Immobilization of silver nanoparticle-decorated silica particles on polyamide thin film composite membranes for antibacterial properties

We present a new strategy to strongly and effectively immobilize silver nanoparticles (AgNPs) on polyamide thin film composite membranes to endow antibacterial activity. This method relies on the immobilization of relatively large silica particles (SiO₂, ~400nm in diameter), where AgNPs of ~30nm in diameter are tightly and densely bound (AgNP@SiO₂), on the membrane surface using cysteamine as a covalent linker. The formation of multiple Ag-S chemical bonds between a "bumpy AgNP@SiO₂ and the rough membrane surface provides a great leaching stability of AgNPs and AgNP@SiO₂. AgNP@SiO₂ particles were well distributed over the entire membrane surface without severe aggregation. The surface coverage of the membrane by AgNP@SiO₂ was tuned by adjusting the deposition time and AgNP@SiO₂ particle concentration. The AgNP@SiO₂-immobilized membrane showed excellent antibacterial properties against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus, even with a relatively low particle coverage. Importantly, the separation performance (water flux and salt rejection) of the membrane was not impaired by particle immobilization. These beneficial effects are attributed mainly to the sparse and good distribution of AgNP@SiO₂, which can reinforce the antibacterial activity of AgNPs while having a negligible impact on the hydraulic resistance.