Enhanced dye adsorption and separation using iterative growth of sulfonated UiO-66 on PTFE membranes

Abstract

Metal-organic frameworks (MOFs) are emerging materials for water purification, offering high microporosity and versatile functionalization. In this study, a MOF-based adsorptive membrane was developed for removing methylene blue (MB) and methyl orange (MO) from aqueous solution, with both static and dynamic adsorption performances evaluated. UiO-66 modified with sulfonic acid groups (UiO-66-SO3H, US) was synthesized on a polytetrafluoroethylene (PTFE) membrane (Omnipore®) via repeated growth cycles. To enhance MOF growth efficiency, a polyethylenimine (PEI) coating was applied prior to synthesis. Adsorption performance was investigated under various conditions, including dye concentration, pH, and contact time. Structural analyses revealed a direct correlation between MOF loading and the number of synthesis cycles, enhancing MB adsorption. In contrast, an inverse relationship was observed for MO adsorption, indicating a charge-specific adsorption mechanism. Adsorption isotherms and kinetics were analyzed using established adsorption models via linear regression, identifying electrostatic and π-π interactions as key mechanisms. For dynamic adsorption of MB at a high concentration of 50 mg/L, the PEI/Omni + US3 membrane demonstrated high performance, achieving a permeance of 28 L/m2 hr bar and rejection of 81 %. These findings provide valuable insights into the design of MOF-based adsorptive membranes for water purification applications.