Li‐doped nanosized TiO2 powder with enhanced photocalatylic acivity under sunlight irradiation

This work reports on the synthesis of Li‐doped TiO₂ nanoparticles using the sol–gel process and solid‐state sintering, and investigates their potential use as a photocatalyst for degradation under sunlight excitation of different organic model compounds in aqueous solution. The structure of the nanocrystals was examined by X‐ray diffraction, UV‐vis ground state diffuse reflectance absorption spectra and X‐ray photoelectron emission spectroscopy. Results showed that samples prepared by sol–gel process and calcined at 400 °C are composed of a mixture of anatase and rutile phases, in contrast to the one prepared by solid‐state sintering, which exhibits an anatase phase with Li being involved in a spinel phase. The photocatalytic degradation of aqueous solutions of different aromatic compounds was successfully achieved under sunlight excitation in presence of Li‐doped TiO₂ prepared via sol–gel process. It was shown that the calcination temperature and the preparation mode greatly affect the photocatalytic efficiency. Copyright © 2010 John Wiley & Sons, Ltd.     

Crystal structure of mixed rubidium–ammonium hydrogen sulfate Rb0.7(NH4)0.3HSO4 at room temperature

The structure of Rb_0.7(NH₄)_0.3HSO₄ has been determined by X-ray analysis. The mixed compound crystallizes in the monoclinic space group P2₁/n with unit cell parameters a = 14.374(6) Å, b = 4.618(6) Å, c = 14.412(2) Å, = 118.03(2)°, V = 844.4(4) ų, and D _cal = 1.536 g cm^–3 for Z = 8. The mixed compound Rb_0.7(NH₄)_0.3HSO₄ is a chain-based structure. The Rb⁺ and NH₄ ⁺ cations are intercalated between chains, formed of HSO₄ ^- groups linked with OHO hydrogen-bonding. Rb_0.7(NH₄)_0.3HSO₄ presents a new type of structural arrangement different from those of pure RbHSO₄ and NH₄HSO₄.     

Raman scattering and X‐ray diffraction on YBiTi2O7 prepared at low temperature

The conditions of preparation of a pure YBiTi₂O₇ phase by sol–gel were optimised. A single phase was obtained at temperature as low as 800 °C when triethanolamine/diethanolamine was used as additional ligands. The expected composition was confirmed by energy dispersive spectroscopy (EDS) and X‐ray diffraction (XRD). YBiTi₂O₇ exhibits the pyrochlore structure with a unit‐cell parameter of 10.2117(5) Å. This structure was confirmed by Raman spectroscopy, which revealed a shift of the main E_g mode towards lower wavenumbers when bismuth is introduced in the structure. Broad bands were observed for all the recorded spectra, which characterise rather a disorder due to bismuth III cations in the structure than an effect of particle size. This study confirmed the possibility to lower the temperature of preparation of pyrochlores containing bismuth, which could be of interest as photocatalyst for the decomposition of organic and toxic materials. Copyright © 2008 John Wiley & Sons, Ltd.     

Stability of TiO2 forms (anatase–rutile) in the Y2O3?Ti(OBu)4?Rb2CO3 system prepared by sol–gel process

Three different sol–gel routes were used in order to study the stability and the crystallinity of the ternary system Y₂O₃, Ti(OBu)₄, Rb₂CO₃. Different techniques such as FTIR, ¹³C NMR TGA, DTA and XRD were used to characterize xerogels and final products. Results demonstrated that using hexanoic acid during the sol step preparation influences structural changes in the precursor gel. The effect of heat treatment to eliminate the organic material from xerogels was investigated by thermal gravimetry and differential thermalanalysis. According to the ratio of acetic acid to hexanoic acid, the phase structure of TiO₂, viz. anatase to rutile phase, could tailored. The photocatalytic activity of the prepared catalysts, under sunlight irradiation, was evaluated using 2‐naphthol as a pollutant model. Results showed a great enhancement in the photocatalytic efficiency for doped TiO₂ sample prepared in the presence of 30acet–70hex. Copyright © 2010 John Wiley & Sons, Ltd.