Visible light responsive TiO2 photocatalysts for degradation of indoor acetaldehyde

Photocatalysis is a promising technique for developing sustainable and environmentally friendly materials to improve indoor air quality. Visible-light-responsive TiO2 has been widely investigated but there are inconsistent results because photocatalytic properties depend strongly on synthetic methods. Herein, we synthesize TiO2 doped with 10 different metal ions (M–TiO2) by conducting a dialysis in a sol–gel method to obtain the best photocatalyst for the degradation of acetaldehyde under LED irradiation. Purification of a sol by dialysis enables us to discuss pure effects of dopants on the photocatalytic activity because impurities such as counter ions of metal salts are removed before sintering. Only Cr–, Pt–, V–, and Fe–TiO2 show photocatalytic activity and the optimal doping amounts are 0.50–1.7, 0.10, 1.0, and 0.10 atom%, respectively. Such differences in the optimal amounts can be explained in terms of the dopant ions having different valence states, suggesting the formation of oxygen vacancies. The Cr–TiO2 powder exhibits high activity even at the doping amount of 4.2 atom%. We also demonstrate that the Cr–TiO2 film prepared on a glass substrate can be used to degrade acetaldehyde by changing the film thickness and the LED intensity depending on the degree of the indoor contamination.