| Metal organic framework materials(MOFs)are three-dimensional ordered porous nano-functional materials formed by self-assembly of transition metal ions and organic ligands containing nitrogen-containing heterocycles or carboxylic acids.Due to their large specific surface area,low crystal density,unsaturated metal sites,high porosity and pore volume,MOFs have been widely studied in gas adsorption storage and they are considered to be the most potential hydrogen storage materials.Traditional hydrogen storage materials have lower hydrogen storage properties since hydrogen is a non-polar molecule.However,the results of the simulation show that BTC has a high binding energy when combined with hydrogen.This is mainly due to that1,3,5-trimellitic acid(BTC)has three strong electron-withdrawing functional groups which make the ring of benzene exhibits an electron-deficient state.The main research works are as follows:(1)Metal organic framework material MOF-808 was optimized synthesized by simple solution method and solvothermal method with using high chemical stability of zirconium as the central ion and 1,3,5-trimellitic acid(BTC)as the organic ligand.The structure was characterized by powder X-ray diffraction,scanning and transmission electron microscopy,infrared spectroscopy and nitrogen adsorption tests.The effects of different reaction conditions on the structure and properties of MOF-808 were investigated.The results showed that the solvothermal synthesis optimized MOF-808's the specific surface area and pore volume were much larger than that of the simple solution method,and it was more conducive to gas adsorption.(2)The transition metal could significantly enhance the hydrogen adsorption capacity and adsorption rate for it is an active substance for generating hydrogen.In this paper,the metal-organic framework material MOF-808 synthesized through simple solution method metal was modified by Pd nanoparticle to obtain the core-shell structure Pd@MOF-808-a and penetrated structure Pd@MOF-808-b.In addition,the effects of different Pd nanoparticles amount on the structure of MOF-808 were studied.(3)The chemical and thermal stabilities of the optimized MOF-808 materials were studied.The powder X-ray diffraction,infrared spectroscopy,scanning electron microscopy,transmission electron microscopy and nuclear magnetic resonance spectroscopy tests were used to observe the structural changes before and after treated.The results showed that all MOFs could stably present in hydrochloric acid,nitric acid and water,while the structure was influenced in phosphoric acid and sodium hydroxide.MOF-808 and Pd@MOF-808 materials could withstand the temperatures up to 300 ° C with the structure remains unbroken.(4)The relationship between hydrogen storage capacity and adsorption pressure of MOF-808 and Pd@MOF-808 materials at different temperatures was studied.The results showed that the hydrogen storage of all materials increased with the increasing pressure due to the reversible physical adsorption,and the amount of hydrogen storage decreased as the test temperature increased since the adsorption reaction is an exothermic reaction.Moreover,the hydrogen isothermal adsorption enthalpy of Pd@MOF-808 series materials was increased,which could reach up to-1.378 kJ/mol. |
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