Acceptor Engineering Boosting Piezoelectricity in Conjugated Microporous Polymers for Piezo-photocatalytic Uranium Separation

Abstract

Photocatalytic uranium separation from radioactive wastewater is a sustainable strategy, yet its efficiency is often hampered by the rapid recombination of charge carriers. Herein, we report two novel bicarbazole-based conjugated microporous polymers (CMPs), CMP-Bz and CMP-Dbz, synthesized via irreversible C-C cross-coupling. The incorporation of bicarbazole units was found to impart significant piezoelectricity to the resulting amorphous frameworks. Building on this, an acceptor engineering strategy was implemented by modulating the number of cyano groups on the acceptor molecules, which simultaneously enhanced the piezoelectric response and the intrinsic charge separation efficiency of the materials. Piezoresponse force microscopy (PFM) reveals that CMP-Dbz (with dicyano-substituted acceptors) achieves a high piezoelectric coefficient (d33) of 55.2 pm/V, significantly exceeding that of its monocyano-substituted counterpart, CMP-Bz (19.4 pm/V) and commercial PVDF. The synergistic effect between an ultrasonication-induced polarized electric field and the spatially separated multiple charge transfer channels, which significantly promote the utilization of photo-generated electrons by directional transfer from bicarbazole groups to the cyano-modified benzene rings. Consequently, the piezo-photocatalytic U(VI) removal rate for CMP-Dbz reaches 0.03037 min-1, approximately 2.5 times that of CMP-Bz under the identical condition and 4.6 times higher than that of CMP-Dbz under light irradiation alone. This work introduces a new class of materials to the family of piezoelectric materials, paving the avenue for designing efficient photocatalysts for U(VI) separation via synergistic effects