Formation and efficacy of TiO2/AC composites prepared under microwave irradiation in the photoinduced transformation of the 2-propanol VOC pollutant in air

Abstract

This article reports on the preparation and characterization (SEM, SEM-EDX, XRD, diffuse reflectance spectroscopy, and BET surface area) of TiO2 particles supported on activated carbon (AC) particulates using a titanium oxysulphate precursor and subjecting the aqueous dispersion to microwave (MW) heating and to a more traditional heating method with an oil bath. The TiO2/AC composites were subsequently tested for their photoactivity through an examination of the transformation of a volatile organic pollutant (VOC) in air: iso-propanol. Under MW irradiation at 70°C the synthesis resulted in the formation of a thin coating about the AC support, while TiO2 particles formed at higher temperatures; the average particle size of TiO2 tended to decrease with increase in reaction temperature from 426nm at 80°C to 243nm at 180°C. The accelerated heating of the AC-dispersed solution above 80°C was confirmed by determining the dielectric loss (ε”) of the dispersion at various temperatures at the microwave frequency of 2.45GHz. Subjecting the dispersion to oil-bath heating only led to formation of a thin film about the AC particulates. In the absence of the AC support TiO2 particle sizes averaged ca. 460nm for the MW method, while they averaged around 682nm with the oil-bath method. The BET specific surface area of the TiO2/AC composites was significantly greater for the MW heating method (ca. 990m2g−1 versus 848m2g−1 for the oil-bath method). Both UV–vis spectroscopy (estimated band-gap energy of TiO2/AC composites was 3.3eV) and XRD spectra confirmed the anatase nature of the TiO2 specimens. The MW-produced TiO2/AC particulates proved to be nearly six-fold more photoactive in the photoinduced degradation of the VOC pollutant than those produced by the oil-bath method. A possible growth mechanism of the TiO2/AC composites is proposed.