Application of Fe(III) or Cu(II) modified montmorillonite in Photo-Fenton type processes for dye degradation

LUCAS GUZ; F. S. GARCÍA EINSCHLAG; ROSA TORRES SANCHEZ; CURUTCHET G.; CANDAL ROBERTO

Jacksonville

Conferencia; 18th International Conference on Advanced Oxidation Technologies for treatment of Water, Air and Soil; 2012

RedoxTech

Photo-Fenton type processes are powerful tools for water decontamination, based in the production of oxidant radicals (typically OH•) by the catalytic decomposition of H2O2 mediated by light. Photo-Fenton process involve the use of UVA light and Fe(III) as catalyst but other transition metals as Co(II) or Cu(II) can be used in the so called Photo-Fenton like processes. The inmobilization of the metal in appropriate supports leads to more versatile catalysts that can be easily removed from solution and even reused. Bentonites, and specially montmorillonite, are interesting supports with high surface area and good affinity for iron and other transition metals. Dyes are persistent contaminants widely use in textile and other industries, that should be removed from waste waters before releasing to natural surface waters. Advanced oxidation processes are alternatives for the elimination of this type of pollutants. In this work we present a study of the degradation kinetic of a water soluble synthetic dye, reactive orange 16 (RO-16), by Photo-Fenton process using Fe(III) or Cu(II) modified montmorillonite (Fe-Mont and Cu-Mont respectively). Fe-Mont and Cu-Mont were prepared from Bentonita neuquina argentina (96% Na montmorillonite determined by DRX - Rietveld analysis). Fe-Mont was obtained by suspending bentonite in acetone containing 1.11 M FeCl3, vacuum drying, rinse with water, and freeze drying. Cu-Mont was prepared by suspending bentonite fired at 500 ºC in 0.050M CuSO4, followed by drying, water rinse and vacuum drying. Incorporation of Fe(III) or Cu(II) in montmorillonite increased the inter-laminar space, as determined by XRD analysis, which suggest that the transition metal ions incorporation is consequence of ionic exchange with Na+. Degradation experiments were run in a cylindrical reactor with central illumination, with 1.0 g/L Fe-Mont or Cu-Mont aqueous suspensions, [RO-16]0=0.16 mM, [H2O2]0=0.10 M and a 40 W black light fluorescent bulb as UVA source. The suspension was contained in a double jacket beaker thermostated at 25 ºC, and circulated to the reactor at a flow of 1L/min. Experiments were run at initial pH 3.0 or 6.0. At pH 3.0 decoloration was total in 1 h using Fe-Mont as catalyst while in the case of Cu-Mont and pure Mont (used as control) decoloration was observed after 6 h. Kinetics was modeled by a pseudo first order equation, although better results were obtained with a biexponential model. At pH 6.0 dye decoloration needed more time than at pH 3.0 when Fe-Mont was used as catalyst and pure Mont as control, but similar rate tan at pH 3.0 was observed for Cu-Mont. These results indicate that with supported catalysts is possible to work at higher pH than in homogeneous Photo-Fenton. This phenomenon may be related with protonic exchange between the solution and the clay. Higher degree of mineralization was obtained using Cu-Mont than with Fe-Mont at longer treatment time, although decoloration was faster with Fe-Mont. Besides, a red intermediate is formed when Cu-Mont is used as catalyst. These results indicate that a different mechanism takes place, depending on the type of catalyst.