Zn-Ce-Ga trimetal oxysulfide as a dual-functional catalyst: Hydrogen evolution and hydrogenation reactions in a mild condition

Highlights: • Codoping of Ce and Ga into Zn(O,S) enhanced the HER and hydrogenation of NB and AB. • The positively charged antisite defects improve the e^-/h⁺ separation and charge transfer. • In-situ generated H⁺ plays as a green reducing agent for hydrogenation reaction. • A plausible photocatalytic hydrogenation mechanism was proposed with different steps. The works on photocatalytic hydrogen production and green chemical conversion have received significant attention due to the current need for clean energy and a secure environment. Herein, Ce and Ga codoped Zn(O,S) has been synthesized with different amounts of Ce using facile precipitation method at a low temperature of 95 °C and characterized by XRD, SEM, HRTEM, XPS, EPR, Raman, DRS, PL, EIS, UV–vis, GC–MS, and photocurrent response measurements. The as-prepared photocatalysts were utilized for hydrogen production and hydrogenation of toxic organic compounds, viz. nitrobenzene (NB) and azobenzene (AB) into a valuable product of aniline. The incorporation of Ce and Ga into Zn(O,S) enhanced the hydrogen evolution and hydrogenation reactions of NB and AB. This notable enhancement was ascribed to the synergistic effects of Ce and Ga dopants to form positively charged defects that trap the photogenerated electron. The trapping mechanism improves the photogenerated charge separation and transfer as confirmed with impedance spectroscopy (EIS), transient photocurrent response, and PL measurements. The highest hydrogen production was attained by 15Ce-5Ga-Zn(O,S) with a rate of 7130 μmol∙g⁻¹∙h⁻¹ in 10% ethanol solution. In addition, NB and AB were effectively converted to aniline in 15 min and 30 min, respectively. A plausible photocatalytic hydrogenation mechanism for both hydrogenation of NB and AB is proposed with the steps of surface adsorption, molecular diffusion, pinning at oxygen vacancy sites, and hydrogenation reaction with the help of in situ generated H⁺ coupled with electrons.