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, however, the possible mechanisms remain unclear. Dynamic light scattering techniques combined with a multiple regression model were applied to explore the influence of FA sub-fractions (FApH3 − FApH13) on the aggregation kinetics of GO in aqueous environments. The ratios of critical coagulation concentration (CCC) values were CCCNa: CCCMg: CCCLa: CCCCe = 1:2–5.15:3–7.31:3–7.35, which were consistent with the Derjaguin−Landau−Verwey−Overbeek (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 pH values 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 the 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 were 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 using the multiple linear regression eq. 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 90 % prediction intervals, and the average error of the 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.