Enhanced photo-electrochemical properties of phosphorus-doped ZnSxO1-x with surface PS· defect species for hydrogenation with in situ generated H+

Abstract

Photocatalytic hydrogenation was successfully conducted in the present work with P-doped ZnS_xO_1-x catalyst to convert 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with in situ generated H⁺. In previous work, pure ZnS_xO_1-x photocatalyst exhibited its ability to evolve hydrogen. However, it cannot convert 4-NP to 4-AP completely since the generated H⁺ is easily reduced to H₂ and released from catalyst surfaces. In this work, phosphorus was doped to ZnS_xO_1-x to purposely create defects to trap the generated electrons on catalyst surfaces, thus decreasing the reduction of adsorbed H⁺ to H₂. XPS analysis indicates the emergence of positively charged $V_O^{\mathrm{··}}$ and $P_S^{·}$ surface defects after doping P to ZnS_xO_1-x. When the photogenerated electron is trapped in the positively charged defects, the H⁺ reduction is diminished. The available H⁺ on catalyst surfaces can be used for a hydrogenation reaction of 4-NP to 4-AP during the photoreaction. To optimize the catalytic system, different amounts of P precursor were doped into ZnS_xO_1-x with a hydrothermal method at 150 °C. The as-synthesized catalysts were characterized with XRD, SEM, TEM, XPS, DRS, PL, EIS, TPC, and CV analysis. It was found that a typical catalyst (ZP-0.2–10 h) can effectively hydrogenate 30 ppm 4-NP to 4-AP in 60 min under a 150-W Xe-lamp illumination. Based on the analysis data, P doping enhances the light absorbance, photocurrent, conductivity, and photocarrier lifetime of ZnS_xO_1-x. The present work indicates a green hydrogenation reaction can be done by modifying a hydrogen-evolved photocatalyst. Finally, a rational hydrogenation conversion mechanism was discussed and proposed in this work.