title: Colloidal properties and stability of aqueous suspensions of few-layer graphene: Importance of graphene concentration.
abstract: Understanding the colloidal stability of graphene is essential for predicting its transport and ecological risks in aquatic environments. We investigated the agglomeration of14C-labeled few-layer graphene (FLG) at concentrations spanning nearly four orders of magnitude (2 μg/L to 10 mg/L) using dynamic light scattering and sedimentation measurements. FLG agglomerates formed rapidly in deionized water at concentrations >3 mg/L. From 1 mg/L to 3 mg/L, salt-induced agglomeration was decreased with dilution of FLG suspensions; the critical coagulation concentration of the more concentrated suspension (3 mg/L) was significantly lower than the dilute suspension (1 mg/L) in the presence of NaCl (1.6 mmol/L and 10 mmol/L, respectively). In contrast, FLG underwent slow agglomeration and settling at concentrations ≤0.1 mg/L in NaCl solutions and ambient waters with low ionic strength (<10 mmol/L). FLG nanoparticles with smaller lateral sizes (25 nm-75 nm) were shown to agglomerate more slowly than larger FLG, and these small FLG particles exhibited greater bioaccumulation in zebrafish embryo and stronger chorion penetration ability than larger FLG particles. These findings suggest that FLG at more environmentally relevant concentration is relatively stable and may have implications for exposure of small FLG to ecological receptors.
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, PR China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Su
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, PR China.
authors.forename: Guoqing
authors.initials: G
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, PR China.
authors.forename: Kun
authors.initials: K
authors.lastname: Lu
authors.affiliation: Material Measurement Laboratory, Biosystems and Biomaterials Division, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8311, Gaithersburg, MD 20899-0001, USA.
authors.forename: Elijah J
authors.initials: EJ
authors.lastname: Petersen
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, PR China. Electronic address: lmao@nju.edu.cn.
authors.forename: Liang
authors.initials: L
authors.lastname: Mao
mesh_terms: D000818:Animals; D004781:Environmental Exposure / Q000032:analysis*; D019015:Geologic Sediments; D006108:Graphite / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D009994:Osmolar Concentration; D010316:Particle Size; D012965:Sodium Chloride; D012996:Solutions; D013535:Suspensions; D014867:Water; D015027:Zebrafish / Q000378:metabolism
chemical_list: D012996:Solutions; D013535:Suspensions; D014867:Water; D012965:Sodium Chloride; D006108:Graphite
keywords: Agglomeration; Bioaccumulation; Graphene; Nanomaterial; Sedimentation