Thermal modification of activated carbon surface chemistry improves its capacity as redox mediator for azo dye reduction

• Published in: Journal of hazardous materials Vol. 183; no. 1; pp. 931 - 939
• Main Authors: Pereira, L., Pereira, R., Pereira, M.F.R., van der Zee, F.P., Cervantes, F.J., Alves, M.M.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15.11.2010; Elsevier
• Subjects: Activated carbon; Applied sciences; Assaying; Azo; Azo Compounds - chemistry; Azo dye; Biomass; Charcoal - chemistry; Charge; Chemical engineering; Coloring Agents - chemistry; Decolourisation; Dyes; Exact sciences and technology; Hot Temperature; Hydrogen; Hydrogen-Ion Concentration; Kinetics; Nitric Acid; Nitrogen; Oxidation-Reduction; Oxygen; Pollution; Reactors; Redox mediator; Reduction; Reproduction; Surface chemistry; Surface Properties; Water Pollutants, Chemical - chemistry; Reduction; Decolourisation; Redox mediator; Activated carbon; Azo dye; Discoloration; Heat treatment; Biomass; Reaction rate; Batchwise; Anaerobe; First order; Trend analysis; Reactive dye; pH; Physicochemical purification; Oxidation; Kinetics; Rate constant
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2010.08.005

The surface chemistry of a commercial AC (AC 0) was selectively modified, without changing significantly its textural properties, by chemical oxidation with HNO 3 ( AC HNO 3 ) and O 2 ( AC O 2 ) , and thermal treatments under H 2 ( AC H 2 ) or N 2 ( AC N 2 ) flow. The effect of modified AC on anaerobic chemical dye reduction was assayed with sulphide at different pH values 5, 7 and 9. Four dyes were tested: Acid Orange 7, Reactive Red 2, Mordant Yellow 10 and Direct Blue 71. Batch experiments with low amounts of AC (0.1 g L −1) demonstrated an increase of the first-order reduction rate constants, up to 9-fold, as compared with assays without AC. Optimum rates were obtained at pH 5 except for MY10, higher at pH 7. In general, rates increased with increasing the pH of point zero charge (pH pzc), following the trend AC HNO 3 < AC O 2 < AC 0 < AC N 2 < AC H 2 . The highest reduction rate was obtained for MY10 with AC H 2 at pH 7, which corresponded to the double, as compared with non-modified AC. In a biological system using granular biomass, AC H 2 also duplicated and increase 4.5-fold the decolourisation rates of MY10 and RR2, respectively. In this last experiment, reaction rate was independent of AC concentration in the tested range 0.1–0.6 g L −1.