Synthesis And Photocatalytic Study Of High-Nuclear Manganese Cluster-Based Polyoxometalates

To meet the global demand for energy and carbon minimization,more and more attention has been paid to the exploration of clean,efficient,sustainable and environmentally friendly energy sources.The photocatalytic splitting of H₂O into H₂ utilizing solar energy is an intriguing approach to realize the storage and conversion of solar energy.Polyoxometalates（POMs）,a large family of early transition metal（V,Nb,Ta,W,Mo）-oxygen anion clusters,are attractive candidates in catalysis,medicine,materials science,and nanotechnology.To data,there are a number of studies on POMs as water reduction catalysts（WRCs）.However,the majority of POM photocatalysts are only active under UV-light irradiation or the use of Pt（0）as a cocatalyst.In order to develop H₂ evolution photocatalysts under visible light irradiation and to reach the level of the commercial application,many works have been focused on developing transition metal（TM）substituted POMs.With the technological development of biomimetic chemistry,some research endeavors have been focused on designing and developing biomimetic molecular clusters based on transition metal elements to mimic the H₂ evolution catalyst（HEC）{Fe₄S₄}of PSⅠ.In this thesis,we have synthesized two target TM cubane clusters by using the lacunary sites of trivacant Keggin POMs as the structure directing agents and incorporating TM Manganese into clusters.This compound was characterized by the single crystal X-ray diffractions,TG,IR etc..The visible-light-driven catalytic activity of these compounds for H₂ evolution have been investigated.1.Compound K₂Na₂₁[Mn₇^ⅡMn₉^Ⅲ（OH）₁₂（PO₄）₄(A-SiW₉O₃₄)₄]·83H₂O（1）containing one{Mn₄O₄}cubane core was synthesized by using trivacant{A-α-SiW₉O₃₄}as the structure directing agent.Using{B-α-SiW₉O₃₄}as the building block,we have developed another compound Na₁₆[Mn^Ⅲ₁₆（OH）₁₂（PO₄）₄(B-SiW₉O₃₄)₄]·74H₂O（2）which contains five{Mn₄O₄}cubane cores.2.The visible-light-driven H2 evolution activities of compounds 1-2 were studied in a Ir（dtbbpy）（ppy）₂]PF₆/TEOA solution under visible illumination.The experimental results not only illustrate that compounds 1-2 have excellent photocatalytic performance,but also demonstrate that the sequence of cubane number is in agreement with that of photocatalytic performance.Systematic stability tests（e.g.,UV-vis absorption,dynamic light scattering）show that catalysts 1-2 remain intact after illumination.