Enhancement of the catalytic activity of ordered mesoporous TiO2 by using carbon fiber support and appropriate evaluation of synergy between surface adsorption and photocatalysis by Langmuir–Hinshelwood (L–H) integration equation

Abstract

Ordered mesoporous titania on carbon fibers (OMT/CFs) were prepared through a simply combined method of liquid crystal template (LCT) technique and supercritical deposition. The OMT/CFs composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, nitrogen adsorption–desorption isotherms, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) emission spectra. These superiorities about small crystalline size, low exciton recombination, numerous activated sites, high hydroxy content and surface areas of OMT/CFs demonstrated functional property with remarkable enhanced degradation efficiency and adsorption capability on AO7 in comparison with nanostructured titania on CFs (NST/CFs) without LCT. Additionally, the OMT/CFs system also exhibited high photocatalytic activity in the repeating application. The photoactivities of OMT/CFs and NST/CFs are higher than those of OMT–CF and NST–CF physical mixtures due to tight combination resulting high synergistic effect of an acid orange 7 (AO7) degradation. This study showed that it is not appropriate to approximate the Langmuir–Hinshelwood (L–H) kinetics to first-order kinetics to evaluate synergy. The synergistic effect estimated by the ratio of apparent rate constant from first-order kinetics is generally increased because its rate constant includes the adsorption effect. It is also proved that the decrease of AO7 content in solution is simultaneously attributed to adsorption of carbon fiber support besides its degradation in photocatalytic process. So the synergistic effect is inaccurate by evaluation of the approximated L–H model. To eliminate the adsorption influence of the catalyst, a L–H integration equation is proposed and found to well describe the photocatalytic behavior and evaluate synergistic effect, which is also verified by AO7 transfer on CFs and adsorption contribution.