Electrochemical Assistant Adsorption Of PFOA And PFOS On Carbon Nanotubes And Activated Carbon Fibers

Both of carbon nanotubes (CNTs) and activated carbon fibers (ACFs) are new type of carbon nanomaterials with large specific surface area, high conductivity and good chemical stability, etc, which make them have promising potential in the field of electrosorption. However, their application as electrodes in electrosorption for the removal of perfluorocompounds (PFCs) is less reported; especially the research in the dynamic mode has not started yet. In this dissertation, a durable and convenient electrosorption device was used in continuous flow mode to investigate and optimize the adsorption of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) on multiwalled carbon nanotubes (MWNTs) and ACFs under electrochemical assistance. The objective of this work was to realize effective removal of PFOX (X=A and S) by conducting dynamic experiments with continuous flow mode, which provides theoretical guidance and reference for further design of the electrosorption device. Correspondingly, several studies were conducted as follows:(1) Electrophoretic deposition was employed to fabricate MWNTs electrodes. After sustaining at a potential of160V, the MWNTs membrane with uniform and compact morphology could obtained in both sides of the Ti plate, which was double-side MWNTs/Ti electrode. The electrochemical adsorption potential window of the electrodes was in the range of±1.5V. After MWNTs films deposition on the Ti plate, the surface electron transfer resistance (Ret) dropped to1.9Ω. from9.0Ω.(2) A durable and convenient electrosorption device with MWNTs electrodes was used to investigate the electrosorption performance for PFOA and PFOS in continuous flow mode. Moreover, voltage, influent concentration, HRT, electrode distance and electrolyte concentration were selected to explor the effects on the removal. The results showed that the highest removal efficiency of both PFOA and PFOS reached approximately90%at1V, and the adsorbed amount was found to be4.9times (PFOA) and4.2times (PFOS) s much as that of open circuit (OC) adsorption. The optimal conditions for our work were a voltage of1V, an influent concentration of50μg/L, HRT of30min, an electrode distance of6mm and electrolyte concentration of1mmol/L. In addition, MWNTs electrodes showed good reusability by reiteration experiments which proved the durability of the electrosorption device could be realized and made it possible to be easily applied in practice. (3) ACFs were preprocessed by HCl and NaOH, and the point of zero charge was6.4. ACFs showed stable electrochemical properties in the range of±1.5V as well. The original electrosorption device was remade with ACFs electrodes to investigate the effects of voltage and pH for PFOA and POFS removal under electrochemical assistance in continuous flow mode. The results showed that the adsorbed amount at1V was found to be2.2times (PFOA) and2.7times (PFOS) as much as that of open circuit (OC) adsorption. The adsorption performance of PFOA was affected by solution pH due to the electrostatic repulsion between ACFs electrode surface and PFOA anion. There was little or no effect on PFOS adsorption by pH, which was inferred to be a combination of electrostatic repulsion and hydrophobic effect.In this work, PFOA and PFOS were removed effectively on MWNTs and ACFs under electrochemical assistance adsorption, which promotes the development of electrosorption technology with carbon nanomaterials as adsorbent for refractory wastewater treatment, and provides reference for the design of the electrosorption device in the future.