Highly efficient photoenzymatic CO2 reduction via integrated structural design of porphyrin covalent organic framework on Ti3C2Tx (MXene)

Nicotinamide adenine dinucleotide (NADH) regeneration is essential for sustainable enzymatic CO2 reduction. On the one hand, this study presents an integrated design combining Ti3C2Tx (MXene) incorporation and [Cp*Rh (bpy)H2O]2+ (abbreviated as [Cp*Rh]) immobilization on a porphyrin-based covalent organic framework (PBC COF). The temperature-dependent photoluminescence (PL) spectra and photoelectrochemical measurements indicate that the synergistic effect of those modifications could greatly reduce exciton binding energy and improve charge separation efficiency. The dual modification strategy of COF not only increases the NADH regeneration yield, but also enhances the stereoselectivity of 1,4-NADH. Consequently, the optimized MX20PBCRh3.5 achieves a 1,4-NADH TOF value of 1.16 h -1, which is 8.9 folds higher than that of bare PBC (0.13 h-1). Subsequently, in the photoenzymatic catalytic cascade system, the MX20PBC-Rh3.5 achieving a considerable formate generation rate (2088 mu mol g-1 h-1). On the other hand, more importantly, even in the absence of [Cp*Rh], the formate generation rates of the noble-metal-free MX20PBC photocatalyst also reached 1219 mu mol g-1 h-1, far superior than that of bare PBC (379 mu mol g-1 h-1), also roughly equivalent to that of PBC containing homogeneous [Cp*Rh]. The current work not only provides a heuristic approach via synergistic effect to design photocatalyst towards NADH regneratation, but also suggests that MXene can act as a promising non-noble metal electron mediator in photoenzymatic catalytic reactions.