One step prepared Janus acid-resistant nanofiltration membranes with opposite surface charges for acidic wastewater treatment

Abstract In order to enhance the membrane separation efficiency of multivalent metal ions and acid, high performance Janus acid-resistant nanofiltration membranes (NFMs) with opposite charge properties (selective layer) were fabricated by polyethyleneimine (PEI) and cyanuric chloride (CC) via interfacial polymerization. A novel and facile method (named LC-CT) was developed to obtain the Janus acid-resistant NFMs in one step, by controlling the organic phase (CC) concentration to be low followed by the curing treatment. It was found that CC concentration had a significant effect on the charge property of the membrane surface. Low CC concentration endowed a loose selective layer with many unreacted –NH2 on the flip side while curing treatment attributed to the less defective layer. Thus, LC-CT method endowed the membrane Janus property with high salt rejection and flux. The new generated Janus NFMs exhibited better acid stability than NFM-1 (commercial, polyamide), and higher MgCl2 rejection than NFM-1 and NFM-2 (commercial, acid-resistant) after soaking in 3 wt% HCl at 25 °C for 1800 h or 50 °C for 72 h. Also, the flux of this polyamine Janus NFM was 4.2 ~ 19 times higher than that of previous reported polyamine acid-resistant NFMs, which indicated a good application potential of this membrane in acidic wastewater treatment.