Thioether-modified covalent aromatic polyimides with enhanced photocatalytic performance for hydrogen peroxide photosynthesis in pure water

Hydrogen peroxide is one of the 100 most commonly used chemical reagents. Sunlight-driven two-electron reduction of O₂ (2e^- ORR) in pure water was a promising H₂O₂ photosynthesis route. Some covalent organic polymers (COPs) have been demonstrated as effective sacrificial agent-free photocatalysts for H₂O₂ photosynthesis, while more COPs are poorly active. In this present work, a simple thioether-modification strategy for covalent aromatic polyimides (CAPs) was developed to obtain high-performance sacrificial agent-free photocatalysts. During solvothermal synthesis of CAP polymers in dimethyl sulfoxide (DMSO) solvent at higher temperature (180 °C), thioether groups resulting from thermal decomposition of DMSO were grafted on dianhydride blocks of CAP polymers (S-CAPs). This enabled less active CAPs to become high active S-CAPs photocatalyst. The H₂O₂ production rate over the optimized S-CAPs reached 2240 μmol·h⁻¹·g⁻¹ without using any additional sacrificial agents, among the best photocatalysts for H₂O₂ photosynthesis. The thioether groups grafting on S-CAP frameworks were found to efficiently enhance visible light absorption and facilitate the separation of photogenerated electron (−) and hole (+) pairs during photosynthesis. It not only provided an impressive sacrificial agent-free photocatalyst for H₂O₂ photosynthesis, but also demonstrated a novel post-modification method to gain high-performance COP-based photocatalyst.