Enhanced capacitive deionization of lead ions using air-plasma treated carbon nanotube electrode

Carbon nanotube (CNT) electrodes, made of the CNT and polytetrafluoroethylene mix coating on stainless steel, were activated by air-plasma for 5 min to prepare P-air electrodes, then the electrodes were assembled into capacitors for capacitive deionization (CDI) of lead (II) ions. After plasma activation, the relative oxygen and nitrogen content (atom %) of the P-air electrodes increased from 3% and 0% to 17.4% and 2.7%, respectively, as compared with electrodes without plasma treatment. As a result, hydrophilicity of the electrode surface was enhanced significantly. In addition, the plasma activation enables the BET specific surface area (SSA) of the P-air electrodes to increase from 95 to 106 m2/g, and the specific capacitance of P-air electrodes to raise from 30 to 43 F/g in 50 mg/L lead solutions. Also, the CDI capacity of P-air electrode, at voltage of 450 mV and initial concentration of 5 mg/L, were enhanced from 1.36 mg/g to 2.40 mg/g with the plasma treatment. Further study demonstrates that the CDI kinetics of the P-air electrodes for removal of lead ions follows pseudo-first-order reaction. The ion removal process agrees with the Gouy–Chapman–Stern model.