Facile fabrication and characterization of multi-type carbon-doped TiO2 for visible light-activated photocatalytic mineralization of gaseous toluene

Abstract

Carbon-doped titanium dioxide (C-TiO₂) nanoparticles were synthesized by conventional mild oxidation of precursor titanium carbide (TiC) at 350 °C for 2 to 50 hours and more aggressive oxidation at the higher temperature of 400 to 600 °C for 2 hours in air. XRD and TEM studies indicated the formation of nano-sized C-TiO₂ with mixed anatase–rutile phases. With prolonged oxidation time or increase in oxidation temperature, an initial decrease in crystallite size was unveiled due to cracking of TiC grains, renucleation of TiO₂ and diffusion of carbon atoms. Raman, FTIR and XPS measurements revealed the presence of graphite-like carbon and the coexistence of substitutional and interstitial carbon in the TiO₂ lattice. This multi-type carbon doping either served as a photosensitizer or resulted in additional electronic states above the valence band of the TiO₂ lattice, directly responsible for the red shift of the absorption edge in the UV-vis absorption spectrum. The band structure and possible visible light photocatalytic mechanism of the C-TiO₂ were thus elucidated. The synthesized C-TiO₂ nanoparticles demonstrated improved photocatalytic performance for the mineralization of gaseous toluene in comparison to commercial P25 TiO₂ under visible light irradiation. The C-TiO₂ nanoparticles prepared at higher oxidation temperature with shorter time exhibited a more pronounced enhancement than those prepared by the mild oxidation process, providing a facile method for large-scale production of C-TiO₂ suitable for indoor photocatalytic applications.