Thermochemical adsorption heat storage performance of functionalized UiO-66: Molecular simulation method

UiO-66 has broad application prospects in thermochemical adsorption heat storage owing to its great adsorption performance and stability. To further improve its performance, UiO-66 can be functionalized. Nevertheless, the adsorption and diffusion mechanism of UiO-66 and its functionalized structures is still unclear. Therefore, in this paper, it investigated the adsorption and diffusion performance of the UiO-66 series by molecular simulation. The effects of different functional groups were analysed, and the underlying mechanism was revealed. The results showed that adding -OH, -NH2, and -NH3+Cl- groups improved the adsorption capacity of UiO-66 at low pressure by 2.16, 3.22 and 4.25 times respectively, whereas adding -NO2 and -(OMe)2 groups reduced it by 46.05% and 86.84%. The adsorbent-water interaction was the strongest for UiO-66-NH3+Cl-, while UiO-66-(OMe)2 exhibited the weakest interaction. For the UiO-66 series, water molecules were preferentially adsorbed near the zirconium clusters, -OH, -NH2, and -NH3+Cl- groups. Then, they gradually filled around the organic ligands, and a very small amount gathered around the -NO2 and -(OMe)2 groups. Owing to the limitation of the pore volume, the water diffusion coefficient of all the structures initially increased and then decreased with the increase of water loading.