Chlorine-resistant positively charged polyamide nanofiltration membranes for heavy metal ions removal

Heavy metal pollution is one of the most serious environmental problems. Nanofiltration (NF) is an effective and potential membrane separation technology for removal of heavy metal ions from water. However, the separation performance and chlorine resistance of NF membranes should be further improved in industry. Herein, to obtain exceptional water permeability and chlorine resistance, novel positively charged polyamide (PA-PDMC) NF membranes were fabricated by surface-initiated atom transfer radical polymerization (SI-ATRP), through which methacryloxyethyltrimethyl ammonium chloride (DMC) was grafted to the 2-bromoisobutyryl bromide (BIBB) exposed on the surface of polyamide (PA-Br1) membrane. The graft length of positively charged polymer chains were controlled by ATRP time, which furtherly exerted influences on the surface structures and properties of PA-PDMC membranes. At the optimal graft content, the retentions to MgCl2, CaCl2, CuCl2, ZnCl2 of the as-prepared PA-PDMC membrane were 92.8%, 90.8%, 93.5% and 96.8% respectively with the flux of 82.5 L m(-2) h(-1), which maintained stability during the long-term operation process of 168 h. Moreover, the PA-PDMC membrane exhibited exceptional chlorine resistance at the chlorination condition of 12,000 ppm h.

Automated summary

This study fabricated novel positively charged polyamide NF membranes with exceptional water permeability and chlorine resistance through surface-initiated ATRP, showing high retentions to heavy metal ions and stability during long-term operation.