Artificial Photosynthetic Assemblies Based On Functional Hyperbranched Polymers And Photoluminescent Nanoparticles

The study on artificial photosynthesis is significant on the production of solar fuels,the development of new catalytic technologies,and the understanding of photosynthesis in nature.The arrangement of the key components,the micro-environment nearby the catalytic center,and the assembly structure of the system are highly affecting the photocatalytic performance for an artificial photosynthetic system.In this thesis,two self-assembly artificial photosynthetic systems were constructed by using functional hyper-branched polymers and photoluminescent nanoparticles,carbon nanoparticles(CNPs)or CdSe quantum dots(QDs),for photocatalytic H₂ production and highly selective photocatalytic CO₂reduction in water.The details were obtained as following:A functional hyper-branched polymer PEI-Co was synthesized by grafting cobalt complexes as active sites onto branched polyethylenimine(PEI).The PEI-Co and CNPs enable to self-assembly into hollow-rod of 2.0-3.0?m length assemblies CNPs@PEI-Co in water.The CNPs@PEI-Co assemblies feature hollow structure and CNPs locating at the edge of the assemblies.Under visible light irradiation,the CNPs@PEI-Co system in aqueous solution in the presence of sodium ascorbate converts protons to H₂ with a turnover number of 198.It exhibits a 50-fold improvement in hydrogen production activity and has a broader p H response of photocatalytic H₂ production compared with a non-assembled system.Mechanism studies revealed that the electrostatic interactions between CNPs and PEI-Co are driving force for the self-assembly.The photoinduced electron transfer process from excited CNPs to cobalt complexes in PEI-Co operates during photocatalysis.An amphiphilic hyper-branched polymer PLA was synthesized by grafting long alkyl chains onto branched polyethylenimine(PEI).A host-guest assembly(HGA)[CdSe&CO₂]@PLA,loading CdSe QDs photocatalysts and CO₂ molecules as two guest components into an host assembly formed by PLA,boosts highly efficient and selective CO₂-to-CO photoreduction in water in the presence of TEOA as electron donors.In comparison to the system containing pristine CdSe QDs,the efficiency and selectivity of CO production are improved by 57 and 1.5 times,respectively,from the HGA system.At optimal conditions,the HGA system produced CO with an efficiency of 28.0?mol·mg^-1 and a selectivity of up to 87.5%.Mechanism studies revealed that the special host-guest assembly configuration enhances local concentration of CO₂nearby CdSe QDs,and a faster photoinduced electron transfer from excited CdSe QDs to CO₂ operates in HGA system.