Ammonia-Treated Graphene Oxide/ZnIn₂S₄ Composite for Enhanced Photocatalytic Hydrogen Production under Visible Light Irradiation

In the pursuit of solar-driven photocatalytic energy generation, environmental remediation, and carbon neutrality, the development of semiconductor-based heterojunction photocatalysts presents a promising strategy. However, the photocatalytic efficiency of pristine ZnIn₂S₄ (ZIS) is hindered by rapid electron-hole recombination and a relatively small surface area. Meanwhile, pure graphene oxide (GO) is not an ideal photocatalyst due to its inappropriate bandgap and the presence of oxygenated functional groups. To overcome these limitations, a surfactant-assisted ZIS synthesis was combined with ammonia-treated GO (NGO) to form an NGO/ZIS composite that enhances light absorption, charge carrier separation and transport, and overall hydrogen production efficiency under visible light illumination. Among the evaluated materials, 0.1NGO/ZIS exhibited the highest hydrogen evolution rate (18.8 mmol·g^-1 h^-1), demonstrating enhancements of 3-fold and 940-fold increased compared to pristine ZIS (5.8 mmol·g^-1 h^-1) and NGO (0.02 mmol·g^-1 h^-1), respectively. This superior photocatalytic performance is attributed to improved interfacial charge transfer between NGO and ZIS, facilitated by the incorporation of amine and amide groups into GO. Furthermore, density functional theory (DFT) calculations were conducted to validate the impact of ammonia treatment on GO and support the experimental findings. The synthesized photocatalysts were characterized by using X-ray diffraction (XRD), Fourier-transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), diffuse reflectance sorption spectroscopy (DRS), photoluminescence (PL), electrochemical impedance spectroscopy (EIS), electron spin resonance (ESR), and time-resolved photoluminescence (TRPL) analyses. This study presents a simple yet effective approach to fabricating NGO/ZIS composites, contributing to the advancement of high-performance photocatalysts for sustainable energy applications.