Rh-functionalized Imino-pyridine Covalent Organic Framework Assembled on Ti₃C₂T_x (MXene) for Efficient NADH Regeneration and Photoenzymatic CO₂ Reduction

Nicotinamide adenine dinucleotide (NADH) regeneration is crucial for sustainable enzymatic CO₂ reduction. In this study, Ti₃C₂T_x (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 Ti₃C₂T_x incorporation and [Cp*Rh] immobilization enables a reduction in exciton binding energy and promotes carrier transfer. Consequently, the optimized Rh_4.0@TDM_0.15 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 Rh_4.0@TDM_0.15 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, Rh_4.0@TDM_0.15 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.