Thylakoid-Inspired Construction And Performance Intensification Of Light-Driven NADH Regeneration System

Converting solar energy into chemical energy by mimicking natural photosynthesis is one of the "Holy Grail" researches in chemistry and chemical engineering.Photo-enzyme coupled artificial photosynthesis system combines the light absorption ability of semiconducting materials and the high-activity/specificity of enzymatic catalysis,offering a green route for "liquid sunshine" fuel production.Nicotinamide adenine dinucleotide(NADH),a cofactor utilized in over 75%oxidoreductase-related reactions,acts as the "energy currency" to bridge the energy and proton transfer between photocatalysis and enzymatic catalysis.The efficient and controllable regeneration of NADH plays a critical role in elevating the overall efficiency of solar-to-chemical energy conversion.In higher plants,the regeneration of NADPH(the phosphorylated form of NADH)by the light reaction of natural photosynthesis primarily operates in the thylakoid membrane.The competitive coordination of three modules,i.e.,electron generation in photosystem ?/?,electron transfer in electron transfer chain and electron utilization in ferredoxin-NADP reductase,in the confined space of thylakoid membrane optimizes the availability of each module,thus approaching the quantum efficiency of the light reaction to the theoretical value.In this thesis,inspired by the structure and function of thylakoid membrane,the three key steps in photocatalytic NADH regeneration,electron generation,electron transfer and electron utilization,are carefully optimized.Through coordinating the steps of electron generation-transfer,multi-step electron transfer and electron transfer-utilization,photocatalysts with rational distribution of functional modules are obtained,i.e.,g-C3N4@?-Fe2O3/C,g-C3N4@C-P25 and URh,to realize the performance intensification of NADH regeneration.Moreover,for the first time,an electron transfer mechanism named light-induced ligand-to-metal charge transfer(li-LMCT)is proposed in MOFs photocatalysis.The main discoveries and details of this thesis are summarized as follows:Competitive coordination of electron generation and electron transfer for photocatalytic NADH regeneration.Inspired by photosystem ? in the thylakoid membrane,g-C3N4@a-Fe2O3/C core-shell photocatalysts were constructed by the calcination of Fe3+/polyphenol coated melamine.During the photocatalytic process,a-Fe2O3 moiety acted as an additional photosensitizer,offering more photogenerated electrons,whereas the C moiety bridged a "highway" to facilitate the electron transfer from ?-Fe2O3 moiety to g-C3N4.The coordination between electron generation and electron transfer abilities were regulated via varying the ratio of ?-Fe2O3 moiety and C moiety,which led to a 3.26-fold enhancement of photocurrent density compared with pristine g-C3N4.When applied for photocatalytic NADH regeneration,g-C3N4@?-Fe2O3/C exhibited a yield of 76.3%(1 mM)with an initial reaction rate of 7.7 mmol h-1 g-1 By coupling g-C3N4@?-Fe2O3/C with alcohol dehydrogenase,the continuous conversion of formaldehyde to methanol was also achieved.Competitive coordination of multi-step electron transfer(charge separation and electron transport)for photocatalytic NADH regeneration.Inspired by electron transfer chain in the thylakoid membrane,g-C3N4@C-P25 ternary heterojunction photocatalysts were constructed by the calcination of one-step formed melamine@polyphenol-P25 composites.During the photocatalytic process,the pre-assemble of polyphenol-P25 coating on melamine created more heterojunction interfaces to facilitate charge separation,while the polyphenol converted C moiety promoted the electron transport at the heterojunction interfaces.The competitive coordination between charge separation and electron transport were adjusted by altering the ratio and distribution of C moiety and P25 moiety.Compared with pristine g-C3N4,g-C3N4@C-P25 exhibited a 4.5-fold enhancement of electron transfer efficiency with a NADH yield of 77.3%(1 mM)and an initial reaction rate of 2.77 mmol h-1 g-1.When applied for enzymatic conversion of propionaldehyde to propanol,the regenerated NADH exhibited similar activity compared with the commercial NADH.Competitive coordination of electron transfer and electron utilization for photocatalytic NADH regeneration.Inspired by photosystem I in the thylakoid membrane,a core-shell metal-organic frameworks(URh)was designed as an "electron buffer tank" for the competitive coordination of electron transfer and electron utilization.During the photocatalytic process,the electrons were generated via light irradiation on photosensitizers(2-aminoterephthalic acid,NH2-BDC)in the core and then transferred to Zr6O8 clusters on the shell.Neighboring reaction centers on the shell of MOFs,[Cp*Rh(bpydc)H2O]2+,behaved as the "electron buffer tanks" and stored these electrons in the form of hydrides for subsequent NADH regeneration.The continuous electron supply via the "electron buffer tank" results in a yield of 78.9%(1 mM)and an initial reaction rate of 5.06 mmol h-1 g-1,which is,respectively,1.87-fold and 2.08-fold of the corresponding homogeneous reaction counterpart.Photo-enzyme artificial photosynthesis was also realized by coupling URh with amino acid dehydrogenases for amino acids production.Light induced ligand-to-metal charge transfer mechanism for MOFs photocatalytic NADH regeneration.The electron transfer mechanism in URh was explored by transient absorption spectroscopy,electron paramagnetic resonance and cyclic voltammetry.The uphill electron transfer from photosensitizers of NH2-BDC to Zr6O8 clusters was realized by light-induced ligand-to-metal charge transfer(li-LMCT),where the step excitation of single electrons by two successive photons provided sufficient energy to overcome the barrier of uphill electron transfer.Meanwhile,1H NMR was performed to investigate the proton source of NAD+hydrogenation reaction.Accordingly,the overall mechanism of photocatalytic NADH regeneration by URh photocatalysts was proposed.The photosensitizer of NH2-BDC absorbed two photons and generated one electron,which was transfer to a Zr6O8 cluster via li-LMCT.Rh extracted two electrons from the Zr6O8 cluster and one proton from water to form a hydride and catalyzed the regeneration of NADH.The understanding of MOFs photocatalytic NADH regeneration offer us an opportunity to explore the electron transfer mechanism in natural photosynthesis,as well as to reproduce or even exceed the superior quantum efficiency of the light reaction with inorganic materials.