Efficient photocatalytic NADH regeneration with Rh-loaded Z-scheme mediator-free system

Nicotinamide adenine dinucleotide (NADH) regeneration is necessary for the sustainable application of enzymatic industry. The Rh-based complex [Cp*Rh(bpy)(H)]+ has been widely used as an important mediator in NADH regeneration systems, but it is limited by complexity and high cost. Here, a Z-scheme was constructed by loading Rh onto carbon nitride nanosheets/carbon nitride quantum dots (CN-CNQD). The resultant catalyst achieved a high yield of NADH in a mediator-free (M-free) system of 0.283 mmol L−1 g−1 min−1, which is 5.29 times that of pure CN. ADH enzyme introduction experiments confirmed that the enzyme active product 1,4-NADH could reach 34.21% selectivity in the M-free system. Mechanism research revealed that the heterojunction between CNs and CNQDs improved the NADH regeneration activity in the traditional M-involved system, while Rh loading was proved to optimize the yield and selectivity of 1,4-NADH in M-free system. The immobilized Rh shows more competitiveness than [Cp*Rh(bpy)(H)]+. This study contributes to the construction of an M-free system for further application in greener, lower-cost enzymatic processes.