Activated charcoal as a capture material for silver nanoparticles in environmental water samples

Silver nanoparticles (AgNPs), due to their antibacterial activity, have been incorporated into numerous consumer products. Their environmental impact however, is currently unclear. Uncertainties surround the concentration, fate, and effects of AgNPs in aquatic environments. This study examined the suitability of activated charcoal as a capture material for AgNPs from water. Samples of 100 ppb AgNPs were initially generated and exposed to activated charcoal for 24 h to examine the ability of charcoal to capture AgNPs. The decrease in Ag concentration was measured using ICP-MS. Following initial investigations, the surface area of the charcoal was increased firstly with a pestle and mortar and secondly by milling the charcoal using a ball mill. The increased surface area of the milled charcoal increased the capture of the AgNPs from 11.9% to 63.6% for the 100 ppb samples. Further investigations were carried out examining the effect on the capture of AgNP concentration (with concentration ranging from 10 to 100 ppb), particle coating and the effect of exposure time to the activated charcoal. The capture of AgNP increased with decreasing concentration. A hydrochloric acid (HCl) leaching procedure was also developed which successfully removed the captured silver allowing the fraction captured by the charcoal to be quantified with an average of 94.8% recovery. The results show that milled activated charcoal, can successfully capture AgNPs from water samples, and that therefore, activated charcoal may prove to be a cost effective material for the remediation of waters impacted by AgNP or other nano-wastes.