Facile synthesis of direct sunlight-driven anatase TiO₂ nanoparticles by in situ modification with trifluoroacetic acid

Anatase TiO₂ nanoparticles with direct sunlight-driven photocatalytic activity have been synthesized via hydrolysis of titanium precursor, tetrabutyl titanate in trifluoroacetic acid (TFA) followed by sol–gel conversion to xerogel and further hydrothermal treatment at low temperature. The structure and morphology of the as-prepared anatase TiO₂ were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, fourier transform infrared spectra, transmission electron microscopy, UV–visible diffuse reflectance spectrophotometer, and photoluminescence spectra. The results showed that TFA was chemically bonded on anatase TiO₂ during the sol–gel process and the size of TFA-modified anatase TiO₂ nanoparticle was about 7 nm. In situ modification of anatase TiO₂ with TFA endowed the photocatalyst with direct sunlight-driven photocatalytic activity. The photodegradation of rhodamine B under direct sunlight irradiation showed that the photodegradation rate constant of TFA-modified anatase TiO₂ was about threefold higher than that of Degussa P25. The higher photocatalytic activity might be attributed to the in situ surface modification with TFA. On one hand, surface modification with TFA extended the light absorption of anatase TiO₂ to the visible light regime. On the other hand, the strong electron-withdrawing effect of CF₃ group can reduce the recombination of photo-generated electron and holes and enhanced the transfer and transport of charge carriers, and thus a higher visible light responding photocatalytic activity was achieved.