Molecular Control Of Preparation Of Functionalized Metal-organic Framework Materials For Efficient Purification Chlorinated Volatile Organic Compounds

With the rapid development of the polyvinyl chloride(PVC)industry and the methyl chloride industry,chlorinated volatile organic compounds(Cl-VOCs)cause great damage to the environment and endanger human health.Thus,the removal of Cl-VOCs is a major environmental concern.Some methods such as adsorption,thermal incineration,biological treatment,photocatalytic oxidation,and electrochemical method have been used for the removal of them.Among the removal technologies,adsorption is a well-established and effective technique for the removal and recovery of Cl-VOCs from polluted air due to the simple adsorption equipment and recyclable adsorbents,and other advantages.Porous adsorbents are the key part of this technique.Several adsorbents have been studied for Cl-VOCs removal from air streams,such as silica gel,zeolites,mesoporous silicate and activated carbons.Metal-organic frameworks(MOFs),or porous coordination polymer(PCPs),have emerged as an important class of porous materials constructed from inorganic secondary building units(SBUs)and bridging organic ligands.MOFs have attracted great attention because they can be applied in gas storage and separation,catalysis,and chemical sensing due to their extra high surface area and pore volume as well as uniform and tunable openings.To the best of the authors' knowledge,MOFs have not been studied in details for Cl-VOCs adsorption.The MOFs has its unique advantages:the size of the channel,the specific surface area,the active site and the rigid flexibility can be controlled by rational selection of metal ions and organic ligands.Therefore,how to use molecular control methods to prepare MOFs and achieve the highly efficient purification of Cl-VOCs,high selectivity adsorption and separation has become a hot spot for scientists.In this work,we have synthesized metal-organic framework materials through molecular control methods for efficient purification of Cl-VOCs.The main contents and findings of this paper are summarized as follows:1.According to the molecular sieve effect,the MOFs suitable for the target Cl-VOCs to be adsorbed and separated is selected.The preparation,characterization and pore structure property of the MOFs as well as the adsorption and separation process of the MOFs were systematically investigated for Cl-VOCs,including thermodynamics,kinetics and adsorption mechanism and so on.In the third chapter of this paper,a typical copper-based MOF,also known as HKUST-1,was successfully synthesized,characterized,and evaluated for selective adsorption and separation of two kinds of Cl-VOCs,which are dichloromethane(DCM)and trichloromethane(TCM).In addition,their binary adsorption selectivity and diffusivity selectivity were predicted via the ideal adsorbed solution theory(LAST)method.The high adsorption selectivity(3.04)and diffusivity selectivity(8.93)at 318 K and 2.8 kPa indicated that HKUST-1 was a great candidate for selective adsorption and separation of DCM and TCM.Based on these results,the mechanism of adsorption and separation process has been discussed in detail.2.The organic ligands in the MOFs are functionally modified to greatly enhance their adsorption capacity and adsorption selectivity thus achieving the goal of separation.In the fourth chapter of this paper,zinc-based metal organic framework MOF-5,and its amino-functionalized form IRMOF-3 were successfully synthesized,characterized,and studied for the effect of amino group on the adsorption and separation properties of DCM and TCM.In spite of the reduced porosity of IRMOF-3,the adsorption capacity of DCM and TCM were improved up to 24.5%and 27.4%when compared with MOF-5.Therefore,the additional amino group in the MOF imparts extra adsorption capability on the MOF.The binary adsorption selectivity and diffusion selectivity of DCM and TCM are predicted via the IAST method.The adsorption selectivity and diffusion selectivity of DCM/TCM on the IRMOF-3 was about 5.62 and 3.88 at 298 K and 2.8 kPa,which were higher than those of MOF-5.The improved adsorption capacity and enhanced adsorption selectivity and diffusion selectivity over IRMOF-3(with amino group)could be attributed to the improved interaction of DCM and TCM with the amino group on MOF.3.From the point of view of inorganic chemistry,it is possible to design the metal clusters as frame nodes to realize the further regulation of the structure and performance of MOFs.In particular,the introduction of metal cavitation on metal clusters can greatly enhance the gas adsorption capacity.In the fifth chapter of this paper,a series of bimetallic metal-organic frameworks CuxZn1-x(BDC)(BDC=1,4-benzenedicarboxylate)have been successfully synthesized using doping technique via solvothermal crystallization process at a relative low copper doping fraction x<0.125.It was found that as the amount of Cu2+ ions exceeds x?0.125 the cubic structure of Cu-Zn-BDC becomes unstable,and the Cu(BDC)structure emerges.The transition from the MOF-5(CuxZn1-x(BDC),x = 0)cubic structure to the Cu(BDC)(CuxZn1-x(BDC),x = 1)rectangle structure is tuned by increasing the copper doping amount and when the doping fraction x in the interval between 0.125 and 1,two kinds of structures are coexist.There was an associated gas adsorption change with crystal morphology that accompanied the addition of copper amount.BET surface area measurements of the desolvated product showed that the surface area of the MOF-5(CuxZn1-x(BDC),x = 0)decreased with the addition of copper amount within the range that copper doping fraction x is lower than 0.125,but increasing when the amount of Cu2+ ions exceeds x?0.125 and the Cu(BDC)has the highest gas ad-sorption amount.This work took the lead in realizing the different amounts of copper elements substitution of the original zinc elements on the metal nodes of the MOF-5,and systematically studied the effect of the different amount of metal elements on the crystal structure and the adsorption properties.4.In chapter 4 and chapter 5,the functional modification of organic ligands and the metal substitution of metal clusters were studied.In order to develop fluorescence sensors for chlorinated gas,the composite materials of MOFs were explored.In the sixth chapter of this paper,ZnO nanoparticle/Metal-organic framework-5(MOF-5)hybrid material was successfully synthesized via two-step solvothermal method.The ZnO/MOF-5 composite exhibited enhanced hydrostability than MOF-5.Besides,the photoluminescence spectra of this hybrid material show two emission peaks located at 460 nm and 550 nm.At present,this work only studied the early,and laid the foundation for the exploration and research of fluorescence sensor for chlorinated gas in the future.