Tuning surface electronic structure of (CuGa) Zn1‒2Ga2S4 photocatalyst for efficient nitrate-to-ammonia conversion

The photocatalytic conversion of nitrate (NO 3 − ) into ammonia (NH 4 + ) under mild conditions offers a promising approach for mitigating environmental nitrate contamination. The efficiency of this process is fundamentally governed by the adsorption and activation of NO 3 − and its intermediates, which are significantly influenced by the surface electronic properties of the catalyst, particularly the position of the d -band center. However, conventional approaches to tune the surface electronic structure such as doping with extraneous elements or forming heterojunctions often alter the overall band structure seriously, typically leading to reduced photocatalytic activity. In this study, the d -band state of (CuGa) x Zn 1‒2 x Ga 2 S 4 semiconductor is engineered through Al 3+ surface decoration without affecting the conduction band or the bandgap to enhance NO 3 − adsorption and activation. X-ray photoelectron spectroscopy and X-ray absorption fine structure analyses reveal that the surface doping of Al 3+ do not induce obviously energy band structure change but the d -band center, which shift more closer to Fermi level in comparison with pristine material. Electronic energy band analyses indicate that Al 3+ decoration does not significantly alter the conduction band or bandgap. Moreover, the Al 3+ -modified material demonstrates a substantial improvement in photocatalytic conversion of NO 3 − into NH 4 + , increasing the NH 4 + production rate from 0.18 to 0.93 mmol h −1 g −1 . Density functional theory calculations further revealed that the d -band center of Al 3+ /(CuGa) x Zn 1–2 x Ga 2 S 4 shifted closer to the Fermi level, moving from –4.75 to –4.54 eV compared to the pristine (CuGa) x Zn 1–2 x Ga 2 S 4 . This shift lowered the Gibbs free energy for the adsorption of NO 3 − reduction intermediates, thereby enhancing the conversion efficiency of NO 3 − into NH 4 + . This work introduces an effective strategy for surface d -band states modulation without altering the intrinsic band structure to improve nitrate reduction performance, offering deep insights into the future design of materials for environmental remediation applications.