Novel ZnFe₂O₄/WO₃, a highly efficient visible-light photocatalytic system operated by a Z-scheme mechanism

Dark red ZnFe₂O₄ (ZFO) nanoparticles (NPs) of ˜9 nm size and pale yellow WO₃ nanowire bundles (NWBs) with high porosity were prepared by hydrothermal reactions, respectively, and coupled to form novel ZFO/WO₃ heterojunctions. Tiny ZFO NPs and highly porous WO₃ NWBs successfully formed intimate heterojunctions, facilitating charge transport at their interfaces. Under visible-light, ZFO/WO₃ composites demonstrated outstanding catalytic activities for decomposing isopropyl alcohol (IPA) in the gas phase and salicylic acid (SA) in aqueous solution. In particular, the amount of CO₂ evolved in 2 h during decomposition of IPA was 24.7 ppmv, which was 3.0 times that produced using typical nitrogen-doped TiO₂ (N-TiO₂). Moreover, its degradation rate constant of SA in the presence of ZFO/WO₃ was ˜7 times that of N-TiO₂. It was determined that •OH and •O₂- radicals were the major active species responsible for oxidation reactions, suggesting that the photocatalytic reactions of ZFO/WO₃ occurred via Z-scheme mechanism.