Nanostructured Ternary Metal Tungstate-Based Photocatalysts for Environmental Purification and Solar Water Splitting: A Review

Abstract

Since Fujishima and Honda in 1972 demonstrated that titanium dioxide (TiO 2 ) can be used as photoanode to split water excited by ultraviolet light, photocatalysis technology has been viewed as among the most promising approaches to solve the global energy crisis and environmental problems [ 1 , 2 , 3 ]. In general, a complete semiconductor photocatalytic cycle involves light-harvesting, photogenerated charge carrier excitation, charge separation and transfer, and surface redox reactions [ 4 , 5 , 6 ] that allow for the formation of reactive oxygen species (ROSs), such as free electrons (e − ), hydrogen peroxide (H 2 O 2 ), hydroxyl (·OH), and superoxide radicals (·O 2 − ) [ 7 , 8 ]. The aforementioned ROSs play crucial roles in various important applications, including photocatalysis [ 9 , 10 , 11 , 12 ], photoelectrocatalysis [ 13 , 14 , 15 , 16 , 17 ], plasma photocatalysis [ 18 , 19 ], and photothermocatalysis [ 20 , 21 , 22 ]. Until now, TiO 2 has been among the most extensively studied semiconductor photocatalysts because of its strong oxidative ability, chemical stability, long durability, and nontoxicity [ 23 , 24 , 25 ]. However, the TiO 2 photocatalyst possesses a wide band gap of ~ 3.2 eV that can only absorb ultraviolet (UV) light, which is a small fraction (~ 5%) of solar light, thereby hardly harvesting the remaining solar energy [ 26 , 27 ]. To efficiently utilize the majority of the solar spectrum, Fe 2 O 3 - [ 28 ], WO 3 - [ 29 , 30 ], Bi 2 WO 6 - [ 31 ], ZnO- [ 32 ], Bi 2 O 3 - [ 33 ], and NiO-based semiconductors [ 34 ] have been widely developed as photocatalysts for environmental treatment and solar water splitting (Fig. 1 ). Nevertheless, low sunlight utilization efficiency and quantum yield, rapid reverse reactions, and poor stability still hinder practical applications of these photocatalytic materials [ 35 , 36 , 37 , 38 , 39 ].