- Efficient quenching of TGA-capped CdTe quantum dot emission by a surface-coordinated europium(III) cyclen complex
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Extremely efficient quenching of the excited state of aqueous CdTe quantum dots (QDs) by photoinduced electron transfer to a europium cyclen complex is facilitated by surface coordination to the thioglycolic acid capping ligand. The quenching dynamics are elucidated using steady-state emission and picosecond transient absorption.
- Gallagher, Shane A.,Comby, Steve,Wojdyla, Michal,Gunnlaugsson, Thorfinnur,Kelly, John M.,Gun'Ko, Yurii K.,Clark, Ian P.,Greetham, Gregory M.,Towrie, Michael,Quinn, Susan J.
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- X-ray luminescence of CdTe quantum dots in LaF3:Ce/CdTe nanocomposites
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CdTe quantum dots have intense photoluminescence but exhibit almost no x-ray luminescence. However, intense x-ray luminescence from CdTe quantum dots is observed in LaF3:Ce/CdTe nanocomposites. This enhancement in the x-ray luminescence of CdTe quantum dots is attributed to the energy transfer from LaF3:Ce to CdTe quantum dots in the nanocomposites. The combination of LaF3:Ce nanoparticles and CdTe quantum dots makes LaF3:Ce/CdTe nanocomposites promising scintillators for radiation detection.
- Hossu, Marius,Liu, Zhongxin,Yao, Mingzhen,Ma, Lun,Chen, Wei
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- Electron energy loss spectroscopy (EELS) of H2O, H2S, H2Se and H2Te
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Electronic excitation in H2O, H2S, H2Se and H2Te molecules has been studied by the EELS technique.Spectra of H2S and H2Se are remarkably similar with the 1b1-nd transition most intense.The intensity of the first transition 1b1-nsa1 decreases through H2O to H2Se and this transition is absent in H2Te.Transitions observed by EELS have been compared with optical absorption studies.A correlation diagram of the occupied and the excited states has been provided for these four molecules by making use of UVPES and EELS.
- Pradeep, T.,Hegde, M. S.
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- Upconversion luminescence of CdTe nanoparticles
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Efficient upconversion luminescence is observed from CdTe nanoparticles in solution and precipitated as solids. In the solids, the upconversion luminescence spectrum is significantly red shifted relative to the photoluminescence spectrum, whereas in solution, there is very little spectral shift. The upconversion luminescence exhibits a near-quadratic laser power dependence, both at room temperature and at 10 K. Both the upconversion and photoluminescence show similar decay dynamics with the solid samples showing shorter lifetimes compared to the solutions. This lifetime shortening is attributed to surface-state quenching. These results indicate that two-photon excitation is the likely upconversion excitation mechanism in these particles and that phonon-populated trap states do not contribute to the upconversion.
- Joly, Alan G.,Chen, Wei,McCready, David E.,Malm, Jan-Olle,Bovin, Jan-Olov
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- Synthesis and structures of new ternary aluminum chalcogenides: LiAlSe2, α-LiAlTe2, and β-LiAlTe2
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The synthesis and crystal structures of new ternary aluminum chalcogenides, LiAlSe2, α-LiAlTe2, and β-LiAlTe2, are reported. These compounds are synthesized by solid-state reaction at 800 °C. The single-crystal X-ray structures of these compounds have been determined. LiAlSe2: a = 6.8228(9) A, b = 8.266(1) A, c = 6.5236(7) A, Pna21 (No. 33, Z = 4). α-LiAlTe2: a = 6.5317(4) A, c = 11.6904(9) A, I42d (No. 122, Z = 4). β-LiAlTe2: a = 4.4810(6) A, c = 7.096(1) A, P3m1 (No. 156, Z = 1). These ternary compounds are formed by fusion of AlQ4 (Q = Se, Te) tetrahedra. LiAlSe2 shows β-NaFeO2 structure type, which can be viewed as a wurtzite superstructure. α-LiAlTe2 adopts chalcopyrite structure type. In LiAlSe2 and α-LiAlTe2, AlQ4 (Q = Se, Te) tetrahedra share four corners to build three-dimensional structures and Li atoms are located in the tetrahedral sites between the chalcogen layers. β-LiAlTe2 has polar layers formed by three-corner shared AlTe4 tetrahedra, and Li cations are in the distorted antiprisms between the layers. 7Li MAS NMR studies show that chemical shifts of Li in these ternary chalcogenides are nearly identical regardless of different chemical environments.
- Kim, Joonyeong,Hughbanks, Timothy
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- The photophysical studies of a mixture of CdTe quantum dots and negatively charged zinc phthalocyanines
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Fluorescence resonance energy transfer (FRET) studies were carried out with quantum dots capped with thioglycolic acid (TGA) and 2-mercaptoethanol (2-ME) and negatively charged phthalocyanines {Zn tetracarboxy (ZnTCPc), Zn octacarboxy (ZnOCPc) and Zn tetrasulfo (ZnTSPc) phthalocyinines} in a 0.1 NaOH:EtOH (50:50) solvent mixture. The best overlap between emission spectra of the donor (QDs) and the absorption spectra of the acceptor (ZnPc derivatives) was observed for TGA capped QDs, very little overlap was obtained for 2-ME QDs. ZnTSPc gave the highest FRET efficiency (0.3), with ZnOCPc and ZnTCPc giving a FRET efficiency of 0.2. The ΦT values of the MPcs generally decreased in the presence of the QD whereas the triplet lifetimes (τT) of the ZnPc derivatives were higher in the presence of QDs.
- Moeno, Sharon,Nyokong, Tebello
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- Spectroscopic behavior of cationic metallophthalocyanines in the presence of anionic quantum dots
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The interactions and spectroscopic properties between cationic zinc phthalocyanine derivatives (peripherally and non-peripherally tetrasubstituted and peripherally octa substituted with 2-diethylmethylaminoethylsulfanyl (βTZnPc, αTZnPc and βOZnPc)) and CdTe core quantum dots (QDs) capped with mercaptopropionic acid or thioglycolic acid (represented as CdTe@MPA and CdTe@TGA, respectively) have been studied in methanol:water mixture. Strong coupling of MPcs was deduced from the interaction since the UV-vis spectroscopic studies of the ground state complex formed on mixing both components showed loss of the phthalocyanine monomeric band with the formation of a dimeric band (spectrum of aggregated species). The dimerization constants were of the order of 104 M-1.
- Idowu, Mopelola,Nyokong, Tebello
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- Synthesis of highly stable CdTe/CdS quantum dots with biocompatibility
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Thioglycolic acid (TGA) is a popular coating material for the preparation of aqueous quantum dots (QDs), yet dihydrolipoic acid (DHLA) has not been studied much. Here we present a detailed study on the aqueous synthesis of CdTe/CdS quantum dots with a DHLA coating. The outer CdS shell and DHLA stabilizer provide efficient confinement of electron and hole wave functions inside the nanocrystal as well as high photochemical stability. At the optimum ratios and reaction conditions, the results indicate that the DHLA-capped CdTe/CdS QDs exhibit high fluorescence quantum yields (QYs) of about 48% over a spectral range of 551-571 nm, and the best QY is 87%. These DHLA-capped core-shell QDs are highly biocompatible and monodisperse. In particular, they have exhibited excellent colloidal and photostability over one year of study. The synthesis of QDs by using DHLA as stabilizer is simple and environmentally friendly, and it can easily be extended to the large-scale, aqueous-phase production of QDs. At a QD dose of 120μg/mL, TGA-stabilized CdTe QDs induce 9.5% hemolysis, whereas DHLA-stabilized CdTe/CdS QDs induce only 3% hemolysis. Hemolytic results indicate that DHLA-slabilized QDs are more biocompatible than TGA-cappod CdTo QDs, which is especially important, for QDs as biomarkers in biological detection and diagnosis.
- Liu, Ying-Fan,Xie, Bing,Yin, Zhi-Gang,Fang, Shao-Ming,Zhao, Jian-Bo
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- Matrix isolation study of D2Te and H2Te molecules in solid argon
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A careful synthesis of H2Te and D2Te and their isolation in solid argon are reported.Rare gas metrix isolated molecules of H2Te and D2Te were studied using Moessbauer spectroscopy.The gaseous species were identified using mass spectrometry.Moessbauer parameters were analyzed using extended Hueckel calculations.A good agreement between the experimental and the calculated value of the quadrupole splitting requires a smaller quadrupole moment for the excited state of 125Te then that reported in the literature.A 10percent increase in the QS for D2Te is explained as due to the enhancement of 3> caused by a slight contraction of the D-Te bond.
- Montano, P. A.,Nagarathna, H. M.,Newlin, D.,Stewart, G. W.
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- NiTe2 Nanowire Outperforms Pt/C in High-Rate Hydrogen Evolution at Extreme pH Conditions
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Better hydrogen generation with nonprecious electrocatalysts over Pt is highly anticipated in water splitting. Such an outperforming nonprecious electrocatalyst, nickel telluride (NiTe2), has been fabricated on Ni foam for electrocatalytic hydrogen evolution in extreme pH conditions, viz., 0 and 14. The morphological outcome of the fabricated NiTe2 was directed by the choice of the Te precursor. Nanoflakes (NFs) were obtained when NaHTe was used, and nanowires (NWs) were obtained when Te metal powder with hydrazine hydrate was used. Both NiTe2 NWs and NiTe2 NFs were comparatively screened for hydrogen evolution reaction (HER) in extreme pH conditions, viz., 0 and 14. NiTe2 NWs delivered current densities of 10, 100, and 500 mA cm-2 at the overpotentials of 125 ± 10, 195 ± 4, and 275 ± 7 mV in 0.5 M H2SO4. Similarly, in 1 M KOH, overpotentials of 113 ± 5, 247 ± 5, and 436 ± 8 mV were required for the same current densities, respectively. On the other hand, NiTe2 NFs showed relatively poorer HER activity than NiTe2 NWs, which required overpotentials of 193 ± 7, 289 ± 5, and 494 ± 8 mV in 0.5 M H2SO4 for the current densities of 10 and 100 mA cm-2 and 157 ± 5 and 335 ± 6 mV in 1 M KOH for the current densities of 10 and 100 mA cm-2, respectively. Notably, NiTe2 NWs outperformed the state-of-the-art Pt/C 20 wt % loaded Ni foam electrode of comparable mass loading. The Pt/C 20 wt % loaded Ni foam electrode reached 500 mA cm-2 at 332 ± 5 mV, whereas NiTe2 NWs drove the same current density with 57 mV less. These encouraging findings emphasize that a NiTe2 NW could be an alternative to noble and expensive Pt as a nonprecious and high-performance HER electrode for proton-exchange membrane and alkaline water electrolyzers.
- Anantharaj, Sengeni,Karthick, Kannimuthu,Kundu, Subrata
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- Self-organization of plasmonic and excitonic nanoparticles into resonant chiral supraparticle assemblies
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Chiral nanostructures exhibit strong coupling to the spin angular momentum of incident photons. The integration of metal nanostructures with semiconductor nanoparticles (NPs) to form hybrid plasmon-exciton nanoscale assemblies can potentially lead to plasmon-induced optical activity and unusual chiroptical properties of plasmon-exciton states. Here we investigate such effects in supraparticles (SPs) spontaneously formed from gold nanorods (NRs) and chiral CdTe NPs. The geometry of this new type of self-limited nanoscale superstructures depends on the molar ratio between NRs and NPs. NR dimers surrounded by CdTe NPs were obtained for the ratio NR/NP = 1:15, whereas increasing the NP content to a ratio of NR/NP = 1:180 leads to single NRs in a shell of NPs. The SPs based on NR dimers exhibit strong optical rotatory activity associated in large part with their twisted scissor-like geometry. The preference for a specific nanoscale enantiomer is attributed to the chiral interactions between CdTe NP in the shell. The SPs based on single NRs also yield surprising chiroptical activity at the frequency of the longitudinal mode of NRs. Numerical simulations reveal that the origin of this chiroptical band is the cross talk between the longitudinal and the transverse plasmon modes, which makes both of them coupled with the NP excitonic state. The chiral SP NR-NP assemblies combine the optical properties of excitons and plasmons that are essential for chiral sensing, chiroptical memory, and chiral catalysis.
- Hu, Tao,Isaacoff, Benjamin P.,Bahng, Joong Hwan,Hao, Changlong,Zhou, Yunlong,Zhu, Jian,Li, Xinyu,Wang, Zhenlong,Liu, Shaoqin,Xu, Chuanlai,Biteen, Julie S.,Kotov, Nicholas A.
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- Reactivity of uranium(iii) with H2E (E = S, Se, Te): Synthesis of a series of mononuclear and dinuclear uranium(iv) hydrochalcogenido complexes
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We report the syntheses, electronic properties, and molecular structures of a series of mono- and dinuclear uranium(iv) hydrochalcogenido complexes supported by the sterically demanding but very flexible, single N-anchored tris(aryloxide) ligand (AdArO)3N)3-. The mononuclear complexes [((AdArO)3N)U(DME)(EH)] (E = S, Se, Te) can be obtained from the reaction of the uranium(iii) starting material [((AdArO)3N)UIII(DME)] in DME via reduction of H2E and the elimination of 0.5 equivalents of H2. The dinuclear complexes [{((AdArO)3N)U}2(μ-EH)2] can be obtained by dissolving their mononuclear counterparts in non-coordinating solvents such as benzene. In order to facilitate the work with the highly toxic gases, we created concentrated THF solutions that can be handled using simple glovebox techniques and can be stored at -35 °C for several weeks. This journal is
- Franke, Sebastian M.,Rosenzweig, Michael W.,Heinemann, Frank W.,Meyer, Karsten
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- Synthesis and Structure of the New Cubane-like Cluster PF6, containing only Terminal Phosphine Ligands
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The cubane-like PF6 and the stellated octahedron PF6 clusters have been obtained by reaction of Fe(ClO4)2 with PEt3 and H2X (X=Te, Se), in the presence of PF6-; a crystal structure of the tellurium derivative has been determined.
- Cecconi, Franco,Ghilardi, Carlo A.,Midollini, Stefano,Orlandini, Annabella
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- Heavy hydrides: H2Te ultraviolet photochemistry
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The room-temperature ultraviolet absorption spectrum of H2 Te has been recorded. Unlike other group-6 hydrides, it displays a long-wavelength tail that extends to 400 nm. Dissociation dynamics have been examined at photolysis wavelengths of 266 nm (which lies in the main absorption feature) and 355 nm (which lies in the long-wavelength tail) by using high- n Rydberg time-of-flight spectroscopy to obtain center-of-mass translational energy distributions for the channels that yield H atoms. Photodissociation at 355 nm yields TeH (Π 12 2) selectively relative to the TeH (Π 32 2) ground state. This is attributed to the role of the 3 A′ state, which has a shallow well at large RH-TeH and correlates to H+TeH (Π 12 2). Note that the Π 12 2 state is analogous to the P 12 2 spin-orbit excited state of atomic iodine, which is isoelectronic with TeH. The 3 A′ state is crossed at large R only by 2 A″, with which it does not interact. The character of 3 A′ at large R is influenced by a strong spin-orbit interaction in the TeH product. Namely, Π 12 2 has a higher degree of spherical symmetry than does Π 32 2 (recall that I (P 12 2) is spherically symmetric), and consequently Π 12 2 is not inclined to form either strongly bonding or antibonding orbitals with the H atom. The 3 A′ ←X transition dipole moment dominates in the long-wavelength region and increases with R. Structure observed in the absorption spectrum in the 380-400 nm region is attributed to vibrations on 3 A′. The main absorption feature that is peaked at ～240 nm might arise from several excited surfaces. On the basis of the high degree of laboratory system spatial anisotropy of the fragments from 266 nm photolysis, as well as high-level theoretical studies, the main contribution is believed to be due to the 4 A″ surface. The 4 A″ ←X transition dipole moment dominates in the Franck-Condon region, and its polarization is in accord with the experimental observations. An extensive secondary photolysis (i.e., of nascent TeH) is observed at 266 and 355 nm, and the corresponding spectral features are assigned. Analyses of the c.m. translational energy distributions yield bond dissociation energies D0. For H2 Te and TeH, these are 65.0±0.1 and 63.8±0.4 kcalmol, respectively, in good agreement with predictions that use high-level relativistic theory.
- Underwood,Chastaing,Lee,Wittig
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- Comparative examination of the stability of semiconductor quantum dots in various biochemical buffers
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Due to their greater photostability compared to established organic fluorescence markers, semiconductor quantum dots provide an attractive alternative for the biolabeling of living cells. On the basis of a comparative investigation using differently sized thiol-stabilized CdTe nanocrystals in a variety of commonly used biological buffers, a method is developed to quantify the stability of such a multicomponent system. Above a certain critical size, the intensity of the photoluminescence of the nanocrystals is found to diminish with pseudo-zero-order kinetics, whereas for specific combinations of particle size, ligand, and buffer there appears to be no decay below this critical particle size, pointing out the necessity for thorough investigations of this kind in the view of prospect applications of semiconductor nanocrystals in the area of biolabeling.
- Boldt, Klaus,Bruns, Oliver T.,Gaponik, Nikolai,Eychmüller, Alexander
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- Dynamic distribution of growth rates within the ensembles of colloidal II-VI and III-V semiconductor nanocrystals as a factor governing their photoluminescence efficiency
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The distribution of properties within ensembles of colloidally grown II-VI and III-V semiconductor nanocrystals was studied. A drastic difference in the photoluminescence efficiencies of size-selected fractions was observed for both organometallically prepared CdSe and InAs colloids and for CdTe nanocrystals synthesized in aqueous medium, indicating a general character of the phenomenon observed. The difference in the photoluminescence efficiencies is attributed to different averaged surface disorder of the nanocrystals originating from the Ostwald ripening growth mechanism when larger particles in the ensemble grow at the expense of dissolving smaller particles. At any stage of growth, only a fraction of particles within the ensemble of growing colloidal nanocrystals has the most perfect surface and, thus, shows the most efficient photoluminescence. This is explained by a theoretical model describing the evolution of an ensemble of nanocrystals in a colloidal solution. In an ensemble of growing nanocrystals, the fraction of particles with the highest photoluminescence corresponds to the particle size having nearly zero average growth rate. The small average growth rate leads to the lowest possible degree of surface disorder at any given reaction conditions.
- Talapin, Dmitri V.,Rogach, Andrey L.,Shevchenko, Elena V.,Kornowski, Andreas,Haase, Markus,Weller, Horst
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- Metal-free inorganic ligands for colloidal nanocrystals: S2-, HS-, Se2-, HSe-, Te2-, HTe -, TeS32-, OH-, and NH 2- as surface ligands
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All-inorganic colloidal nanocrystals were synthesized by replacing organic capping ligands on chemically synthesized nanocrystals with metal-free inorganic ions such as S2-, HS-, Se2-, HSe-, Te2-, HTe-, TeS32-, OH- and NH2-. These simple ligands adhered to the NC surface and provided colloidal stability in polar solvents. The versatility of such ligand exchange has been demonstrated for various semiconductor and metal nanocrystals of different size and shape. We showed that the key aspects of Pearsons hard and soft acids and bases (HSAB) principle, originally developed for metal coordination compounds, can be applied to the bonding of molecular species to the nanocrystal surface. The use of small inorganic ligands instead of traditional ligands with long hydrocarbon tails facilitated the charge transport between individual nanocrystals and opened up interesting opportunities for device integration of colloidal nanostructures.
- Nag, Angshuman,Kovalenko, Maksym V.,Lee, Jong-Soo,Liu, Wenyong,Spokoyny, Boris,Talapin, Dmitri V.
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p. 10612 - 10620
(2011/08/07)
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- Colloidal HgTe nanocrystals with widely tunable narrow band gap energies: From telecommunications to molecular vibrations
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A convenient, aqueous-based synthesis of stable HgTe nanocrystals with widely size-tunable room temperature emission between wavelengths of 1.2 to 3.7 μm is demonstrated. By the choice of the thiols, applied as stabilizers, we optimized the growth dynamics, the luminescence quantum yields (up to 40%), and a ligand-exchange procedure, required to transfer the nanocrystals from water to nonpolar organic solvents. The latter is greatly improved and facilitated by the use of mercaptoethylamine as initial stabilizer. The possibility to tune the HgTe nanocrystal sizes from 3 to 12 nm and to control their surface functionalities (hydrophobic and hydrophilic) makes them very promising for the development of infrared optical devices, emitting in the wavelength region between the telecommunications and the molecular vibrations. Copyright
- Kovalenko, Maksym V.,Kaufmann, Erich,Pachinger, Dietmar,Roither, Juergen,Huber, Martin,Stangl, Julian,Hesser, Guenter,Schaeffler, Friedrich,Heiss, Wolfgang
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p. 3516 - 3517
(2007/10/03)
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- Electrochemical preparation of H2S and H2Se
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H2S and H2Se have been electrolytically prepared by electrolysis in aqueous H2SO4 solutions of composite cathodes made of S or Se and graphite. The efficiencies depended strongly on the electrolyte composition, in particular on the acid concentration and presence of K+. Faradaic efficiencies of 80% were obtained in dilute (0.05 M) acid, and this increased to 100% with added K2SO4. The efficiencies dropped drastically in concentrated acid (>a few moles). H 2Te and AsH3 generation were also briefly studied for comparison. The mechanisms of hydride formation are discussed. Both the reaction of nascent hydrogen with the free element and direct reduction of the element are considered. The latter is believed to be the dominant mechanism.
- Bastide, Stephane,Huegel, Paul,Levy-Clement, Claude,Hodes, Gary
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- BIOFUNCTIONALIZED QUANTUM DOTS FOR BIOLOGICAL IMAGING
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Novel biofunctionalized quantum dots include a mercaptoalkanoic acid linked to the surface of a nanocrystalline core and a bio-functional group linked to the surface. Biofunctionalized quantum dots are made by a novel synthesis method. Biofunctionalized quantum dots can be used in imaging or therapy applications.
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(2008/06/13)
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- A DELIVERY SYSTEM
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Therapeutic drug delivery and diagnostics systems comprise biologically active compounds associated with particulate carriers of less than 20nm. These systems can be utilised for targeted modification of growth, development and functions, such as gene expression, protein synthesis, intracellular energy production and transport mechanisms in prokaryotic and eukaryotic organisms. The systems are also applicable for controlled modification of structural and functional properties of extracellular components and tissue constituents. The characteristics of a biological site are evaluated and an entity is provided which is dependent on the site characteristics. The entity comprises nanoparticles of less than 20nm. A probe comprising nanoparticles of less than 5nm is also provided.
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(2008/06/13)
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- The intriguing near-ultraviolet photochemistry of H2Te
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The ultraviolet absorption spectrum of H2Te has a long wavelength tail that extends to 400 nm. Photodissociation at 355 nm yields TeH(2 1/2) selectively relative to the 2 3/2 ground state; the transition moments for these channels lie in, and perpendicular to, the molecular plane, respectively. Vibrational structure in the region 380-400 nm is consistent with a shallow well in the adiabat leading to 2 1/2, akin to the one in HI leading to I(2P1/2). These effects have no counterparts with the light Group 6A dihydrides.
- Underwood,Chastaing,Lee,Boothe,Flood,Wittig
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p. 483 - 490
(2008/10/08)
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- Sinthesis and High-Pressure Behaviour of Quaternary Chalcogenide Halides M2M'X3Y (M = Zn, Cd; M' = Al, Ga, In; X = Se, Te; Y = Cl, Br, I)
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Quaternary chalcogenide halides M2M'X3Y (M = Zn, Cd; M' = Al, Ga, In; X = Se, Te; Y = Cl, Br, I) can be synthesized by heating stoichiometric amounts of the binary components MX, MY2, and M'2X3 in evacuated sealed quartz ampoules.In the case of aluminium and gallium compounds, a mixture of the M' and X elements rather than the binary compounds has been used.The products are typical tetrahedral compounds, crystallizing with either the defect wurtzite-type or the defect zinc-blende-type structure.At 25 kbar, and 1400 deg C, Cd2InSe3Cl, Cd2InSe3Br, and Cd2InSe3I transform from the defect wurtzite-type structure to quenchable high-pressure phases with defect NaCl-type structure.The retransformation to the ambient-pressure phases proceeds via intermediates having the defect zinc-blende-type structure.Some aspects of the apparent nonstoichiometry in the high-pressure phases are discussed. - Keywords: Quaternary Chalcogenide Halides, Synthesis, Crystal Structure, High-Pressure Reactions
- Range, Klaus-Juergen,Handrick, Karin
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p. 153 - 158
(2007/10/02)
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- Al7Te10 - the First Chalcogenide of Divalent Aluminum
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Al7Te10 is prepared from a melt of the elements in stoichiometric amounts in a corundum crucible contained in a sealed quartz ampoule.The ruby red cube shaped crystals are stable below 840 K.The structure of Al7Te10 (R32-D37; a = 1439.5 pm, c = 1793.2 pm, Z = 6, R = 0.03) is a distorted defect variant of a tetrahedral arrangement of the 4H-polytype.The central unit, a double barrelane , contains an Al-Al bond of 260 pm, which is somewhat longer (n = 0.83) than an expected single bond (250 pm, n = 1).This homopolar bond disturbs the electrostatically favorable (Al-Te-)n sequence in the structure which is compensated by the occurence of four-membered Al2Te2 rings.Al7Te10 is a Zintl phase according to 1/21220> and exhibits semiconducting and diamagnetic behaviour. - Synthesis, Crystal Structure, Divalent Aluminum, Aluminum-Aluminum Bonds
- Nesper, Reinhard,Curda, Jan
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p. 557 - 564
(2007/10/02)
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- CHARACTERISTICS OF CATHODIC DISSOLUTION OF TELLURIUM IN PHOSPHORIC ACID.
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The yield of hydrogen telluride during cathodic dissolution of tellurium in phosphoric acid increases with current density and acid concentration, and falls with rise of temperature. The relative amount of hydrogen telluride decomposing within the electrolyte increases with rise of temperature and dilution of the solution. The Tafel coefficients were determined by analysis of the dependence of phi on log i. The values of the effective activation energy calculated from the temperature dependence of the partial polarization curves show that the rate of cathodic dissolution of tellurium during synthesis of hydrogen telluride at potentials on the positive side of minus 0. 5 V is controlled by kinetics factors.
- Kozin,Chubanov,Novikova,Ivanov,Glushachenko
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p. 1191 - 1196
(2008/10/08)
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- Process for improving activity of tellurium containing metal oxide catalysts
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A regeneration process for tellurium-containing metal oxide catalysts used in the process for oxidation, ammoxidation or oxidative dehydrogenation of organic compounds at a temperature of about 300° C. to about 600° C. The process can be effectively applied to such catalysts which have become partially deactivated during the reaction. According to the present process, the deactivated catalyst is regenerated at the reaction temperature under a non-reductive atompshere by contacting the deactivated catalyst with a tellurium-enriched metal oxide catalyst having a tellurium content higher than that of a fresh metal oxide catalyst used in the reaction, or by contacting the deactivated catalyst at the reaction temperature with a tellurium-molybdenum-enriched catalyst system selected from the group consisting of (i) a physical blend of a tellurium-enriched catalyst and a molybdenum-enriched catalyst and (ii) a tellurium-molybdenum-enriched catalyst, the tellurium and molybdenum contents being higher than those of the fresh metal oxide catalyst used in the reaction. In a particularly preferred embodiment, the process is applied to tellurium-containing metal oxide catalysts in a fluidized bed. More preferably, the process is carried out during the oxidation, ammoxidation or oxidative dehydrogenation reaction.
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- Ammoxidation with tellurium catalysts
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Tellurium catalysts containing at least iron, tellurium and molybdenum plus one of nickel, cobalt or magnesium have been discovered to be especially useful for ammoxidation reactions.
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- Process for the production of unsaturated esters
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The invention relates to a process for the production of an unsaturated glycol diester by the reaction of a conjugated diene compound, a carboxylic acid and molecular oxygen in the presence of a solid catalyst. For example, 1,4-diacetoxy-2-butene is prepared at high conversion and high selectivity by reacting butadiene, molecular oxygen and acetic acid in the presence of a solid catalyst containing palladium, tellurium and at least one element selected from the group consisting of tin, germanium and lead. The product is an intermediate for the preparation of 1,4-butanediol.
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