Semiconductor-cluster-loaded ionic covalent organic nanosheets with enhanced photocatalytic reduction reactivity of nitroarenes

Abstract

Achieving efficient multi-electron-involved photoreduction, e.g. the reduction of nitroaromatics to amines, remains challenging yet highly demanded. Two-dimensional (2D) covalent organic nanosheets (CONs) present promising platforms for such reactions due to their exceptional properties, including structural tunability and unique photoelectronic properties. Nevertheless, the exploration of CON-based composites for catalyzing organic reactions is still in its infancy, with examples of CONs acting as intrinsic catalysts being relatively scarce. In this study, we developed hybrid catalysts, denoted as T4-Mn/QA-CONs, by decorating anionic semiconductor clusters (T4-Mn) onto 2D cationic CONs (QA-CONs) via electrostatic self-assembly. Remarkably, T4-Mn/QA-CONs exhibited exceptional performance, achieving a 99% conversion rate and 100% selectivity with a turnover frequency (TOF) of 2.68 h⁻¹ in the reduction of nitroarenes to amines under visible light irradiation. In addition, T4-Mn/QA-CONs demonstrated excellent stability and recyclability, along with remarkable functional group tolerance. The outstanding activity can be attributed to the effective charge separation facilitated by the photoinduced strong internal electric field and II-scheme mechanism, as confirmed by in situ X-ray photoelectron spectroscopy along with femtosecond transient absorption spectroscopy. This study presents a novel strategy for designing CONs as crucial catalytic centers and highlights the potential of CON-based heterojunction photocatalysts for efficient organic transformations.