Synergistic enhancement of hexavalent chromium electroremediation via phosphonium-modified chitosan electrode under alternating potential

Electrochemical removal of hexavalent chromium, Cr(VI), from aqueous systems is a kinetically challenging process. In this study, the influence of sorptive electrode and alternating potential on the kinetics of Cr(VI) electrochemical removal was investigated using electrodes with different Cr(VI) adsorption performance. The phosphonium-modified chitosan (CS-P) electrode outperformed chitosan and carbon paper electrodes, achieving 36.4 % and 63.2 % higher removal efficiencies, respectively. Notably, the Cr(VI) removal efficiency of the CS-P electrode under alternating potential was 1.78 times that under direct potential. CS-P electrode operated under periodic anodic (+0 V vs. Ag/AgCl) and cathodic potentials (−1.0 V vs. Ag/AgCl) with durations of 0.5 s and 1 s, respectively, reduced 5–50 mg/L Cr(VI) at pH ∼ 3.0 to < 0.5 mg/L within 15–30 min. Cr(VI) was removed as Cr(III) with ∼60 % remaining in the solution and ∼40 % deposited on the electrode. The initial Cr(VI) removal kinetics was found to increase linearly (R 2  = 0.978) with the increase in the adsorbed amount of Cr(VI) on the electrode, which could be explained by an adsorption-electroreduction model. The results give insights into the key factors governing Cr(VI) electroreduction and provide a simple and effective way for the treatment of water contaminated by Cr(VI).