Wet peroxide oxidation of dye-containing wastewaters using nanosized Au supported on Al2O3

Abstract

The degradation of a model dye compound (Orange II) was evaluated by wet peroxide oxidation using gold supported on alumina (Au/Al2O3) as a catalyst, in a slurry batch reactor. The material was prepared by the deposition-precipitation method, which yielded nanosized gold particles well dispersed on the support, with a mean particle size of 3.6nm. It was concluded that both adsorption and catalyzed oxidation (via hydroxyl radical formation) contribute to the dye removal. The catalyst was reused for five consecutive cycles, with no Au leaching being detected into the solution (detection limit <0.5mg/L), showing its high stability. This was also confirmed by textural and chemical characterization of the fresh and used materials. A parametric study was carried out to assess the influence of the most important variables (hydrogen peroxide amount, catalyst concentration, reaction pH and temperature) in both dye and total organic carbon (TOC) removal. In all runs performed, gold leaching was not detected. In the best operating conditions found, high efficiencies were reached (i.e., ∼100% of dye removal, 50% of TOC reduction, 42% of chemical oxygen demand – COD – elimination). The treatment improved the biodegradability of the effluent and the obtained waste remained non-toxic (as inferred from the inhibition of Vibrio fischeri test).A simulated industrial acrylic dyeing effluent was also treated by wet peroxidation. It was found that the gold support on alumina catalyst was stable and achieved considerable removal of color (33%) and organic compounds (42% for TOC and 50% for COD) and improved the biodegradability of the wastewater.