High-performance Cu2+ adsorption of birnessite using electrochemically controlled redox reactions

Manganese oxides are proposed as superior adsorbents for heavy metal ions, and their adsorption capacities can be greatly improved by electrochemical methods. In this work, birnessite was used as electrode material for Cu2+ adsorption by multi-cycle electrochemical redox reaction. The effects of solution pH and potential window on Cu2+ electrosorption capacity were further investigated. The results showed that the electrosorption capacity for Cu2+ reached as high as 372.3 mg g(-1) by electrochemical redox, which was remarkably larger than the adsorption isotherm capacity (44.3 mg g(-1)). In addition, birnessite could be reused for many times after electrochemical activation. In the process of electrosorption, the amount of copper electrodeposited on the counter electrode accounted for less than 3.2% of the total removal capacity. The enhancement of Cu2+ adsorption capacity could be attributed to the changes in the chemical composition and the dissolution-recrystallization processes of birnessite during the electrochemical redox reactions. The electrosorption capacity increased with increasing pH from 3.0 to 5.0 and potential window width. The present work shows that controllable redox reaction of birnessite is a promising method for the removal of Cu2+ from wastewater.