The effects of water chemistry on the detachment and dissolution of differently stabilized silver nanoparticles from ceramic membranes†
Silver nanoparticles (Ag NPs) are an attractive addition to membranes used for drinking water treatment due to their antimicrobial properties. This research examined the role of stabilizing agents, used during the synthesis of Ag NPs, on their detachment/dissolution from ceramic membranes exposed to different types of drinking water sources typical in the United States. Ag NPs that had been stabilized by citrate, polyvinylpyrrolidone (PVP), or branched polyethylenimine (BPEI) were deposited on the surface of porous aluminum oxide membranes, which are commonly used for municipal water treatment. Results demonstrated that Ag NP stabilizer influenced release from the membranes. For Ag NPs electrostatically stabilized (citrate), hard water was found to remove the Ag NPs for longer periods of time and in higher quantities than in water without hardness. The reverse was found for sterically stabilized Ag NPs (BPEI and PVP). Additions of natural organic matter (NOM) to waters filtered by membranes coated in citrate Ag NPs were found to prolong the release of the citrate Ag NPs in the hard water test conditions. Variations in total Ag released from ceramic membranes were explained by differential impacts on the NP and membrane electrical double layers when switching from Ag NP deposition to filtration water chemistry conditions (zeta potential measurements are provided in this paper). Despite these differences, our findings show that, in waters that do not contain NOM, Ag release quickly falls below silver drinking water standards (0.1 mg L−1) and greater than 50% remained on the membranes. This study demonstrates that the type of Ag NP stabilizing agent and water chemistry should be considered when these membranes are utilized for municipal water treatment.