UV–visible light-activated Au@ pre-sulphated, monodisperse TiO2 aggregates for treatment of congo red and phthalylsulfathiazole

Liquid-phase photocatalytic oxidation of a secondary diazo dye compound, Congo red (CR, C32H22N6Na2O6S2) and pharmaceutical phthalylsulfathiazole, was carried out in a cylindrical photochemical reactor on gold-loaded titania systems. The deposition of Au nanoparticles was performed by photochemical deposition methods on the surface of pre-sulphated titania. The detailed structural, compositional and optical characterization and physico-chemical properties of the obtained products are analyzed by X-ray diffraction (XRD), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), high resolution TEM (HRTEM), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), Fourier transformation infrared spectroscopy (FTIR) and photoluminescence spectra (PL) analysis. Notable enhancements in the photocatalytic activity of TiO2 were achieved by deposition of gold onto titania, which can be attributed to the enhanced surface electron excitation and effective electron-hole separation on gold-deposited TiO2 nanoparticles. The present study shows that the higher rate of photodegradation observed on Au-TiO2 at pH 6.5 can be correlated to the ratios of the concentrations of the ionized to the neutral dye molecules and also to the higher concentration of hydroxylated surface, which are able to effectively scavenge photogenerated valence band holes. Accumulation of the holes in the semiconductor particles increases the probability of formation of excited oxygen atom which is a reactive species readily oxidizing the organic dye molecule or environmental pollutant such as pharmaceutical phthalylsulfathiazole. The reaction mechanism of the photocatalytic system was detected by a photoluminescence method using terephthalic acid as a probe molecule.