Constructing positively charged acid-resistant nanofiltration membranes via surface postgrafting for efficient removal of metal ions from electroplating rinse wastewater

To efficiently recycle metal ions from electroplating wastewater, a positively charged acid-resistant nano filtration membrane was prepared by coupling interfacial polymerization and postgrafting modification with an ethanol grafting solution containing N-(3-aminopropyl)-imidazole (ANPI). Ethanol, as the grafting solvent, not only slightly swelled the original polyamide (PA) layer but also is mutually miscible with n-hexane, which prevented the formation of additional PA layers. ANPI, as the grafting monomer, was covalently bound to the-COCl groups of the PA layer to guarantee grafting stability. Due to the inhibited hydrolysis of the-COCl group by ethanol, more ANPI was grafted on the PA layer, which could be easily protonated under low pH. This resulted in a looser, thinner and positively charged selectivity layer. The membrane permeability was improved by 56.0 +/- 0.55% with high interception performance (> 98% for Cu2+ and Ni2+ ions) in electroplating rinse wastewater. The formed positive protective layer prevented H+ ions from attacking the -CO -NH-bonds, resulting in strong stability after immersion in 10 wt% H2SO4 and H3PO4. Therefore, the obtained membrane shows promise for application in highly acidic wastewater.

Automated summary

A positively charged acid-resistant nano filtration membrane was prepared for efficient recycling of metal ions from electroplating wastewater. The membrane showed high interception performance and improved permeability, and maintained stability in highly acidic environments.