The Surface-Structure Sensitivity of Dioxygen Activation in the Anatase-Photocatalyzed Oxidation Reaction

Surface structure-dependent photocatalytic O2 activation for pollutant removal with bismuth oxyhalides

The purification of water and air by semiconductor photocatalysis is a rapidly growing area for academic research and industrial innovation, featured with ambient removal of organic or inorganic pollutants by using solar light as the energy source and atmospheric O₂ as the green oxidant. Both charge transfer and energy transfer from excited photocatalysts can overcome the spin-forbidden nature of O₂. Layered bismuth oxyhalides are a new group of two-dimensional photocatalysts with an appealing geometric and surface structure that allows the dynamic and selective tuning of O₂ activation at the surface molecular level. In this Feature Article, we specifically summarize our recent progress in selective O₂ activation by engineering surface structures of bismuth oxyhalides. Then, we demonstrate selective photocatalytic O₂ activation of bismuth oxyhalides for environmental control, including water decontamination, volatile organic compound oxidation and nitrogen oxide removal, as well as selective catalytic oxidations. Challenges and opportunities regarding the design of photocatalysts with satisfactory performance for potential environmental control applications are also presented.

Effect of Surface Defect States on Valence Band and Charge Separation and Transfer Efficiency

Both energy band and charge separation and transfer are the crucial affecting factor for a photochemical reaction. Herein, the BiOCl nanosheets without and with surface bismuth vacancy (BOC, V-BOC) are prepared by a simple hydrothermal method. It is found that the new surface defect states caused by bismuth vacancy have greatly up-shifted the valence band and efficiently enhanced the separation and transfer rates of photogenerated electron and hole. It is amazing that the photocatalytic activity of V-BOC is 13.6 times higher than that of BOC for the degradation methyl orange (MO). We can develop an efficient photocatalyst by the introduction of defects.

Template-free synthesis of core-shell TiO2 microspheres covered with high-energy {116}-facet-exposed N-doped nanosheets and enhanced photocatalytic activity under visible light

Core-shell TiO2 microspheres possess a unique structure and interesting properties, and therefore, they have received much attention. The high-energy facets of TiO2 also are being widely studied for the high photocatalytic activities they are associated with. However, the synthesis of the core-shell structure is difficult to achieve and requires multiple-steps and/or is expensive. Hydrofluoric acid (HF), which is highly corrosive, is usually used in the controlling high-energy facet production. Therefore, it is still a significant challenge to develop low-temperature, template-free, shape-controlled, and relative green self-assembly routes for the formation of core-shell-structured TiO2 microspheres with high-energy facets. Here, we report a template- and hydrofluoric acid free solvothermal self-assembly approach to synthesize core-shell TiO2 microspheres covered with high-energy {116}-facet-exposed nanosheets, an approach in which 1,4-butanediamine plays a key role in the formation of nanosheets with exposed {116} facets and the doping of nitrogen in situ. In the structure, nanoparticle aggregates and nanosheets with {116} high-energy facets exposed act as core and shell, respectively. The photocatalytic activity for degradation of 2,4,6-tribromophenol and Rhodamine B under visible irradiation and UV/Vis irradiation has been examined, and improved photocatalytic activity under visible light owing to the hierarchical core-shell structure, {116}-plane-oriented nanosheets, in situ N doping, and large surface areas has been found.

The pure shape effect with a removing facet effect of single-crystalline anatase TiO₂ (101) for photocatalytic application

3D TiO₂ nanobipyramids (TiO₂-NPs) and 1D TiO₂ nanobelts (TiO₂-NBs) were synthesized from potassium titanate K₂Ti₆O₁₃ and characterized by X-ray diffraction (XRD) patterns, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) patterns and fast Fourier transform (FFT). The as-synthesized 3D TiO₂ nanobipyramids and 1D TiO₂ nanobelts all show high {101} facet exposed percentages and were used to investigate the shape effect of TiO₂ with the same facet exposure. 3D TiO₂ nanobipyramids (101) showed higher photocatalytic activity than 1D TiO₂ nanobelts (101). The reasons were discussed using ROS (reactive oxygen species) production, time-resolved photoluminescence spectra, XPS (X-ray photoelectron spectroscopy) spectra and ATR-IR (attenuated total reflectance infrared spectroscopy) spectra. The postulated mechanism suggests that 3D TiO₂ nanobipyramids have more step edges which results in more -OH/H₂O molecule adsorption and longer life times of photoinduced carriers than 1D TiO₂ nanobelts.