Rh-functionalized Imino-pyridine Covalent Organic Framework Assembled on Ti3C2Tx (MXene) for Efficient NADH Regeneration and Photoenzymatic CO2 Reduction

Nicotinamide adenine dinucleotide (NADH) regeneration is crucial for sustainable enzymatic CO2 reduction. In this study, Ti3C2Tx (MXene) and [Cp*Rh(bpy)(H2O)]2+ (labeled as [Cp*Rh]) were sequentially assembled onto imino-pyridine structured covalent organic frameworks (TD-COF) to construct Rh@TDM photocatalysts with dual cocatalyst. The photoelectrochemical tests and temperature-dependent photoluminescence spectra suggest that the synergistic effect of Ti3C2Tx incorporation and [Cp*Rh] immobilization enables a reduction in exciton binding energy and promotes carrier transfer. Consequently, the optimized Rh4.0@TDM0.15 photocatalyst achieves a 95.0% NADH regeneration yield, significantly higher than that of TD-COF with free [Cp*Rh] (32.7%). Additionally, the dual modification strategy applied to TD-COF also enhances the selectivity for 1,4-NADH. Therefore, the turnover frequency of 1,4-NADH for Rh4.0@TDM0.15 achieves 1.06 h–1, which is 7.1 times higher than that of TD-COF with free [Cp*Rh] (0.15 h–1). Subsequently, in the photoenzymatic cascade catalytic system, Rh4.0@TDM0.15 obtained a remarkable formate generation rate of 2137.7 μmol g–1 h–1. This work not only provides a novel example of using COF containing an imino-pyridine structure to immobilize [Cp*Rh] for NADH regeneration but also reveals that the synergetic effect of MXene and [Cp*Rh] facilitates 1,4-NADH regeneration and photoenzymatic CO2 reduction. These findings offer new insights and opportunities for the design and application of artificial photoenzymatic systems for CO2 reduction.