Integration of ohmic junction and step-scheme heterojunction for enhanced photocatalysis

A novel and efficient photocatalyst, Cu₂WS₄/MoS₂-Au plasmonic Step-scheme (S-scheme) heterojunction, was constructed for the first time and applied to remove environmental pollutants. Among all the prepared photocatalysts, the. Cu₂WS₄/MoS₂-Au-5 exhibited the highest catalytic activity with an 89.1% reduction efficiency for Cr⁶⁺ and a 98.7% oxidation efficiency for Benzophenone-1 (BP-1) under visible light irradiation. The Cu₂WS₄/MoS₂-Au photocatalyst exhibits stable performance and efficient photocatalytic activity due to effective charge separation, enhanced light absorption from localized surface plasmon resonance (LSPR) of gold nanoparticles, and the formation of an S-scheme heterojunction with strong oxidation-reduction capabilities. In addition, through analysis of experiments and theoretical calculations, it is speculated that the Cu₂WS₄/MoS₂-Au follows a typical S-scheme photogenerated carrier transferring mechanism, which is verified by the finite difference time domain simulation, the free radical quenching experiments, the electron paramagnetic resonance analysis and the simulated charge density distribution. More importantly, the simulations of the work function and charge density distribution confirm the built-in electric field and the ohmic junction have been established at the interfaces between the Cu₂WS₄ and MoS₂ (Cu₂WS₄/MoS₂) as well as the interface between MoS₂ and Au (MoS₂-Au), respectively. The built-in electric field and ohmic junction enable efficient separation of photogenerated electrons and holes, ensuring the superior catalytic oxidation and reduction activities of the Cu₂WS₄/MoS₂-Au photocatalyst. Finally, we propose a photocatalytic mechanism for the Cu₂WS₄/MoS₂-Au plasmonic S-scheme heterojunction based on experimental results and simulated calculations. The research results of this study are significance for the development of the plasmonic S-scheme photocatalytic system.