title: [Aggregation and deaggregation behaviors of hematite nanoparticles at different pHs].
abstract: The aggregation and deaggregation behaviors have profound impacts on the fate of nanoparticles in the environment. In this work, the aggregation and deaggregation kinetics of hematite nanoparticles at different pHs were examined using a Zetasizer. In the pH range of 7.0-8.7, aggregation occurred quickly(e. g., the average size increased from 31 nm to 1 400 nm with 400 s at pH = 8.2), whereas at pH below 6.2, no aggregation was observed. Deggregation of hematite nanoparticles without aging was slower than aggregation and not completely reversible, demonstrating hysteresis. Aging caused more hematite nanoparticles to aggregate irreversibly. At point of zero charge (pH = 8.2), no deaggregation of aged particles was observed. At pH = 7.0 and 8.9, the average sizes of aged samples (about 500 nm) after deaggregation was greater than those of the samples without aging (about 250 nm). The hyteresis of the aggregation-deaggregation process poses significant difficulty to predict the fate and ecological effects of nanoparticles in the environment.
authors.affiliation: Laboratory of Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China. janeshenxin@gmail.com
authors.forename: Xin
authors.initials: X
authors.lastname: Shen
authors.forename: Kai-Yang
authors.initials: KY
authors.lastname: Li
authors.forename: Xi-Qing
authors.initials: XQ
authors.lastname: Li
mesh_terms: D017753:Ecosystem; D004784:Environmental Monitoring; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D053768:Metal Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D044367:Phase Transition; D013499:Surface Properties
chemical_list: D005290:Ferric Compounds; C000499:ferric oxide