Mesoporous Carbons and their Modification with Aliphatic Quaternary Amines for Adsorption, Thermal Treatment, and Preconcentration of Perfluorooctanoic Acid (PFOA)

Abstract

The establishment of the EPA’s new legally enforceable maximum levels for toxic per- and polyfluoroalkyl substances (PFAS) underscores the need for better remediation and low-level detection capabilities. With a unique porous structure and physicochemical properties, mesoporous carbon (MC) is a promising candidate as an adsorbent to capture PFAS and as a substrate to functionalize for improving selectivity and performance. Despite this potential, a comprehensive study with MC or their modification for the remediation and detection of PFAS is still lacking. Herein, we evaluated the adsorption, thermal stability, and preconcentration of perfluorooctanoic acid (PFOA) on three different MC materials: disordered carbon (DC) and two ordered carbons, CMK-3 and CMK-8. The MC materials were further successfully modified by functionalization with methyltrialkyl (C₈–C₁₀)ammonium (MTA). Adsorption isotherms for both functionalized and bare MC were constructed to understand the PFOA adsorption behavior. The adsorption capacity of MC ranged between 57.7 and 142.6 mg/g with the best performance observed for CMK-3. MTA functionalization of MC improved the PFOA adsorption capacity by 26–34% relative to bare MC. In addition, we demonstrated that the thermal degradation of PFOA may be improved using functionalized materials by inhibiting PFOA vaporization at temperatures insufficient for chemical decomposition. We also developed a method that used MC as a preconcentrator to analyze PFOA in a solution at a lower concentration.