Heterogeneous photocatalytic degradation of anthraquinone dye Reactive Blue 19: optimization, comparison between processes and identification of intermediate products

Abstract

Treatment of textile wastewater using heterogeneous photocatalysis began in the the last decade and attracted the attention of researchers due to its versatile application. The variety of applications of TiO₂ as a photocatalyst was due toits numerous positive properties, such as low operating temperature, biologically inert nature, low energy consumption, water insolubility, availability and photoactivity, low toxicity, high chemical stability, suitable flat band potential, narrow bandgap and the fact that it is environmentally benign. Heterogeneous UV-TiO₂ photocatalysis is capable of removing organic pollutants from textile wastewater; this has been widely studied, with the technology also having been commercialized in many developing countries. Decolorization of anthraquinone dye Reactive Blue 19 (RB 19) by heterogeneous advanced oxidation processes TiO₂/UV/H₂O₂, TiO₂/UV/KBrO₃ and TiO₂/UV/(NH₄)₂S₂O₈ was studied under different conditions and in the presence of electron acceptors such as hydrogen peroxide (H₂O₂), potassium bromate (KBrO₃) and ammonium persulphate ((NH₄)₂S₂O₈). Decolorization was very fast for all three processes, and complete dye decolorization was achieved in 10 min. The effect of various ions (Cl^–, SO₄^2– and HCO₃^–) on RB 19 decolorization was also studied. The optimal condition for the decolorization of the dye were determined to be: TiO₂ concentration 1 g∙dm^–3, electron acceptor concentration 30.0 mmol∙dm^–3, dye concentration 50.0 mg∙dm^–3, UV intensity 1 950 μW∙cm^–2, at temperature 25 ± 0.5°C. In addition, experiments were performed and compared in three different matrices. In the surface water and dyebath effluent water, the removal efficiency for RB 19 was lower than that achieved in the deionized water because of the interference of complex constituents in the surface water and effluent. LC-MS analysis was carried out and the detected intermediates were compared with the previously published data for anthraquinone dyes.