Half-wave rectified alternating current electrochemical-assembled devices for high-capacity extraction of Pb2+ from dilute wastewater

The selective capacitive removal (SCR) of toxic but valued lead ions (Pb2+) from dilute wastewater is challenging for water purification since valueless and nontoxic alkali metal ions (like Na+) often dominate typical metal-containing industrial effluents. Herein, novel devices were assembled based on the half-wave rectified alternating current electrochemical (HWACE) method, and a self-support chitosan-modified carbon felt (Chitosan/CF) electrode was constructed to boost the SCR of (Pb2+) from dilute wastewater. The characterization results of the Chitosan/CF electrodes indicated robust mechanical stability, good hydrophilia, and highly capacitive properties owing to the presence of abundant surface functional groups (-NH2, –OH). The assembled devices exhibited high extract performances under various conditions. Nearly complete removal of Pb2+ was achieved in a binary solution containing 50 ppm Pb2+ and 100 ppm Na+ at power supply parameters of the voltage of 5 V, frequency of 600 Hz, and flow rate of 8 mL/min within 24 h with a maximum removal efficiency reaching ∼99.4% and barely changed the concentration of Na+. Here, the fast growth of lead dendrites on the electrode surface was readily visible with naked eyes after 6 h. The characterization data of the Chitosan/CF electrode after HWACE extraction showed the presence of metallic lead (Pb0), suggesting further electroreduction of Pb2+ into neutral particles after adsorption on the electrode surface. The mechanism taking place at the cathode during the whole HWACE extraction process can best be described by Pb2+ reduction as the dominant process in early-stage and layered double hydroxide (LDH) precipitation at the late stage. The neutralized lead particles alleviated the Coulombic repulsion for sequent Pb2+ transformation, instantaneously leading to a nucleation mechanism for the continuous revival of lead particles. As a result, a rather high capacity >2500 mg/g was recorded, outperforming traditional SCR methods. Therefore, the constructed devices provided a new promising way for SCR of Pb2+ from typical metal-containing wastewater. In addition, the suggested process can be scalable and integrable with dilute wastewater treatment or full resource recovery sewage treatment plant.