Decomposition of the Methylene Blue Dye Using Layered Manganese Oxide Materials Synthesized by Solid State Reactions

Figure 6

Proposed mechanism for the formation of the superoxide and hydroxyl radicals in MB degradation. (a) Hydrogen peroxide adsorption at an Mn⁴⁺ active site (oxygen vacant) with a posterior electron transfer to the Mn⁴⁺ active site and formation of a superoxide radical and an Mn³⁺ inactive site. There is an electron transfer process from an Mn³⁺ ion to an adjacent Mn⁴⁺ ion via an oxobridge (electronic hopping) to finally regenerate the Mn⁴⁺ active site. (b) A similar step as in (a) but in this case without regeneration of the active side. (c) Oxidation of Mn³⁺ with O₂ at the oxygen vacant site to restore the Mn⁴⁺ active site and superoxide radical. (d) Formation of hydroxyl radical (OH^•) and regeneration of hydrogen peroxide.

(a)

(b)

(c)

(d)