Mixed-charged polyamide-4-sulfocalix [4] arene hollow fiber nanofiltration membranes for heavy metal removal under various pH

The presence of heavy metal ions in water sources poses significant risks to both human health and environments; hence, it is critical to develop effective and trustworthy removal techniques. This research aims to fabricate a novel hollow fiber membrane consisting of mixed-charged characteristics via the formation of a positively charged thin film composite (TFC), followed by the infiltration of 4-sulfocalix [4] arene (SCA4). The formation, architecture and separation performance of the mixed-charged nanofiltration (NF) membrane have been confirmed by various characterizations. The SCA4-0.03 NF hollow fiber membrane shows excellent rejection performance up to 99.2 % for a variety of ion removals such as common arsenate, nickel (II), and lead (II) ions over a broad pH range. Additionally, the mixed-charged membrane exhibits higher performance stability over 48 h and fouling resistance in both basic and acidic conditions. Consequently, the mixed-charged membrane described in this work is promising to treat both cationic and anionic liquids, and eliminate a variety of ecologically harmful ion species in industries.