Phosphotungstic Acid Clusters Decorated Znln2S4 Nanoflowers as Molecular-Scale S-Scheme Heterojunctions for Simultaneous H2 Evolution and Benzyl Alcohol Upgrading.

Simultaneous utilization of photogenerated electrons and holes to achieve overall redox reactions is attractive but still far from practical application. The emerging step (S)-scheme mechanism has proven to be an ideal approach to inhibit charge recombination and supply photoinduced charges with highest redox potentials. Herein, a hierarchical phosphotungstic acid (H3PW12O40, HPW)@Znln2S4 (ZISW) heterojunction was prepared through one-pot hydrothermal method for simultaneous hydrogen (H2) evolution and benzyl alcohol upgrading. The fabricated HPW-based heterojunctions indicated much enhanced visible-light absorption, promoted photogenerated charge transfer and inhibited charge recombination, owing to hierarchical architecture based on visible-light responsive Znln2S4 microspheres, and S-scheme charge transfer pathway. The S-scheme mechanism was further verified by free-radical trapping electron spin resonance (ESR) spectra. Moreover, the wettability of composite heterojunction was improved by the modification of hydrophilic HPW, contributing to gaining active hydrogen (H+) from water sustainably. The optimal ZISW-30 heterojunction photocatalyst indicated an enhanced hydrogen evolution rate of 27.59 mmol g-1 h-1 in benzyl alcohol (10 vol. %) solution under full-spectrum irradiation, along with highest benzaldehyde production rate is 8.32 mmol g-1 h-1. This work provides a promising guideline for incorporating HPW into S-scheme heterojunctions to achieve efficient overall redox reactions.

Incorporating Ni-Polyoxometalate into the S-Scheme Heterojunction to Accelerate Charge Separation and Resist Photocorrosion for Promoting Photocatalytic Activity and Stability.

The emerging polyoxometalate (POM) nanomaterials are transition metal oxygen anion clusters with d0 electronic configurations, which could be attractive and potential photocatalysts. Hence, a nickel (Ni)-substituted polyoxometalate K6Na4[Ni4(H2O)2(PW9O34)2]·32H2O (Ni4POM)-incorporating step (S)-scheme heterojunction was developed to promote photocatalytic activity and stability in H2 and H2O2 production. The multielectron transfer through variable valence metal centers in Ni4POM would facilitate the recombination of invalid charges through the S-scheme pathway. Moreover, incorporating Ni4POM into the S-scheme heterojunction can broaden the light absorption range and meanwhile lead to resistance to photocorrosion to promote the optical and chemical stability of Cd0.5Zn0.5S (CZS). The optimized CZSNi-70 exhibited a H2 evolution rate of 42.32 mmol g-1 h-1 under visible-light irradiation with an apparent quantum yield of 32.27% at 420 nm and a H2O2 production rate of 295.4 µmol L-1 h-1 under 420 nm light-emitting diode irradiation. This work can provide a new view for the development of transition metal-substituted POM-based stable and efficient S-scheme photocatalysts.