Tuning Adsorption Capacity by Alkoxy Groups: A Study on Acetic Acid Adsorption on UiO-66 Analogues from Aqueous Solution

A series of alkoxy groups are introduced to the UiO-66 structure to enhance its adsorption performance toward acetic acid in water. The adsorption kinetics, isotherm, thermodynamics, and regeneration of these adsorbents have been investigated, and the excellent adsorption capacity of n-propyloxy-substituted adsorbent (UiO-66-3) is illustrated. The adsorption of acetic acid on UiO-66-3 was a complex multistep process, and the close contact between O of the ether bond of the adsorbent and H of the carboxyl group of acetic acid played an important role in adsorption. The kinetic results could be fitted well to the pseudo-second-order model. The adsorption isotherm followed the Langmuir isotherm, which indicated that the adsorption process involved a strong interaction between adsorbate and adsorbent. The thermodynamic parameters (ΔG, ΔH, and ΔS) had also been calculated, which verified that acetic acid adsorption on UiO-66-3 was a spontaneously endothermic process. The adsorbent exhibited good stability under specified experimental conditions, which consolidated its potential as a solution to wastewater containing dilute acetic acid.