Photodegradation of an azo dye with reusable SrF2–TiO2 under UV light and influence of operational parameters

SrF2 loaded TiO2 (SrF2–TiO2), prepared by sol–gel method, was characterized by Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance spectra (DRS), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), atomic force microscopy (AFM) and BET surface area measurements. TEM images reveal that the sizes of SrF2–TiO2 particles are in the range of 3–20 nm. Presence of metal halide (SrF2) in the catalyst was confirmed by FT-IR, XRD, XPS and CV measurements. SrF2 loading increases the absorption of UV and visible light. AFM images show a cavity which increases the surface area and photocatalytic activity of the catalyst. 3 wt% SrF2 loaded TiO2 was found to be more photoactive than bare TiO2 in Reactive Yellow 84 (RY 84) dye degradation. The effects of operational parameters such as the amount of photocatalyst, dye concentration, initial pH on photomineralization by SrF2–TiO2 have been analyzed. The optimum pH and catalyst amount for efficient removal of dye are found to be 5 and 4 g L−1, respectively. The intermediates identified by GC–MS analysis during photodegradation, are 2-amino-4-[(4-amino-6-chloro-1,3,5-triazin-2-yl)amino]phenol (1), 6-chloro-N-phenyl-1,3,5-triazin-2,4-diamine (2), 2,4-diaminophenol (3) and 1,3,5-triazin-2,4-diamine (4) based on their molecular ion and mass spectrometric fragmentation peaks. The mineralization of RY 84 has also been confirmed by CV and chemical oxygen demand (COD) measurements. Mechanism of dye degradation by SrF2–TiO2 is proposed on the basis of hole trapping property of SrF2. The catalyst was found to be stable and reusable.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Nanosized SrF2–TiO2 was successfully synthesized by sol–gel method. ► SrF2–TiO2 was more efficient than bare TiO2 in Reactive Yellow 84 degradation. ► This catalyst was found to be stable and reusable. ► Higher efficiency of SrF2–TiO2 is due to its hole trapping property. ► Treatment of dye effluent using SrF2–TiO2 will be more economical and eco-friendly.