Dual-function graphene based aerogels for photocatalytic coenzyme regeneration and enzymatic CO₂ reduction

With formate dehydrogenase (FDH) as the biocatalyst and reduced nicotinamide adenine dinucleotide (NADH) as the cofactor, enzyme catalysis achieves high-selectivity CO₂ reduction to formic acid under ambient conditions. However, this route relies on susceptible and costly enzyme and cofactor, and faces difficulties in their recovery and reuse. Enzyme immobilization and cofactor regeneration are essential strategies to address these issues. Herein we designed a dual-function Ti₃C₂T_x/graphene (GA)/TiO₂ (TGT) composite aerogel, after amino modification, FDH was immobilized on the aerogel via glutaraldehyde chemistry. Then it was innovatively applied in a photo-enzyme coupled system (PECS) that mimics natural photosynthesis and engenders sustainable CO₂ reduction by integrating photocatalytic NADH regeneration with enzymatic CO₂ reduction. Porous GA aerogel not only enables high specific surface area that facilitates enzyme immobilization and substrate adsorption, but also extends the light response of TiO₂ from ultraviolet to visible light range and reduces band gap. Ti₃C₂T_x contributes simultaneously to photocatalysis and enzyme reaction through its excellent electronic conductivity, large two-dimension surface and good CO₂ affinity. Ultimately, TGT demonstrated photocatalytic activity of 58.8 μM/(g·min) and NADH yield of 14.9 %. TGT immobilized FDH exhibited an enzyme activity recovery of 81.4 % and produced 0.24 mM formate. With 2 mM cofactor, formate yield reached 12.4 % in the PECS, surpassing most reported systems.