Enhanced adsorption of perfluorooctanesulfonic acid (PFOS) in fluorine doped mesoporous carbon: Experiment and simulation

Abstract

Per- and polyfluoroalkyl substances (PFAS) are new types of emerging pollutants that have contaminated major water sources of developed and developing countries. Porous carbon-based materials are considered as universal adsorbents of all types of PFAS molecules. We have synthesized bimodal mesoporous carbon with fluorine and nitrogen functionalities for better removal for perfluorooctanesulfonic acid (PFOS) as the model PFAS molecule. All the mesoporous carbons with fluorine functionalities demonstrated the better adsorption of PFOS, and the adsorption amounts were better than that of commercial activated carbon. Kinetics measurements confirmed a remarkable improvement in saturation time of mesoporous carbon (1 h) compared to that commercial carbon (50 h). This mesoporous carbon also successfully removed PFAS from different complex matrices, including influent and effluent wastewater, and landfill leachate. Molecular simulation results revealed that presence of fluorine on the carbon surface increases the hydrophobicity of the carbon surface and Lennard-Jones (LJ) potential of the PFOS with the carbon leading to the enhanced adsorption of PFOS. Simulation study confirms that the presence of fluorine provides a good interaction of PFOS with the carbon surface. Molecular simulation also revealed that, despite nitrogen functionalities decrease hydrophobicity of the carbon surface, it may increase the LJ potential of PFOS with carbon surface leading to enhanced PFOS adsorption. However, as the improvement in LJ potential may be caused by much higher nitrogen content than what is present in the current system, it can be confirmed that the elevated PFOS adsorption is primarily contributed by the fluorine functionalities.