Preparation of TiO2-pillared montmorillonite as photocatalyst Part II: Photocatalytic degradation of a textile azo dye

Use of a photocatalyst based on TiO2-pillared montmorillonite prepared by microwave has been studied with respect to photodegradation of Solophenyl red 3BL, an azo dye produced from textile plants. Experiments were carried out with an aqueous dye concentration of 100 mg L− 1, at different pH and photocatalyst contents (400–5000 mg L− 1). The lower the pH, the higher the dye photodegradation rate constants: 0.0966 and 0.0006 min− 1, obtained at pH = 2.5 and pH = 11 respectively. This is in agreement with a higher adsorption of the dye on the catalyst at acidic rather than at basic pH. At pH = 5.8 and 2.5 g L− 1 of TiO2-pillared montmorillonite, initial degradation rate constant of the dye (0.0096 min− 1) was 1.4 fold lower with the synthesized photocatalyst than with commercial Degussa P25 (1 g L− 1) for about the same molar amount of TiO2 in dispersion. According to XRD patterns, rate constants were related to the rate of TiO2 crystallization within the catalyst. A photosensitized oxidation accounted for about 25 ± 5%, and a direct excitation of the photocatalyst accounted for 80 ± 10% of the global photodegradation process, leading mainly to oxidation of the dye by HO°.