Mechanistic insights into the removal of PFOA by 2D MXene/CNT membrane with the influence of Ca2+ and humic acid

Abstract

Perfluorooctanoic acid (PFOA) is regarded as persistent and hazardous to ecosystems and human health, and its removal is therefore highly important. Herein, a two-dimensional MXene/CNT membrane was fabricated and evaluated for the removal of PFOA from aqueous solution, wherein the membrane exhibited outstanding water permeation without the sacrifice of PFOA rejection. To clarify the mechanistic of PFOA coexistence with Ca2+ and humic acid on membrane fouling, the fouling experiments were carried out by MXene/CNT membrane over a range of feed concentrations. Density functional theory (DFT) further revealed the interactions during the fouling process at the molecular level. The results demonstrated that hydrogen bonding interaction was dominant when the contaminants interacted with membrane at the initial stage and there was a decrease in the hydrogen bonding with the Ca2+ concentrations increased. Subsequently, the complexation interaction was predominant during the formation of cake layer. The complexation interaction was strengthened with the increasing of Ca2+ concentrations, forming the complexes with larger and looser structures, which would be responsible for the higher permeability. These results offer an important insight into the mechanism of MXene-CNT membrane fouling and demonstrate that DFT could be a useful tool to explore other complicated interaction processes in membrane fouling.