Preferential interaction of Na+ over K+ with carboxylate-functionalized silver nanoparticles.
Elucidating mechanistic interactions between monovalent cations (Na(+)/K(+)) and engineered nanoparticle surfaces to alter particle stability in polar media have received little attention. We investigated relative preferential interaction of Na(+) and K(+) with carboxylate-functionalized silver nanoparticles (carboxylate-AgNPs) to determine if interaction preference followed the Hofmeister series (Na(+)>K(+)). We hypothesized that Na(+) will show greater affinity than K(+) to pair with carboxylates on AgNP surfaces, thereby destabilizing the colloidal system. Destabilization upon Na(+) or K(+) interacting with carboxylate-AgNPs was evaluated probing changes in multiple physicochemical characteristics: surface plasmon resonance/optical absorbance, electrical conductivity, pH, hydrodynamic diameter, electrophoretic mobility, surface charge, amount of Na(+)/K(+) directly associated with AgNPs, and Ag(+) dissociation kinetics. We show that Na(+) and K(+) react differently, indicating local Na(+) pairing with carboxylates on AgNP surfaces is kinetically faster and remarkably favored over K(+), thus supporting Hofmeister ordering. Our results suggest that AgNPs may transform into micron-size aggregates upon release into aqueous environments and that the fate of such aggregates may need consideration when assessing environmental risk.
National Research Council, 500 Fifth Street, NW, Washington, DC 20001, USA; US Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Western Ecology Division, 200 SW 35th St., Corvallis, OR 97333, USA. Electronic address: Pokhrel.Lok@epa.gov.
Lok R
LR
Pokhrel
US Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Western Ecology Division, 200 SW 35th St., Corvallis, OR 97333, USA.
Christian P
CP
Andersen
US Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Western Ecology Division, 200 SW 35th St., Corvallis, OR 97333, USA.
Paul T
PT
Rygiewicz
US Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Western Ecology Division, 200 SW 35th St., Corvallis, OR 97333, USA.
Mark G
MG
Johnson
D007700:Kinetics; D053768:Metal Nanoparticles / Q000737:chemistry*; D008956:Models, Chemical; D010316:Particle Size; D011188:Potassium / Q000737:chemistry*; D012834:Silver / Q000737:chemistry*; D012964:Sodium / Q000737:chemistry*
D012834:Silver; D012964:Sodium; D011188:Potassium
Hofmeister series; colloidal stability; interaction preference; monovalent cations; silver nanoparticles