Impacts of pore size in binding dynamics of per- and polyfluoroalkyl substances (PFAS) on modified graphene materials

Abstract

Per- and polyfluoroalkyl substances (PFAS) have become ubiquitous surfactants in the environment with long lifetimes, and emerging toxic effects. Capture and removal of PFAS from aqueous media is an important step in the treatment train along with the concentration and destruction of PFAS. Particularly PFAS with shorter alkyl chain lengths have proven to be difficult to remove from water. As a result of partial degradation from longer PFAS's as well as their enhanced mobility in the environment, short-chain PFAS are very prolific making them a high-target focus for PFAS removal research. Using molecular dynamics simulations of functionalized graphene oxide pores, we have shown that the selectivity and capacity of adsorption media for differing tail lengths of linear PFAS are impacted by the size of the material's nanoporosity. The relationship between PFAS transport and pore size is not monotonic and different PFAS have different critical pore diameters with a minimum in transport resistance enabling an effective mechanism for PFAS specificity. More pragmatically, we have identified critical pore diameters that impact the thermodynamics and kinetics of PFAS binding and transport. For example, selectivity towards PFBA is highest in pores of 9 Å diameter. These results imply design parameters with which to tune adsorption media to different partitioning, transport, and selectivity towards different PFAS.