Transportation mechanisms of bubble-enhanced PFOS degradation by plasma

Plasma treatment demonstrated effective degradation of perfluorooctane sulfonic acid (PFOS), with bubble injection in liquid surface discharge systems serving to substantially accelerate the reaction kinetics and improve overall efficiency. This study analyzed the mechanisms promoting decomposition, with particular emphasis on bubble-mediated mass transfer. Bubble generation in the liquid phase created new gas-liquid interfaces where PFOS molecules adsorb onto bubble surfaces and were transported to the liquid surface during bubble ascent. Through measurements of static and dynamic surface tension of PFOS solutions at different concentrations, the variation patterns of surface concentration at different bulk solution concentrations and the temporal evolution of surface concentration during the adsorption process were determined using the Gibbs adsorption isotherm and the Langmuir model. Degradation experiments were conducted at shorter time intervals to gain deeper insights into the dynamic changes in bubble transport rates during PFOS decomposition. Calculations revealed that the quantity of PFOS transported by bubbles was nearly four orders of magnitude lower than the total amount decomposed. This indicates that mass transfer resulting from adsorption on rising bubbles did not play a dominant role. Liquid flow was observed and simulated, and the results demonstrated that the promotional effect of bubble supply on decomposition primarily originates from liquid convection and foam formation.