Electrodeposited birnessite thin film: An efficient eco-friendly sorbent for removing heavy metals from water

Abstract

Sorption is an efficient process for transferring heavy metals from polluted water to solid phase. Birnessite, which is a non-toxic layered manganese oxide, is particularly interesting for this objective due to its high sorption capacities towards heavy metals. In this paper, pure and nanostructured birnessite was synthesized as adherent thin films onto a solid substrate by electrochemistry with different characteristics for high sorption (e.g. mass, Average Oxidation States of Mn (AOS)). Sorption of lead (Pb (II)) and cadmium (Cd (II)) by these films was studied in terms of pH, ionic strength, sorption isotherm and kinetic order. The birnessite thin film with the highest AOS after synthesis (3.76) presents significant adsorption capacity for Pb (II) (538 mg-Pb/g) and Cd (II) (254 mg-Cd/g). A total decontamination at room temperature without filtration and energy input was obtained on model solutions and real effluents by increasing only the number of samples or the surface of electrodeposited birnessite on one sample. These birnessite thin films appear as very interesting eco-friendly sorbents for eliminating Pb (II) and Cd (II) from polluted aquatic media due to their easy synthesis and optimization process, and the possible reuses by efficient desorption in very low-cost conditions.