Iron-pillared clays as catalysts for dye removal by the heterogeneous photo-Fenton technique

The catalytic activity of iron pillared montmorillonitic clays in the discoloration of methylene blue aqueous solutions by the heterogeneous photo-Fenton process was studied. Catalysts were prepared using two different-sized aggregate fractions of the clay, ranging below 250 μm and within the range of 250–450 μm. Two calcination temperatures, 400 and 600 °C, were used. The solids were characterized by thermo-gravimetric analysis, nitrogen adsorption isotherms, elemental analysis, X-ray diffraction and iron content. A higher specific surface area and specific pore volume were found for the solid obtained from the finer aggregates of the clay and the lowest calcination temperature. Under photo-Fenton like conditions, this catalyst also displayed the highest catalytic activity which remained practically the same at pHs 3.0 and 5.6 and for H2O2 concentrations in the range from 5 to 20 mM. The observed differences in catalytic performance can be explained on the basis of the catalysts’ iron content and textural properties. Leaching of iron ions from the catalysts could not be detected. Long term stability for dye waste water treatment could thus be expected for these catalysts.