Triazine- and Heptazine-Based Porous Organic Polymer Networks for the Efficient Removal of Perfluorooctanoic Acid

The presence of perfluorooctanoic acid, a perfluoralkyl substance, in water sources has raised health concerns due to its toxicity. Finding effective adsorbents is essential to ensure healthy sources of water for consumption. In this study, a heptazine-based polymer network (Py-HPOP) was synthesized using a one-pot nucleophilic substitution of 2,5,8-trichloro-s-heptazine (TCH) with 4,4′,4″,4‴-(pyrene-1,3,6,8-tetrayl) tetraaniline (Py-TA). For comparison, a triazine-based polymeric network (Py-TPOP) was also prepared using 2,4,6-trichloro-1,3,5-triazine under similar conditions. Both polymers were used to treat aqueous solutions containing 1 mg/L PFOA. Py-TPOP exhibited superior adsorption capacity (98.4% PFOA removal) relative to Py-HPOP (80.8% PFOA removal) despite Py-HPOP’s higher Brunauer–Emmett–Teller (BET) surface area SBET at 205 m2 g–1. The effect of electrostatic interactions was also observed as a critical factor for PFOA adsorption as demonstrated by the change in PFOA adsorption by both polymers under basic, neutral, and acidic conditions. This investigation illustrates a facile synthesis of amorphous covalent frameworks as strong, competitive adsorbents for PFOA removal from water.