The Influence of Anions on the Release of Ag(I) Ions from Silver Nanoparticles (AgNPs)

Abstract

Silver nanoparticles (AgNPs) are widely being incorporated into products such as socks [1, 2], sports wears and wound dressings [3, 4] to serve as antibacterials and to inhibit unwanted odours. As these products are washed, the silver nanoparticles leach out, dispersing in water where they may release silver ions. Although the only contraindication of high levels of silver in humans is argyria [5], it is said to be very toxic to aquatic organisms that make up the base of a series of food chains. In this study, silver nanoparticles were synthesised by the citrate reduction method following the procedure of Lee and Meisel [6]. The nanoparticles were prepared in the presence of various anions and in pure water in order to examine the effect of the medium on the release of Ag(I). AgNPs were characterised by UV-Vis spectrometry, dynamic light scattering (DLS) and atomic force microscopy (AFM). The decrease in surface plasmon resonance (SPR) peak of the nanoparticles after dialysis indicates that quite a number of conduction electrons have gone into reaction, hence lowering of resonant frequency. The diameters of the nanoparticles as measured by DLS ranged from 102 nm in the 10 mM chloride AgNPs before dialysis to 892 nm in the 50 mM sample after dialysis, indicating aggregation over the dialysis period. On the other hand, particle sizes in terms of both height and diameter as measured by AFM decreased after dialysis. This could be explained that in spite of aggregation in solution, the AgNPs deposit as islands about 1 particle in height on the AFM substrate (Si wafer). Release of Ag(I) from the NPs was monitored by anodic stripping voltammetry at glassy carbon electrodes. Two interesting observations were made: (i) there is substantial (90 mM) Ag(I) present in the initial NP preparation and (ii) the concentration of Ag(I) after 73 h of dialysis remained easily detectable at about 4 µM irrespective of the concentration of chloride present. References 1 T.M. Benn, P.Westerhoff. Environ. Sci. Technol. 2008, 42, 4133-4139. 2 D.E Meyer, M.A. Curran, M.A. Gonzalez. J Nanopart Res. 2011, 13, 147-156. 3 A. Hebeish, M.H. El-Rafie, M.A. El-Sheikh, A.A. Saleem, M.E. El-Naggar. Intnal. Journ. of Macromolecules. 2014, 65, 509-515. 4 T. Maneerung, S. Tokura, R. Rujiavanit. Carbohydrate Polymers. 2008, 72, 43-51. 5 WHO Guidelines for Drinking-water quality. 2003. World Health Organisation, Geneva. 6 P.C. Lee, D. Meisel. J. Phys. Chem. 1982, 86, 3391-3395. Figure 1