Uncovering the dual function of phytic acid in stabilizing graphene oxide nanomembranes and enabling selective permeation for oil-water separation by molecular dynamics simulations

Abstract

Phytic acid functionalized graphene oxide (GO-PA) is a promising membrane material for oily wastewater treatment. However, the effects of its structural parameters on membrane stability and oil-water separation performance remains unclear. This study performed molecular dynamics simulations to elucidate the underlying microscopic mechanisms. Results revealed that GO and PA spontaneously assembled into a stable sandwich-like membrane structure, wherein a highly oxidized lamellar GO framework enhanced PA accommodation. PA adsorbed robustly onto the GO surface through dense oxygen-containing functional groups, cross-liking adjacent GO sheets to precisely control interlayer spacing and suppress GO self-scrolling. Simulations further revealed that reduced GO oxygen coverage accelerated water permeation, while increasing the PA mixing ratio significantly improved oil-water separation performance, yielding a water flux of 4.1 molecules ns-1 and a separation efficiency of 96.3%. Energy analysis demonstrated that PA content dominated membrane hydrophilicity, imposing higher energy barriers for oil permeation than water. PA functionalization substantially enhanced the oil-water separation capability of GO membrane, with theoretical maxima reaching 97.5% separation efficiency and 98.8% water purity. These findings confirmed the dual role of phytic acid in stabilizing GO nanomembranes and promoting selective permeation of water and oil. The theoretical data derived from this study offered critical input for macroscopic process modelling and provided a foundation for engineering applications through rational design of materials and separation units (e.g. membrane reactor) under realistic operating conditions.