Decomposition of perfluorooctanic acid by carbon aerogel with persulfate

Thermally-activated persulfate (PS) has been recognized as one of the most effective Advanced oxidation processes (AOPs) to oxidize Persistent perfluorooctanoic acid (PFOA). Applications of Carbon aerogel (CA)-activated PS for PFOA decomposition at 25, 40, 50 and 60 °C were evaluated. With the presence of CA in PS oxidation, 85.7% of PFOA was decomposed to fluoride ions and intermediates of short-chain perfluorinated carboxylic acids (PFCAs) with a 34.5% defluorination efficiency at 60 °C after 8 h. PFOA was decomposed and mineralized to fluoride ions in the CA + PS system following a stepwise degradation process of C₆F₁₃COOH → C₅F₁₁COOH → C₄F₉COOH → C₃F₇COOH → C₂F₅COOH → CF₃COOH at 60 °C. The decomposition and defluorination rates of the combined CA + PS system at 60 °C were approximately 1.83 and 1.61 times faster than those of the PS-only system, respectively. With CA in the PS system, activation energies of PFOA removal and defluorination were significantly reduced from 66.8 to 37.2 and 97.3 to 49.2 kJ/mol, respectively. It implies that applying CA could effectively promote the PFOA degradation that leads to significant savings in energy consumption and reductions in process time. Characteristics of CA used were evaluated by using N₂ adsorption, zeta potential, Raman, SEM, XRD, XPS and FT-IR techniques. A quenching test was conducted by using methanol as an inhibitor and Electron spin resonance (ESR) spectra of free radicals were analyzed for development of proposed reaction mechanisms.