Positional isomerism engineering toward minimizing exciton binding energy in sulfone copolymers for enhanced uranyl photoreduction

Abstract

Conjugated microporous polymers (CMPs) have emerged as promising platforms for photocatalytic separation and enrichment of radionuclides. However, the development of CMPs with efficient exciton dissociation and free charge generation is still highly hindered by their high exciton binding energy (Eb). Herein, for the first time, three sulfone-containing CMPs are fabricated to regulate Eb by position isomerism of altering linkage sites. Temperature-dependent photoluminescence spectra reveals that ECUT-3,7-SO with 3,7-site linkage achieves a diminished Eb of 40.1 meV. DFT calculation complementally demonstrate that the Eb is related to its strongly polarized electric field and large conjugation degree, which can be easily regulated via position isomerism of its building blocks. Among the three, ECUT-3,7-SO exhibits a completely conjugated structure and a large molecular dipole moment, thus significantly reducing the Eb. As a result, ECUT-3,7-SO exhibits the highest photoreduction uranium rate constant (k, T = 298.15 K) of 0.081 min−1, and the maximum uranium extraction capacity of 918.0 mg g−1 under visible-light irradiation. This work highlights the importance of positional isomerization to the development of low exciton binding energy photocatalyst for uranium resource field.