Selective photocatalytic oxidation of benzene to phenol using carbon nanotube (CNT)-supported Cu and TiO2 heterogeneous catalysts

Nanostructured composite photocatalysts, comprising multi-walled carbon nanotubes (CNT), the anatase phase of titanium dioxide, and copper oxide, were prepared by sol-gel methodology. The synthesized materials were consequently characterised by various techniques. Nanocomposite heterogeneous catalysts, combining Cu and TiO2 with CNT, were utilized for the direct photocatalytic oxidation of benzene to phenol. A correlation between the presence of nano-metal and the variations in absorption was observed, especially in the UV-vis spectral range. This behaviour was explained by a strong interphase interaction among Cu, TiO2 and CNT. Benzene conversion and turnover was due to an improved adsorption. The selectivity towards phenol production was enhanced by supporting TiO2 with CNT and by impregnating copper, thereby suppressing the mineralisation of benzene and favouring the evolution of phenolic compounds. The synergy between TiO2 and CNT was also observed through a high rate and kinetics of benzene oxidation. The sequential interactions of the hydroxyl radicals (formed from water) with the ad-sorbed state of benzene on copper or titania surfaces led to an intensified catalysis, and in turn, phenol or hydroquinone product formation. A combination of high activity and stability made the prepared hierarchical catalysts potentially interesting for the photocatalysis applications in selective phenol synthesis. (C) 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.