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

Abstract

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.