Fate of 14C-labeled few-layer graphene in natural soils: competitive roles of ferric oxides

Abstract

Extensive application of graphene-based nanomaterials will inevitably lead their release into soil. However, the retention and migration of graphene in natural soils are still unknown, due to the limitation on quantification methods. In this study, a carbon-14 isotope labeling technique was applied to systematically investigate the immobilization, transportation and transformation of ¹⁴C-labeled few-layer graphene (FLG) in two typical soils (red soil and black soil) with specifically different compositions. The adsorption capacity of red soil for FLG was 10.2 times higher than that of black soil at the same initial FLG concentration. Ferric oxides were identified as the predominant component governing the retention of FLG in soils through electrostatic attraction, leading to a significant difference on the adsorption performance between the two soils. Meanwhile, in the presence of naturally generated H₂O₂, ferric oxides were spontaneously employed as a catalyst to trigger a heterogeneous Fenton reaction to degrade FLG into the gas phase as CO₂, indicating an important pathway for the discharging of FLG from soil. Thus, this study clearly indicates the competitive roles of ferric oxides in restricting the mobility or facilitating the transformative release of graphene in natural soils, providing new insights into the environmental fate of carbon nanomaterials in real soil.