Engineering MXene-based photocatalyst for efficient NADH regeneration and photoenzymatic CO2 reduction without electron mediator

In this study, an MXene-based photocatalyst, ARTM to regenerate NADH without electron mediator is reported. The ARTM was able to achieve a regenerated NADH yield of 65% within 50 min in the absence of electron mediator, with a 1,4-NADH selectivity of 90.8%. The turnover frequency (TOF) of 1,4-NADH was as high as 0.148 h-1, which was 74 and 148 times higher than that of A-TiO2 and R-TiO2, respectively. The synergetic effect between anatase/rutile TiO2 phase junction (ART-PJ) and TiO2@Ti3C2Tx heterojunction (TM-HJ) facilitates the efficient carriers separation and NADH regeneration. Enzymatic assay and HNMR revealed that the incorporation of Ti3C2Tx promoted the highly selective generation of 1,4-NADH. DFT calculation elucidated that this could be attributed to the end-on adsorption of the nicotinamide ring of NAD+. Subsequently, an electron mediator free photoenzyme cascade catalysis system was constructed, which could effectively promote CO2 photoreduction to formate (594 μmol g-1 h-1).