Insights into photocatalytic mechanism over a novel Cu₂WS₄/MoS₂ S-scheme heterojunction

A novel efficient Cu₂WS₄/MoS₂ step-scheme (S-scheme) heterojunction photocatalyst was constructed for the first time and applied in the removal of environmental pollutants. Among the as-prepared photocatalysts, the Cu₂WS₄/MoS₂-8% heterojunction photocatalyst demonstrates the optimal photocatalytic performance, with the catalytic oxidation efficiency of tetracycline (TC) and the catalytic reduction efficiency of Cr⁶⁺ reaching 93.3% and 82.1%, respectively. The excellent catalytic properties of Cu₂WS₄/MoS₂ heterojunction photocatalysts are attributed to the effective separation pathways of charges and the presence of S-scheme heterojunctions, together with stronger redox capabilities. It is speculated that the photogenerated carrier migration path of the Cu₂WS₄/MoS₂ catalyst follows the typical S-scheme photocatalytic mechanism, which is verified by the in-depth experimental study and simulated calculations including the electron paramagnetic resonance (EPR) analysis, free radical quenching experiments, charge density distribution, and simulated built-in electric field formation at the interface, which acts as driving force to promote the separation of photoinduced electrons and holes. Finally, the photocatalytic mechanism of S-scheme photogenerated carrier migration for the Cu₂WS₄/MoS₂ catalyst is revealed based on the systematic experimental techniques and simulated calculations, accounting for its superior photocatalytic oxidation and reduction activities. This study provides inspiring implications to develop high-efficient S-scheme photocatalytic systems for versatile applications in solar-energy conversion.