Star polymer-assembled adsorptive membranes for effective Cr(VI) removal

There is a strong demand for materials that can effectively remove highly toxic hexavalent chromium (Cr(VI)) ions from wastewater. Herein, we present a new class of Cr(VI)-adsorptive membranes assembled with a Cr(VI)adsorptive and cross-linkable star polymer. The poly(acryloyl hydrazide)-branched star polymer (PAH-SP) with numerous amine groups enabled rapid and high-capacity Cr(VI) adsorption and was suitable for assembly into a selective layer via interfacial polymerization (IP). The IP-assembled PAH-SP (PAH-TFC) membrane synergistically rejected Cr(VI) over the entire pH range via a combination of adsorption (under acidic conditions) and membrane filtration (under basic conditions). Furthermore, the PAH-TFC membrane was more resistant to oxidation by acidic Cr(VI) than commercial reverse osmosis (RO) and nanofiltration membranes because of the self-sacrificing effect of its abundant amine groups. Consequently, PAH-TFC exhibited significantly higher Cr(VI) rejection (-99.5% at pH 3) under acidic conditions than a representative commercial RO membrane (Cr(VI) rejection of -55% at pH 3) with similar water permeance, while demonstrating comparable Cr(VI) rejection under basic conditions. Furthermore, PAH-TFC displayed excellent regeneration ability, maintaining its Cr(VI) rejection above the commercial RO level by proper base/acid rinsing.

Automated summary

This study presents a new Cr(VI)-adsorptive membrane that has rapid and high-capacity adsorption ability and can effectively remove Cr(VI) ions under both acidic and basic conditions. The membrane is more resistant to acidic Cr(VI) oxidation compared to commercial membranes and can be regenerated to maintain high Cr(VI) rejection levels.