Measuring Adsorption Enthalpies of PFOS and Organics on Carbon Fiber Paper

In the PFAS remediation process developed by the Müller group, PFAS are electrocatalytically defluorinated using electrodes made from hydrophilic carbon fiber paper [1]. This process relies on the PFAS first adsorbing to the carbon fiber paper electrode. This study aims to investigate whether the enthalpy of this adsorption has any correlation to the efficiency of the defluorination across various PFASs. We started with perfluorooctane sulfate (PFOS) to develop a protocol. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to identify the temperature region of desorption and subsequently measure the heat capacity change over this range of desorption. The heat capacity was then integrated according to the formula ΔH= ∫CpdT to derive the change in enthalpy of the process. It was found that PFOS desorbs from the carbon fiber paper at 400°C. However, the DSC is not able to differentiate between heat capacity changes due to desorption and those due to degradation of PFOS or the carbon fiber paper, so further research is needed to separate these events and determine the desorption enthalpy.

[1] Z. Meng, M.K. Wilsey, C.P. Cox, A.M. Müller, Complete electrocatalytic defluorination of perfluorooctane sulfonate in aqueous solution with nonprecious materials. J. Catal. 2024, 431, 115403.