环境地球化学国家重点实验室知识库

The surface properties, chemical compositions, and crystal structures of manganese oxides can be altered by redox reactions, which affect their heavy metal ion adsorption capacities. Here, birnessite nanosheets (delta-MnO2) were synthesized from the photochemical reaction of Mn-aq(2+) and nitrate under solar irradiation, and Zn2+ was electrochemically adsorbed using the as-obtained birnessite nanosheets by galvanostatic charge-discharge. The effects of current density and electrochemical techniques (symmetric electrode and three-electrode systems) on Zn2+ adsorption capacity were also investigated. The results showed that the maximum Zn2+ adsorption capacity of the birnessite in the presence of electrochemical redox reactions could reach 383.2 mg g(-1) (589.0 mmol mol(-1)) and 442.6 mg g-(1) (680.3 mmol mol(-1)) in the symmetric electrode and three-electrode system, respectively; however, the Mn2+ release capacity in the three-electrode system was higher than that in the symmetric electrode system. With increasing current density, the Zn2+ adsorption capacity decreased. In addition, the system for heavy metal ion removal driven by electrochemical redox reactions could also be used as a supercapacitor for power storage. The present work proposes a "green" and sustainable approach for preparing nanosized birnessite, and it clarifies the adsorption mechanism of birnessite for Zn2+ in the presence of electrochemical redox reactions.