Influence of Fulvic Acid Sub-Fractions on Aggregation Kinetics of Graphene Oxide in Aqueous Environments

Abstract

Fulvic acid (FA) can affect the dispersion of graphene oxide (GO) in aquatic environments, while the possible mechanisms were still unclear. Dynamic light scattering techniques combined with a multiple regression model were applied to explore the influences of FA sub-fractions (FApH3-FApH13) on aggregation kinetics of GO in aqueous environments. The ratios of CCC values were CCCNa: CCCMg: CCCLa: CCCCe = 1:2-5.15:3-7.31:3-7.35, which were consistent with the DLVO theory and Schulze-Hardy rules. The GO remained stable at pH 3-10 and aggregated at pH <3 or pH >10, and its critical coagulation pHs (CCP) were 1.44 and 12.25 with 10 mM NaCl as background. The CCC values of GO in the presence of FApH3-FApH13 were greater than those in the absence of FA sub-fractions. The ratios of CCC values of GO (r) increased in the presence of FA sub-fractions in order of FApH13 > FApH9 > FApH7 > FApH5 > FApH3, and ranged from 1.01 to 2.15 for certain metal ions including Na+, Mg2+, La3+, and Ce3+. The CCC values of GO have significantly related to C, H, O, N, S, H/C, O/C, Carboxylic C, and Carbonyl C of FA sub-fractions (P <0.05), respectively, and could be predicted with the multiple linear regression equation of CCC, CCC = Z-n (98.959 - 60.911 * O/C + 4.799 * O-alkyl C - 0.845 * Aromatic C - 6.237 * Carbonyl C). The predicted CCC values for GO were within the 90% prediction intervals and the average error of CCC values was 3.3% and R2 =0.986. This investigation is expected to provide a scientific basis for the transport and ecotoxicity of GO in environments.

Keywords: Fulvic acid sub-fractions, Graphene oxide, Aggregation kinetics, Model prediction