Covalent bond enhanced highly stable urea perylene diimide polymer for concurrent photocatalysis-persulfate activation

Abstract

The self-assembled perylene diimide (SAPDI) connected by hydrogen bonds is limited by the instability of easy disintegration under alkaline conditions. The covalently linked urea PDI (UPDI) was synthesized under air conditions, and concurrent photocatalysis-persulfate activation (CPPA) system was constructed. A distinct synergistic effect was attained when UPDI/peroxymonosulfate (UPDI/PMS, 0.012 min−1) system was combined with photocatalysis (UPDI/PMS/Vis, 0.115 min−1) to degrade iohexol (IOX). The import of the light field can accelerate the electron migration between the electron donor and the acceptor with more reactive oxygen species (ROS) generation. Evidenced by quenching tests, electron paramagnetic resonance, the dominated reactive species in UPDI/PMS system tended to be holes and 1O2. The utilization efficiency of ROS is crucial to improve the performance of CPPA. The stability of the UPDI system is superior to that of previously reported SAPDI and its derivatives or heterojunctions. The higher content of adsorbed oxygen can produce more reactive oxygen species (ROS), which is one of the reasons for the stable activity of UPDI in cyclic experiments. An enhancement for PMS activation on covalently bonded UPDI was observed based on density functional theory calculation. This study provides a new perspective for the application of stable and efficient metal-free water treatment technology.