Enhanced hole–proton-coupled electron transfer of spin polarized photocatalyst via Mo–S₄ coordination for sequential activation of C(sp³)-H and O-H bonds

Photocatalytic oxidative dehydrogenation of biomass feedstocks offers the possibility for synthesizing value-added chemicals, but the sluggish transport kinetics and rapid recombination of photogenerated charge carriers constrain photocatalysis efficiency. Spin-polarized photocatalysts, by accelerating the separation of photogenerated electrons and holes, offer a promising strategy for selective biomass valorization. Herein, polarization unit Mo was incorporated into ZnIn₂S₄ (ZIS) with S-vacancy through Mo–S₄ coordination (Mo-Vs-ZIS) to enhance hole and proton-coupled electron transfer (PCET). Mo-Vs-ZIS spin polarized photocatalyst applied to 5-hydroxymethylfurfural (HMF) afforded a 2,5-diformylfuran (DFF) selectivity of 92.3 % at a production rate of 1105.3 µmol g_cat⁻¹ h⁻¹, attributed to carrier transport and reaction processes. The Mo-Vs-ZIS photocatalyst efficiently (100 min) converted benzyl and furfuryl alcohols, aromatic alcohols bearing electron-rich substituents, and halogen-substituted aromatic alcohols into their corresponding aldehydes. Piezoelectric force microscopy (PFM) and Kelvin probe force microscopy analyses (KPFM) revealed that the full-space polarized electric field was formed to drive directional transfer of photogenerated carriers, facilitating bulk-to-surface charge separation. Moreover, Mo-Vs-ZIS showed high Bader charge transfer to O₂, where Mo atomic sites functioned as an electron reservoir, driving the activation of O₂ to form •O₂⁻, a kinetically favorable step for HMF oxidation and induced transfer of holes to activate C(sp³)-H bonds, which is a rate-determining step. Then, the critical step of PCET (•O₂⁻ + H⁺ → •OOH) over Mo-Vs-ZIS gave •OOH for O-H activation to complete the reaction sequence. This spin-polarized modification strategy featuring atomic-level catalytic sites enables its application to other semiconductor photocatalysts for biomass conversion.