The Application Of Metal-organic Frameworks In Heavy Metal Adsorption And Catalysis

Metal-organic frameworks(MOFs)are novel porous materials with one-dimensional,two-dimensional or three-dimensional structure synthesized by self-assembling metal ions with organic ligands under certain conditions.Compared with traditional materials,MOFs have the characteristics of high porosity,high surface areas,large amount of active metal sites,adjustable pore size and surface properties.These unique properties make MOFs promising in many fields,such as gas storage and separation,adsorption,catalysis,sensing and drug delivery,among which the most studied are the adsorption and catalytic properties of MOFsThe large porosity and strong coordination ability of MOFs make them attractive in the field of heavy metal adsorption.A variety of MOFs have been used to remove heavy metal ions in aqueous solution.However,the researches on the use of MOFs as preparation materials for real samples containing heavy metal ions have not been popular to date.The real sample preparation requires that the MOFs used not only have a highly efficient adsorption,but also solid crystal structures stable in complicated sample environmentsMOFs with high density of active metal sites and holes have also attracted much attention in the field of heterogeneous catalysis.In order to enhance the catalytic activity of MOFs,some researchers have combined MOFs with some traditional materials such as metal nanoparticles and carbon-based materials to form composites which have synergistic catalytic activity.The research is still in its infancy,and the kinds of MOFs,the composites formed and the catalytic reactions are becoming rich gradually,which will attract more and more attentionIn this research paper,based on the high adsorption efficiency and heterogeneous catalytic activity of MOFs,the application in the preparation of real samples containing heavy metal ions and the oxidation of TMB by H2O2 catalyzed by Fe3O4-MOF core-shell magnetic composites were investigated.The main parts of the results are briefly summarized as follows:1.Preparation of a tea sample using thiol-functionalized[Cu4O(BDC)]n for the detection of heavy metal ions.A novel thiol-functionalized porous MOF,namely thiol-functionalized[Cu4O(BDC)]n(BDC=Terephthalic acid),was synthesized by postsynthetic method at room temperature.The successful modification was certified by Fourier transform infrared spectroscopy and X-ray powder diffraction.The modified MOFs were further characterized by scanning electron microscopy and thermogravimetric measurements.The adsorption of the modified MOF s for both common and heavy metals was investigated.The modified MOFs showed remarkable and selective adsorption for four heavy metals(Hg2+,Cr6+,Pb2+,Cd2+),especially for Hg2+.The static and dynamic adsorption tests showed that the modified MOFs exhibited high adsorption capacity and selectivity for Hg2+,and offered a fast kinetics for the adsorption of Hg2+.The as-synthesized modified MOFs were successfully used as adsorbents to selectively enrich the above four heavy metals in preparation of a tea sample2.Preparation of tea and mushroom samples using JUC-62 for the detection of Hg2+.JUC-62,based on copper and 3,3',5,5'-azobenzenetetracarboxylic acid,was prepared by a solvothermal method.The prepared MOF was crystalline and porous and was characterized by scanning electron microscopy,thermogravimetric analysis and N2 sorption-desorption isotherms.The MOF was used as sorbent for the adsorption of Hg2+ with superior adsorption capacity.The adsorption performances,in both static and kinetic conditions,were investigated strictly and the experimental data fitted the Langmuir model and pseudo-second-order equation very well.The maximum adsorption capacity of JUC-62 for Hg2+was 836.7 mg/g,which was the largest compared with that of various materials.And the adsorption reached equilibrium in 15 min with the concentration of 0.1 mg/mL Hg2+,offering a fast adsorption process.JUC-62 as solid phase extraction sorbents,was successfully applied to the pretreatment of tea and mushroom samples for Hg2+ detection with satisfactory results.3.Synthesis of two novel MOFs and the application in Pb2+ adsorption.Two porous MOFs have been prepared by the solvothermal reaction of N,N,N',N'-tetrakis(4-carboxyphenyl)biphenyl-4,4'-diamine(H4TCPBDA)and Cu(NO3)2·3H2O/Cd(NO3)2·4H2O in DMF.The crystal structures and properties of the two MOFs were characterized by scanning electron microscopy,X-ray powder diffraction and nitrogen adsorption-desorption isotherms.The adsorption capacities of the two MOFs for Pb2+ were investigated and compared with that of the commercially available sorbent Al2O3.The adsorption capacity was the order of Cu(TCPBDA)>Al2O3>Cd(TCPBDA),and the maximum adsorption capacity of Cu(TCPBDA)for Pb2+ is 300 mg/g.Cu(TCPBDA)was applied to the preparation of toner and lotion before the determination of Pb2+.All these results showed that Cu(TCPBDA)had good adsorption capacity and enrichment ability for Pb2+,and the results were accurate and credible4.Application of Fe3O4@MIL-100(Fe)as a peroxidase in the determination of cholesterol in serum samples.Metal-organic framework coated Fe3O4 magnetic nanoparticles,Fe3O4@MIL-100(Fe),was prepared using a step-by-step assembly procedure.Fe3O4@MIL-100(Fe)had a remarkable ability to decompose H2O2 into·OH which can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine(TMB)to produce a blue product.The catalytic activity of Fe3O4@MIL-100(Fe)was compared with Fe3O4,MIL-100(Fe)and Fe3O4+MIL-100(Fe).The peroxidase activity of core-shell Fe3O4@MIL-100(Fe)was remarkably enhanced.The catalytic behavior of Fe3O4@MIL-100(Fe)followed Michaelis-Menten equation and the affinity of Fe3O4@MIL-100(Fe)to the substrate was higher than horseradish peroxidase.Under the optimal conditions,the absorbance of the oxidized TMB at 652 nm is linearly correlated with the concentration of H2O2.As H2O2 is the oxidative product of cholesterol in the presence of cholesterol oxidase,a sensitive and selective method of cholesterol detection was also developed.As low as 0.8 ?M of cholesterol could be detected with a linear range from 2 to 50?M(r=0.999).The proposed method was successfully applied to the detection of cholesterol levels in serum samples.As an artificial peroxidase,Fe3O4@MIL-100(Fe)has advantages of high catalytic efficiency,low cost,good stability,easy preparation and storage.