title: Aggregation and charge behavior of metallic and nonmetallic nanoparticles in the presence of competing similarly-charged inorganic ions.
abstract: The influence of competing, similarly charged, inorganic ions on the size and charge behavior of suspended titanium-dioxide (nTiO(2)), silver (nAg) and fullerene (nC(60)) nanoparticles (NPs) was investigated. Under pH and ionic conditions similar to natural water bodies, Ca(2+) induced aggregation of nTiO(2) and nAg NPs more strongly than K(+) and Na(+). Although K(+) and Na(+) had a similar effect on aggregation, K(+) provided better screening of the particle surface charge presumably because of its small hydrated radius. These effects were decidedly more prominent for TiO(2) than Ag. Anions (co-ions), SO(4)(2-) and Cl(-), affected the surface charge behavior of nTiO(2) but not of nAg NPs. The zeta potential (ZP) of nTiO(2) NPs was more negative at higher SO(4)(2-)/Cl(-) ratios than lower. When Mg(2+) was the counterion, charge inversion and rapid aggregation of nC(60) NPs occurred under alkaline conditions, with a more pronounced effect for Cl(-) than SO(4)(2-). Response dissimilarities suggest fundamental differences in the interfacial-interaction characteristics of these NPs in the aquatic environment with corresponding differences in transport of these particles. Our study also shows the important role played by the iso-electric point pH (pH(iep)) of the NPs in determining their aggregation kinetics in the environment.
authors.affiliation: National Research Council Research Associate, and National Exposure Research Laboratory, U.S. Environmental Protection Agency, Athens Georgia 30605, USA. mukherjee.biplab@epa.gov
authors.forename: Biplab
authors.initials: B
authors.lastname: Mukherjee
authors.forename: James W
authors.initials: JW
authors.lastname: Weaver
mesh_terms: D000838:Anions; D002118:Calcium / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D002412:Cations; D002621:Chemistry / Q000379:methods; D004573:Electrolytes; D037741:Fullerenes / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007477:Ions; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry; D053758:Nanoparticles / Q000737:chemistry*; D012834:Silver / Q000737:chemistry*; D014025:Titanium / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D000838:Anions; D002412:Cations; D004573:Electrolytes; D037741:Fullerenes; D007477:Ions; D014867:Water; C009495:titanium dioxide; D012834:Silver; D002244:Carbon; D014025:Titanium; D008274:Magnesium; D002118:Calcium