Recent progress in photocatalytic applications of metal tungstates based Z-scheme and S-scheme heterojunctions

Substantial attention has been paid over recent years to explore potential high performance photocatalysts for environmental and energy applications. Metal tungstate-based materials are highly suited for challenging photocatalytic conditions due to their high chemical stability, tuneable band structures and resilience. Various methods have been employed to improve the photocatalytic potential of molybdates as heteroatom doping, co-catalyst, morphology control and heterojunctions formation. The construction of metal tungstate-based Z-scheme and S-scheme heterostructured photocatalysts has been found to be highly promising owing to the charge separation and transfer capacity to accelerate the surface reaction. The variable band gaps and high valence band positions make most of them apt as oxidation type photocatalyst, however, may be applicable as reduction type. However, it might be challenging to construct well-defined metal tungstate-based heterojunction structures while maintaining exact control over the synthesis conditions. To improve photocatalytic activity, tight contact and efficient charge transfer at the heterojunction interface are required. Several synthetic routes have been reported tungstates catalysts with various morphologies/band structures and high photocatalytic activities. This review also covers the various popular and advanced synthesis techniques for designing metal tungstate-based Z-scheme and S-scheme heterostructures and recent advancements for efficient photocatalytic energy and environmental applications.