title: Effect of different-sized colloids on the transport and deposition of titanium dioxide nanoparticles in quartz sand.
abstract: Colloids (non-biological and biological) with different sizes are ubiquitous in natural environment. The investigations regarding the influence of different-sized colloids on the transport and deposition behaviors of engineered-nanoparticles in porous media yet are still largely lacking. This study investigated the effects of different-sized non-biological and biological colloids on the transport of titanium dioxide nanoparticles (nTiO2) in quartz sand under both electrostatically favorable and unfavorable conditions. Fluorescent carboxylate-modified polystyrene latex microspheres (CML) with sizes of 0.2-2 μm were utilized as model non-biological colloids, while Gram-negative Escherichia coli (∼ 1 μm) and Gram-positive Bacillus subtilis (∼ 2 μm) were employed as model biological colloids. Under the examined solution conditions, both breakthrough curves and retained profiles of nTiO2 with different-sized CML particles/bacteria were similar as those without colloids under favorable conditions, indicating that the copresence of model colloids in suspensions had negligible effects on the transport and deposition of nTiO2 under favorable conditions. In contrast, higher breakthrough curves and lower retained profiles of nTiO2 with CML particles/bacteria relative to those without copresent colloids were observed under unfavorable conditions. Clearly, the copresence of model colloids increased the transport and decreased the deposition of nTiO2 in quartz sand under unfavorable conditions (solution conditions examined in present study). Both competition of deposition sites on quartz sand surfaces and the enhanced stability/dispersion of nTiO2 induced by copresent colloids were found to be responsible for the increased nTiO2 transport with colloids under unfavorable conditions. Moreover, the smallest colloids had the highest coverage on sand surface and most significant dispersion effect on nTiO2, resulting in the greatest nTiO2 transport.
authors.affiliation: The Key Laboratory of Water and Sediment Sciences, Ministry of Education, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871, PR China; Currently at Natural History Research Center, Shanghai Natural History Museum, Shanghai Science and Technology Museum, Shanghai, 200127, PR China.
authors.forename: Li
authors.initials: L
authors.lastname: Cai
authors.affiliation: School of Environment and Energy, Shenzhen, Shenzhen Graduate School of Peking University, Shenzhen, 518055, PR China.
authors.forename: Shengnan
authors.initials: S
authors.lastname: Peng
authors.affiliation: The Key Laboratory of Water and Sediment Sciences, Ministry of Education, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871, PR China.
authors.forename: Dan
authors.initials: D
authors.lastname: Wu
authors.affiliation: The Key Laboratory of Water and Sediment Sciences, Ministry of Education, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871, PR China. Electronic address: tongmeiping@pku.edu.cn.
authors.forename: Meiping
authors.initials: M
authors.lastname: Tong
mesh_terms: D003102:Colloids; D008863:Microspheres; D008956:Models, Chemical; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D011137:Polystyrenes; D016062:Porosity; D011791:Quartz; D012822:Silicon Dioxide / Q000737:chemistry*; D012996:Solutions; D055672:Static Electricity; D014025:Titanium / Q000032:analysis*
chemical_list: D003102:Colloids; D011137:Polystyrenes; D012996:Solutions; D011791:Quartz; C009495:titanium dioxide; D012822:Silicon Dioxide; C024075:styrofoam; D014025:Titanium
keywords: Bacteria; Different-sized colloids; Microspheres; Quartz sand; nTiO(2)