Adsorption of crystal violet on montmorillonite (or iron modified montmorillonite) followed by degradation through Fenton or photo-Fenton type reactions

In this work we demonstrate the feasibility to couple adsorption with Fenton and photo-Fenton process to separate and mineralize crystal violet (CV) dissolved in water. Montmorillonite (MMT) and iron modified montmorillonite (MMT-Fe) were studied as adsorbents and heterogeneous catalysts for Fenton and photo-Fenton like oxidation of cationic dye CV. The clays were characterized by XRD, SEM, EDX, BET surface area and electrophoretic mobility. MMT-Fe presents iron in the interlayer space and oxohydroxide particles on its surface. Both clays present a high CV adsorption capacity that can be modeled by a two-site Langmuir equation. MMT-Fe oxidizes faster and have a higher mineralization rate of adsorbed CV than MMT with Fe(II) or Fe(III) added externally. The oxidation of the adsorbed dye release organics to the solution which are further mineralized in solution. The Fenton oxidation can be modeled by a double exponential decay and photo-Fenton oxidation by a pseudo-first order kinetic model. Photo-Fenton oxidation leads to higher mineralization rates than Fenton.