Evaluation of hematin-catalyzed Orange II degradation as a potential alternative to horseradish peroxidase

The catalytic performance of hematin was evaluated for the decolorization of solutions of the monoazoic textile dye Orange II in comparison to horseradish peroxidase (HRP) by means of response surface methodology. Conversions were affected mostly by the pH of the medium, followed by the catalyst and peroxide concentrations, whereas temperature impact was negligible. Both catalysts removed more than 92% of the color from 75 mg l−1 solutions after 60 min. Catalytic performance was optimal at alkaline pH and low peroxide-to-dye molar ratio (2.5 for HRP and 5 for hematin). Conversion results suggest a catalatic route for activity recovery and a lower sensitivity of hematin to peroxide and organic radical attack. Chemical oxygen demand values revealed lack of mineralization after treatment. UV/visible and FTIR spectra of treated solutions confirmed azo bond cleavage and the presence of oxygenated aliphatic hydrocarbon moieties as main products with both catalysts, whereas in the case of HRP coupling products are also produced after 24 h. These results are presented for the first time for hematin as biomimetic of peroxidase for dye degradation with a systematic study of variables using the Doehlert array. As a result, hematin emerges as an effective alternative to HRP for azo-dyes removal.

Different coordination of Orange II to Hematin and to the Heme group in HRP-with Fe=O. (Source: Berglund et al., 2002).Figure optionsDownload as PowerPoint slideHighlights
► Evaluation of hematin as a biomimetic catalyst for decolorization purposes.
► Hematin emerges as an efficient biomimetic of HRP for Orange II decolorization.
► Best responses were obtained at the alkaline conditions of textile effluents.
► Degradative instead of expected polymerizing catalytic action was observed.
► Degradation products contain mainly oxygenated and aliphatic hydrocarbon moieties.