Synthesis And Hydrogen Storage Properties Of Two-ligand MOFs With Dabco Bridged

Metal-organic frameworks are a coordination polymer formed by metal ions and exo-multidentate ligands (mostly aromatic polycarboxylic acids, multi-amine) through the self-organization process metal ions. It has shown interesting properties which includes large surface area, porosity, variable frame size and chemical modification, and potential applications for gas transport, adsorption, separation and catalytic. Fuel exhaustion and the deterioration of the environment encourage people to pay more attention to hydrogen which is an efficient and clean energy, however, hydrogen storage and transportation constraints hydrogen utilization. MOF-5 was first synthesized and reported on its hydrogen storage by Yaghi group. MOFs in hydrogen storage field recently have become a research hotspot. Researches on porous materials for hydrogen storage by our group have shown:specific surface area and pore size are two important factors that affect the hydrogen storage properties of porous materials. While using two organic ligands to produce MOFs is an effective way to modulation physical-chemical parameters of MOFs materials, to achieve the optimization of the surface area and pore size, and to make MOFs materials in the structure and performance with better adjustable ability.In this paper, Ni2(bdc)2dabco^ Ni2(2,6-ndc)2dabco、Ni2(1,4-ndc)2dabco、 Ni2(bpdc)2dabco^ Zn2(bdc)2dabco and Zn2(NO2-bdc)2dabco were synthesized respectively using terephthalic acid,2,6-Naphthalenedicarboxylic acid, 1,4-Naphthalenedicarboxylic acid,4,4’-Biphenyldicarboxylic acid,2-Nitro-terephthalic acid,1,4-diazabicyclo [2.2.2] octane,1,3,5-Benzenetricarboxylic acid as organic ligand by solvent-thermal synthesis process. In the experiment, we investigated the impact of the synthesis temperature, reaction time, solvents, material ratio of the sample to obtained optimal synthesis conditions. Several these structures have a similar coordination manner, so the synthesis conditions are similar. The best synthesis temperature of these samples were 120℃,100℃, 100℃,120℃,120℃,100℃. The best synthesis time of the sample were 48h, 24h,48h,48h,24h,12h. The molar ratio of n(DMF):n(M2+) is 420. the molar ratio of n(M2+):n(L):n(dabco) is 2:2:1.The samples were characterized by thermo gravimetric-differential thermal, scanning electron microscopy, Fourier transform infrared, and nitrogen adsorption, etc. Using thermo gravimetric-differential thermal analysis to examine the thermal stability of the samples, experimental results show that thermal stability temperature of Ni2(bdc)2dabco, Ni2(2,6-ndc)2dabco, Ni2(1,4-ndc)2dabco, Ni2(bpdc)2dabco, Zn2(bdc)2dabco, Zn2(N02-bdc)2dabco can reach 385℃,350℃,383℃,340℃,320℃,350℃ in the nitrogen atmosphere. Heating the samples up between 30℃-230℃ to completely remove the guest molecules in their pores, and keep the weight constant, then to achieve rapid weight loss in the stability of the temperature and make the sample skeleton collapsed. Nitrogen adsorption was to measure specific surface area of the samples at 77K, and the specific surface area of Ni2(bdc)2dabco, Ni2(2,6-ndc)2dabco, Ni2(1,4-ndc)2dabco, Ni2(bpdc)2dabco, Zn2(bdc)2dabco, Zn2(NO2-bdc)2dabco were 1807m2/g,1922m2/g,1236m2/g,918m2/g,2019m2/g, 1481 m2/g, respectively.We investigated hydrogen storage capacity of samples with different activation temperatures. The hydrogen storage capacity of Ni2(bdc)2dabco, Ni2(2,6-ndc)2dabco, Ni2(1,4-ndc)2dabco, Ni2(bpdc)2dabco, Zn2(bdc)2dabco, Zn2(NO2-bdc)2dabco at activation temperature of 100℃ were 1.8wt%,2.31wt%, 2.38wt%,2.04wt%,1.57wt%,1.92wt%. The hydrogen storage capacity at activation temperature of 120 were 2.6wt%.68wt%,3.09wt%,2.6wt%, 2.19wt%. The hydrogen storage capacity at activation temperature of 150℃ were 2.47wt%,4.07wt%,4.12wt%,4.18wt%,3.37wt%,3.39wt%,3.8wt%. Comprehensive analysis of samples of hydrogen storage performance descending in order of Ni2(1,4-ndc)2dabco, Ni2(2,6-ndc)2dabco, Ni2(bdc)2dabco, Zn2(NO2-bdc)2dabco, Zn2(bdc)2dabco, Ni2(bpdc)2dabco.