Different Cr(VI)-sequestration behaviors between carbon nanoparticles and their agglomerates

Abstract

Aggregation of carbon nanoparticles (CNPs) exerts significant influence on its surrounding environment. To comprehensively evaluate their environmental impacts, it is essential to clarify the relationship between CNP monomers, agglomerates, and their sorption and photocatalysis behaviors. In this work, three agglomerates were prepared by crosslinking one-dimensional oxidized carbon nanotubes (OCNTs), quasi one-dimensional oxidized graphene ribbons (OGRs), and two-dimensional graphene oxide sheets (GOs) with polyacrylamide hydrochloride (PA). Notably, the sorption and photo-reduction behaviors of Cr(VI) are different on the surfaces of CNPs monomers and agglomerates. Overall, all the agglomerates demonstrated higher Cr(VI)-sequestration capacities than the corresponding monomers regardless of dark environment and light irradiation. For CNPs monomers, chromium species were scarcely adsorbed on the particle surface in the dark; the sunlight illumination promoted significantly the transformation of Cr(VI) ions to solid Cr(OH)3, resulting in sequestration capacities of 16.7, 47.7, and 115.4 mg/g in OCNTs, OGRs and GOs, respectively. After crosslinked by PA, the total sequestration capacity of Cr(VI) pollutants in the agglomerates increased by 3.4 ∼ 21.4 times compared to their corresponding monomers. It was noteworthy that the agglomerates almost converted all of Cr(VI) to Cr2O3 under the illumination. This study highlights the discrepancies in Cr(VI)-sequestration behavior between CNPs and their agglomerates, which provides a novel insight into environmental impacts of CNPs and their agglomerates in nature.