Adsorption of per- and polyfluoroalkyl substances (PFAS) such as PFOS using conventional adsorbents like activated carbon is challenging due to the nonselective removal mechanisms of activated carbons, and the low concentration of PFAS in environmental waters. Molecularly imprinted polymers (MIPs) are polymers synthesized by imprinting template compounds (e.g., PFOS) which results in high selectivity and demonstrated success for adsorption of long and short chain PFAS. However, MIPs produce fine particles amenable to packing in chromatography columns and may not be suitable for large-scale water treatment. To facilitate selective removal of PFAS over co-occurring contaminants, we modified biochar substrate surfaces with molecularly imprinted polymers (MIPs) templated with PFOS molecules. The biochar was prepared from pyrolysis and chemical activation (with potassium hydroxide, KOH) of spent coffee grounds (SCG) to generate a high surface area, carbonaceous substrate. The so-called “SCGKOH” biochar surface was modified with amine functional groups to chemically bind the synthesized PFOS-MIP. The PFOS adsorption removal was compared for three different functional monomers employed during MIP synthesis: vinylbenzyl trimethylammonium chloride, 2-(trifluoromethyl)acrylic acid and methacryloyloxyethyl trimethyl ammonium chloride. The vinylbenzyl trimethylammonium chloride-prepared PFOS-MIP composite, which exhibited the greatest PFOS removal, was further examined for adsorption selectivity over other co-occurring PFAS as well as other organic contaminants. Regeneration of the SCGKOH-MIP composite was also achieved using an 86% methanol and 14% acetic acid wash to enable multiple reuse cycles of the composite media. This material presents a more cost effective and sustainable alternative for targeted PFAS removal in water treatment through reduction of pretreatment requirements and increased material lifetime with low resource regeneration capability.

Targeted adsorption of perfluorooctanesulfonate (PFOS) using molecularly imprinted polymer-modified biochar

ACS Spring 2022

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