Electron Paramagnetic Resonance Investigation of UV-irradiated TiO2 Powder

• Main Authors: Ting-Chun Wang, 王鼎鈞
• Other Authors: Shyue -Chu Ke
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/16765711657298531868

碩士 === 國立東華大學 === 應用物理研究所 === 93 === Electron Paramagnetic Resonance（EPR）, optical absorption and XRD studies have been carried out on irradiated anatase （Hombikat UV100）and rutile TiO2 nanoparticles. XRD results confirmed the crystal structure and the particle size of the TiO2 powders. The band gaps of the TiO2 powders were measured from the absorption edges of the optical absorption spectra. The EPR spectra of the anatase TiO2 powders were obtained in air, nitrogen and vacuum after one hour UV light illumination at 5 K. Photoinduced electrons were trapped on the lattice Ti4＋ sites to form Ti3＋ at surface lattice and interior lattice. The holes were trapped at lattice oxygen ions at surface. The kinetics of radicals, which are produced under UV irradiation has been studied from 5 K to ambient temperature in different atmospheric conditions. The trap sites of electron were not so powerful than the trap sites of hole in same phase of anatase TiO2 with increasing temperature. The signals of trapped electrons decreased and disappeared in air as warmed up from 5 K to 60 K, probably because of the substrates present in air or the adsorption on the surface of anatase TiO¬2. The signals of trapped holes were still observeable in air until warmed up to 150 K. After UV light illumination, the trapped electrons and trapped holes were also observed by EPR for rutile TiO2. The trapped electrons of rutile were more stable than anatase, the phenomenon of trapped holes for rutile are opposite to anatase. The trapped electrons and holes in irradiated TiO2 have been investigated by EPR spectroscopy under air, nitrogen and vacuum at different temperature. From the temperature dependence EPR data, activation energy of electrons and holes have be calculated. TiO２ is a great powerful redox substance that can be explained by activation energy.