Polymer of Intrinsic Microporosity Enabled pH-Responsive Adsorptive Membrane: Selectivity and Mechanism

We designed and fabricated a pH-responsive amidoxime-modified polymer of intrinsic microporosity (AOPIM) membrane for the selective separation of charged dyes under varying pH conditions. The membrane was fabricated using a nonsolvent-induced phase separation method with ethanol as the nonsolvent. By utilizing the amidoxime group as the selective affinity site, the AOPIM membrane manifested charge reversals, enabling high adsorption capacity, notably with methylene blue (MB) uptake reaching 444.2 mg g–1. In dye filtration, it achieved substantial separation efficiencies for both anionic (IC: 94.7 L m–2h–1bar–1; 80% rejection) and cationic dyes (MB: 94.9 L m–2h–1bar–1; 99% rejection). Furthermore, the AOPIM membrane also possesses high separation selectivity for cationic dye in a dual dye mixture at a high pH environment. Results reported here underscore the unique pH-responsive properties of the AOPIM membrane, shedding light on the application of adsorptive membranes for pollution control.