Modelling of PFAS-surface interactions: Effect of surface charge and solution ions

Area of Science:

• Environmental Chemistry
• Surface Science
• Computational Chemistry

Background:

• Per- and poly-fluoroalkyl substances (PFAS) are persistent environmental contaminants of growing concern.
• Understanding PFAS interactions with surfaces is crucial for predicting their environmental fate and developing remediation strategies.
• Previous research indicates PFAS adsorption is influenced by factors like pH, organic matter, particle size, PFAS functional group, and carbon chain length.

Purpose of the Study:

• To theoretically examine per- and poly-fluoroalkyl substances (PFAS)-surface interactions using Monte Carlo molecular simulations.
• To investigate the impact of varying surface charge, H+, OH-, Ca2+ concentrations, and PFAS carbon chain length on PFAS adsorption.
• To provide insights into the thermodynamic equilibrium behavior of PFAS at low concentrations for remediation applications.

Main Methods:

• Monte Carlo molecular simulations were employed to model the interactions between perfluorooctane and perfluorobutane sulfonic acids and a graphite surface in an aqueous environment.
• Simulations systematically varied surface charge, and concentrations of H+, OH-, and Ca2+.
• Adsorption was quantified by analyzing the distance-dependent density of molecules near the surface.

Main Results:

• Simulation results demonstrated that surface charge, H+, OH-, and Ca2+ concentrations, and PFAS carbon chain length all influence PFAS surface behavior.
• Surface charge was identified as the most significant factor controlling PFAS adsorption.
• Divalent cation bridging, specifically with Ca2+, was observed for PFAS adsorption onto negatively charged surfaces.

Conclusions:

• Theoretical modeling of PFAS-surface interactions provides valuable data for understanding PFAS environmental behavior.
• Surface charge plays a dominant role in regulating PFAS adsorption, with implications for remediation.
• This modeling approach can aid in the design and evaluation of sorptive materials for PFAS remediation, particularly in scenarios involving both adsorption and mobility.