Preparation Of Carbon Nitride Nanosheets And Bioinspired Photoelectrochemical NADH Regeneration Study

Enzyme catalysis has the advantages of fast reaction rate,high stereoselectivity,mild reaction conditions and few by-products.Oxidoreductases are the most widely used enzymes in biocatalysis.They exhibit high catalytic efficiency in reactions such as carbonyl reduction,carbon-hydrogen bond oxidation,and carbon-carbon double bond cyclization,greatly promoting the development of biopharmaceuticals and fine chemicals industries.However,oxidoreductase often requires cofactors for accomplishing the transformation.One of the coenzymes widely present in nature is Nicotinamide adenine dinucleotide?NAD⁺/NADH?.Due to the stoichiometric consumption of NADH in dehydrogenase reduction catalysis?each catalytic substrate requires the participation of a molecule of coenzyme?and the high cost of NADH,it is important and necessary to realize the efficient and low-cost regeneration of NADH for the enzyme-catalysis industry.In natural photosynthesis,light energy stimulates chlorophyll to produce photo-generated electrons.The photo-generated electrons are transferred to NADP⁺through an electron transport chain,which is ultimately reduced to NADPH.Inspired by natural photosynthesis,it is promising to use solar energy to design an efficient photocatalyst featuring with biocompatible components to achieve light-driven NADH regeneration.In recent years,graphitic carbon nitride?g-C₃N₄?has received widespread attention,due to its advantages of simple synthesis,high thermal stability,excellent chemical stability,and visible light response.It has also been applied in the regeneration of photocatalytic coenzymes,but its further application potential remains to be discovered.This thesis focuses on the use of graphitic carbon nitride nanosheet materials for developing highly efficient photo-/electrochemical NADH regeneration systems.The main contents include:?1?Uniform g-C₃N₄ film electrode can be fabricated by interfacial self-assembly of nanosheets for photoelectrochemical NADH regeneration.g-C₃N₄ nanosheets are first obtained by wet ball milling method.The subsequent self-assembly occurred at the air/water interface via slow injecting of the nanosheet dispersioninto water,a process induced by the Marangoni effect.By plunging the conductive glass?FTO?into water,the high-quality carbon nitride film could be obtained.Subsequently,graphene is mixed with g-C₃N₄ nanosheet dispersion,and the assembly-transfer strategy can also be used to prepare carbon nitride-graphene composite films.When using carbon nitride film/carbon nitride-graphene composite film as photoelectrode for photoelectrocatalytic NADH regeneration,the yield of carbon nitride-graphene composite film is double than that of pure carbon nitride film.This part provides a novel method for preparing high-quality carbon nitride hybrid films,and also provides a new way for the conversion of renewable energy for biocatalysis.?2?Single cobalt atom anchored on carbon nitride with well-defined active sites for photo-enzyme catalysis.In this part,ultrathin and two dimensional carbon nitride nanosheets with uniform atomic Co dopants featuring abundant open active sites were obtained via crystal template method.The single-atom catalyst exhibits excellent catalytic performance in the photocatalytic coenzyme regeneration reaction,and the yield of biologically active 1,4-NADH can be as high as 99%.Subsequently,the in situ regenerated 1,4-NADH coupling with alcohol dehydrogenase realized the efficient conversion of benzaldehyde to benzyl alcohol.Spectral experiments and theoretical calculations revealed that the catalytic activity center of the single-atom catalyst in the reaction system is CoN₃-Cp*?Cp*,pentamethylcyclopentadiene?.This part opens up the application of single-atom catalysts in bioenzymatic catalysis and provides new ideas for designing efficient and stable heterogeneous catalysts.