multiparametric study of the hydrothermal synthesis of ThSiO4, thorite, was performed with the aim of determining the most efficient conditions to form single-phase samples. Among the experimental parameters examined, significant effects were found for the concentration of reactants in the starting mixture, pH of the reactive media, and temperature of the hydrothermal process. Such parameters affected both the rate of formation of thorite and the morphology of the final products synthesized. Precipitation of pure ThSiO4 was obtained over a wide range of pH on going from CHNO3 = 0.3 mol L-1 to pH 9.1 with a yield of over 95%. Temperatures higher than 160 °C favor the formation of thorite. Finally, thorium and silicon concentrations above 2.1 × 10-3 mol L-1 are required to obtain pure thorium silicate.
Estevenon, Paul,Welcomme, Eleonore,Szenknect, Stephanie,Mesbah, Adel,Moisy, Philippe,Poinssot, Christophe,Dacheux, Nicolas
p. 9393 - 9402
(2018/08/17)

Kinetic analysis for cyclic CO2 capture using lithium orthosilicate sorbents derived from different silicon precursors
A series of Li4SiO4 was synthesized using LiNO3 and six different silicon precursors. The precipitated-silica-derived Li4SiO4 presented the highest CO2 capacity in a 10 h sorption test, and ZSM-5-derived Li4SiO4 demonstrated the most rapid CO2 sorption. The CO2 sorption kinetics predominantly followed the nucleation mode and could be accurately described by the Avrami-Erofeev model. The Avrami-Erofeev model provided an in-depth analysis of correlation between sorption performance and material properties. Both the nucleation speed and nucleation dimensionality affected the overall sorption kinetics. The kinetics and pore-size distribution suggest that the sorption kinetics was dependent on the quantity of ～4 nm-pores which favors nucleation dimensionality. For the cyclic tests, the precipitated-silica-derived sample presented the poorest performance with the capacity decreasing from 31.33 wt% at the 1st cycle to only 11.52 wt% at the 30th cycle. However, the sample made from fumed silica displayed an opposite trend with the capacity increasing from 19.90 wt% at the 1st cycle to 34.23 wt% at the 30th cycle. The radically distinct behaviour of samples during cycles was on account of the alternation of sorption kinetics. The decrease in ～4 nm-pores after cycles was responsible for the decrease of nucleation dimensionality for the precipitated-silica-derived sample. The rearrangement during cycles could enrich the pores of ～4 nm for the fumed silica-derived sample, which improved the nucleation growth, thus enhancing the kinetics with cycles.
Zhao, Ming,Fan, Hanlu,Yan, Feng,Song, Yinqiang,He, Xu,Memon, Muhammad Zaki,Bhatia, Suresh K.,Ji, Guozhao
p. 9038 - 9050
(2018/07/25)

Effects of sintering temperature and V2O5 additive on the properties of SiC-Al2O3 ceramic foams
In this study, a series of SiC-Al2O3 ceramic foams (SACFs) were fabricated from the powders of commercial silicon carbide and fused white corundum by polymeric foam replication method combined with reaction sintering process. Effects of sintering temperature (1250 °C-1350 °C) and addition amounts of V2O5 (0–3 wt%) on the sintering properties and post-sintering properties of as-prepared SACFs such as appearances, microstructures, phase compositions, apparent porosity, bulk density, cold compressive strength and thermal shock resistance have been investigated. During the sintering process, SiC was oxidized in air and formed SiO2, then part of as-formed SiO2 reacted with Al2O3 to produce Al6Si2O13 ceramic phase. The mechanical properties of as-prepared SACFs were found to be remarkably increased due to the increase of the sintering temperature and the introduction of V2O5. The phase transformation towards mullite was also found to be promoted, and the mullitization temperature was reduced because of the formation of Si-rich liquid phase due to the addition of V2O5. The improvements in sintering properties, cold compressive strength and thermal shock resistance of as-prepared SACFs were attributed to the formation of mullite and silica ceramic bonding phases in the ceramic matrix during the sintering process in air. The SACFs doped with 1 wt% V2O5 and sintered at 1450 °C for 2 h, achieved their maximum cold compressive strength of 2.45 MPa, and the apparent porosity was still 69.08%.
Ren, Xinming,Ma, Beiyue,Zhang, Yaran,Zhu, Qiang,Li, Dongxu,Li, Shiming,Yuan, Lei,Yu, Jingkun,Liu, Guoqi,Li, Hongxia
p. 716 - 724
(2017/11/07)

Fabrication of TiO2 nanostructures on Ti3SiC2 substrate by anodic oxidation
A TiO2 nanostructure was prepared on a Ti3SiC2 substrate with different water and NH4F concentrations in a fluoride-containing ethylene glycol electrolyte via an anodization process using the same constant-anodization potentials, anodization duration and temperature. The as-prepared samples were characterized by a field-emission scanning electron microscope equipped with an energy dispersive X-ray spectroscope, as well as by X-ray diffraction and X-ray photoelectron spectroscopy. The influence of the anodizing parameters and annealing temperature on the morphology of the nanostructure and the phase structure was studied. The results showed that the scattered TiO2 nanotubes and TiO2 nanoporous films were successfully fabricated in the glycol electrolyte containing (3.0 wt%) NH4F + (5.0 vol%) H2O. The as-prepared samples before calcination were amorphous and could transform to the anatase phase at temperatures higher than 500 °C. As the annealing temperature increased, the crystallization of the anatase phase was enhanced, and the rutile phase appeared at 600 °C. The as-prepared samples mainly consisted of oxides. Ti2O3 and SiO2 oxides were present in addition to TiO2.
Hou, Qin,Yin, Hong-Feng,Yuan, Hu-Die,Tang, Yun,Cai, Yan-Zhi
p. 1983 - 1988
(2018/01/11)

Improved performance of the rechargeable hybrid aqueous battery at near full state-of-charge
For the first time, a green lignin/silica nanocomposite (LSC) is introduced to the rechargeable hybrid aqueous Zn/LiMn2O4 battery (ReHAB) as additive in the cathode formulation. Lignin acts as a key role to regulate and control the structure of LSC, intending to enhance the stability of the ReHAB by improving the float charge performance while maintaining other electrochemical performances of the battery. The lignin/silica nanocomposites (LSCs) are characterized by X-ray diffraction, scanning electron microscopy, surface area and porosimetry analyzer, and transmission electron microscopy. The results show that amorphous, uniform and mesoporous LSC-1 is prepared at the mass ratio of 1:2 of lignin to silica. LSC-1 used as the cathode additive improves the float charge performance of ReHAB via decreasing the float charge capacity by 57%. To compensate the loss of conductivity caused by LSC-1 and increase the capacity of the battery, graphene (G) is added. Compared to the reference battery, battery using the cathode containing 3 wt% combined additive of LSC-1 and G at mass ratio of 1:1, has 50% lower float charge capacity, higher rate performance and better cyclability. Up to a discharge capacity of 95 mAh g?1 is still obtained after 300 cycles of 100% depth-of-discharge.
Xiong, Wenlong,Yang, Dongjie,Zhi, Jian,Hoang, Tuan K.A.,Qiu, Xueqing,Chen
p. 481 - 489
(2018/04/11)

An investigation about the evolution of microstructure and composition difference between two interfaces of plasma electrolytic oxidation coatings on Al
The plasma electrolytic oxidation (PEO) coatings were fabricated on AA1060 aluminum alloy at a constant current density of 4.4 A/dm2. The images of discharge sparks and voltage-time response were recorded during the PEO process. The characteristics of the two interfaces of coatings were investigated as a function of PEO processing time by using X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). Hundreds of coatings were detached from the substrate by an electrochemical method and ground into homogeneous powders to carry out differential scanning calorimeter (DSC) and further XRD qualitative test. In addition, matrix-flushing method was employed to quantitatively measure the content evolution of phase compositions of Al-based detached PEO coatings. The distribution rule of amorphous phases in the PEO coatings was investigated by thickness-reduction method for the first time. Based on the experiments above, gaining an insight into the formation, distribution and evolution of the amorphous and crystalline phases in the PEO process.
Wang, Rui-qiang,Wu, Ye-kang,Wu, Guo-rui,Chen, Dong,He, Dong-lei,Li, Dalong,Guo, Changhong,Zhou, Yefei,Shen, Dejiu,Nash, Philip
p. 272 - 281
(2018/05/09)

Silica-Protection-Assisted Encapsulation of Cu2O Nanocubes into a Metal–Organic Framework (ZIF-8) To Provide a Composite Catalyst
The integration of metal/metal oxide nanoparticles (NPs) into metal–organic frameworks (MOFs) to form composite materials has attracted great interest due to the broad range of applications. However, to date, it has not been possible to encapsulate metastable NPs with high catalytic activity into MOFs, due to their instability during the preparation process. For the first time, we have successfully developed a template protection–sacrifice (TPS) method to encapsulate metastable NPs such as Cu2O into MOFs. SiO2 was used as both a protective shell for Cu2O nanocubes and a sacrificial template for forming a yolk–shell structure. The obtained Cu2O@ZIF-8 composite exhibits excellent cycle stability in the catalytic hydrogenation of 4-nitrophenol with high activity. This is the first report of a Cu2O@MOF-type composite material. The TPS method provides an efficient strategy for encapsulating unstable active metal/metal oxide NPs into MOFs or maybe other porous materials.
Li, Bo,Ma, Jian-Gong,Cheng, Peng
supporting information
p. 6834 - 6837
(2018/03/28)

One-dimension diffusion preparation of concentration-gradient Fe2O3/SiO2Aerogel
Concentration-gradient Fe2O3/SiO2 aerogels were prepared by placing an MTMS (methyltrimethoxysilane)-derived SiO2 aerogel on an iron gauze with an HCl atmosphere via one-dimensional diffusion, ammonia-atmosphere fixing, supercritical fluid drying and thermal treatment. The energy dispersive spectra show that the Fe/Si molar ratios change gradually from 2.14% to 18.48% with a height of 40 mm. Pore-size distribution results show that the average pore size of the sample decreases from 15.8 nm to 3.1 nm after diffusion. This corresponds well with TEM results, indicating a pore-filling effect of the Fe compound. In order to precisely control the gradient, diffusion kinetics are further studied by analyzing the influence of time and position on the concentration of the wet gel. At last, it is found that the diffusion process could be fitted well with the one-dimensional model of Fick’s second law, demonstrating the feasibility of the precise design and control of the concentration gradient.
Zhang, Ting,Wang, Haoran,Zhou, Bin,Ji, Xiujie,Wang, Hongqiang,Du, Ai
(2018/07/10)

Controlling Fast Nucleation and Crystallization of Two New Polyoxoniobates
Applying identical amounts of starting materials allowed the solvothermal preparation of two new polyoxoniobates by controlling the pH value of the reaction mixture. Stirring the slurries afforded crystallization of K5[Cu(H2O)2(cyclam)]1.5{[Cu(cyclam)][Cu(H2O)(cyclam)]2HSiNb18O54}(NO3)·30H2O (I) and {[Cu(cyclam)(H2O)]2[Cu(cyclam)][Nb10O28]}n·9nH2O (II) within short reaction times and in high yields. While compound I crystallizes from the mother liquor at room temperature after hydrothermal treatment at pH values >10.3, compound II is isolated at pH 18O54]14- anion is found, which is surrounded by [Cu(cyclam)]2+ complexes and K+ cations. The water molecules form a very unusual hydrogen bonding pattern which may be classified as a L4(2)4(4)5(4)10(4)16(6)42(14) water cluster. Compound II features the decaniobate anion [Nb10O28]6-, is obtained after short reaction time in high yields and exhibits a reversible release/uptake of crystal water molecules.
Dopta, Joanna,Krause, Dana-Céline,N?ther, Christian,Bensch, Wolfgang
p. 4130 - 4139
(2018/06/25)

Direct electrochemical preparation of nanostructured silicon carbide and its nitridation behavior
Silicon carbide was synthesized from mixtures of SiO2 and graphite by applying the concept of the FFC-Cambridge process and several fundamental aspects of the synthesis route were investigated. Porous disks composed of powders of SiO2 and graphite in molar ratios of 1:0.5, 1:1 and 1:1.5 were prepared by sintering in inert atmosphere and subjected to electro-deoxidation in molten CaCl2 at 1173 K under a range of experimental conditions. Disks of molar ratio 1:1.5, reduced at an applied voltage of 2.8 V for a duration of 6 h, yielded exclusively phase-pure SiC of nanowire morphology as the reaction product, while the other precursor compositions provided significant amounts of calcium silicides. Voltages lower than 2.8 V gave mixtures of SiC with elemental Si and graphite, and voltages higher than that gave CaSi alone. Shorter electro-deoxidation times led to incomplete reduction and allowed for the identification of CaSiO3 as a transient phase. Based on the experimental results a multipath reaction mechanism is proposed, consisting of the electrochemical reduction of SiO2 and CaSiO3 to Si and the subsequent in-situ carbonization of the Si formed to SiC. The effect of N2 at high temperature on the electrochemically synthesized SiC was investigated and the formation of nanowire Si2N2O was observed. Overall, the process presented is a facile single-step and low-temperature method for the synthesis of SiC with possible commercial prospects.
Vishnu, D. Sri Maha,Sure, Jagadeesh,Kim, Hyun-Kyung,Kim, Ji-Young,Kumar, R. Vasant,Schwandt, Carsten
p. D731 - D742
(2019/01/03)

Photochemical Bionanoreactor for Efficient Visible-Light-Driven in Vitro Drug Metabolism
In light of the significance of cytochrome P450 (CYP) catalyzed drug metabolism for drug development and toxicity screening, it is very important to imitate natural metabolic pathways accurately and efficiently in vitro. Herein, a novel and simple photochemical bionanoreactor has been constructed for efficient visible-light-driven in vitro drug metabolism based on eosin-Y-functionalized macroporous ordered silica foams (MOSF-EY). Because of the unique transfer of photoinduced electrons from photosensitizers to CYP heme domain, CYP catalyzed drug metabolism can be in vitro driven by the MOSF-EY nanoreactor under the irradiation of visible light. In such a case, the utilization of expensive electron donors, such as NADPH, can be avoided. Meanwhile, the in vitro drug metabolism approach exhibits high efficiency because of the fast adsorption of both CYP and drug molecules from the bulk solution into the nanopores of MOSF-EY, where the enzyme and substrate are highly concentrated and confined in nanospace to achieve a high reaction rate. Taking advantage of these attractive merits, the first example of photochemical bionanoreactor has been successfully applied in in vitro metabolism of both purified drug molecules and real tablets. Not only excellent CYP-catalyzed drug metabolism but also enzyme inhibition assay has been performed with the MOSF-EY photochemical bionanoreactor.
Fang, Xiaoni,Duan, Yaokai,Liu, Yujie,Adkins, Gary,Zang, Weijun,Zhong, Wenwan,Qiao, Liang,Liu, Baohong
p. 7365 - 7372
(2017/07/28)

Super-microporous silica-supported platinum catalyst for highly regioselective hydrosilylation
Super-microporous micelle-templated platinum on silica catalysts were successfully prepared by an improved one-pot procedure, using a water/acetonitrile/n-dodecylamine mixture. The catalyst showed high surface area and narrow pore size and was further characterized by powder X-ray diffraction and inductively coupled plasma mass spectrometry. The unique super-microporous materials were proven to be highly active for the microwave-assisted hydrosilylation reaction of terminal alkenes or alkynes using dichloromethylsilane as silicon source. The super-microporous structure was beneficial for the control of hydrosilylation regioselectivity, as the selectivity to the β-adduct reached 99%. Moreover, the catalyst could be easily recovered by simple filtration and re-used seven times without appreciable loss of activity and selectivity.
Hu, Wenbin,Xie, Huilin,Yue, Hangbo,Prinsen, Pepijn,Luque, Rafael
p. 51 - 55
(2017/05/10)

Revealing the structural chemistry of the group 12 halide coordination compounds with 2,2′-bipyridine and 1,10-phenanthroline
The coordination compounds of group 12 halides with 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen), 2[CdF2(bpy)2]·7H2O (1), [ZnI(bpy)2]+·I3 ? (2), [CdI2(bpy)2] (3), [Cd(SiF6)H2O(phen)2]·[Cd(H2O)2(phen)2]2+·F–·0.5(SiF6)2–·9H2O (4), [Hg(phen)3]2+·(SiF6)2–·5H2O (5), [ZnBr2(phen)2] (6), 6[Zn(phen)3]2+·12Br–·26H2O (7) and [ZnI(phen)2]+·I– (8), have been synthesized and characterized by X-ray crystallography, IR spectroscopy, elemental and thermal analysis. Structural investigations revealed that metal : ligand stoichiometry in the inner coordination sphere is 1 : 2 or 1 : 3. A diversity of intra- and intermolecular interactions exists in structures of 1–8, including the rare halogen?halogen and halogen?π interactions. The thermal and spectroscopic properties were correlated with the molecular structures of 1–8. Structural review of all currently known coordination compounds of group 12 halides with bpy and phen is presented.
Swiatkowski, Marcin,Kruszynski, Rafal
p. 642 - 675
(2017/02/05)

8,10,12 as nanoreactors for non-enzymatic introduction of: Ortho, meta or para -hydroxyl groups to aromatic molecules
Traditional electrophilic bromination follows long established "rules": electron-withdrawing substituents cause bromination selective for meta positions, whereas electron-donating substituents favor ortho and para bromination. In contrast, in the [PhSiO1.5]8,10,12 silsesquioxanes, the cages act as bulky, electron withdrawing groups equivalent to CF3; yet bromination under mild conditions, without a catalyst, greatly favors ortho substitution. Surprisingly, ICl iodination without a catalyst favors (>90%) para substitution [p-IC6H4SiO1.5]8,10,12. Finally, nitration and Friedel-Crafts acylation and sulfonylation are highly meta selective, >80%. In principle, the two halogenation formats coupled with the traditional electrophilic reactions provide selective functionalization at each position on the aromatic ring. Furthermore, halogenation serves as a starting point for the synthesis of two structural isomers of practical utility, i.e. in drug prospecting. The o-bromo and p-iodo compounds are easily modified by catalytic cross-coupling to append diverse functional groups. Thereafter, F-/H2O2 treatment cleaves the Si-C bonds replacing Si with OH. This represents a rare opportunity to introduce hydroxyl groups to aromatic rings, a process not easily accomplished using traditional organic synthesis methods. The as-produced phenol provides additional opportunities for modification. Each cage can be considered a nanoreactor generating 8-12 product molecules. Examples given include syntheses of 4,2′-R,OH-stilbenes and 4,4′-R,OH-stilbenes (R = Me, CN). Unoptimized cleavage of the Br/I derivatives yields 55-85% phenol. Unoptimized cleavage of the stilbene derivatives yields 35-40% (3-5 equivalents of phenol) in the preliminary studies presented here. In contrast, meta R-phenol yields are 80% (7-10 mol per cage).
Bahrami, Mozhgan,Zhang, Xingwen,Ehsani, Morteza,Jahani, Yousef,Laine, Richard M.
p. 8797 - 8808
(2017/07/22)

Y2Si4N6C:Ce3+ carbidonitride green-yellow phosphors: Novel synthesis, photoluminescence properties, and applications
The Y2Si4N6C:Ce3+ carbidonitride phosphor has been successfully synthesized via a novel acid-driven carbonization and carbothermal reduction nitridation method (ADC-CRN). This novel approach for Y2Si4N6C:Ce3+ promises lower heating temperature and shorter heating time than classical methods, indicative of a cost-effective and facile way to search for new silicon-based carbidonitrides. In contrast to Ce3+ activated (oxy)nitrides showing blue-green emissions, Y2Si4N6C:Ce3+ exhibits an individual green-yellowish emission band centered at 550 nm which is ascribed to the incorporation of highly covalent C4- into the host lattice. The sp3 hybrid C4- was identified through high resolution electron energy loss spectroscopy analysis (EELS). Direct evidence for sole substitution of Ce3+ for Y3+ in Y2Si4N6C is represented for the first time using electron paramagnetic resonance (EPR) spectra. The red shift induced by the increasing Ce3+ content in Y2Si4N6C is reasonably deduced by the energy transfer model of intra-Ce3+ and inter-Ce3+ ions. A pc-w-LED packaging was fabricated via a combination of the yellow Y2Si4N6C:Ce3+ and blue La2Si4N6C:Ce3+ phosphors prepared using a 365 nm n-UV chip. The w-LED device shows a good color rendering index (Ra), CIE chromaticity coordinates and correlated color temperature (CCT) of 83.8, (0.3258, 0.3314) and 5819 K, respectively. These results suggest that Y2Si4N6C:Ce3+ has great potential for use in UV-LED-driven white emitting diodes.
Wan, Jieqiong,Liu, Qian,Liu, Guanghui,Zhou, Zhenzhen,Xie, Rong-Jun
p. 6061 - 6070
(2017/07/10)

Anatase TiO2 nanoparticle coating on porous COK-12 platelets as highly active and reusable photocatalysts
Nanoscale TiO2 photocatalysts are widely used for biomedical applications, self-cleaning processes and wastewater treatments. The impregnation/deposition of TiO2 nanoparticles is indispensable for facile handling and separation as well as the improvement of their photocatalytic performance. In the present study, ordered mesoporous COK-12 silica thin platelets with a high-aspect-ratio and rough surfaces are demonstrated as a potential nanoporous support for homogeneous TiO2 nanoparticle coatings with high loading up to 16.7 wt%. The photocatalytic composite of COK-12 platelets and TiO2 nanoparticles is characterized in detail by HRSEM, SAXS, XRD, N2 physisorption analysis, solid-state UV-vis spectroscopy, HAADF-STEM, EDX analysis, and electron tomography. HAADF-STEM-EDX and electron tomography studies reveal a homogeneous dispersion of nanosized TiO2 nanoparticles over COK-12 platelets. The final composite material with anatase TiO2 nanoparticles that demonstrate a blueshifted semiconductor band gap energy of 3.2 eV coated on a highly porous COK-12 support shows exceptional photocatalytic catalytic activity for photodegradation of organic dyes (rhodamine 6G and methylene blue) and an organic pollutant (1-adamantanol) under UV light radiation, outperforming the commercial P25 TiO2 (Degussa) catalyst.
Wee,Meledina,Turner,Custers,Kerkhofs,Sree,Gobechiya,Kirschhock,Van Tendeloo,Martens
p. 46678 - 46685
(2016/06/01)

Hybrid Hierarchical Porous Silica Templated in Nanoemulsions for Drug Release
A new nanocarrier for loading and releasing drugs is reported, and ketoprofen was used as a model drug. More precisely, the carrier is a hybrid material prepared by combining oil-in-water (O/W) nanoemulsions, into which the drug has been solubilized, with mesostructured silica. This organic-inorganic hybrid material shows a controlled release of the drug that is pH dependent. If the drug is impregnated into the bare hierarchical meso-/macroporous dual silica material, obtained after the removal of the organic components by extraction, only 8 wt.-% of ketoprofen is released in a phosphate buffer medium (pH 7.4), probably owing to its low solubility in the aqueous phase. The drug solubility and release are increased strongly by the addition of Pluronic micelles to the receptor phase; this suggests a micelle-promoted and -assisted release mechanism. Whatever the vehicle, the release profiles of ketoprofen always follow the Korsmeyer-Peppas model with a diffusional release exponent value lower than 0.5, characteristic of a pseudo-Fickian release mechanism. Moreover, the release of ketoprofen is better controlled from the hybrid nanocarrier than from the hierarchical bare porous silica.
Riachy, Philippe,Roig, Ferran,García-Celma, Maria-José,Stébé, Marie-José,Pasc, Andrea,Esquena, Jordi,Solans, Conxita,Blin, Jean Luc
p. 1989 - 1997
(2016/05/19)

Formation of Fe3O4@MnO2 ball-in-ball hollow spheres as a high performance catalyst with enhanced catalytic performances
While the synthesis of heterogeneous catalysts is well established, it is extremely challenging to fabricate complex hollow structures with mixed transition metal oxides. Herein, we report a facile in situ growth process of SiO2@Fe3O4@MnO2, followed by an etching method to synthesize a hierarchical hollow structure, namely Fe3O4@MnO2 ball-in-ball hollow spheres (Fe3O4@MnO2 BBHs). The as-prepared Fe3O4@MnO2 BBHs were applied to degrade methylene blue (MB) by catalytic generation of active radicals from peroxymonosulfate (PMS), exhibiting the merits of excellent catalytic performance, easy separation, good stability and recyclability. In this architecture, the degradation process can be divided into three layers. The outer hierarchical MnO2 nanosheets could accumulate and transport the pollutants by electrostatic interactions and catalyze the generation of active radicals for degradation. Both the inner MnO2 nanosheets and the outer Fe3O4 hollows could produce active radicals to accelerate the pollutant degradation. The active catalytic sites also existed in the inner Fe3O4 hollows, which could further degrade the highly concentrated pollutants in the hollows. This work provides new strategies for the controllable synthesis of complex hollow structures and their application in environmental remediation.
Zhang, Shouwei,Fan, Qiaohui,Gao, Huihui,Huang, Yongshun,Liu, Xia,Li, Jiaxing,Xu, Xijin,Wang, Xiangke
p. 1414 - 1422
(2016/02/03)

Smart design of hollow AuPt nanospheres with a porous shell as superior electrocatalysts for ethylene glycol oxidation
Hollow bimetallic electrocatalysts have recently stimulated increasing attention due to their accessible interior surface and bimetallic synergetic effect. Herein, for the first time, we successfully anchor a porous AuPt shell on modified silica spheres with the assistance of Pluronic F127. The whole process consists of simple ultrasonic mixing for 30 min at room temperature without any organic solvent. After metal deposition and silica etching, well-defined hollow structures are obtained in high yield. The hollow spheres are further characterized by scanning electron microscopy and transmission electron microscopy. The electrochemical analysis reveals that the as-prepared samples demonstrate superior electrocatalytic activity and durability relative to the commercial Pt/C catalyst, showcasing the potential of these AuPt hollow spheres as electrocatalysts for ethylene glycol oxidation in an alkaline medium.
Lu, Qingqing,Wei, Changting,Sun, Litai,Alothman, Zeid A.,Malgras, Victor,Yamauchi, Yusuke,Wang, Hongjing,Wang, Liang
p. 19632 - 19637
(2016/03/01)

Band gap and morphology engineering of TiO2 by silica and fluorine co-doping for efficient ultraviolet and visible photocatalysis
Silicon and fluorine co-doped anatase TiO2 (Si-F-TiO2) photocatalysts with enhanced photocatalytic activity were successfully prepared via a facile two-step synthetic method by using SiO2 powders and (NH4)2TiF6 as the precursors. The obtained products were thoroughly characterized using various techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance spectroscopy and N2 adsorption-desorption analysis. The characterization revealed the effects of molar ratio of silica to titanium (R) and pH value on morphology, size and crystal structure of Si-F-TiO2 samples. We find that the band gap of the catalyst can be engineered from 3.16 to 2.88 eV via altering the molar ratio of Si : Ti and the pH value. Compared with un-doped or F-doped TiO2, co-doped Si-F-TiO2 samples exhibited improved photocatalytic degradation toward different dye molecules under both ultraviolet and visible light illumination. With the aid of hole and radical trapping experiments, we proposed a photocatalytic mechanism for the examined systems. Furthermore, first-principle calculations provide theoretical insights for the enhanced photocatalytic performance of codoped Si-F-TiO2 photocatalyst.
Tang, Hua,Chang, Shufang,Wu, Kongqiang,Tang, Guogang,Fu, Yanhui,Liu, Qinqin,Yang, Xiaofei
p. 63117 - 63130
(2016/07/19)

Avoiding carbothermal reduction: Distillation of alkoxysilanes from biogenic, green, and sustainable sources
The direct depolymerization of SiO2 to distillable alkoxysilanes has been explored repeatedly without success for 85 years as an alternative to carbothermal reduction (1900 °C) to Simet, followed by treatment with ROH. We report herein the base-catalyzed depolymerization of SiO2 with diols to form distillable spirocyclic alkoxysilanes and Si(OEt)4. Thus, 2-methyl-2,4-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, or ethylene glycol (EGH2) react with silica sources, such as rice hull ash, in the presence of NaOH (10 %) to form H2O and distillable spirocyclic alkoxysilanes [bis(2-methyl-2,4-pentanediolato) silicate, bis(2,2,4-trimethyl-1,3-pentanediolato) silicate or Si(eg)2 polymer with 5-98 % conversion, as governed by surface area/crystallinity. Si(eg)2 or bis(2-methyl-2,4-pentanediolato) silicate reacted with EtOH and catalytic acid to give Si(OEt)4 in 60 % yield, thus providing inexpensive routes to high-purity precipitated or fumed silica and compounds with single Si-C bonds. No detours: The base-catalyzed depolymerization of SiO2 from different sources with diols led directly to distillable alkoxysilanes, including spirocyclic compounds, thus providing inexpensive routes to high-purity silica and compounds with single Si-C bonds (see scheme): The alkoxysilanes could be converted either into Si(OEt)4 by treatment with EtOH and a catalytic amount of acid or into high-purity precipitated (ppt) or fumed silica.
Laine, Richard M.,Furgal, Joseph C.,Doan, Phi,Pan, David,Popova, Vera,Zhang, Xingwen
supporting information
p. 1065 - 1069
(2016/01/20)

MoSi2 Oxidation in 670-1498 K Water Vapor
Molybdenum disilicide (MoSi2) has well documented oxidation resistance at high temperature (T > 1273 K) in dry O2 containing atmospheres due to the formation of a passive SiO2 surface layer. However, its behavior under atmospheres where water vapor is the dominant species has received far less attention. Oxidation testing of MoSi2 was performed at temperatures ranging from 670-1498 K in both 75% water vapor and synthetic air (Ar-O2, 80%-20%) containing atmospheres. Here the thermogravimetric and microscopy data describing these phenomena are presented. Over the temperature range investigated, MoSi2 displays more mass gain in water vapor than in air. The oxidation kinetics observed in water vapor differ from that of the air samples. Two volatile oxides, MoO2(OH)2 and Si(OH)4, are thought to be the species responsible for the varied kinetics, at 670-877 K and at 1498 K, respectively. Increased oxidation (140-300 mg/cm2) was observed from 980-1084 K in water vapor, where passivation is observed in air.
Sooby Wood, Elizabeth,Parker, Stephen S.,Nelson, Andrew T.,Maloy, Stuart A.
p. 1412 - 1419
(2016/04/20)