“Hydrogen bond locks” promoted exciton dissociation and carrier separation in copolymers for enhancing uranyl photoreduction†

Abstract

Achieving uranyl photoreduction using copolymers with low exciton binding energy (E_b) from radioactive wastewater holds great promise, but is extremely challenging. Side chain engineering offers more opportunities for developing new copolymers with lower E_b. However, the introduction of side chains is not completely “painless” and often leads to molecular skeleton distortions, which significantly reduce photocatalytic activity. Herein, a promising strategy is employed to balance the twisted structures by enabling “hydrogen bond locks” on the side chains, thereby promoting exciton dissociation and enhancing uranyl photoreduction. As a proof of concept, two conjugated polymers with identical poly(benzene-benzothiadiazole) backbones but different side chains (methyl and methoxy) on the benzene ring are investigated. These variations in side chains greatly impact the optical gap, electronic structure, and exciton dissociation of the polymers. Through the intramolecular noncovalent O⋯H interactions between the oxygen atoms in methoxy groups and the adjacent hydrogen atoms in benzothiadiazole units, the methoxy functionalized copolymer (CP-OMe) with minimized E_b exhibits an exceptional uranium extraction capacity of 946.5 mg g⁻¹ without adding any sacrificial agent, surpassing those of most currently reported polymers.