title: Aggregation and disaggregation of ZnO nanoparticles: influence of pH and adsorption of Suwannee River humic acid.
abstract: The surface charge and average size of manufactured ZnO nanoparticles (NPs) were studied as a function of pH to understand the aggregation behavior and importance of the electrostatic interactions in solution. The interactions between ZnO and Suwannee River humic acid (SRHA) were then investigated under a range of environmentally relevant conditions with the ZnO nanoparticles pHPZC as the point of reference. The anionic charges carried by aquatic humic substances were found to play a major role in the aggregation and disaggregation of ZnO nanoparticles. At low concentrations of SRHA (<0.05 mg/L) and below the pHPZC, anionic SRHA was rapidly adsorbed onto the positively charged ZnO NPs hence promoting aggregation. With similar SHRA concentrations, at pHPZC, SRHA was able to control the suspension behavior of the ZnO and promote partial disaggregation in small volumes. This was more distinguishable when the pH was greater than pHPZC as SRHA formed a surface coating on the ZnO nanoparticles and enhanced stability via electrostatic and steric interactions. In most cases, the NP coating by SRHA induced disaggregation behavior in the ZnO nanoparticles and decreased the aggregate size in parallel to increasing SRHA concentrations. Results also suggest that environmental aquatic concentration ranges of humic acids largely modify the stability of aggregated or dispersed ZnO nanoparticles.
authors.affiliation: F.-A. Forel Institute, University of Geneva, 10 route de Suisse, 1209 Versoix, Switzerland. Electronic address: mohdoma9@etu.unige.ch.
authors.forename: Fatehah
authors.initials: F
authors.lastname: Mohd Omar
authors.forename: Hamidi
authors.initials: H
authors.lastname: Abdul Aziz
authors.forename: Serge
authors.initials: S
authors.lastname: Stoll
mesh_terms: D000327:Adsorption; D006812:Humic Substances / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D053758:Nanoparticles / Q000032:analysis* / Q000737:chemistry; D010316:Particle Size; D055672:Static Electricity; D013535:Suspensions / Q000737:chemistry; D015034:Zinc Oxide / Q000032:analysis* / Q000737:chemistry
chemical_list: D006812:Humic Substances; D013535:Suspensions; D015034:Zinc Oxide
keywords: Aggregation; Disaggregation; Suwannee River humic acid; Zeta potential; ZnO nanoparticles