Colloidal Properties and Stability of Aqueous Suspensions of Few Layer Graphene: Importance of Graphene Concentration
Yu Su, Elijah Petersen, Liang Mao
Understanding the agglomeration behaviors and stability of graphene in natural waters is essential for predicting its transport and fate in aquatic environments. In this study, the agglomeration and stability of 14C labeled few layer graphene (FLG) were investigated at concentrations spanning over four orders of magnitude (2 μg/L to 10 mg/L) by using dynamic light scattering and sedimentation measurements. Our results showed that transition from concentrated to dilute suspension significantly retarded the agglomeration of FLG. At higher FLG concentrations (≥ 2.5 mg/L), rapid agglomeration of FLG was initiated within one hour at low electrolyte concentration (e.g., 1.1 mmol/L NaCl) and even in de-ionized water. In contrast, FLG suspensions with lower concentrations (≤ 0.5 mg/L) were less susceptible to cation-induced agglomeration (up to 1000 mmol/L NaCl), and the formation of FLG aggregates typically took several hours. Nevertheless, at FLG concentration greater than 2.0 mg/L, the agglomeration of FLG varied with ionic strength (IS) and valence of the cation in a manner consistent with the DLVO theory. The critical coagulation concentration (CCC) of FLG (1 mg/L) was determined to be 10 mmol/L NaCl and 2.8 mmol/L CaCl2. The presence of natural organic matter (NOM) effectively enhanced the stability of FLG due to electrostatic and steric repulsion, as evidenced by the higher CCC for the two salt types (95 mmol/L NaCl and 11 mmol/L CaCl2). Long-term stability studies verified that as a result of combined effects of IS and NOM FLG at low concentrations (4 μg/L and 50 μg/L) undergo slow agglomeration and sedimentation in most ambient waters except for seawater. These findings suggest that FLG is relatively stable in natural and engineered aqueous systems at low concentrations (≤50 μg/L) but unstable at concentrations higher concentrations (≥ 2.5 mg/L).
, Petersen, E.
and Mao, L.
Colloidal Properties and Stability of Aqueous Suspensions of Few Layer Graphene: Importance of Graphene Concentration, Environmental Science and Technology, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=918821
(Accessed June 7, 2023)