Metal-Organic Framework Composites:Design,Syntheses And Photocatalytic Properties

In this paper,three MOF-composites,Ag@Uio-66-NH2,g-C3N4/Uio-66-NH2 and PMo12O40^3-@Cd-TTPB-4,based on metal-organic frameworks（MOFs）were designed and prepared.All MOF-composites were characterized by X-ray diffraction,FT-IR,solid UV-Vis absorption spectroscopy and solid fluorescence spectroscopy etc.and their potential properties in dyes photodegradation and CO2 photoreduction were discussed.The details were as follows:（1）Ag@Uio-66-NH2:According to the conventional method,Ag@Uio-66-NH2was successfully synthesized by introducing Ag nanoparticles into Uio-66-NH2without structural damage.The AgNO3 in acetonitrile solution was added into Uio-66-NH2 to obtain the intermediate Ag⁺@Uio-66-NH2,and then Ag⁺was reduced to Ag nanoparticles using NaBH4 solution,resulting in Ag@Uio-66-NH2.The composites with different Ag NPs rate were obtained by controlling the the amount of AgNO3 added,and the samples were named Ag-1,Ag-2,Ag-3 and Ag-4.The recombination with Ag nanoparticles enhances the visible light absorption of the sample,and reduces the charge-hole recombination rate under the light irradination,boosting the photocatalytic activity of the sample.Ag@Uio-66-NH2 could effectively degrade Rhodamine B（RhB）and Methyl Orange（MO）under UV-Vis light irradiation.The photodegradation efficiency of MO by Ag-2 was 66.2%in 50min,and the decomposition efficiency of RhB reached 96.4%in 40min.In addition,the reduction efficiency of CO₂ to CO and CH₄ was 105.28μmol/g and 21.94μmol/g in 8 hours by Ag-1 as photocatalyst,which shows better selectivity for CO.（2）g-C₃N₄/Uio-66-NH₂:G-C₃N₄ and the precursors of Uio-66-NH₂ were put into the Teflon lined stainless-steel autoclave at the same time,and a heterojunction was built between g-C3N4 and Uio-66-NH2 by solvothermal method.The composite of g-C3N4/Uio-66-NH2 shows improved absorption of visible light and reduced electron-hole recombination rate,leading to an enhancement in photocatalytic activity.The composites with different g-C3N4 rate were obtained by controlling the the amount of g-C3N4 added,and the samples were named CN-1,CN-2 and CN-3.Under the irradiation of UV-Vis light,the photodegradation of Acid Orange 7 and RhB could be achieved by g-C3N4/Uio-66-NH2.Among which,the degradation efficiency of RhB by CN-1 was 91.6%in 40min,while the decomposition efficiency of Acid Orange 7by CN-3 reached 97.4%in 35min.（3）PMo₁₂O₄₀^3-@Cd-TTPB-4:CdI₂,TTPB-4 and Na₃PMo₁₂O₄₀0 were put into the Teflon lined stainless-steel autoclave and a metal-organic framework PMo₁₂O₄₀^3-@Cd-TTPB-4 with Keggin type polyoxometalate(PMo₁₂O₄₀^3-)as template was synthesized by solvothermal method.It exhibits a four-fold interpenetrating 3-D network with highly stability in various pH-valued（2¹0）aqueous solutions.In addition,PMo12O40^3-@Cd-TTPB-4 possesses excellent photodegradation activity towards organic dyes of Crystal Violet（CV）and Basic Red 2 in aqueous solutions with different pH values.Under neutral conditions,the degradation efficiency of crystal violet was 94.3%within 36 min,and the degradation efficiency of Basic Red 2reached 95.0%within 18 min.The degradation efficiency of Crystal Violet by PMo12O40^3-@Cd-TTPB-4 is gradually enhanced with the pH value of the dye solution increasing,while Basic Red 2 shows the opposite trend.