Abstract: The present invention relates to composite beads coated with H-Birnessite layered manganese oxide with a sheet nanostructure, the average thickness of the sheets being between 1 and 50 nm, and the length L of the sheets being between 0.2 ?m and 3 ?m, as well as the manufacturing method thereof and a cell for producing said composite beads. The present invention also relates to the use of such beads in treatments for decontaminating fluids containing toxic elements such as heavy metals or organic pollutants.

Abstract: The present invention concerns a method for electrochemically depolluting an aqueous solution containing at least one heavy metal, said method comprising the following steps: a) a step of measuring the pH of the aqueous solution, optionally followed by a step of adapting said pH by adding a strong acid or a strong base, b) bringing said aqueous solution into contact with a reference electrode, a counter-electrode and a working electrode comprising a conductive substrate, c) applying a constant potential to the arrangement, as a result of which a film of at least one heavy metal oxide is formed on said working electrode, this step being capable of being repeated when the aqueous solution contains several heavy metals, and d) recovering a depolluted aqueous solution and said film.

Abstract: Process for depositing a film of a metal oxide or of a metal hydroxide on a substrate in an electrochemical cell, wherein (i) the metal hydroxide is of formula M(OH).sub.x A.sub.y, M representing at least one metallic species in an oxidation state i chosen from the elements in Groups II and III of the Periodic Table, A being an anion whose number of charges is n, 0<x.ltoreq.i and x+ny=i,(ii) the electrochemical cell comprises (a) an electrode comprising the substrate, (b) a counterelectrode, (c) a reference electrode and (d) an electrolyte comprising a conducting solution comprising at least one salt of the metal M, the process comprising the steps of:dissolving oxygen in the electrolyte andimposing a cathode potential of less than the oxygen reduction potential and greater than the potential for deposition of the metal M in the electrolyte in question on the electrochemical cell.