Decolorization of CI Reactive Red 2 by UV/TiO2/PAC and visible light/TiO2/PAC systems

In this work, the sol-gel method is utilized to synthesize TiO2/powder-activated carbon (PAC) from TiCl4 and PAC. The TiO2/PAC system was used to decolorize C.I. Reactive Red 2 (RR2) under ultraviolet (UV) and visible light irradiation. The surface characteristics of TiO2 and TiO2/PAC were analyzed by X-ray diffractometer, scanning electron microscopy, transmission electron microscopy, UV-vis spectroscopy, BET surface area analysis, and X-ray photoelectron spectroscopy (XPS). The effects of the C/Ti ratio, calcination temperature, photocatalyst dose, RR2 concentration, wavelength of light, and pH on the decolorization of RR2 by TiO2/PAC were evaluated. The optimal calcination temperature for forming TiO2 and TiO2/PAC was 400 degrees C; moreover, the surface areas of TiO2 and TiO2/PAC were 42 and 108m(2)/g, respectively. The sizes of the aggregates of TiO2 and TiO2/PAC particles were approximately 40 and 30nm, respectively. Experimental results reveal that the percentage of anatase increased with the amount of PAC in TiO2/PAC. The spectra indicate that C doping of TiO2 shifted the absorption edge from 418nm to a longer wavelength of 471nm. XPS characterization verifies the substitution of the C species in the crystal lattice in TiO2/PAC for O species, forming Ti-O-C. As the C/Ti ratio and the TiO2/PAC dosage increased, the decolorization efficiency increased. Conversely, the decolorization rate decreased as the RR2 concentration and pH increased. The TiO2/PAC was photoexcited by irradiation by UV and visible light; however, TiO2 was photoexcited only by UV irradiation. The efficiency of TiO2/PAC was better than that of TiO2 in both decolorization and total organic carbon removal.