Polyoxometalate immobilized on sulfur-vacancy-engineered ZnIn₂S₄/tubular carbon nitride for efficient photocatalytic...

To address the low separation efficiency of photogenerated charge carriers, which restricts photocatalytic water splitting, multi-component synergistic ternary photocatalysts were rationally designed. Hollow tubular carbon nitride (TCN, tubular carbon nitride) was used as the substrate, zinc indium sulfide (ZnIn₂S₄, ZIS) rich in sulfur vacancies (Vs) was integrated with TCN, and dopamine (PDA), which acted as both an adhesive and interface modifier, was employed to load polyoxometalates ([Co₄(H₂O)₂(PW₉O₃₄)₂]^10-, PW₉Co and [Ni₄(H₂O)₂(PW₉O₃₄)₂]^10-, PW₉Ni) onto Vs-ZIS/TCN, yielding the ternary PW₉Co/Vs-ZIS/TCN and PW₉Ni/Vs-ZIS/TCN composites. Systematic characterizations (PXRD, FT-IR spectroscopy, and XPS) confirmed the successful synthesis of these composites, with the existence of stable Vs and inter-component interactions, and N₂ adsorption-desorption revealed their mesoporous structure (PW₉Co/Vs-ZIS/TCN-75: 62.59 m² g^-1) with abundant active sites. Optical and electrochemical tests showed that the ternary composites had enhanced visible-light absorption and photogenerated carrier separation efficiency compared with their binary counterparts. Photocatalytic hydrogen evolution experiments indicated that PW₉Co/Vs-ZIS/TCN-75 had the highest hydrogen evolution rate (11.50 mmol g^-1 h^-1, 2.98 times that of Vs-ZIS/TCN-100) and excellent long-term stability (14.3% activity decay after 30 h of cyclic testing). Mechanistic analysis attributed the improved performance to the synergistic effect of the Z-scheme heterojunction, PDA interface modification and Vs-mediated carrier capture. This work provides a feasible approach for the development of high-performance photocatalytic systems and insights for the rational design of efficient, stable multi-component photocatalysts for solar-driven hydrogen production.