Synergistic Sulfur Vacancy and Polydopamine Engineering in S v-CdS@PDA Z-scheme Heterojunctions for Photocatalytic H2O2 Production with Robust Anticorrosion
Metal sulfides such as CdS are promising for solar-driven H2O2 production but suffer from rapid charge recombination and severe photocorrosion. This study introduces a dual-functional strategy synergizing sulfur vacancy (Sv) engineering and polydopamine (PDA) coating to overcome these limitations. Sv-CdS nanorods were hydrothermally synthesized with tunable vacancy concentrations, followed by in-situ PDA deposition to construct a direct Z-scheme heterojunction. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations reveal that the introduction of S vacancies reduces the work function of CdS, facilitating energy level alignment with PDA and enabling efficient electron transfer from CdS to PDA. By tuning the concentration of S vacancies, the charge transfer efficiency can be maximized. As a result, the photocatalytic H2O2 production rate reaches 2539.5 μmol g−1 h−1 under visible light, and further increases to 4395.5 μmol g−1 h−1 after PDA encapsulation—15.6 times higher than that of pristine CdS. Concurrently, PDA enhances O2 adsorption and protects Sv-CdS from photocorrosion. Sv-CdS@PDA exhibited superior photostability compared to Sv-CdS after three consecutive photocatalytic cycles. Mechanistic studies suggest that the Z-scheme heterojunction effectively separates electron-hole pairs: electrons in the conduction band of CdS reduce O2 to ·O2−, which is subsequently converted to H2O2, while holes in the valence band of Sv-CdS oxidize water to replenish O2. This work provides fundamental insights into engineering charge transfer and stability in sulfide-based photocatalysts.