Waste plastics promoted photocatalytic H2 evolution over S-scheme NiCr2O4/twinned-Cd0.5Zn0.5S homo-heterojunction

Abstract

The simultaneous enhancement of separation and utilization of bulk and surface charges is crucial for achieving efficient photocatalytic H₂ evolution reactions. In this study, NiCr₂O₄/T-CZS composites were fabricated by incorporating NiCr₂O₄ nanosheets onto the surface of twinned Cd_0.5Zn_0.5S (T-CZS) nanoparticles using a solvent evaporation strategy. After optimization, the 6% NiCr₂O₄/T-CZS exhibited an impressive hydrogen (H₂) evolution rate (r_H2) of 81.4 ​mmol·h⁻¹·g⁻¹ when employing polylactic acid (PLA) plastic as a sacrificial agent in NaOH solution. The reason behind this can be mainly attributed to the fact that T-CZS consists of wurtzite Cd_0.5Zn_0.5S (WZ-CZS) and zinc blende Cd_0.5Zn_0.5S (ZB-CZS) with slight band structure differences, thereby facilitating rapid bulk phase and interface charge separation due to the S-scheme charge transfer routes between WZ-CZS and ZB-CZS, as well as T-CZS and NiCr₂O₄. Moreover, this system can effectively retain electrons with strong reducing ability for efficient H₂ evolution reaction (HER) and generate hot electrons through the localized surface plasmon resonance (LSPR) effect of NiCr₂O₄, which enhances the absorption of UV–Vis–NIR light energy, thereby facilitating the HER process. What's more, NaOH solution can indirectly promote the HER kinetics by enhancing the oxidative driving force of holes. Additionally, other metal chromates (MCr_xO_y), such as CoCr₂O₄, AgCrO₂, Bi₆CrO₁₂, BaCrO₄, ZnCr₂O₄, CdCr₂O₄, CuCr₂O₄ etc., were employed to enhance the activity of T-CZS too. The results show that above homo-heterojunction composites can integrate waste plastic degradation and photocatalytic H₂ evolution effectively based on their S-scheme bulk phase and interface charge separation mechanisms. This work provides new insights into energy and environmental challenges.