AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Nanosilver Toxicity: Enhanced Ag+ Ion Release from Aqueous Nanosilver Suspensions by Absorption of Ambient CO2
Kakeru Fujiwara, Georgios A. Sotiriou, SOTIRIS E. PRATSINIS, ETH Zurich
Abstract Number: 317 Working Group: Nanoparticles and Materials Synthesis
Abstract Nanosilver is the largest engineered nanomaterial by volume and value after carbon black and fumed silica, alumina and titania as it is present in many consumer products. Here nanosilver with closely controlled average particle diameter (7 - 30 nm) immobilized on nanosilica aerosols is prepared and characterized by X-ray diffraction and transmission electron microscopy. The presence of Ag$_2O on the metallic nanosilver surface is confirmed by UV-vis spectroscopy and quantified by thermogravimetric analysis and mass spectrometry. The dissolved Ag as Ag$^+ ions, [Ag$^+], from nanosilver in de-ionized water exposed to ambient laboratory air containing 580 ppm of CO$_2 is monitored electrochemically. For all air compositions, the [Ag+] instantly reaches the level that corresponds to the dissolved preexisting Ag$_2O layer on the nanosilver surface. Under CO2-free synthetic air, the [Ag+] levels for all nanosilver sizes do not change for seven days indicating that only metallic Ag remains. In contrast, under laboratory air (CO$_2 580 ppm), the [Ag$^+] of all three nanosilver suspensions slowly increases indicating additional release of Ag$^+ ions from the metallic Ag core that depends on solution pH. The pH rapidly increases during preexisting Ag$_2O dissolution by the released OH$^- species along with Ag$^+ ions resulting in basic pH solutions. This prevents further Ag$^+ ion release by metallic Ag dissolution resulting in constant [Ag+]. When these solutions are exposed to CO$_2-containing atmospheres, absorption of CO$_2 in the host solution leads to its acidification and facilitates metallic Ag dissolution. So the pH of nanosilver solutions increases first rapidly by dissolution of preexisting Ag$_2O and release of OH$^-. Thus, metallic Ag dissolution in water exposed to CO2-containing ambient air during its prolonged storage is enhanced by acidification resulting from atmospheric CO$_2 absorption in solution, which significantly increases the risk to environment.