One-Step Solvothermal Synthesis of Black TiO2 Films for Enhanced Visible Absorption.

An economic and facile solvothermal method was reported to prepare black TiO2 films on Ti foils that possessed the property of optical absorption in the visible region. The UV-vis spectra showed that the black TiO2 samples exhibited highly enhanced visible-light absorption from 400-600 nm. The black TiO2 films were compact and uniform, composed of nanoparticles and nanosheets. Moreover, a mixed structure of anatase and rutile was present in black TiO2 films. The electron paramagnetic resonance (EPR) spectra confirmed the presence of Ti3+ in samples, which accounted for longer wavelength optical absorption. The results showed that the TiO2 films had retained their black color upon storage in ambient atmosphere for more than one month. Therefore, it was supposed that the ethylene glycol in solvothermal reaction was the key factor for the extension of the absorption spectrum.