Influence of Fe dopant concentrations on physicochemical and photocatalytic properties of Bi2WO6/CeO2 nanocomposites for rhodamine B degradation

High-performance photocatalytic reduction of Cr(VI) using a retrievable Fe-doped WO3/SiO2 heterostructure

The enhancement of the photocatalytic performance of pristine WO3 was systematically adjusted due to its fast recombination rate and low reduction potential. A designed heterostructure photocatalyst was necessarily synthesised by Fe3+ metal ions doping into WO3 structure with and composition modification. In this study, we synthesised a retrievable Fe-doped WO3/SiO2 heterostructure using a surfactant-assisted hydrothermal method. This heterostructure was then employed as an effective photocatalyst for the removal of Cr(VI) under visible light irradiation. Enlarged photocatalytic reduction was observed over a synergetic 7.5 mol% Fe-doped WO3/SiO2-20 nanocomposite, resulting in dramatically increased activity compared with undoped WO3 and SiO2 nanomaterials under visible light illumination within 90 min. The presence of 7.5 mol% Fe3+ ion dopant in WO3 optimised electron-hole recombination, consequently reducing WO3 photocorrosion. After adding SiO2 nanoparticles, the binary WO3-SiO2 nanocomposite played roles as both adsorbent and photocatalyst to increase specific surface area. Thus, the 7.5 mol% Fe-doped WO3/SiO2-20 nanocomposite catalyst had more active sites on the surface of catalyst, and enhanced photocatalytic reduction was significantly achieved. The results showed 91.1% photocatalytic reduction over the optimum photocatalyst, with a photoreduction kinetic rate of 21.1 × 10-3 min-1, which was approximately four times faster than pristine WO3. Therefore, the superior optimal photocatalyst demonstrated reusability, with activities decreasing by only 9.8% after five cycles. The high photocatalytic performance and excellent stability of our photocatalyst indicate great potential for water pollution treatments.

Roles of Mo dopant in Bi2WO6 for enhancing photocatalytic activities

We present the investigation of the roles of molybdenum (Mo) dopant with a concentration of 0.0625% to 1.0% Mo into bismuth tungstate (Bi₂WO₆) by a one-step hydrothermal method for the enhancement of photocatalytic activities. The obtained materials and doping effects were characterized by the morphology, crystal structure, chemical states, and optical properties. By combining XRD, XANES, and EXAFS studies, the distortion of the local structure with substitutional doping was revealed as doping with Mo ions was located at the lattice sites of the tungsten ions. Photocatalytic reactions of Mo-doped Bi₂WO₆ were studied by the degradation of methyl orange dye under visible light irradiation. The results show that the optimal concentration of Mo dopant is 0.25%, with the highest photocatalytic activity up to ∼2-fold compared to the bare Bi₂WO₆. From our investigation, we propose that the impurity level is located below the conduction band edge of Bi₂WO₆ after doping with Mo⁶⁺ ions. This impurity level acts as an electron trapping site to prevent the transition of excited electrons from the conduction band to the valence band. By trapping experiments, the superoxide anion radicals (O₂˙^-) as the main active species to enhance photocatalytic efficiency was established.