Highly effective removal of perfluorooctanoic acid (PFOA) in water with DBD-plasma-enhanced rice husks

Abstract

Adsorption is regarded as an efficient method to eliminate per- and polyfluoroalkyl substances from an aqueous solution. In the present investigation, an adsorbent based on rice husks (RHs) was successfully prepared by phosphoric acid (PA) activation and dielectric barrier discharge (DBD) plasma treatment, and it was used to adsorb perfluorooctanoic acid (PFOA) from water. The electrodes employed in the experiment were planar type. This research investigated RH surface properties and adsorption capacity before and after modification using DBD plasma. The results revealed that the He–O2 plasma modification introduced oxygen-containing functional groups and increased the PFOA removal efficiency. Increasing the oxygen content and total gas flow rate to 30 vol.% and 1.5 L/min, respectively, with 10 min of RH plasma treatment time at 100 W plasma discharge power enhanced the PFOA removal efficiency to 92.0%, while non-treated RH showed the removal efficiency of only 46.4%. The removal efficiency of the solution increased to 96.7% upon adjusting the pH to 4. The adsorption equilibrium isotherms fitted the Langmuir model, and the adsorption kinetic followed the pseudo-second-order model. The maximum adsorption capacity was 565 mg/g when the Langmuir isotherm model was applied.

Investigation of Kinetic, Equilibrium, and Thermodynamic Modeling of Perfluorooctanoic Acid (PFOA) Adsorption in the Presence of Natural Organic Matter (NOM) by Dielectric Barrier Discharge Plasma-Modified Granular Activated Carbon (GAC)

“…The adsorption mechanism of PFOA onto GAC can occur through direct adsorption and bridging effects facilitated by NOM. PFOA can adsorb directly onto the GAC through the hydrogen bond interaction with the OCFGs [64]. However, NOM can act as a bridge, enhancing the affinity of GAC for PFOA and thereby increasing the ACP at equilibrium.…”

“…Furthermore, these charged species within NOM can interact with the charged sites on the GAC surface through electrostatic interaction. The oxygen content introduced by the plasma treatment can increase the negative surface charge on the GAC surface [64]. Both of the GAC surface and NOM species that carry negative charges may be more electrostatically repelled by this enhanced negative charge.…”