A green strategy to immobilize silver nanoparticles onto reverse osmosis membrane for enhanced anti-biofouling property

In this work, a green and facile approach was developed to in situ immobilize silver nanoparticles (AgNPs) onto the commercial polyamide reverse osmosis (RO) membrane (virgin membrane) surface via a two-step surface modification process. First, an ultrathin precursor layer of tannic acid-ferric ion-polyethylenimine (TA-Fe-PEI) complex was deposited onto the virgin membrane surface. Then, due to the strong reducibility of TA, AgNPs were in situ formed on the membrane surface to obtain the TA-Fe-PEI/Ag-modified membrane. The materials used to form the precursor layer are environmentally friendly and low-cost. Meanwhile, no additional reductants are needed in the AgNPs formation process. SEM analysis confirmed the uniform distribution of AgNPs on the membrane surface. Water contact angle measurement indicated increased surface hydrophilicity after the modification. Compared with the virgin membrane, the water flux and salt rejection of TA-Fe-PEI/Ag-modified membrane increased. After contacting with Escherichia coli and Bacillus subtilis for 1.5 h, the bacteria mortalities of TA-Fe-PEI/Ag-modified membrane could reach 100%. Moreover, the membrane biofouling test indicated that compared with the virgin membrane, the TA-Fe-PEI/Ag-modified membrane processed higher anti-biofouling property. Static immersion experiment demonstrated that AgNPs were stably immobilized on the membrane surface.