S defect-rich MoS2: differences of S point defects and S stripping defects in photocatalysis†

Defect engineering is a pivotal avenue to improve the efficiency and activity of photocatalysts in the realm of photocatalysis. In this work, we synthesized MoS₂ with different S defect concentrations by adding lithium iodide to the synthetic MoS₂ precursor solution. The existence of S defects and their concentration were confirmed by TEM and XPS techniques. The results showed that the defect concentration exhibits a volcano-type variation with the addition of lithium iodide. NMSL-6 (adding 6 mmol lithium iodide) has the highest total S defect concentration of 24.5%. Furthermore, we proved that NMSL-6 mainly existed in the type of S stripping defects by EPR techniques, while other samples were mainly composed of S point defects. NMSL-6 exhibited the best methylene blue adsorption capacity and photocatalytic activity due to its large specific surface area and S stripping defects. Compared to high concentrations of S point defects, S stripping defects on the one hand promote the separation of photogenerated electrons and holes, and on the other hand improve the adsorption capacity for O₂, which was 9.4 times that of S point defects, thereby augmenting the ability of NMSL-6 to generate H₂O₂ in photocatalytic reactions. In view of this discovery, this research broadens the field of defect design and provides a new design idea for the practical application of defect engineering in two-dimensional materials.