title: Detachment of fullerene nC60 nanoparticles in saturated porous media under flow/stop-flow conditions: Column experiments and mechanistic explanations.
abstract: This study was aimed at investigating the detachment of fullerene nC60 nanoparticles (NPs) in saturated sand porous media under transient and static conditions. The nC60 NPs were first attached at primary minima of Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy profiles in electrolyte solutions with different ionic strengths (ISs). The columns were then eluted with deionized water to initiate nC60 NP detachment by decreasing solution IS. Finally, the flow of the columns was periodically interrupted to investigate nC60 NP detachment under static condition. Our results show that the detachment of nC60 NPs occurred under both transient and static conditions. The detachment under transient conditions was attributed to the fact that the attractions acting on the nC60 NPs at primary minima were weakened by nanoscale physical heterogeneities and overcome by hydrodynamic drags at lower ISs. However, a fraction of nC60 NPs remained at shallow primary minima in low flow regions, and detached via Brownian diffusion during flow interruptions. Greater detachment of nC60 NPs occurred under both transient and static conditions if the NPs were initially retained in electrolyte solutions with lower valent cations due to lower attractions between the NPs and collectors. Decrease in collector surface chemical heterogeneities and addition of dissolved organic matter also increased the extent of detachment by increasing electrostatic and steric repulsions, respectively. While particle attachment in and subsequent detachment from secondary minima occur in the same electrolyte solution, our results indicate that perturbation in solution chemistry is necessary to lower the primary minimum depths to initiate spontaneous detachment from the primary minima. These findings have important implications for predicting the fate and transport of nC60 NPs in subsurface environments during multiple rainfall events and accordingly for accurately assessing their environmental risks.
authors.affiliation: Department of Soil and Water Sciences, China Agricultural University, Beijing 100193, China; College of Land and Environment, Shenyang Agricultural University, Shenyang, Liaoning 110866, China.
authors.forename: Zhan
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19716, United States.
authors.forename: Dengjun
authors.initials: D
authors.lastname: Wang
authors.affiliation: Department of Soil and Water Sciences, China Agricultural University, Beijing 100193, China.
authors.forename: Baoguo
authors.initials: B
authors.lastname: Li
authors.affiliation: School of Resources and Environmental Engineering, Hefei University of Technology, Hefei, Anhui 230009, China.
authors.forename: Jizhong
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Soil and Water Sciences, China Agricultural University, Beijing 100193, China.
authors.forename: Tiantian
authors.initials: T
authors.lastname: Li
authors.affiliation: Department of Soil and Water Sciences, China Agricultural University, Beijing 100193, China.
authors.forename: Mengjia
authors.initials: M
authors.lastname: Zhang
authors.affiliation: Department of Soil and Water Sciences, China Agricultural University, Beijing 100193, China.
authors.forename: Yuanfang
authors.initials: Y
authors.lastname: Huang
authors.affiliation: Department of Soil and Water Sciences, China Agricultural University, Beijing 100193, China. Electronic address: chongyang.shen@cau.edu.cn.
authors.forename: Chongyang
authors.initials: C
authors.lastname: Shen
mesh_terms: D004058:Diffusion; D037741:Fullerenes / Q000737:chemistry*; D057446:Hydrodynamics; D009994:Osmolar Concentration; D016062:Porosity; D012822:Silicon Dioxide / Q000737:chemistry; D055672:Static Electricity
chemical_list: D037741:Fullerenes; D012822:Silicon Dioxide; C069837:fullerene C60
keywords: Attachment; Brownian diffusion; Detachment; Fullerene nC(60) nanoparticles; Porous media; Transport