Synthesis and Characterization of Co/Al-PILCs for the Oxidation of an Azo Dye Using the Bicarbonate-Activated Hydrogen Peroxide System

Aluminum pillared clay (Al-PILC) was synthesized and impregnated with Co(II) nitrate (1.0, 3.0 and 6.0 wt.% cobalt), using an incipient wetness impregnation method. The obtained solids were characterized by XRF, XRD, N₂ adsorption–desorption at 77 K and point of zero charge. This is the first study using cobalt impregnated in a pillared clay (Co/Al-PILC) as a catalyst for sunset yellow (SY) degradation, with bicarbonate-activated hydrogen peroxide (BAP) as the oxidizing agent. The influence of the amount of H₂O₂, the H₂O₂/NaHCO₃ molar ratio, and the amount of Co impregnated in Al-PILC on azo dye oxidation in an aqueous solution was studied. The toxicity of by-products formed after dye oxidation with the BAP system was explored in an anaerobic digestion test. Total decolorizations were obtained for the reactions carried out with three cobalt impregnated catalysts, with 8 times the stoichiometric dose of H₂O₂ and H₂O₂/NaHCO₃ molar ratios of 0.25 and 4.0. Textural properties of Co (1.0 wt.%)/Al-PILC can be related to its good catalytic performance in the oxidation of SY, using the BAP system, as it preserved 68.8% of the S_BET and 66.0% of the microporous area of support. The concentration of leached cobalt in the tests, with the catalysts impregnated with 1.0 and 3.0 wt.% cobalt, was lower than the detection limit (< 0.01 mg/L), which indicated that the active phase was very stable at a basic pH. By-products generated during the oxidation of SY in the BAP system did not inhibit the specific methanogenic activity in anaerobic digestion. Graphic Abstract: This is the first study using cobalt impregnated in a pillared clay (Co/Al-PILC) as a catalyst for an azo-dye degradation, with bicarbonate-activated hydrogen peroxide (BAP) as the oxidizing agent. Total decolorizations were obtained for the reactions carried out under the conditions studied. However, total carbon and nitrogen removals were low. [Figure not available: see fulltext.]