Structures And Properties Of Rare Earth Metal Organic Frameworks Based On Tetradentate Carboxylate

Metal-organic frameworks（MOFs） are kind of porous materials, which possess 3D crystal structure composed of metal unit and organic ligands. Owing to the well-defined porous structures, tunable pore sizes and high surface areas,MOFs are hopeful to solve the the low photo-quantum efficiency and low solar absoption of inorganic semiconductor photocatalysts. In this paper,3,3′,5,5′-azobenzene tetracarboxylic acid（H4abtc） was chosen as organic linker to build two stable MOFs with Gd3+ and Dy3+ under hydrothermal method:[Gd₂（abtc）（H₂O）₂（OH）₂]·2H₂O complex 1[Dy₂（abtc）（H₂O）₂（OH）₂]·2H₂O complex 2Compound 1and 2 were characterized by single crystal X-ray diffractions,IR and PXRD to reveal their structures. The structure of compound 1 and 2 are the 3D porous frameworks. The UV-vis spectra of the powders are recorded with well-defined optical adsorption associated with the LUMO-HOMO gap at 2.35 e V and 2.17 e V, respectively. The CV curves have been utilized to further confirm the levels is-1.95 V and-1.74 V, respectively. Meanwhile, TG and the water stability with different p H were also employed to explore the stability of MOFs. They preserve their structural characters with temperature less than450 °C and also after soaked in water solutions for 48 h with p H = 3-14 adjusted by concentrated H2SO4 and TEOA.Moreover, the photocatalytic hydrogen productions of compound 1 and 2have been also studied. In the photocatalytic reactions, the photocatalyst（50 mg）was dispersed in 100 ml of 40 vol % triethanolamine（TEOA） aqueous solution.The results show that compound 1 exhibits more excellent photocatalytic activities with a rate of 7.71 μmol h-1 hydrogen production than compound 2under the same conditions. The successful synthesis of this efficient and stable photocatalysts provides a new method to construct a new green catalyst.The noble metal can efficiently fast the charge transfer and promote charge separation. In our work, Ag was chosen as the co-catalyst to enhance the efficiency of the photocatalytic hydrogen production activity with the reduction of Na BH4. The characterization results of XRD and XPS reveal that the deposition process does not influence the structure of compound 1 and the metal Ag exists as a metal but not ion or oxide as general speaking. PL analysis result shows the composite have a lower peak than that of compound 1, which indicates that the composite improve the separation efficiency of the photo-induced electron-hole pairs. In addition, the EIS declare the observed arc radii of composite are decreased after depositing Ag on the compound 1. It indicates that the separation of photo generated electron-hole pairs and accelerates interfacial reaction rate.The photocatalitic activitis of different amounts of Ag deposited Gd-MOF were carried out, and the optimal loading content is determined to be 1.5 wt%.Ag（1.5）/Gd-MOF exhibits a rate of 10.68 μmol h-1 for hydrogen production which improved approximately fifty percent greater than that of Gd-MOF.