Synthesis And Hydrogen Storage Of Metal Organic Framework Compound MOF-5

Metal organic framework compound is a zeolite-like material. This material shows rich, adjustable structure, various pore channels and high surface area and is widely regarded as a promising material in catalysis, separation, gas storage, especially attracts considerable attention in gas storage. Metal organic framework MOF-5 is a typical structure among metal organic framework compounds, which is of a three dimension cubic structure and shows better hydrogen storage behavior due to high surface area, uniform pore and large pore volume.Due to different results from reports of literatures, synthesis and hydrogen storage of MOF-5 were elaborately investigated in this paper. MOF-5 was synthesized by direct mixing of TEA method, slow diffusion of TEA and solvothermal synthesis method. The effects of reaction time, reaction temperature, N, N-dimethylformamide (DMF) and triethylamine (TEA) on synthesis were studied in experiments. The samples were characterized by XRD,IR,TG-DTA and SEM. The experiment results indicated that MOF-5 with the highest relative crystal intensity was obtained at Zn(NO₃)₂·6H₂O/ 1, 4-benzenedicarboxylic acid (H₂BDC) =2/1 (mol/mol) in all synthesis methods. Powder MOF-5 with the highest relative crystal intensity was obtained at synthesis condition of DMF/H₂BDC=258.5 (mol/mol), TEA/H₂BDC=7.91 (tool/tool) and 2h reaction time in direct mixing method of TEA. At synthesis condition of DMF/H₂BDC=258.5, TEA/H₂BDC=7.91 and 48h reaction time, powder MOF-5 with the highest relative crystal intensity was obtained in slow diffusion approach. The big single crystal MOF-5 was grown when DMF/H₂BDC=161.5, the reaction temperature of 100℃and 24h reaction time in solvothermal synthesis method. The experiments of introduction of H₂O₂ into direct mixing of TEA and slow diffusion of TEA methods showed that H₂O₂ favored the growth of MOF-5 with higher relative crystal intensity in slow diffusion of TEA method but did not do in direct mixing of TEA method.The organic guests of DMF contained in MOF-5 frameworks affect the hydrogen storage ability of sample, because these guests occupy majority of useful voids in frameworks and block abundant pore channels. In order to improve the hydrogen storage ability of MOF-5, the temperature activation and chloroform extraction were taken to remove these guests. The results showed that guests were fully removed when the sample was heated at 250℃for 12h; samples disposed with chloroform could totally remove guests, but considering the convenience of experiment, the heat-treated method was finally adopted to remove guests in frameworks.This paper measured the hydrogen storage of MOF-5 synthesized by direct mixing of TEA, slow diffusion of TEA and solvothermal synthesis methods and with addition of H₂O₂ to direct mixing of TEA and slow diffusion of TEA synthesis system. XRD,SEM and nitrogen adsorption were used to characterize these samples. The differences of MOF-5 synthesized by three methods and with addition H₂O₂ from morphology and pore parameters were found, the crystal size of samples were not same in appearance; the pore parameters were shown at different surface area and pore volume. The final experiments demonstrated that the hydrogen storage of MOF-5 had something with surface area and pore volume. The larger surface areas and pore volume, the better hydrogen storage behavior, which also demonstrated that the mechanism of hydrogen storage of MOF-5 belongs to typical physical adsorption.