Elucidation of the electron energy structure of TiO2(B) and anatase photocatalysts through analysis of electron trap density

Well-dispersed Au co-catalyst deposited on a rutile TiO2 photocatalyst via electron traps

We deposited Au nanoparticles as a co-catalyst onto a TiO₂ photocatalyst by reducing [AuCl₄]^- using electrons trapped in the oxygen vacancies of TiO₂. The dispersibility and hydrogen production ability of the Au co-catalyst are higher than those prepared using the conventional photodeposition method.

Construction of TiO2(B)/Anatase Heterophase Junctions via a Water-Induced Phase Transformation Strategy for Enhanced Photocatalytic Hydrogen Production

The development of facile and green solution-phase routes toward the fabrication of TiO₂-based heterophase junctions with a delicate control of phase and structure is a challenging task. Herein, we report a simple and convenient method to controllably fabricate TiO₂(B)/anatase heterophase junctions, which was successfully realized by utilizing the ideal great solvent of water to treat the presynthesized TiO₂(B) nanosheet precursor at a low temperature of 80 °C. On the basis of phase structure transformation and morphology evolution data, the formation of these TiO₂(B)/anatase heterophase junctions was reasonably explained by a novel water-induced TiO₂(B) → anatase phase transformation mechanism. Benefiting from the desirable structural and photoelectronic advantages of more exposed active sites, enhanced light absorbance, and promoted separation of photogenerated electron-hole pairs, the thus-transformed TiO₂(B)/anatase heterophase junctions exhibit fascinating photocatalytic performance in water splitting. Specifically, with the help of Pt as a cocatalyst and methanol as a sacrificial agent, the H₂ production rate of optimized TiO₂(B)/anatase heterophase junction reaches 6.92 mmol·g^-1·h^-1, which is almost 7.1 and 2.1 times higher than those of the pristine TiO₂(B) nanosheets and the final anatase nanocrystals. More interestingly, the TiO₂(B)/anatase heterophase junction also delivers prominent activity toward pure water splitting to simultaneously produce H₂ and H₂O₂, with evolution rates of up to 1.10 and 0.55 mmol·g^-1·h^-1, respectively. Our work may advance the facile green solvent-mediated synthesis of metal oxide-based heterophase junctions for applications in energy- and environmental-related areas.

Highly Efficient Photocatalytic Degradation of Hydrogen Sulfide in the Gas Phase Using Anatase/TiO2(B) Nanotubes

Hydrogen sulfide (H₂S) is a highly toxic and corrosive gas that causes a foul odor even at very low concentrations [several parts per billion (ppb)]. However, industrially discharged H₂S has a concentration range of several tens of ppb to several parts per million (ppm), which conventional methods are unable to process. Therefore, advanced and sustainable methods for treating very low concentrations of H₂S are urgently needed. TiO₂-based photocatalysts are eco-friendly and have the ability to treat environmental pollutants, such as low-concentration gases, using light energy. However, there are no reports on H₂S decomposition or oxidation at concentrations below several ppb. Therefore, in this study, we employed anatase/TiO₂(B) nanotubes, which have a high specific surface area and an efficient charge-transfer interface, to treat H₂S. We successfully reduced 10 ppm of H₂S to 1 ppb or less at a kinetic rate of 75 μmol h^-1 g^-1. The suitability of our method was further demonstrated by the generation of sulfate ions and sulfur (as detected by X-ray photoelectron spectroscopy and ion chromatography), which are industrially useful as oxidation products, whereas sulfur dioxide, a harmful substance, was not produced. This is the first study to report H₂S decomposition down to the ppb level, providing meaningful solutions for malodor problems and potential health hazards associated with H₂S.

In Situ Construction of Bronze/Anatase TiO2 Homogeneous Heterojunctions and Their Photocatalytic Performances

Photocatalytic degradation is one of the most promising emerging technologies for environmental pollution control. However, the preparation of efficient, low-cost photocatalysts still faces many challenges. TiO2 is a widely available and inexpensive photocatalyst material, but improving its catalytic degradation performance has posed a significant challenge due to its shortcomings, such as the easy recombination of its photogenerated electron-hole pairs and its difficulty in absorbing visible light. The construction of homogeneous heterojunctions is an effective means to enhance the photocatalytic performances of photocatalysts. In this study, a TiO2(B)/TiO2(A) homogeneous heterojunction composite photocatalyst (with B and A denoting bronze and anatase phases, respectively) was successfully constructed in situ. Although the construction of homogeneous heterojunctions did not improve the light absorption performance of the material, its photocatalytic degradation performance was substantially enhanced. This was due to the suppression of the recombination of photogenerated electron-hole pairs and the enhancement of the carrier mobility. The photocatalytic ability of the TiO2(B)/TiO2(A) homogeneous heterojunction composite photocatalyst was up to three times higher than that of raw TiO2 (pure anatase TiO2).

Mechanistic understanding of the increased photoactivity of TiO2 nanosheets upon tantalum doping

Anatase TiO₂ is doped with Ta cations through a hydrothermal route. Based on X-ray photoelectron spectroscopy and X-ray absorption near-edge structure spectroscopy, the Ta dopants exist in the 5+-oxidation state. The oxidation state is insensitive to the Ta loading amount. Extended X-ray absorption fine structure spectroscopy confirms that the local structure around Ta cations is not identical between the Ta-doped samples. The Ta-O distance monotonically increases with the Ta loading amount due to a gradually expanding lattice. The Ta-doped samples show higher activity than pristine TiO₂ for photomineralizing recalcitrant organics. The enhanced photocatalytic activity is proposed to be due to an enhanced population of photoexcited electrons, as probed using light-induced IR absorption spectroscopy, and an extended electron lifetime, as probed using time-resolved microwave conductivity, which are associated with the formation of Ti³⁺ defect states acting as shallow electron traps. The maximum photocatalytic activity is observed for TiO₂ doped with 2 mol% of Ta, which shows enhancement of mineralization efficiency (about 3 times) and enhancement of electron population (up to 20 times), as compared to those of pristine TiO₂. The fundamental question of why a proper metal doping into TiO₂ increases photocatalytic activity is discussed in this study.