Defect-Induced Yellow Color in Nb-Doped TiO2 and Its Impact on Visible-Light Photocatalysis

• Published in: Journal of physical chemistry. C
• Main Authors: Kong, Lina, Wang, Changhua, Zheng, Han, Zhang, Xintong, Liu, Yichun
• Format: Journal Article
• Language: English
• Published: American Chemical Society 23.07.2015
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.5b03448

Doping TiO2 photocatalysts with foreign ions has been deemed an effective method to enhance visible light absorption and thus increase their photocatalytic performance. Herein, we report that Nb-doped TiO2 porous microspheres prepared by ultrasonic spray pyrolysis of peroxide precursor solution are yellow, and the yellow coloration becomes increasingly conspicuous with increasing Nb dopant concentration. Comprehensive spectral analyses show that both surface peroxo species and bulk Ti3+ are introduced into TiO2 microsphere samples together by charge compensation with Nb5+ dopant and are responsible for the coloration of TiO2. The Nb-doped microspheres show higher photocatalytic rates than undoped TiO2 for the degradation of gaseous acetaldehyde under visible irradiation but slower rates under ultraviolet light. Moreover, the photocatalytic mineralization rates of acetaldehyde to CO2 are lowered with Nb doping under both visible and UV irradiation. Correlation between the results of surface photovoltage spectroscopic (SPS) characterizations and photocatalytic tests suggests that surface peroxo states are relevant to the visible-light-stimulated charge separation and photocatalytic reactions, albeit holes trapped in these states have lower reactivity than in valence band. On the other hand, the enhanced photoluminescence in the near-infrared region, reduced SPS response in the UV region, and photochromic phenomena during photocatalytic process indicated that Ti3+ defects serve as charge carrier recombination centers and display adverse effect to photocatalytic activity of Nb-doped TiO2, especially under UV irradiation.