Engineering and Photocatalysis of Functional Polyoxometalate-Based Hybrid Materials

Author:Sun Wen Long

Supervisor:liu tao duan chun ying


Degree Year:2019





Polyoxometalates(POMs)are composed of cations and polyanion clusters with structural diversity,thermal stability,high activity,and donate electrons to electron acceptors.POMs have occupied researchers’ interests for owing to their unique properties,they have been applied to catalysis field.Metal-Organic Frameworks(MOFs)are some of the most promptly rising fields in chemical and material sciences,not only due to the fascinating structural topologies but also because of their potential as functional materials in various applications.Compared with traditional inorganic materials,the MOFs possess higher porosity,thermal stability and designability.A new class of hybrid materials has emerged by introducing POMs into MOFs.called POMOFs materials.Combination of POMs and MOFs increase the stability of structure and the diversity of function,the POMOFs materials possess their advantages and overcome their shortcomings.The POMOFs materials can obtain some new functional characteristics.In this paper,based on coordination chemistry,taking advantage of POMs and MOFs possess chemical stability,structural diversity and functional diversity,a series of POMs and POMOFs materials were synthesized by self-assembly strategy.Based on the catalytic mechanism of POMs,the catalytic properties of POMs and POMOFs materials were studied.POMs and POMOFs photocatalysts for hydrogen and oxygen production,the main contents are as follows:(1)Using 4,4-(1,4-phenyl)bis-pyridyl-(PBPY),oxalic acid,cobalt nitrate/zinc nitrate and[P2W18O62]6-under hydrothermal method,two isomorphic POMOFs materials have been synthetised.Co-POM and Zn-POM,respectively.Co-POM photocatalytic dehydrogenation involving tetrahydroisoquinoline oxidation and reduction coupling,generating 3,4-dihydroisoquinoline(TON=640)and hydrogen gas(TON=630),exhibited higher activity.In the designed Co-POM polymer,Uv light excitation gives the excited state of the polyoxometalate firstly to obtain electron from donors;the reduced formed(i.e.,heteropolyblue)adsorbs visible light to achieve a new excited state,which reduced the cobalt redox sites and facilitates hydrogen evolution reaction(2)The[P2w18O62]6-ions act as photosensitive and photooxidation centres,and the Cu-Ni-POM(POMOFs materials)was synthetised with Cu(Ⅱ)/Ni(Ⅱ)as the metal nodes and 4,4’-(1,4-phenylene)bis-pyridine(PBPY)and oxalate(OX)linkers to balance the charge of the[P2W18O62]6-anions under hydrothermal method.The Cu-Ni-POM material photocatalytic hydrogen evolution(TON=550),exhibited higher activity.The Cu-Ni-POM framework contains Cu,Ni and POM units,which allows a concerted mechanism,the multi-metal material concerted catalysis than a single metal material exhibited higher activity.(3)Based on POMs modifiability,compound 3(POMs)were synthesized with Dawson-type[P2W18O62]6-as the basic unit and Co atom as the modification unit under solvothermal method.Compound 3 split into compound 1 and 2 by adjusting the types of acids and solvents in the reaction.Compounds 1-3 photocatalysts for hydrogen and oxygen evolution reaction,the H2 evolution amount were achieved for 1 and 3,respectively,the calculated turnover number of the entire reaction was approximately 200 and 214 per mole of photocatalyst;the O2 evolution amount were achieved for 1-3,approximately 122uL,110uL and 65uL,respectively.