In Situ Doping Brushite On Zinc Manganese Oxide Toward Enhanced Water Oxidation Performance: Mimicry Of An Oxygen-evolving Complex

Metal organic frameworks?MOFs?are infinite network-like polymer materials formed by the coordination of ligands and metal ions through coordination bonds,which have advantages of high porosity,large specific surface area,and tailorability.MOF-derived metal oxides exhibit promising application prospects in heterogeneous catalysis,gas adsorption and separation,drug delivery,and fuel cells due to their inheritance of the structure and morphological advantages of the original MOF.On the other hand,inspired by plant photosynthesis,producing hydrogen and oxygen by water splitting is viewed as an intuitive and feasible solution to solve the current energy crisis.However,water oxidation turns out to be the bottleneck of full water splitting since it is a complex and slow process.Combining the characteristics of the oxygen-evolution complex and the structural merits of MOFs materials,we designed and synthesized a MOF-derived metal oxide and studied its water oxidation performance.By comparing the O₂ evolution in the presence and absence of Ca²⁺,the role of calcium-phosphate in promoting the water oxidation activity was disclosed.This work might provide new ideas and theoretical aspects for further efficient solar energy conversion,decomposition of water and energy storage in the form of hydrogen.In this thesis,zinc-manganese oxide?ZMO?was successfully synthesized by calcining ZIF-8 impregnated with manganese salt.Photocatalytic water oxidation was carried out in neutral phosphate buffer solution containing calcium triflate and exhibited excellent water oxidation performance with an optimized turnover frequency of 0.18 mmol_O2 mol_Mn^-1 s^-1which is 10 times higher than that of ZMO in the absence of Ca²⁺.A series of characterizations have demonstrated that brushite,acting as a co-catalyst,was dopped in-situ on the surface of ZMO,improving the photocatalytic oxygen evolution performance of Zn-Mn oxides.To figure out the role of brushite in water oxidation performance of ZMO,we studied the influence of irradiation time on the deposition amount of brushite and its water oxidation activity.We found that the loading contents of brushite increased with the prolonged irradiation time.Excessive loading contents of CaP significantly reduced the specific surface area of the ZMO catalyst and had a negative effect on water oxidation activity.By analyzing the properties of recycled sample after the water oxidation,the reasons for the greatly reduced water oxidation performance of the recycled sample were studied,and the possible mechanism was proposed.Oxygen-evolving complex?OEC?in photosystem II?PSII?is the active center of photosynthesis which contains a CaMn₄O₅ cluster surrounded by protein matries.Our catalytic system mainly uses the transition metals?zinc,manganese?and calcium,and is carried out under ambient temperature and neutral conditions.Thus,it can be regarded as an efficient mimicry to the oxygen-evolving complex in photosystem?.