Synthesis,Modification And Hydrogen Storage Properties Of Hafnium Metal Organic Framework UiO-66-DTPA

Metal organic frameworks(MOFs)are derived from metal ion and organic ligands by self-assembly of a new type of nano-microstructure functional materials.Since the metal organic framework materials having high the specific surface area,controllable topology and pore structure,etc.,it is most likely as a hydrogen storage material.The main research works are as follows:(1)Hafnium-metal organic frameworks UiO-66-DTPA was synthesized using hafnium ion as the central node and 2,5-dihydroxyterephthalic acid(DTPA)as organic linker through solvothermal method and canonical modulated hydrothermal.The influence of different reaction conditions on the structure of UiO-66-DTPA was investigated.The structures of UiO-66-DTPA were characterized by the powder X-ray diffraction,infrared spectroscopy and nitrogen sorption technique.The results show that the crystal structure of UiO-66-DTPA synthesized through modulated hydrothermal was better,the BET specific surface area was bigger and the average pore size was smaller.(2)The UiO-66-DTPA material was post-synthetic modifications by using hydrochloric acid and triethylamine as catalysts,glutaraldehyde and formaldehyde as modifier.The phenolic hydroxyl group on the UiO-66-DTPA reacted with small molecule aldehyde(glutaraldehyde and formaldehyde)from the results of FT-IR and 13C-NMR.The BET specific surface area and the average pore size of the modified UiO-66-DTPA were larger than that the pristine UiO-66-DTPA.(3)Chemical stability and heat-resistance stability of the pristine and modified UiO-66-DTPA were studied.And the powder X-ray diffraction and infrared spectra were used to trace the structure changes of MOFs.All the samples were both stable in 1 mol/L hydrochloric acid and triethylamine.What’s more,the stability of the modified UiO-66-DTPA was better.The pristine and modified UiO-66-DTPA materials could withstand the high temperature of 400℃,and the carbon residue rate of the modified UiO-66-DTPA improved.(4)The relationship between hydrogen storage capacity and the test pressure under different temperature conditions was investigated for the pristine and modified UiO-66-DTPA.The modified UiO-66-DTPA,which was synthesized with hydrochloric acid as catalyst and glutaraldehyde as modifier,was the highest hydrogen storage capacity 55.55 mmol/g at 77 K,2 MPa in all of samples.All of the hydrogen storage capacity would increase with the increase in pressure at the same temperature.And all of the hydrogen storage capacity decreased with increasing test temperature at the same pressure(2 MPa).The hydrogen isothermal adsorption enthalpy of the modified UiO-66-DTPA increased than the pristine UiO-66-DTPA.And the largest hydrogen isothermal adsorption enthalpy was 6.22 kJ/mol from UiO-66-TEA-GA,which was synthesized with triethylamine as catalyst and glutaraldehyde as modifier.