Dynamics of silver elution from functionalised antimicrobial nanofiltration membranes

Abstract

In an effort to mitigate biofouling on thin film composite membranes such as nanofiltration and reverse osmosis, a myriad of different surface modification strategies has been published. The use of silver nanoparticles (Ag-NPs) has emerged as being particularly promising. Nevertheless, the stability of these surface modifications is still poorly understood, particularly under permeate flux conditions. Leaching or elution of Ag-NPs from the membrane surface can not only affect the antimicrobial characteristics of the membrane, but could also potentially present an environmental liability when applied in industrial-scale systems. This study sought to investigate the dynamics of silver elution and the bactericidal effect of an Ag-NP functionalised NF270 membrane. Inductively coupled plasma-atomic emission spectroscopy was used to show that the bulk of leached silver occurred at the start of experimental runs, and was found to be independent of salt or permeate conditions used. Cumulative amounts of leached silver did, however, stabilise following the initial release, and were shown to have maintained the biocidal characteristics of the modified membrane, as observed by a higher fraction of structurally damaged Pseudomonas fluorescens cells. These results highlight the need to comprehensively assess the time-dependent nature of bactericidal membranes.

Keywords:

• Nanofiltration
• silver modification
• leaching
• ICP
• biofouling

Acknowledgements

The authors would like to thank Mr Pat O’Halloran for his invaluable technical assistance, and Mr Liam Morris for the construction of the MFS devices. The authors especially thank Dr Ellen L. Lagendijk from the Institute of Biology Leiden, the Netherlands for the gift of the Pseudomonas fluorescens PCL1701. Dr Ian Reid from UCD’s Nano Imaging and Material Analysis Centre (NIMAC) is acknowledged for his assistance with XPS analysis.