| dc.description.abstract | The UiO family, a series of relatively new zirconium-based MOF, has attracted much attention due to its high thermal, chemical, and mechanical stability. Coupled with the high surface area, these features make it a suitable material for gas storage and separation. UiO-66, one such material with benzene-1,4-dicarboxylic acid (BDC) as its linker, possesses good crystallinity. Recent studies have shown that the missing-linker defect can be introduced in the crystal lattice by use of modulators. Such structural disorder is believed to enhance the porosity and free volume so as to improve gas adsorption performance.
In this work, Monte Carlo simulations and density functional theory (DFT) are applied to explain adsorption behavior of ideal and defect-containing UiO-66. Under high pressure, the accessible free volume is the main factor of adsorption behavior in the framework, while the isosteric heat (or adsorption energy) plays the dominant role at low pressure. Because of the different mechanism of gas adsorption under different pressure, defect-free UiO-66 shows the lowest CO2 adsorption capacity under high pressure but the highest uptake under low pressure. The adsorption energy was further quantified by DFT in the single gas adsorption condition as an aid to explain the adsorption behavior under low pressure. In our experimental works, different defect-level samples had been tuned by varying the concentration of formic acid (FA) in the synthesis process and quantified by thermogravimetric analysis (TGA). Same features of the CO2 adsorption mechanism were found, confirming the influence of adsorption energy and capacity seen in simulations. This combined study gives us a systematic discussion in understanding gas adsorption behavior in zirconium-based MOFs. | en_US |