In Situ Growth of g-C₃N₄ on Hexangular Flowerlike FeWO₄ Microcrystals: Highly Efficient Catalyst and the Crucial Roles of Fe³⁺/Fe²⁺ Couple in the Photoassisted Oxidation and Reduction Reactions

Novel highly efficient heterostructured photocatalysts consisting of g-C₃N₄ nanosheets on hexangular flowerlike FeWO₄ microcrystals were first fabricated via an in situ growth approach. The intimate g-C₃N₄ coating layers (ca. 50–130 nm) on the surface of FeWO₄ microcrystals were observed through transmission electron microscopy. An all-side evaluation of its performance toward typical photoassisted oxidation and reduction reactions was carried out, which exhibited drastically improved performance for photocatalytic oxygen production and photodegradation, while obviously suppressed hydrogen evolution activity when compared with the bulk g-C₃N₄(CNU). The optimal photocatalyst CNU–FW90 (90 mg of FeWO₄ in 15 g of urea) displayed an oxygen evolution rate of 303 μmol/(g h), about 2.4 and 3.8 times as much as that of CNU and FeWO₄, respectively. Not only that, CNU–FW90 showed superior degradation activity with a reaction kinetics rate constant of 0.1192 min^–1, nearly 5-fold higher than that of the pure CNU. By correlating the performance with the band structures and surface valence states of g-C₃N₄@FeWO₄ heterojunctions, a possible mechanism was proposed to uncover the differences between oxidation and reduction reactions in this system, which highlighted the crucial role of Fe³⁺/Fe²⁺ couple in tuning the performance of photocatalytic reactions. This work put forward a promising strategy to design highly efficient semiconductor photocatalysts and shed light on the vital effect of surface valence state of Fe element in tuning the performance of Fe-related photocatalysts.

J. Phys. Chem. C122, 24, 12900-12912

https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.8b03575