Synergistic effect of sulfur vacancies and spin polarization on photoreforming of plastic waste to hydrogen over Ni, Co-substitutionally doped ZnCdS2

Abstract

Efficient photoreforming of plastic waste to hydrogen (H₂) necessitates photocatalysts with robust redox capacity and rapid charge separation. Employing NiCo-LDH templates as doping precursors, we synthesized Ni, Co-substitutionally doped ZnCdS₂ (ZCS-NiCo-SD) that exhibited higher sulfur vacancies (V_S) concentration and spin polarization than the interstitially doped ZnCdS₂ (ZCS-NiCo-ID) prepared using mixed Ni, Co acetates as precursors. Multiple characterizations and theoretical calculations confirm that V_S promote the generation of hydroxyl radicals, while the spin polarization of electrons in the Ni, Co-3d and S-2p orbitals facilitates charge separation and inhibits charge recombination. Synergistically enhanced by the high V_S concentration and spin polarization in promoting the oxidation-reduction reactions, ZCS-NiCo-SD achieved an impressive H₂ evolution rate of 48.62 mmol g^-1 h^-1 in the photoreforming of polylactic acid plastic waste, which is 1.9 and 5.2 times higher than those of ZCS-NiCo-ID and ZCS, respectively. This work demonstrates a novel doping strategy for designing high-efficiency photocatalysts for photoreforming of plastic waste to H₂.

Keywords: Hydrogen evolution; Plastic photoreforming; Spin polarization; Substitutional doping; Sulfur vacancies.