In situ immobilization of silver nanoparticles for improving permeability, antifouling and anti-bacterial properties of ultrafiltration membrane

In this work, silver nanoparticles (AgNPs) were in situ immobilized on polysulfone (PSf) ultrafiltration membrane via polydopamine (PDA) deposition and in situ reduction of silver ammonia aqueous solution (Ag(NH3)2OH). The adhesive and reductive PDA layer existing on the membrane surface induced the reduction of Ag+ on the site of surface without surface pore blockage, and also favored to the firm attachment and uniform distribution of AgNPs onto the membrane. The diameter and density of the immobilized AgNPs were regulated by changing [Ag(NH3)2]+ ion concentration, which exerted an influence on membrane hydrophilicity and permeation flux. The prepared AgNPs-PDA/PSf membranes were characterized by X-ray photoelectron spectroscopy (XPS), scanning election microscope (SEM), atomic force microscopy (AFM), water contact angle measurement and thermogravimetric analysis (TGA). The results indicated that AgNPs were immobilized on the surface as well as the top layer cross section of the membranes. The increase of Ag+ ion concentration led to an increase in the size and density of AgNPs anchored onto the membrane. Compared with PSf membrane, AgNPs-PDA/PSf (20 mM) membrane showed higher water flux, slower flux decline rate during BSA solution filtration and higher flux recovery ratio after simple water flushing. The AgNPs-PDA/PSf (20 mM) membrane possessed excellent stability with little release of silver during the filtrate operation or static immersion in water for 12 days. Besides, AgNPs-PDA/PSf (20 mM) membrane displayed excellent anti-bacterial and ani-biofouling properties against E. coli and B. subtilis.