Solvent-free Synthesis And Characterization Of MIL-100(Cr)and MIL-53(Cr)

Metal-organic frameworks（MOFs）as a class of porous crystalline materials have received considerable attention in recent years due to its large specific surface area,rich porosity,tunable pore structure and easy functionalization.At present,the solvothermal method is a widely-used method for the synthesis of MOFs.However,generally this method requires the addition of a large amount of solvent that suffered from time-consuming,low autoclave availability and environmental pollution.Therefore,developing a facile and green method to prepare MOFs is an important research subject.In this dissertation,solvent-free synthesis of two important MOFs MIL-100（Cr）and MIL-53（Cr）were investigated.The specific contents are as follows:Firstly,solvent-free synthesis of MIL-100（Cr）was explored using chromium nitrate as a chromium source.The influence of some synthetic parameters including ratio of Cr（NO₃）3·9H₂O and BTC and crystallization time on the formation of MIL-100（Cr）was studied.The optimized synthetic conditions were Cr（NO₃）₃·9H₂O/BTC molar ratio of 1:2,crystallization time of 24 h.The optimized MIL-100（Cr）had lower BET surface area（1077 m²/g）than that（1741m²/g）by traditional method.This method is extended to the synthesis of MIL-53（Cr）and can not achieve the desired effect.Then,solvent-free synthesis of MIL-100（Cr）was explored using chloride hexahydrate as a chromium source.The influence of some synthetic parameters including ratio of CrCl₃·6H₂O and BTC,crystallization time and crystallization temperature on the formation of MIL-100（Cr）was studied.The optimized synthetic conditions were CrCl₃·6H₂O/BTC molar ratio of 2:1,crystallization time of 15 h,crystallization temperature was 220℃.The optimized MIL-100（Cr）had higher BET surface area（1848 m²/g）and pore volume（1.40 cm³/g）than that（1741m²/g,1.19cm³/g）by traditional method.Those values were improved by 5.8% and 18% respectively.Further,in the oxidation reaction of benzyl alcohol,the conversion of benzyl alcohol reached 53% over MIL-100（Cr）prepared via solvent-free method,due to it exposed more active sites,attributed to the small partical size of MIL-100（Cr）synthesized by solvent-free method.Comparatively,under the same reaction conditions,the conversion of benzyl alcohol was 40% over MIL-100（Cr）prepared via solvothemal method.Solvent-free method was extended to the synthesis of MIL-53（Cr）.Similarly,the influence of some synthetic parameters including chromium source,molar ratio of CrCl₃·6H₂O and BDC,crystallization time was investigated.The optimized conditions were CrCl₃·6H₂O as chromium source,CrCl₃·6H₂O/BDC molar ratio of 1.5:1,crystallization time of 48 h.Subsequently,the optimized sample under the solvent-free conditions were compared with that synthesized by solvothermal method.The results indicated that the sample prepared by solvent-free method displayed a morphology of triangular pyramid-like shape with particle length of about 1.5² μm.Meanwhile,this matierla gave high BET surface area（1310 m²/g）and pore volume（0.84 cm³/g）close to those of MIL-53（Cr）prepared via solvothermal method.Finally,MIL-100（Cr）and MIL-53（Cr）materials with high specific surface area have been successfully prepared by solvent-free method.Also,it can be expected that this synthesis method may be further applied to the synthesis of other MOFs materials.