title: Influence of extracellular polymeric substances on the aggregation kinetics of TiO2nanoparticles.
abstract: The early stage of aggregation of titanium oxide (TiO2) nanoparticles was investigated in the presence of extracellular polymeric substance (EPS) constituents and common monovalent and divalent electrolytes through time-resolved dynamic light scattering (DLS). The hydrodynamic diameter was measured and the subsequent aggregation kinetics and attachment efficiencies were calculated across a range of 1-500 mM NaCl and 0.05-40 mM CaCl2solutions. TiO2particles were significantly aggregated in the tested range of monovalent and divalent electrolyte concentrations. The aggregation behavior of TiO2particles in electrolyte solutions was in excellent agreement with the predictions based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Divalent electrolytes were more efficient in destabilizing TiO2particles, as indicated by the considerably lower critical coagulation concentrations (CCC) (1.3 mM CaCl2vs 11 mM NaCl). The addition of EPS to the NaCl and low concentration CaCl2(0.05-10 mM) solutions resulted in a dramatic decrease in the aggregation rate and an increase in the CCC values. For solutions of 11 mM NaCl (the CCC values of TiO2in the absence of EPS) and above, the resulting attachment efficiency was less than one, suggesting that the adsorbed EPS on the TiO2nanoparticles led to steric repulsion, which effectively stabilized the nanoparticle suspension. At high CaCl2concentrations (10-40 mM), however, the presence of EPS increased the aggregation rate. This is attributed to the aggregation of the dissolved extracellular polymeric macromolecules via intermolecular bridging, which in turn linked the TiO2nanoparticles and aggregates together, resulting in enhanced aggregate growth. These results have important implications for assessing the fate and transport of TiO2nanomaterials released in aquatic environments.
authors: State Key Laboratory of Agricultural Microbiology, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China.
authors: Di
authors: D
authors: Lin
authors: Department of Chemical and Environmental Engineering, University of California, Riverside, CA 92521, USA.
authors: S
authors: S
authors: Drew Story
authors: Department of Chemical and Environmental Engineering, University of California, Riverside, CA 92521, USA.
authors: Sharon L
authors: SL
authors: Walker
authors: State Key Laboratory of Agricultural Microbiology, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China.
authors: Qiaoyun
authors: Q
authors: Huang
authors: State Key Laboratory of Agricultural Microbiology, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China. Electronic address: cp@mail.hzau.edu.cn.
authors: Peng
authors: P
authors: Cai
mesh_terms: D000327:Adsorption; D004573:Electrolytes; D007700:Kinetics; D053758:Nanoparticles; D011108:Polymers
chemical_list: D004573:Electrolytes; D011108:Polymers
keywords: Aggregation; DLS; EPS; TiO(2)