Preparation Of Two-dimensional Polymer And Their Photocatalytic NADH Regeneration Performance

Photobiocatalysis,thanks to its mild reaction conditions,remarkable tolerance to various substrates and excellent reaction selectivity,has shown increasing attention in recent decades in the synthesis of high-value chemicals and chiral drugs.However,the activation of enzymes requires the participation of an expensive and unstable coenzyme（nicotinamide adenine dinucleotide,NADH）.Therefore,the design of photocatalyst for in situ NADH regeneration is a prerequisite for creating an efficient photobiocatalysis system.There are still some problems to be solved in the research of photocatalytic NADH regeneration.Firstly,most reported photocatalytic NADH systems use organic amines and acids as sacrificial electron donors.However,the excessive use of those organic electron donors will inevitably lead to not only the accumulation of by-products but also the formation of toxic intermediates,which is adverse to the stability of the whole catalytic system.Secondly,the catalytic efficiency of photocatalyst needs to be further improved.While different kinds of photocatalysts have been reported for NADH regeneration,most of them have the limited catalytic capacity and the design of efficient photocatalysts is still highly appealing.Based on those problems,we prepare two different photocatalysts,i.e.carbon nitride/graphene composite and two-dimensional conjugated microporous polymer,for in situ NADH regeneration in visible light.Afterward,a photo-enzyme coupling catalytic system was constructed for photocatalytic CO₂reduction via combing the photocatalytic and enzymatic reactions.The main contents are as follows:（1）A single Co atom anchored carbon nitride/graphene composite photocatalyst,CoSAC@PCN,was prepared by step-by-step thermal polymerization using melamine,glucose and cobalt porphyrins as precursors.The obtained CoSAC@PCN can be further employed as visible light photocatalytic for NADH regeneration and photo-enzyme coupling catalytic CO₂reduction with water as a green electron donor.Carbon nitride was coplanar with graphene,and synchrotron radiation test shows that the single Co atoms are uniformly distributed on the surface of CoSAC@PCN via Co-N₅structure.The introduction of graphene and single Co atoms can broaden the visible light absorption and improve the charge separation and transfer.Using water as an electron donor,CoSAC@PCN delivers a high reaction conversion of 33.6%in NADH regeneration within 120 min.In addition,H₂O₂is the main product during the water oxidation process.DFT calculation reveals that the presence of single Co atoms can significantly reduce the activation energy of water oxidation,especially in H₂O₂generation.Lastly,CoSAC@PCN photocatalytic NADH regeneration was combined with formate dehydrogenase（FDH）to achieve the reduction of CO₂to formic acid.（2）Two-dimensional polymers including conjugated microporous polymers2D@CMP-1 and 2D@CMP-2 were synthesized by liquid-liquid interface polymerization with dibenzothiophene sulfone as photosensitive unit and phenyl ring as linkage unit based on Pd catalyzed Suzuki-Miyaura coupling reaction.TEM reveals a two-dimensional lamellar morphology for both two polymers.Compared to 2D@CMP-2,2D@CMP-1 has higher conjugation degree,wider light absorption,more efficient charge separation and migration,thus displaying a better photocatalytic activity in NADH regeneration.When TEOA was used as the electron donor,a conversion of 62%was determined for 2D@CMP-1.In addition,the prepared two-dimensional polymer has good photothermal stability and the structure keeps intact after the reaction.