(537a) Altering Å-Scale Interfacial Clusters Using Functionalized Nano-Porous Graphene for Enhanced Evaporative Separations of Methanol Water Solutions.

Functionalized nanoporous graphene (FNPG) has recently been shown to enhance the room temperature evaporative flux of water 30-fold, by altering the local interfacial thermodynamics and relaxation dynamics [ACS Nano 16,15328, 2022]. Using molecular dynamics simulations, we exploit the enhanced evaporation potential of graphene nanopores to study the potential for evaporative separation of water-methanol mixtures with d_eff~1 nm -H and -OH edge functionalized pores placed at the vapor-liquid interface. The evaporative flux of both methanol and water are enhanced by a factor of 2.5 - 6 at lower methanol concentrations when compared with the bare interface evaporation, with greater enhancements observed for -OH functionalized pores. A strong selectivity preference for methanol occurs at higher methanol compositions. Enhanced local demixing of methanol and water, leads to a substantial reduction in water evaporative flux for select conditions, yielding large enhancements in methanol selectivity ranging from 10 to 17 compared to bare interface evaporation.

For the bare interface, methanol exists predominantly as single molecule clusters and evaporation is found to occur from methanol rich regions of the interface. In contrast, water evaporation requires a water molecule to be released by breakage from strongly hydrogen bonded interfacial water clusters. The nanopore edge retards interfacial water cluster dynamics with relaxation times increasing three to fourfold at higher methanol fractions. Our study provides molecular insights into the structure and dynamics at methanol-water interfaces and how interfacial structures are modified in the presence of functionalization nanporous graphene. Specific edge functionalization can be used to suppress water evaporation to potentially create energy efficient liquid mixture separation systems