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Query: UMLS:C0276640 (TEM)
 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Silica-modified titanium dioxides were prepared by a hydrothermal method and then characterized by XRD, FT-IR, XPS, TEM, and UV-visible spectroscopy. The silica-modified titanium dioxides were in anatase phase and had large surface areas. There was strong interaction between SiO2 and TiO2, and TiOSi bonds formed during the hydrothermal process. The addition of silica in TiO2 particles could effectively suppress the formation of the rutile phase and the growth of titanium dioxide crystals. DRS spectra proved an increase in the band-gap transition with the increase of silica. The silica-modified TiO2 nanoparticles exhibited better photocatalytic activity, which increased with the silica amount, in comparison with pure TiO2 nanoparticles. Due to better thermal stability, the photocatalytic activity of the silica-modified TiO2 sample held good photocatalytic activity even after calcined at 1273 K.
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PMID:Hydrothermal synthesis, characterization, and photocatalytic performance of silica-modified titanium dioxide nanoparticles. 1592 73

A series of Au/alpha-Fe2O3 catalysts promoted with ZrO2 and Nb2O5 were prepared by parallel co-precipitation method. Detailed characterizations were conducted by techniques including UV-Vis-DRS, XPS, TEM and XRF. Results indicated that the enrichment of Au, ZrO2 and Nb2O5 on the surface induced by the strong interaction between ZrO2 and Nb2O5 kept the nanoparticles apart, delaying sintering. Performance tests carried out in the reformed methanol steam showed that its CO conversion almost reached the maximum value of 99% at 200 degrees C, and maintained a better stability compared with unmodified samples within 50 h on-stream. All these indicated that ZrO2 and Nb2O5 promoters efficiently improved the performance of the Au/alpha-Fe2O3 catalysts.
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PMID:[Study on the spectra of Au/alpha-Fe2O3 catalysts modified by ZrO2 and Nb2O5 promoters]. 1760 98

Mesoporous TiO(2) materials with various pore-size distributions were synthesized by using diblock copolymers via a sol-gel process in aqueous solution. The properties of these materials were characterized by FE-SEM, HR-TEM, XRD, DRS, BET, and BJH analysis. All particles have spherical morphology with a diameter range of 1-3 mum. The mesoporous TiO(2) materials calcined at 400 degrees C were found to have different specific surface areas - 186, 210, and 192 m(2) g(-1) - and average pore sizes depending on the type of diblock copolymer-5.1, 6.1, and 6.4 nm-and their crystallite sizes were found to be 8.1, 8.3, and 8.8 nm. The photocatalytic activity of each sample was investigated by measuring the photodecomposition of methylene blue (MB), and the small crystallite size, large surface area, and small pore size were found to exhibit better photocatalytic activities. In addition, the photocatalytic activities of all the mesoporous TiO(2) materials were found to be better than that of commercial TiO(2).
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PMID:Synthesis and photocatalytic activity of mesoporous TiO(2) with the surface area, crystallite size, and pore size. 1776 Nov 91

A series of mesoporous titania materials modified with tungstophosphoric acid (TPA) were successfully synthesized by using urea as low-cost template via sol-gel reactions, followed by removing the urea by extraction with water. They were characterized by FT-IR, 31P MAS-NMR, XRD, DTA-TGA, DRS, TEM and BET. The samples presented mesopores with a diameter higher than 3.0 nm. The S(BET) of the solids decreases with the increase of the TPA content and with the increase of the calcination temperature. According to FT-IR and 31P MAS-NMR studies the main species present in the samples is [PW12O40]3- anions, which was partially transformed into [P2W21O71]6- and [PW11O39]7- anion during the synthesis and drying step. The XRD patterns of the modified samples only exhibited the characteristic peaks of anatase phase. The presence of TPA retarded the crystallization of the anatase phase and its transformation into rutile phase. The point of zero charge decreased in parallel with the increment of tungstophosphoric acid in the samples and with the increase of the calcination temperature. The band gap energy decreased as a result of the introduction of TPA into the TiO2 matrix, but remained practically constant with the increase of the calcination temperature.
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PMID:Direct modification with tungstophosphoric acid of mesoporous titania synthesized by urea-templated sol-gel reactions. 1879 Apr 94

In the present paper, ordered mesoporous silica (KIT-6) as support, nanosized TiO2 into KIT-6 was synthesized by titanium tetraisopropoxide hydrolysis. Then silver was loaded by deposition-precipitation method. Ag-TiO2/KIT-6 composite nanosized photocatalyst was firstly synthesized and a series of correlated catalysts were synthesized by the same preparation method. Methyl orange is presently adopted as a representative organic pollutant to evaluate the photocatalytic performance of the as-synthesized catalysts. The order of photocatalytic activity of the as-synthesized samples was found as Ag-TiO2/KIT-6 > Ag/TiO2 > TiO2/KIT-6 > TiO2 > Ag/KIT-6. Detailed characterizations were conducted by techniques including XRD, N2 physical adsorption, XPS, UV-Vis DRS and TEM. It was found that the Ag-TiO2 /KIT-6 sample shows the highest photocatalytic activity, which should be attributed to the Ag-TiO2 heterojunction structure and higher BET surface area of the Ag-TiO2/KIT-6 sample. Ag-TiO2 heterojunction improves the separation of photogenerated electron-hole pairs, thus enhancing the photocatalytic activity; Ag-TiO2/KIT-6 sample possesses high BET surface area, which facilitates adsorption and transportation of dye molecules, also leading to higher photocatalytic activity.
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PMID:[Studies on Ag-TiO2/KIT-6 composite nanosized photocatalyst]. 1983 31

An acrylic acid emulsion mixture is used for synthesis of novel porous silica (E-Si) material. The photocatalytic activity of TiO2 under solar light irradiation for isoproturon (herbicide) degradation is drastically increased when dispersed over E-Si support using solid state dispersion (SSD) technique. The composite material is characterized by XRD, nitrogen adsorption-desorption isotherms, UV-vis DRS, SEM and TEM measurements. The photocatalytic activities of the composite catalysts are evaluated for different parameters. The 5 wt% TiO2/E-Si is found to be highly active for isoproturon degradation.
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PMID:TiO2 supported over porous silica photocatalysts for pesticide degradation using solar light: Part 2. Silica prepared using acrylic acid emulsion. 1996 29

N-doped TiO(2) (N-TiO(2)) nanocrystals with anatase and rutile mixed phases were prepared by partial oxidation of TiN. The samples were further modified by Fe-ions through incipient wetness impregnation method. The as-prepared samples were characterized by XRD, TEM, XPS, Raman, EPR, UV-vis DRS, and PL in detail. The results indicated that Fe mainly existed as Fe(3+)/Fe(2+) ions on the catalyst surface. The addition of small amounts of Fe-ions to N-TiO(2) nanocrystals caused several times enhancement of the photocatalytic activity under visible, UV and UV-vis light irradiation in degradation of gaseous toluene. The optimized Fe-ions content in this investigation was 0.02 wt.%. EPR and PL clearly showed that Fe(3+)/Fe(2+) redox cycle facilitated electron/hole charge separation, and contributed to the enhanced photocatalytic performance. Moreover, the photochemical stability of N-TiO(2) nanocrystals under visible light was improved due to the stabilization of nitrogen atoms in TiO(2) lattice by surface Fe-ions modification. The N-doped TiO(2) nanocrystals without Fe-ions modification suffered from a gradual deactivation due mainly to the loss of lattice-nitrogen during the photocatalytic reaction. The way to modification of nonmetal-doped TiO(2) nanomaterials brought new concept in enhancing the photocatalytic performance from the viewpoint of practical application.
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PMID:Marked enhancement of photocatalytic activity and photochemical stability of N-doped TiO2 nanocrystals by Fe3+/Fe2+ surface modification. 1996 3

Si-doped and un-doped nanocrystalline TiO(2) samples have been synthesized by simple one-pot water-organic two-phase separated hydrolysis-solvothermal (HST) processes, and characterized by XRD, BET, TEM, FT-IR, DRS and surface photovoltage techniques. The effects of the solvothermal temperature and Si doping on the anatase thermal stability, and on the photocatalytic activity for degrading rhodamine B were investigated in detail. The results show that, as the solvothermal temperature rises, the crystallinity and thermal stability of the resulting nano-sized anatase TiO(2) gradually increase. Noticeably, the as-prepared TiO(2) obtained at appropriate solvothermal temperature (160 degrees C) exhibits high photocatalytic activity. Moreover, although Si doping does not improve the photocatalytic activity of the as-prepared anatase TiO(2), it greatly enhances the anatase thermal stability and inhibits crystallite growth during the process of post-thermal treatment. Interestingly, the Si-doped TiO(2) post-treated at high temperature displays much higher photocatalytic activity than commercial P25 TiO(2). It is clearly demonstrated that the joint effects of high anatase crystallinity and large surface area lead to high photocatalytic activity. This work provides a simple and effective strategy for the synthesis of high-performance TiO(2)-based functional nanomaterials.
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PMID:Synthesis of nanocrystalline anatase TiO2 by one-pot two-phase separated hydrolysis-solvothermal processes and its high activity for photocatalytic degradation of rhodamine B. 2004 83

The morphology of supported metal nanoparticles on TiO2/silical gel (TSO) and photothermal synergism were investigated for destruction of ethylene. During photocatalytic deposition of metal nanopartilces, the effects of pH and light intensity on the morphology of coated platinum, palladium, gold on TiO2/silical gel were studied. Moreover, these catalysts were characterized by TEM, UV-Vis DRS. The pH of preparing solution have strong influence on dispersion, size and sites ofPt, Pd and Au on TSO, which were controlled by the electrostatic binding of HPtCl6-, AuCl4- and TiOH2+, Pd2+ and TiO- respectively. Platinum, gold and palladium nanoparticles were uniformly highly dispersed on the titanol sites not silanol of TiO2 /silical gel under pH = 2, pH = 9.9 respectively. For the photodegradation of ethylene, they show higher photothermal efficiency than those prepared with other pH conditions under UV illumination in a non-circulating photoreactor. The optimum weight loadings of Pt, Au, and Pd were 0.25 wt%, 0.5 wt%, 1 wt%, respectively. The synergistic effect enhanced ethylene removal and CO2 production. These results verify that the best photothermal synergistic effect depends on the dispersion, size of noble metal nano-particles. FTIR analyses of the used Pt-, Pd-TSO catalysts indicated that no significant by-products were accumulated on the surface of the catalysts, leading to them longer lifetime.
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PMID:Morphology of metal nanoparticles photodeposited on TiO2/silical gel and photothermal activity for destruction of ethylene. 2005 May 52

Nanocrystalline Zn(2)SnO(4) microcubes were hydrothermally synthesized and systematically characterized by XRD, SEM, TEM, XPS, N(2) adsorption-desorption, and UV-vis DRS analysis. The resulting Zn(2)SnO(4) microcubes with the edge size ranging from 0.8 to 1.2 microm were composed of numerous nanoparticles with size of 10-20 nm, and their optical band gap energy was estimated to be 3.25 eV from the UV-vis diffuse reflectance spectra. On degradation of nitrogen monoxide (NO) and formaldehyde (HCHO) at typical concentrations for indoor air quality, these nanocrystalline Zn(2)SnO(4) microcubes exhibited superior photocatalytic activity to the hydrothermally synthesized ZnO, SnO(2), and Degussa TiO(2) P25, as well as C doped TiO(2) under UV-vis light irradiation. This enhanced photocatalytic activity of the nanocrystalline Zn(2)SnO(4) microcubes was attributed to their bigger surface areas, smaller particle size, special porous structures, and special electronic configuration. The nanocrystalline Zn(2)SnO(4) microcubes were chemically stable as there was no obvious deactivation during the multiple photocatalytic reactions. This work presents a promising approach for scaling-up industrial production of Zn(2)SnO(4) nanostructures and suggests that the synthesized nanocrystalline Zn(2)SnO(4) microcubes are promising photocatalysts for indoor air purification.
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PMID:Photocatalytic removal of NO and HCHO over nanocrystalline Zn2SnO4 microcubes for indoor air purification. 2034 86


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