Climate-zone-dependent effect mechanism of humic acid and fulvic acid extracted from river sediments on aggregation behavior of graphene oxide

Abstract

Climate factors could affect the physicochemical properties of dissolved organic matter (DOM) in river sediments, which potentially influence the stability of nanoparticles in natural waters. In this study, we extracted humic acid (HA) and fulvic acid (FA) from river sediments in different climate zones of China. Their effect with different concentrations (0.2 and 1 mg·C·L−1) on the aggregation kinetics of large (589 nm) and small graphene oxide (GO, 200 nm) in NaCl solutions was investigated. Both concentrations of HA/FA significantly inhibited the aggregation of small GO because of the steric forces rendered by DOM. For large GO, the inhibition effect of HA on aggregation was higher than FA because of the higher molecular weight, longer carbon chain length, and more structure complexity of HA. Interestingly, with 0.2 mg·C·L−1 HA and large GO, Makou in Subtropical monsoon climate zone decreased the aggregation rate more significantly due to its larger molecular weight, while, Maqin in the Plateau and mountain (PM) climate zone with smaller molecular weight and greater hydrophobicity showed lower inhibition effect on the aggregation. One mg·C·L−1 FA with high polarity from Tangke in PM climate zone and Panjin from Temperate monsoon climate zone showed more stability ability towards large GO. Derjaguin-landau-verwey-overbeek (DLVO) theory indicated that the interaction energy barrier between GO particles dependent on physicochemical characteristics of DOM and GO size. Understanding the climate-zone-dependent effect of sediment DOM on stability of GO is essential for anticipating its fate in natural systems.