Adsorption and Photocatalytic Kinetics of Visible-Light Response N-Doped TiO2Nanocatalyst for Indoor Acetaldehyde Removal under Dark and Light Conditions

Abstract

Understanding the removal nature of the indoor volatile organic compounds under realistic environment conditions would give clear guidance for the development of air purification devices. The study investigated the removal of indoor acetaldehyde using visible-light-responsive N-doped TiO ₂(N-TiO ₂) photocatalyst under visible-light irradiation (light) and in the absence of light (dark). The adsorption kinetics of acetaldehyde onto N-TiO ₂followed a pseudo-second-order model. The magnitude of acetaldehyde adsorption is proportional to temperature, and the results were fitted to the Langmuir isotherm model. Moreover, the effect of initial acetaldehyde concentration and visible-light intensity on the photooxidation of acetaldehyde was well described by the Langmuir-Hinshelwood model. Results show that the mesoporous N-TiO ₂catalyst had a high ability to absorb acetaldehyde in the dark condition, and then acetaldehyde was subsequently photooxidized under visible-light irradiation. The adsorption capacity was found to increase with decreasing temperature. The negative value of $\mathrm{\Delta }G$° and the positive value of $\Delta S$° indicate that the adsorption of acetaldehyde onto N-TiO ₂was a spontaneous process. Finally, a reaction scheme for removal process of indoor acetaldehyde by N-TiO ₂was proposed.