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7440-67-7Relevant articles and documents
A New Patterning Method Using Photocatalytic Lithography and Selective Atomic Layer Deposition
Lee, Jae P.,Sung, Myung M.
, p. 28 - 29 (2004)
We report a new patterning method using photocatalytic lithography of alkylsiloxane self-assembled monolayers and selective atomic layer deposition of thin films. The photocatalytic lithography is based on the fact that the decomposition rate of the alkylsiloxane monolayers in contact with TiO2 is much faster than that with SiO2 under UV irradiation in air. The photocatalytic lithography, using a quartz plate coated with patterned TiO2 thin films, was done to prepare patterned monolayers of the alkylsiloxane on Si substrates. A ZrO2 thin film was selectively deposited onto the monolayer-patterned Si substrate by atomic layer deposition. Copyright
Search for ferromagnetism in manganese-stabilized zirconia
Dimri, M. Chandra,Kooskora,Pahapill,Joon,Heinmaa,Subbi,Stern
, p. 172 - 179 (2011)
Magnetic properties of Mn-stabilized cubic zirconia (ZrO2) powder samples were investigated to verify the recent theoretical predictions of ferromagnetism in transition-metal-doped ZrO2. It was found that 5% Mn-doped cubic ZrO2
Preparation of ultrafine zirconium dioxide particles by thermal decomposition of zirconium alkoxide vapour
Adachi, Motoaki,Okuyama, Kikuo,Moon, Seongwon,Tohge, Noboru,Kousaka, Yasuo
, (1989)
Ultrafine zirconia particles are produced by thermal decomposition of zirconium tetratertiary butoxide (ZrTB) vapour. The introduction of ZrTB vapour into the cylindrical electric furnace, is achieved by three different methods: (evaporator, pressurized n
One-step controllable synthesis for high-quality ultrafine metal oxide semiconductor nanocrystals via a separated two-phase hydrolysis reaction
Tang, Kangjian,Zhang, Jianan,Yan, Wenfu,Li, Zhonghua,Wang, Yangdong,Yang, Weimin,Xie, Zaiku,Sun, Taolei,Fuchs, Harald
, p. 2676 - 2680 (2008)
A one-step synthesis method is described to prepare high-quality ultrafine inorganic semiconductor nanocrystals via a two-phase interface hydrolysis reaction under hydrothermal conditions. With the synthesis of ZrO2 quantum dots as an example, we show that the prepared nanocrystals have good monodispersity and high crystallinity, as well as other related superior properties, e.g., strong photoluminescence and excellent photocatalytic activities. Also the crystal size can be conveniently adjusted in the range below 10 nm through controlling the reaction temperature. Besides that, this method also shows other distinct advantages compared with other methods reported previously. First, the preparation process is simple and cheap and does not contain any complicated posttreatment procedure. Second, products (without coating) can be collected from the organic phase which effectively avoids grain aggregation induced by the capillary concentration in the water environment. Third, the production yield is very high (almost 100%) and the organic and water phases after reaction can be easily recycled for next reaction. Therefore, it provides a promising strategy for the large-scale industrial production of different kinds of high-quality inorganic nanocrystals.
Synthesis of ZrO2 nanoparticles in microwave hydrolysis of Zr (IV) salt solutions-Ionic conductivity of PVdF-co-HFP-based polymer electrolyte by the inclusion of ZrO2 nanoparticles
Kalyana Sundaram,Vasudevan,Subramania
, p. 264 - 271 (2007)
Nanocrystalline ZrO2 particles have been prepared by microwave hydrolysis of Zr(IV) salt solutions at 400 {ring operator} C for 6 h. The paper describes the PVdF - co - HFP - ZrO2-based NCPEMs prepared by a simple solvent casting technique. The incorporation of ZrO2 nanoparticles in the PVdF-co-HFP matrix, improved the ionic conductivity due to the availability of a large amount of oxygen vacancies on ZrO2 surface which may act as the active Lewis acidic site that interact with ClO4- ions. On the other hand, a high concentration of ZrO2 [10 wt(%)] leads to depression in ionic conductivity due to the formation of more crystalline phase in the PVdF-co-HFP matrix. DSC, XRD, SEM and DC-polarization studies were carried out. This paper also explores and proposes a structure-conductivity correlation in the PVdF - co - HFP - LiClO4 - ZrO2-based NCPEMs system. The proposed correlation is derived from the interpretation of DSC, XRD and AC-impedance measurements. The temperature dependence of the ionic conductivity of NCPEMs follows the Arrhenius behaviour. Finally, the LSV experiment has been carried out to investigate the electrochemical stability in the polymer electrolytes.
Thermal behavior of the Ti(IV), Zr(IV) and Pb(II) complexes with 5-nitro-8-hydroxyquinoline
Crespi,Zorel Jr.,Ribeiro
, p. 507 - 514 (2003)
Ti(IV), Zr(IV) and Pb(II) complexes with 5-nitro-8-hydroxyquinoline (5-NQ) were obtained by precipitation in acetone/ammonium solution medium. The compounds TiO(C9H5N2O3)2·0.5 H2O, ZrO(Csu
Jackson, Nancy B.,Ekerdt, John G.
, p. 31 - 45 (1990)
Polar solvation dynamics of H2O and D2O at the surface of zirconia nanoparticles
Pant, Debi,Levinger, Nancy E.
, p. 7846 - 7852 (1999)
Time-resolved fluorescence-upconversion spectroscopy has been used to study the polar solvation dynamics of H2O and D2O at the surface of zirconia (ZrO2) nanoparticles. While an isotope effect is observed for the solvation dynamics of bulk D2O, there is no isotope effect on the interfacial solvation dynamics. The interfacial solvation dynamics are the same for H2O and D2O and are faster than the bulk solutions. The bulk isotope effect is due to stronger hydrogen bonding in D2O compared to H2O, slowing the reorientation of the excited-state dipoles in the bulk D2O. The lack of isotope effect for the interfacial dynamics is explained in terms of the solvent interacting with the ZrO2 surface. ? 1999 American Chemical Society.
Sulfated zirconia as an efficient catalyst for organic synthesis and transformation reactions
Reddy, Benjaram M.,Sreekanth, Pavani M.,Lakshmanan, Pandian
, p. 93 - 100 (2005)
The efficacy of sulfated zirconia catalyst was investigated towards various acid-catalyzed organic syntheses and transformation reactions in the liquid phase. The SO42-/ZrO2 efficiently catalyzes synthesis of 1,5-benzodiazepine derivatives, electrophilic substitution of indoles with aldehydes to afford the corresponding bis(indolyl)methanes, synthesis of 3,4-dihydropyrimidinones, synthesis of diaryl sulfoxides, and tetrahydropyranylation of alcohols and phenols. Various advantages associated with these protocols include, simple work-up procedure, solvent-free conditions, short reaction times, high product yields and easy recovery and reusability of the catalyst. The SO4 2-/ZrO2 catalyst was obtained by immersing a finely powdered hydrous Zr(OH)4 into 1 M H2SO4 solution and subsequent drying and calcination at 923 K. The Zr(OH)4 was prepared from aqueous ZrOCl2·8H2O solution by hydrolysis with dilute ammonium hydroxide. The bulk and surface properties of the prepared catalysts were examined by X-ray powder diffraction, BET surface area, ammonia-TPD and Raman spectroscopy techniques. All characterization results revealed that the incorporated sulfate ions show a significant influence on the surface and bulk properties of the ZrO2. In particular, XRD and Raman results suggest that impregnated sulfate ions stabilize the metastable tetragonal phase of ZrO2 at ambient conditions. Ammonia-TPD and BET surface area results indicate that sulfated catalyst exhibits enhanced acid strength and specific surface area than that of unprompted ZrO2.
Catalytic reduction of NO by CO over Cu/CexZr1- xO2 prepared by flame synthesis
Zhang, Runduo,Teoh, Wey Yang,Amal, Rose,Chen, Biaohua,Kaliaguine, Serge
, p. 210 - 219 (2010)
Mixed oxides of 4% Cu/CexZr1-xO 2 (x = 0, 0.25, 0.50, 0.75, 1) were synthesized by flame spray pyrolysis and characterized by N2 adsorption, XRD, XPS, O 2-TPD and H2-TPR. The as-prepared catalysts were assessed for the equimolar reduction of NO by CO (3000 ppm each, space velocity 50,000 h-1). Incorporation of Zr4+ in the form of solid solution with CeO2 stabilizes the Cu+ species, which was in turn beneficial for the initial reductive chemisorption of NO to N2O. A peculiar low-temperature activity giving 40% N2 yield was found with the composition of Cu/Ce0.75Zr0.25O2 at 150 °C. This is traced to the low-temperature activation of rapid CO oxidation (as probed by in situ DRIFTS), related to the abundance of surface reactive lattice oxygen sites and their high reducibility. At 250 °C and above, a N2 yield of >85% (and ～100% at 350 °C) was obtained for all Zr-containing catalysts i.e. Cu/CexZr1- xO2 (x 2O detected in the exhaust gas stream. An organonitrogen mechanism is occurring in this case.
Effect of Cr2O3addition on crystallization, microstructure and properties of Li2O–Al2O3–SiO2glass-ceramics
Li, Bo,Wang, Shanlin,Fang, Yi
, p. 9 - 15 (2017)
A new glass-ceramic with high flexural strength and low thermal expansion based on Li2O–Al2O3–SiO2(LAS) was prepared in this study. The effects of Cr2O3addition on the crystallization, microstructure, flexural strength, thermal expansion, and electrical properties of LAS system were investigated. The crystallization kinetics based on DSC analysis was calculated using Kissinger and Ozawa methods, which showed that the activation energy E decreases from 158.5 to 149.3?kJ/mol, indicating that Cr2O3is beneficial to the crystallization of LAS; the crystallization index n varies between 4.46 and 5.09, indicating that the crystallization manner is the volumetric crystallization. XRD analysis was estimated by the whole pattern fitting method, demonstrating that Cr2O3addition could change the phase contents and promote the crystallinity. The crystallization of CaMgSi2O6and Cr2O3with higher CTE not only properly adjusted CTE for matching Si, but also dramatically improved the flexural strength for LAS glass-ceramic. Moreover, we provided a modified formula to calculate CTE of glass-ceramic in the acceptable range. LAS glass-ceramic with 3?wt% Cr2O3sintered at 800?°C exhibited good properties: σ?=?208?MPa, α?=?2.64?×?10?6/°C, ε?=?8.3, tanδ?=?3.6?×?10?3, ρ?=?8.82?×?1012?Ω?cm, indicating its suitability for LTCC application.
A comparative study of the surface structure, acidity, and catalytic performance of tungstated zirconia prepared from crystalline zirconia or amorphous zirconium oxyhydroxide
Lebarbier, Vanessa,Clet, Guillaume,Houalla, Marwan
, p. 13905 - 13911 (2006)
Tungstated zirconias prepared from W deposition on zirconium oxyhydroxide are reportedly active for alkane isomerization, whereas solids synthesized by impregnation of zirconia are inactive. The origin of the differences between the two preparations is not fully understood. The present paper examines the influence of W surface density and the nature of the support on the surface structure, development of the acidity, and catalytic performance of WO x/ZrO2 catalysts. Two series of catalysts containing W surface densities up to 5.2 at. W/nm2 were prepared by pore volume impregnation of two different supports: zirconium oxyhydroxide and predominantly tetragonal zirconia (65% tetragonal, 35% monoclinic). The texture and structure of the catalysts were investigated by BET measurements, X-ray diffraction, Roman and infrared spectroscopy. The catalytic activity was tested for 2-propanol dehydration and n-hexane isomerization. For catalysts obtained by impregnation of Zr oxyhydroxide, Raman results showed that W was present as a surface phase. Infrared spectra indicated an increase in the degree of polymerization of W species with increasing W surface density. The development of the acidity was monitored by lutidine adsorption and desorption at 523 K, followed by infrared spectroscopy. The results indicated the presence of a threshold of W surface density at 1.3 at. W/ nm2 for the detection of these acid sites, followed by a progressive increase in their abundance with increasing W surface density. The development of Br?nsted acidity correlated with the evolution of the infrared bands attributed to extensively polymerized W species. A direct relationship was observed between the abundance of Br?nsted acid sites and the catalytic activity for 2-propanol dehydration. For n-hexane isomerization, compared to 2-propanol dehydration, a higher threshold of W surface densities (3.4 at. W/ nm2) for the development of activity was observed. The difference was attributed to stronger Br?nsted acid sites required for n-hexane.isomerization. The catalysts prepared by impregnation of zirconia exhibited comparable behavior. For a given W surface density, the crystalline composition of the support (tetragonal/monoclinic zirconia), the W surface structure, abundance of Br?nsted acid sites, and catalytic performance were similar. Thus, in an apparent variance with some of the results reported in the literature with respect to the influence of preparation methods, no significant effect of the initial form of the support (Zr oxyhydroxide versus predominantly tetragonal zirconia) was evidenced.
Variation of fundamental and higher-order Raman spectra of ZrO2 nanograins with annealing temperature
Siu,Stokes,Liu, Yulong
, p. 3173 - 3179 (1999)
ZrO2 nanograins annealed at different temperatures are systematically investigated using x-ray diffraction (XRD) and Raman spectroscopy. Our results show that bulk properties of nano-ZrO2 diminish but the defect-, surface-, and size-related features display as grain size decreases. A critical size that divides respective predominance is determined to be about 15 nm. Both XRD and Raman spectra of nano-ZrO2 of size above 15 nm are similar to bulk ones. On the contrary, those of nano-ZrO2 of size below 15 nm are deteriorated bulk spectra with spectroscopic line broadening and merging, line intensity reducing, and position shifting. Deteriorated XRD spectra are essentially associated with increasing defects in small nanograins. General mode softening, a surface mode around 1040 cm-1 and 14 weak second-order (overtone and combination) modes are characteristics of Raman spectra of nano-ZrO2 below 15 nm. They are associated with microstructure change of nanograins, i.e., they reflect the effects of grain size, surface, and the interaction between nanograins. 1999 The American Physical Society.
Effect of nanocrystallite structure on the lower activation energy for Sm2O3-doped ZrO2
Chen, Shou-Gang,Yin, Yan-Sheng,Wang, Dao-Ping,Wang, Xin
, p. 19 - 23 (2004)
Pure and 2mol% Sm2O3-doped ZrO2 nanopowders were synthesized via the precipitation method. The very lower activation energy (～25.979 kJ/mol) related to the bulk counterpart is observed for the grain growth within the calcination temperature range of 600-1000°C. Experimental results show that two factors were contributed to the lower activation energy of grain growth. Firstly, the introduction of oxygen vacancies in nano-2SmSZ grain surface reduces the activation energy of the formation of necks between grains. Secondly, the rotation process between coherent grains has very lower activation energy or even a zero-kinetic barrier.
Structural and magnetic properties of iron doped ZrO2
De Souza, Ant?nio O.,Ivashita, Flávio F.,Biondo, Valdecir,Paesano, Andrea,Mosca, Dante H.
, p. 701 - 710 (2016)
Zr1-xFexO2 samples were synthesized by a freeze-drying process, varying the iron concentration from x = 0 to x = 0.40. The solid solutions prepared were structurally and magnetically characterized. The results showed that the samples crystallized with the tetragonal structure of zirconia for low iron concentrations, with the respective cubic structure for intermediate iron concentrations, and that hematite is formed secondarily at the highest doping levels. It was also revealed that the lattice parameter of the zirconia solid solutions decreases almost linearly with increasing dopant concentration. All the monophasic samples are paramagnetic at room and low temperatures, except for the x = 0.25 sample, which revealed an incipient magnetization at 13 K. The fluctuations are antiferromagnetic throughout the temperature range and the exchange interaction was attributed to two mechanisms occurring simultaneously: a direct exchange interaction between nearest neighbors magnetic moments, dominant at the lowest temperatures and an indirect exchange interaction, induced by charge carriers, more effective at the highest temperatures. Both mechanisms are more active for higher iron concentrations.
Synergetic effect of Cu active sites and oxygen vacancies in Cu/CeO2-ZrO2for the water-gas shift reaction
Hu, Yuanwu,Wang, Na,Zhou, Zhiming
, p. 2518 - 2528 (2021)
A series of Cu/CeO2-ZrO2catalysts with different Ce/(Ce + Zr) molar ratios and Cu loadings were prepared by a simple citrate sol-gel method, characterized by various techniques, and evaluated for water-gas shift (WGS) under H2-rich and low H2O/CO molar ratio conditions of the sorption enhanced WGS process. It was shown that the oxygen vacancy concentration and the Cu dispersion were important structural factors affecting the catalytic activity of Cu/CeO2-ZrO2, but neither of them alone was capable of correlating with the turnover frequency (TOF) for WGS based on kinetic analysis. By contrast, a positive linear correlation was established between the TOF and the ratio of oxygen vacancy concentration to Cu dispersion, demonstrating the synergetic effect of Cu active sites and oxygen vacancies for WGS. The stability of Cu/CeO2-ZrO2was found to be dependent on the crystal structure of CeO2-ZrO2solid solution, and the cubic to tetragonal phase transformation of CeO2-ZrO2led to a decreased stability. Among all Cu/CeO2-ZrO2investigated, the catalyst with a Ce/(Ce + Zr) molar ratio of 0.6 and a Cu loading of 50 wt% showed the highest activity and stability under 20% H2, 40% CO and 40% steam in a gas hourly space velocity of 20?000 h?1at 350 °C, with the CO conversion slightly varying from 77% to 75% over 60 h on stream and meanwhile 100% selectivities to H2and CO2
Formation of Acetonitrile from Triethylamine on Oxide Catalysts
Xu, Bo-Qing,Yamaguchi, Tsutomu,Tanabe, Kozo
, p. 1053 - 1056 (1987)
Acetonitrile was found to be formed from triethylamine over ZrO2 by TPD and IR experiments.The activity was higher than that of a strongly acidic SiO2-Al2O3.No acetonitrile was formed over a strongly basic MgO.
Influence of synthesis methods on tungsten dispersion, structural deformation, and surface acidity in binary WO3-ZrO2 system
Cortes-Jacome,Toledo,Angeles-Chavez,Aguilar,Wang
, p. 22730 - 22739 (2005)
WO3-ZrO2 catalysts were synthesized by precipitating the aqueous solutions of zirconium oxynitrate and ammonium metatungstate with ammonium hydroxide. The white slurry precipitate was treated under three different conditions. In the as-made materials, the amorphous phase was formed in the aged and refluxed samples, while well-crystallized tetragonal and monoclinic phases were obtained in the hydrothermally treated sample. The real amount of tungsten loaded in the samples was similar for the three samples, independently of the treatments; however, the tungsten surface atomic density in the annealed WO3-ZrO2 samples varied between 6 and 9 W atoms/nm2. Two different contrast types of aggregates were determined by scanning electron microscopy, the white particles which are rich in W, and the gray ones which are rich in zirconium; both of them were formed in the calcined solids prepared under aging or reflux condition. A very high dispersion of tungsten species on the zirconia surface was achieved in the hydrothermally treated sample. The degree of the interaction between WOx and ZrO2 surface strongly modified the Zr-O bond lengths and bond angles in the structure of tetragonal zirconia as proved by X-ray diffraction analysis and the Rietveld refinement. The catalyst obtained under hydrothermal condition exhibited the highest dispersion of tungsten species in the zirconia, which in turn causes strong structural deformation of the tetragonal ZrO2 phase responsible of the strongest surface acidity and, consequently, the optimum catalytic activity for n-hexane isomerization.
Surface properties and CO adsorption on zirconia polymorphs
Ma, Zhong-Yi,Yang, Cheng,Wei, Wei,Li, Wen-Huai,Sun, Yu-Han
, p. 119 - 124 (2005)
FT-IR spectroscopy and TPD profiles were performed to determine and compare the surface properties of amorphous, monoclinic and tetragonal zirconia polymorphs. It was found that zirconia polymorphs exhibited different surface hydroxyl and acid-base proper
Oxidation of carbon monoxide over MLaOx perovskites supported on mesoporous zirconia
Davshan, Nikolai A.,Kustov, Alexander L.,Tkachenko, Olga P.,Kustov, Leonid M.,Kim, Chang Hwan
, p. 1990 - 1997 (2014)
The oxidation of CO was studied on a series of MLaO3 perovskites (M=Co, Fe, Ni) supported on mesoporous zirconia that are synthesized by using a glycine-mediated method and characterized by using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy. The activity of the catalysts in the CO oxidation reaction follows the order Co>Ni>Fe.
Gas phase decarbonylation of diethyl oxalate to diethyl carbonate over alkali-containing catalyst
Hao, CuiYing,Wang, Shengping,Ma, Xinbin
, p. 130 - 135 (2009)
A detailed alkali catalytic preparation of diethyl carbonate (DEC) from diethyl oxalate (DEO) via gaseous phase decarbonylation was investigated in the paper. Evaluation results showed that 6 wt% (based on potassium) K2CO3/AC (activa
Synthesis, spectral characterisation and thermal studies of zirconyl complexes of biologically active molecules
Jisha,Suma,Sudarsanakumar
, p. 509 - 513 (2010)
Zirconyl complexes of hippuric acid (C9H9NO 3, hipH) and monophenylbutazone (4-butyl-1-phenyl-3,5- pyrazolidinedione,MPB) were prepared using ZrOCl2 . 8H2O and ZrO(NO3)3 . xHsub
Low-temperature glass bonding for development of silicon carbide/zirconium tungsten oxide porous ceramics with near zero thermal expansion coefficient
Poowancum, Anurat,Matsumaru, Koji,Ishizaki, Kozo
, p. 1354 - 1356 (2011)
Near zero thermal expanding porous ceramics are useful in many applications in advanced manufacturing techniques, especially electronics engineering. Zirconium tungsten oxide (ZrW2O8) has been expected to be an excellent negative thermal expansion material for reducing thermal expansivity of composites. However, at 777°C ZrW2O8 decomposes to ZrO2 and WO3, which have positive thermal expansion coefficient and limit applications of ZrW2O8. Therefore, a low temperature sintering technique is required to use ZrW 2O8 in zero thermal expanding composite. This work develops a low temperature glassy bonding agent to fabricate near zero thermal expanding SiC/ZrW2O8 porous ceramics. The results show ZrW2O8 reacts with alkali and alkaline earth oxides at lower temperatures than the decomposition temperature of ZrW2O 8. Nevertheless, ZrW2O8 is inert with Al 2O3, B2O3, and SiO2. By using borosilicate glass (B2O3-SiO2) as a bonding agent, SiC/ZrW2O8 porous ceramics are sintered at temperatures lower than the decomposition temperature of ZrW2O 8 and have near zero thermal expansion coefficient (-0.2×10-6 K-1). No reaction is found between the glassy bonding agent and ZrW2O8 or SiC.
Rate enhancement by Cu in NixCu1-x/ZrO2 bimetallic catalysts for hydrodeoxygenation of stearic acid
Denk, Christoph,Foraita, Sebastian,Kovarik, Libor,Stoerzinger, Kelsey,Liu, Yue,Baráth, Eszter,Lercher, Johannes A.
, p. 2620 - 2629 (2019)
Hydrodeoxygenation of stearic acid on Ni/ZrO2 to n-heptadecane occurs via the reduction to 1-octadecanal, followed by decarbonylation of the aldehyde to n-heptadecane. Stearic acid binds stronger than 1-octadecanal on Ni, causing decarbonylation to start only once stearic acid is almost fully converted. This first step is enhanced by addition of Cu either in the form of Cu/ZrO2 or in the form of a ZrO2 supported NixCu1-x nano-alloy. Cu has not only a higher activity for the reduction of stearic acid, it also increases the activity of Ni for decarbonylation of 1-octadecanal by increasing the electron density of Ni in the bimetal catalyst. The combination of these two effects leads to high activity of Ni-Cu bimetallic catalysts.
Influence of treatment with sulfuric acid on the angularity of a zirconia system
Benedetti, Alvise,Polizzi, Stefano,Pinna, Francesco
, p. 451 - 452 (1996)
Small-angle X-ray scattering (SAXS) measurements have been used to determine the influence of sulfation on the morphology of zirconia particles. Two samples were investigated: a zirconium oxide powder before (sample A) and after (sample B) a sulfation treatment with H2SO4. The decrease of about one order of magnitude in the angularity value for sample B provided quantitative proof of transmission electronic microscopy (TEM) evidence.
Optical Properties of Molybdates Containing a Combination of Rare-Earth Elements
Dorzhieva,Sofich,Bazarov,Shendrik, R. Yu,Bazarova
, p. 54 - 59 (2021/03/22)
Abstract—: We have synthesized new molybdates, Cs2LnZrTi(MoO4)6.5 (Ln = Eu + Yb, Eu + Dy, and Gd + Dy lanthanides), containing pairs of rare-earth elements in the ratio 1 : 1. The synthesized compounds have been shown to be single-phase and isostructural with each other. We have determined their crystallographic characteristics and assessed their thermal stability. In the dysprosium-containing molybdates, the Dy3+ luminescence intensity is low as a result of concentration quenching. The molybdate containing the Eu + Dy pair of rare-earth elements shows predominant high-intensity luminescence in the red spectral region. In addition to usual infrared emission due to ytterbium, the Eu + Yb compound demonstrates emission in the ultraviolet spectral region. We have measured luminescence decay kinetic characteristics at the peak emission wavelengths. In the case of the molybdate containing the Eu + Yb pair of rare-earth elements, energy transfer from europium ions to ytterbium has been observed. We have demonstrated high-intensity luminescence that can be excited both on intraconfigurational transitions and in the region of charge transfer bands of oxygen–molybdenum complexes.
Synthesis of ZrO2:Pr3+,Gd3+nanocrystals for optical thermometry with a thermal sensitivity above 2.32% K?1over 270 K of sensing range
Huang, Feifei,Lei, Ruoshan,Li, Minghui,Wang, Huanping,Xu, Shiqing,Zhou, Jun
, p. 15688 - 15695 (2021/12/01)
Nowadays, there is enthusiastic effort to develop luminescent thermometers used for remote and high-sensitivity temperature readout over a wide sensing range. Herein, Pr3+and Gd3+co-doped ZrO2nanocrystals are designed, prepared and investigated by XRD, Raman spectroscopy, XPS, TEM, EDS, DRS, PLE and PL spectroscopy. Upon 275 nm irradiation, the PL spectrum of ZrO2:Pr3+,Gd3+is found to be composed of a narrow emission peak at 314 nm (Gd3+ 6P7/2-8S7/2), a broad defect-related emission band at 400 nm, and several emission peaks in the wavelength region of 585-700 nm (Pr3+ 1D2-3H43P0-3H6, and3P0-3F2), which exhibit different thermal responses owing to the effects of the various non-radiative relaxation processes and trap energy levels. Accordingly, the luminescence intensity ratio (LIR) between the Pr3+ 1D2-3H4and Gd3+ 6P7/2-8S7/2transitions demonstrates excellent relative sensing sensitivity values ((2.32 ± 0.01)% K?1-(8.32 ± 0.05)% K?1) and low temperature uncertainties (0.08 K-0.28 K) over a wide temperature sensing range of 303 K to 573 K, which are remarkably better than those of many other luminescence thermometers. What is discussed in the present study may be conducive to broadening the research region of RE3+doped luminescence thermometric phosphors, especially for materials with rich 4f-4f transition lines and defect-related luminescence.
Methanol synthesis over Cu/CeO2-ZrO2catalysts: The key role of multiple active components
Zabilskiy, Maxim,Ma, Kaibo,Beck, Arik,Van Bokhoven, Jeroen A.
, p. 349 - 358 (2021/01/29)
High surface area ceria-zirconia synthesized by a glycothermal approach was used as a support for copper nanoparticles. Cu-CeO2/ZrO2 catalysts containing 5-25 wt% copper demonstrate high carbon dioxide-to-methanol conversion rates (120-180 gMeOH kgcat-1 h-1) at 260 °C and 50 bar. The sample containing 5 wt% copper in the form of small nanoparticles (≤5 nm) demonstrates the highest activity normalized per mass of copper, while higher copper loading results in copper segregation and correspondingly lower activity. We attribute the high activity to a unique synergetic effect between the active components, copper, ceria and zirconia, where activation of hydrogen and carbon dioxide and subsequent methanol synthesis take place. The redox properties of the ceria-zirconia support and its ability to form oxygen vacancy sites play a crucial role in carbon dioxide activation. This journal is