Qinghong Zhang

Effects of calcination on the photocatalytic properties of nanosized TiO2 powders prepared by TiCl4 hydrolysis

Abstract The ultra fine nanosized TiO2 photocatalysts in the anatase, rutile, and both phases were prepared by the hydrolysis of TiCl4 solution. The resulting materials have been characterized by HREM, XRD, BET and UV–VIS absorption spectroscopy. The photoactivity, effective degradation, and the selectivity for complete mineralization of these catalysts were tested in the photocatalytic degradation of phenol. For this reaction, the quantum-sized catalyst particles (4xa0nm) in the anatase phase shows the highest selectivity, the concentrations of p-benzoquinone and hydroquinol as the photocatalytic products were at very low level. However, the selectivity of the quantum-sized crystallites in the rutile phase was not improved in comparison with that of catalysts which bandgap corresponding bulk rutile. HREM micrographs show the quantum-sized catalysts were crystallized partially or many defects occurred on their crystal planes, they are responsible for their relative low photoactivity. Calcination is an effective treatment to increase the photoactivity of nanosized TiO2 photocatalysts resulting from the improvement of crystallinity. Mixtures of both phases exhibit higher photoactivity as well as effective degradation in comparison with pure anatase or rutile catalysts. To the best of our knowledge, we are first to report that the quantum-sized TiO2 crystallite exhibit high selectivity for complete mineralization in the photocatalytic degradation of phenol solution.

Effect of hydrolysis conditions on morphology and crystallization of nanosized TiO2 powder

Abstract Nanosized titania powders were prepared by controlling the hydrolysis of TiCl4 in aqueous solution. The powders were characterised by TEM, HREM, XRD, ED, and BET techniques. In the presence of a small amount sulphate ions, when TiCl4 solution hydrolysed at 70°C, the obtained powder was pure anatase and its primary particle size was 3.5 nm, which is finer than that of alkoxide-derived powders, moreover, its anatase-rutile transformation was retarded. However, at the same temperature, in the absence of SO42− the synthetic powder was a mixture of the anatase and rutile, the primary particle size in the rutile phase was 4.3 nm. When TiCl4 solution hydrolysed at 20°C, the prepared TiO2 powder was amorphous and its BET surface area was as high as 501 m2/g. The results of UV–Vis absorption spectra indicate that the presence of sulphate ions accelerated the growth of TiO2 clusters to anatase.

Synthesis, characterization and photocatalytic properties of titania-modified mesoporous silicate MCM-41

A series of titania modified mesoporous silicate MCM-41 (MCM-TiO2) samples with variable Ti/Si ratios have been synthesized from tetrabutyltitanate and calcined MCM-41. The samples were characterized by powder X-ray diffraction (XRD), FTIR spectroscopy, thermal analysis (DTA–TG), nitrogen adsorption–desorption at 77xa0K, transmission electron microscopy (TEM), and solid state diffuse reflectance UV–VIS spectroscopy. It was found that tetrabutyltitanate cocondensation occurred with pendant OH groups of MCM-41 leading to Si–O–Ti bonds so modifying the inner pore surface of MCM-41 after hydrolysis and calcination. In the titania modified MCM-41 samples, although titania species were in tetrahedral rather than octahedral coordination which is predominant in crystalline titania, it still exhibited good photocatalytic activity for oxidizing phenol to carbon dioxide and water.

Preparation, characterization and photocatalytic properties of singly and doubly titania-modified mesoporous silicate MCM-41 by varying titanium precursors

A series of titania-modified MCM-41 have been synthesized nfrom varying three kinds of titanium precursors [Ti(OBun)4, nTi(OBun)3(acac), Ti(OBun)2(acac)2] respectively and mesoporous molecular sieve MCM-41, in which titania nexisted as single or double layers. The samples were characterized by powder nX-ray diffraction (XRD), nitrogen adsorption–desorption nat 77xa0K, 29Si MAS NMR, FTIR and Raman spectroscopy, as well nas by solid state diffuse reflectance UV–VIS spectroscopy. The titanium nprecursor was cocondensed with the active silanol groups of MCM-41 via nSi–O–Ti bonds and the resulting titania modified the mesopore nwalls of MCM-41 after hydrolysis and calcination. In the titania-modified nMCM-41 samples, although the titania species were in an amorphous state nand in tetrahedral coordination rather than octahedral coordination, which nexists extensively in crystalline titania, they exhibited high photocatalytic nactivity for the photodecomposition of phenol and the photoreduction of Cr(VI) nto Cr(III).

Preparation of ultrafine InN powder by the nitridation of In2O3 or In(OH)3 and its thermal stability

Crystalline InN powder has been prepared by the nitridation of In2O3 and In(OH)3 with NH3 gas for the first time, and ultrafine InN powder in the size range 50–300 nm and with a specific surface area of 8 m2 g−1 has been obtained using In2O3 nanoparticles as the starting material. The resulting powders were characterized by XRD, FE-SEM, TEM, TG-DSC and BET surface area techniques. It was found that nanosized In2O3 was completely converted into InN at 600 °C within 8 h. The thermal stability of the ultrafine InN powder in air and under a nitrogen atmosphere was also investigated. It was observed that InN began to be oxidized into In2O3 at 389 °C and decomposed in the narrow temperature range of 595–696 °C in flows of air and N2, respectively.