Shunhang Wei,Rong Wu,Xiaoxiang Xu,Jikang Jian,Haixia Wang,Yanfei Sun
Black core-shelled anatase titania were successfully prepared using a simple one-step synthetic method by calcining colloid titania precursor in N 2 flow under atmospheric pressure. The physicochemical properties of the as-prepared samples were characterized by various techniques such as X-ray diffraction, high resolution transmission electron microcopy, etc. The samples demonstrate a unique core-shelled structure and electron paramagnetic resonance spectra reveal the presence of high concentration of Ti 3+ and oxygen vacancies at the surface, which accounts for their black appearance. A possible mechanism for the formation of such core–shell structure is proposed based on the results (X-ray photoelectron spectra, etc) of products prepared under different ration between urea and hydrochloric acid. Ethanol absolute is found to have critical effect in preventing phase transition of titania (from anatase to rutile) upon elevated temperatures. The black appearance of the sample powder (high visible light absorption) as well as slow electron/hole recombination rate after introducing oxygen vacancies/N species signify the core-shelled anatase titania as an efficient visible light active photocatalyst.
Single-crystalline chromium doped bismuth titanate (Bi4Ti3−xCrxO12, x = 0.0–0.5) nanosheets with exposed {110} facets have been synthesized via a facile hydrothermal process. The Bi4Ti3−xCrxO12nanosheets possess well-defined tetragonal shapes with landscape dimension of 100–300 nm and thickness of 10–30 nm. The in-plane surfaces of the nanosheets lies on {001}, and the side surfaces are (110) and (10). Extension of the light absorption from the ultraviolet region to the visible-light region arises from the Cr 2p levels confirmed by XPS spectra. The Bi4Ti2.6Cr0.4O12 nanosheets with high stability showed the highest photocatalytic performance of H2 evolution from water under visible-light irradiation. Furthermore, the heterostructures by using the NiOx nanoparticles tightly coupled on the surface of Bi4Ti2.6Cr0.4O12 nanosheets, exhibited an enhanced photocatalytic activity due to the decrease in the recombination rate of the photoinduced electrons and holes, demonstrating that NiOx/Bi4Ti2.6Cr0.4O12 nanosheet is a promising candidate as a visible light photocatalyst.
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