Bi2WO6‐based Z-scheme photocatalysts: Principles, mechanisms and photocatalytic applications

The development of novel photocatalysts for efficient utilization of solar energy is highly essential for the most critical humanitarian challenges, i.e., energy and water crises as well as environmental pollution. Bismuth tungstate (Bi2WO6), an outstanding Aurivillius phase perovskite, has attracted intensive attention as a visible-light-responsive photocatalyst because of its non-toxicity, low cost, and outstanding physicochemical characteristics, i.e., nonlinear dielectric susceptibility, ferroelectric piezoelectricity, pyroelectricity, catalytic behavior, modifiable morphology, strong oxidation power, and good photochemical stability. However, the photocatalytic activity of bare Bi2WO6 is restricted because of the inherent drawbacks such as poor light-harvesting efficiency, weak reduction potential, relatively low specific surface area, the fast recombination rate of photoinduced charge carriers, and thus poor quantum yields of photocatalytic reactions. Moreover, the impossibility of simultaneous strong redox ability (demanding wide bandgap) and high light-harvesting efficiency (requiring narrow bandgap) is considered as a big challenge for the practical application of Bi2WO6. Undeniably, the construction of Z-scheme photocatalytic systems is recommended strategy to overcome the above-mentioned disadvantages because of the efficient spatial separation of photogenerated charge carriers and the boosting the redox performance. This review summarizes the principles and recent developments on Z-scheme photocatalytic systems with special emphasis on the Bi2WO6-based photocatalysts, including the types, photocatalytic mechanisms and practical applications. Moreover, major differences between type-II heterojunction and Z-scheme photocatalyst have also been discussed. Additionally, the significant role of unique structures (e.g., core-shell and 2D/2D) for the improvement of photocatalytic activity of Z-scheme photocatalyst has been presented. Indeed, Bi2WO6-based Z-scheme photocatalysts have exhibited superior photocatalytic activity for various applications. For example, they show high photocatalytic activity towards water/wastewater treatment (removal of organic and inorganic pollutants, as well as microorganisms), air purification (decomposition of volatile organic compounds and inorganic matters), “green” energy conversion (e.g., generation of H2 and CH4 fuels under solar irradiation), and organic synthesis. It is thought that this remarkable activity of Bi2WO6-based Z-scheme photocatalysts might be attributed to the efficient solar light harvesting, separation and further transfer of charge carriers and strong redox ability. To the best of our knowledge, the present paper is the first attempt to summarize the Bi2WO6-based Z-scheme photocatalytic reactions, providing important insights and up-to-date information for the scientific community to fully explore the potential of Bi2WO6-based photocatalysts for renewable environmental remediation, energy conversion, and chemical synthesis.