Photo-Redox Active Metal-Organic Frameworks:Synthesis,Characterization And Photocatalytic Research

Metal organic frameworks(MOFs)are multi-dimensional porous crystalline materials formed by metal cations or clusters and organic ligands with multiple coordination modes.Because of its remarkable characteristics such as high internal surface area and porous structure,MOFs are often regarded as nano-reaction carriers.By adjusting the interaction between guest molecules,pore environment,solvents and reagents,MOFs could perform various chemical reactions including photocatalysis under heterogeneous conditions.Polyoxometalates(POMs),as common metal oxide clusters,are well known for their abundant structural types,unique photoinduced charge transfer properties,photoactivity and redox activity.In particular,they have been widely used as efficient photoredox reagents in various photocatalytic reactions.By incorporating POMs within a single framework,new POM-incorporated metal-organic frameworks(POMOFs)were synthesized under hydrothermal conditions.The POMOFs material could not only have excellent properties such as high porosity and good stability,but also improve the photocatalytic effect and achieve efficient photocatalytic reactions through the synergy of POMs and MOFsIn this paper,2,4,6-tris(4-pyridyl)triazine(TPT)and tris(4-imidazolylphenyl)amine(TIPA)two bridging ligands are selected to investigated.These functional organic ligands are combined with different metal ions and polyoxometalates to obtain heterogeneous photocatalysts with various structures and excellent catalytic properties,{NiW-TPT-1}(1),{NiW-TPT-2}(2),{Co-PW11-TPT}(3),{Cu-BW12-TPT}(4),Cd-TIPA(5).Meanwhile,their properties characterization,structural analysis and catalytic properties were exploredIn the chapter one,simple sodium tungstate was used as raw material and reacted with metal salt Ni(ClO4)2·6H2O and rigid bridging ligand TPT under different acidity conditions.Two new heterogeneous tungstate-based MOFs {NiW-TPT-1}(1)and {NiW-TPT-2}(2)were synthesized by hydrothermal method,respectively.A series of property structures such as X-ray single crystal diffraction,IR,TG,X-ray powder diffraction,gas adsorption,diffuse reflectance UV-Vis absorption methods and band gap energy level were characterized.The results indicated that compounds 1 and 2 had satisfying thermal stability and negative reduction potential,meanwhile compound 1 was taken as an example to further explore its photoreduction performance.It could be found from the control experiment and substrates expansion that compound 1,as a heterogeneous photocatalyst,has excellent catalytic activity and cycling stability in the photocatalytic reduction of aromatic nitro compoundsIn the second chapter,the three-deficient Keggin type polyoxometalate[?-PW9O34]10-was first selected as a precursor and reacted with metal ion Co2+ and functional organic ligand TPT to construct a novel porous three-dimensional POMOF material,{Co-PW11-TPT}(3).A series of property structures such as X-ray single crystal diffraction,IR,TG,X-ray powder diffraction,diffuse reflectance UV-Vis absorption methods,solid fluorescence spectrum and band gap energy level were characterized.At the same time,the photocatalytic reduction reaction of aryl iodinated hydrocarbons was further investigated with compound 3 using photocatalyst and the catalytic results were analyzed.It could be found from the control experiment and substrates expansion that compound 3,as a heterogeneous photocatalyst,has excellent catalytic activity and cycling stability in the photocatalytic reduction of aryl iodine hydrocarbons.Based on compound 3,a novel porous three-dimensional POMOF material,{Cu-BW12-TPT}(4)was further constructed through hydrothermal synthesis method.Herein,the saturated Keggin polyoxometalate anion[BW12O40]5-was selected as a precursor and reacted with metal ion Cu2+and functional organic ligand TPT.A series of property structures of compound 4 such as X-ray single crystal diffraction,IR,TG,X-ray powder diffraction,diffuse reflectance UV-Vis absorption methods,solid fluorescence spectrum and band gap energy level were characterized.At the same time,the catalytic reaction of photoreduction of aryl halohydrocarbons was further explored.It could be found that compound 4 has better applicability than compound 3,which can simultaneously photo-reduction with aryl iodohydrocarbons and aryl bromohydrocarbons.In addition,the catalytic results indicated compound 4 was an excellent heterogeneous photocatalyst and had excellent catalytic activity with cycling stability in the photocatalytic reduction of aryl iodine hydrocarbonsIn the third chapter,a photoactive metal-organic framework material,Cd-TIPA(5),was synthesized by cadmium ion and an stretched triangular rigid N-containing ligand TIPA with both rigidity and flexibility(tris-(4-imidazolylphenyl)amine)as strong electron donor through traditional hydrothermal method.A series of structure and composition of compound 5 such as X-ray single crystal diffraction,IR,X-ray powder diffraction,XPS spectroscopy,gas adsorption,diffuse reflectance UV-Vis absorption methods,solid fluorescence spectrum and band gap energy level were investigated deeply.Cd-TIPA features a potential of the conduction band(LUMO)level(-1.30 V vs.NHE),which is more negative than that of Cr2O72-/Cr3+,thus providing the theoretical possibility of reduction.The observable quenching effect of Cr2O72-anions on the emission of the suspension of Cd-TIPA indicates the efficiency electron transfer between them,the photocatalytic process for the Cr(?)reduction is explored consequently.The catalytic results indicated that compound 5 was a heterogeneous photocatalyst,and exhibited very high catalytic efficiency(93%)in a short time and better cycling stability.