Electrochemical dechlorination of chloroacetic acids (CAAs) using hemoglobin-loaded carbon nanotube electrode

Hemoglobin (Hb) was immobilized on carbon nanotube (CNT) electrode to catalyze the dechlorination of chloroacetic acids (CAAs), and the electrocatalytic behaviors of the Hb-loaded electrode for the dechlorination of trichloroacetic acid (TCAA) were studied by cyclic voltammetry and constant-potential electrolysis technique. An Hb-loaded packed-bed flow reactor was also constructed for bioelectrocatalytic dechloriantion of CAAs from drinking water. The results showed that the reduced heme of Hb immobilized on CNT electrode was easily regenerated, and Hb exhibited a stable and high activity for reductive dechlorination of CAAs with significant lowering of overpotential. TCAA could be reduced at -0.450 V (vs. saturated calomel electrode (SCE)) with catalysis of Hb-loaded electrode and its dechlorination was stepwise, following the pathway of TCAA-->dichloroacetic acid (DCAA)-->monochloroacetic acid (MCAA)-->acetic acid. It was also found that all CAAs, e.g., TCAA, DCAA and MCAA, could be dechlorinated completely at -0.450 V. The removal of 30.0 mM TCAA and DCAA is ca. 40% and 31%, respectively, with electrolysis for 100 min at -0.600 V (vs. SCE) using the Hb-loaded packed-bed flow reactor. The dechlorination activities of CAAs follow the decreasing order: TCAA>DCAA>MCAA, and the average current efficiency is over 90%.