In-situ silver recovery for biofouling mitigation with catechol-assisted nanofiltration membrane

Silver (Ag) has been in widespread use in the field of medical/pharmaceutical and chemical industries. The discharge of produced Ag-containing wastewater not only threats the ecosystem but also causes resource exhaustion of non-renewable Ag. For a sustainable environment, a catechol-based membrane-assisted recovery-filtration concept is put forward, exemplified by integrating two processes of I) efficient silver ion (Ag+) retention and Ag resource recovery by a catechol-rich thin film composite membrane, and II) biofouling mitigation using the resultant antibacterial membrane in salt separation. Due to the strong affinity and reduction capacity of the catechol groups on membrane surface and pores to Ag+, the retained silver ions onto the membrane are spontaneously in-situ reduced into Ag nanoparticles. Consequently, the membrane achieves a remarkable Ag+ retention efficiency of 91.1 %. More importantly, the resultant membrane with recovered Ag holds a good separation efficiency towards common salt and excellent anti-microbial property over the ultra-long term, owing to the satisfactory Ag loading and well-regulated release of silver ions from the membrane surface. This membrane-based recovery-filtration pathway gives a new insight towards sustainable Ag resource recovery/reuse and nanofiltration technology for industrial wastewater with minimum facilities.