Efficient photocatalytic degradation of acid orange 7 over N-doped ordered mesoporous titania on carbon fibers under visible-light irradiation based on three synergistic effects

N-Doped ordered mesoporous titania on carbon fibers (NOMT/CFs) has been prepared by a liquid-crystal template (LCT) method with the aid of supercritical deposition. The NOMT/CFs product has been characterized by X-ray diffraction analysis, scanning electron and transmission electron microscopies, X-ray photoelectron spectroscopy, N2 sorption, UV/Vis diffuse reflectance spectrophotometry, and photoluminescence. The photoactivity of the obtained product in the degradation of acid orange 7 (AO7) solution under visible-light irradiation has been evaluated. A photocatalytic mechanism involving three synergistic effects of NOMT/CFs is proposed, whereby the titania acts as an electron/hole generator with its ordered mesostructure facilitating electron–hole separation, N-doping enhances visible-light adsorption, and the CFs serve to concentrate the pollutant around the active sites, favor electron transfer, and facilitate convenient recycling. Gas chromatography and mass spectrometry have been used to analyze the intermediates generated in the conversion of AO7, allowing a tentative decomposition pathway to be proposed. The effects of catalyst amount, pH, and initial AO7 concentration have been examined as operational parameters. The photocatalytic reactions follow pseudo-first-order kinetics and are discussed in terms of a modified Langmuir–Hinshelwood model.