The role of adsorption in the photocatalytic decomposition of Orange II on carbon-modified TiO₂

Carbon-modified TiO₂ was successfully prepared via simple heat treatment of TiO₂ in alcohol vapors (1-butanol and 2-butanol) at a constant temperature (500 °C). The prepared samples were characterized by means of X-ray diffraction (XRD) and Fourier transform infrared diffuse reflectance spectroscopy (FTIR/DRS). Brunauer-Emmett-Teller (BET) adsorption and zeta potential analyses were also conducted. The Freundlich adsorption model fitted both carbon-modified and original TiO₂, which provide a heterogeneous surface for the adsorption of Orange II. The carbon-modified TiO₂ was used as a photocatalyst to remove Orange II from aqueous solution by combined processes of adsorption and photocatalytic decomposition. The adsorption performance of the carbon-modified TiO₂ was higher than that of the unmodified TiO₂. Carbon adsorption approached synchronicity with oxidation, leading to the higher activity. This enhanced adsorption capacity may be a promising factor for the photocatalytic removal of Orange II onto carbon-modified TiO₂. The prepared Carbon-modified TiO₂ samples had higher BET surface area than unmodified TiO₂ (44, 54.48 and 49.72 m²/g for TiO₂, C1B-TiO₂ and C2B-TiO₂, respectively) and exhibited higher hydrophobicity and a positively charged surface, which were favorable for adsorption of Orange II. High adsorption of dye on the porous structure of C-TiO₂ enhanced its photocatalytic decomposition under visible light.