| Metal-organic frameworks(MOFs),also known as porous coordination polymers(PCPs),are hybrid porous solids built up from inorganic metal ion subunits connected by polytopic organic ligands.It has been widely used in the fields of gas storage,gas separation and catalysis because of its large specific surface area,adjustable pore size and functionalization of pore surface.However,the poor stability of MOFs derived from the reversible nature of coordination bonds is commonly regarded as the major drawback for their practical applications in most research fields.With excellent stability,the zirconium-based metal organic framework(Zr-MOFs)stand out,and gradually attracted people's attention.In this thesis,we have successfully synthesized and characterized two highly porous and stable zirconium-based MOF materials.In addition to the thermal and the hydrothermal stability,their gas adsorption properties were also investigated in detail.1.Synthesis of two stable Zirconium-based metal-organic frameworksIn this thesis,we report the solvothermal synthesis of two Zr-MOFs as ZJNU-30 and ZJNU-31 based on Zr6 clusters and C3-symmetrical trigonal tricarboxylate linkers,4,4',4"-benzene-1,3,5-triyl-1,1',1"-trinaphthoic acid(H3L1)and 5,5',5"-benzene-1,3,5-triyl-1,1',1"-trinaphthoic acid(H3L2),respectively.They were fully characterized by XRD,FTIR,thermogravimetric analysis as well as single-crystal X-ray studies.Although the organic ligands employed are positional isomers,the two compounds are isostructural.The interesting structural characteristic is a hierarchical combination of microporous octahedral and mesoporous cuboctahedral cages,as well as the the thermal and hydrothermal stability of ZJNU-30 was also explored.Adsorption studies revealed that almost no loss in the amount of N2 adsorbed was observed when the activated sample was exposed to air for one month,whereas exposure of the activated sample in water or 2 M HCl for one week led to a certain reduction of the adsorption amount of N2.2.Application of Zr-MOFs in selective adsorption and separation of C4 hydrocarbon gasIn order to explore its potential for the separation of C4 mixed gases,the equilibrium adsorption isotherms of ZJNU-30a for C4 gases were tested at three diufferent temperatures of 288 K,298 K and 308 K under the conditions of atmospheric pressure,IAST(ideal solution adsorption theory)and simulated breakthrough calculations reveal that ZJNU-30a is most suited to the separation of 1-butene/isobutylene/cis-2-butene/trans-2-butene mixture.At the total pressure of 100 kPa,we obtaion the following hierarchy of component loadings:cis-2-butene>trans-2-butene>1-butene>isobutylene.Thus the Zr-MOF ZJNU-30a can be used as a promising adsorbent for the separation of butene isomer mixtures.3.Application of Zr-MOFs in high-pressure methane storageIn this thesis,we presented the methane adsorption properties of two isoreticular Zr-based MOFs,ZJNU-30 and ZJNU-31.The two highly porous and stable Zr-based MOF materials show remarkable adsorption capacity with regard to methane.These two compounds after activation exhibit the volumetric CH4 adsorption uptakes of 179.3 and 135.7 cm3(STP)cm-3 at 298 K and 65 bar respectively.In the range of 5-65 bar,the volumetric methane working capacities are 151.9 and 115.4 cm3(STP)cm-3,respectively.The methane storage and working capacities are among the highest reported for Zr-MOF materials.The good methane uptake capacity and exceptional hydrostability make them very attractive materials for methane storage applications. |
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