Novel Perfluorooctanesulfonate-Imprinted Polymer Immobilized on Spent Coffee Grounds Biochar for Selective Removal of Perfluoroalkyl Acids in Synthetic Wastewater

Wastewater is an important source of perfluoroalkyl acids (PFAAs) to environmental waters. PFAAs are poorly removed during conventional wastewater treatment and only moderately removed by non-selective adsorbents [e.g., activated carbon (AC)]. Molecularly imprinted polymers (MIPs) enable selective adsorption of trace organics (e.g., PFAAs) by templating polymerization with a target compound; however, MIP morphology limits use for wastewater treatment. To overcome this obstacle, a perfluorooctanesulfonate (PFOS)-templated MIP was immobilized on spent coffee grounds biochar─an eco-friendly AC alternative─via radical initiated polymerization. Vinylbenzyl trimethylammonium chloride (VBTAC) and/or 2-(trifluoromethyl)acrylic acid served as functional monomers for MIP synthesis. First, biochar surfaces were functionalized with −NH MIP attachment points via (i) electrophilic aromatic substitution followed by reduction or (ii) heat-catalyzed addition of melamine. Melamine-modified biochar functionalized with VBTAC-MIP (BC-M@MIP-V) demonstrated high PFOS selectivity (Kselectivity of 4.52 for perfluorobutanesulfonic acid and 3.76 for perfluorooctanoic acid) and PFAA adsorption comparable to unmodified biochar in ultrapure water (0.043 and 0.039 mg PFAA/g*g/m2, respectively). Adsorption by BC-M@MIP-V increased by 0.012 mg PFAA/g*g/m2 in synthetic wastewater due to reduced MIP swelling and non-specific binding. Single-cycle regeneration of the BC@MIP composites suggest that long material lifetimes are possible. These novel, selective adsorbents present a potential alternative for effective wastewater PFAA treatment.