Study On Photocatalytic Activities Of Titanium Dioxide Modified By Polypyrrole

TiO₂ nanoparticles were prepared by sol-gel method, factors affecting photocatalytic activities of TiO₂ nanoparticles such as water amount, depressor amount, dispersant amount, calcine temperature, calcine time were studied by the degradation of methyl orange aqueous solutions under UV light. TiO₂ nanoparticles showed optimal phtocatolytic activities when the volume ratio of TNB, ethanol, acetic acid and distilled water was 10:19:8.:4, calcined at 500℃for 2 hours.PPy/TiO₂ nanocomposites were prepared by in situ method, and nanoparticles were characterized by means of transmission electron microscopy (TEM), X-ray diffractiometer (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrocopy (FTIR), specific surface area (SSA) and UV-vis-diffuse reflectance spectroscope (DRS). Results showed the mean sizes of TiO₂ nanoparticles modified by PPy didn't change obviously, but the SSA of TiO₂ nanoparticles increased, the aggregation were alleviated; the crystallization performance of TiO₂ nanoparticles modified by PPy didn't change, they were still anatase crystal. It can be concluded that PPy polymerized on the surface of TiO₂ nanoparticles were not crystal phase; the absorption PPy/TiO₂ nanocomposites increased in the visible region, the banding energy of PPy/TiO₂ nanocomposites decreased; there was a strong interaction between PPy and TiO₂.The polymerization conditions that affected the photocatalytic activities of PPy/TiO₂ nanocomposites were studied by the degradation reaction of methyl orange aqueous solutions under UV light and sunlight. Results showed the photocatalytic activities of all the PPy/TiO₂ nanocomposites were higher than those of TiO₂ nanoparticles, and when the molar ratio of Py and TiO₂ was 1:100, FeCl₃ as oxidant, the molar ratio of FeCl₃ and Py was 2:1, p-Toluenesulfonic acid or 1.0 mol·L^-1 HCl aqueous solution as dopant, polymerized at 0℃for 4 h, PPy/TiO₂ nanocomposites showed perfect photocatalytic activities.Photocatalytic degradation reactions of methyl orange with PPy/TiO₂ nanocomposites and TiO₂ were one-order kinetic reactions. It can be concluded that the activation energy of TiO₂ modified by PPy decreased 2.38 kJ·mol^-1 by the degradation of methyl orange with PPy/TiO₂ nanocomposites and TiO₂ particles at different temperature.The photodegradation results of methyl orange, rhodamine B and malachite-green under UV light and sunlight irradiation showed the photocatalytic activities of PPy/TiO₂ nanocomposites were superior to those of TiO₂ nanoparticles, these results showed that the photocatalytic activities of PPy/TiO₂ nanocomposites were higher than those of TiO₂ nanoparticles was not accidental.The reason that the photocatalytic activities of PPy/TiO₂ nanocomposites were higher than those of TiO₂ nanoparticles was analysed. It can be concluded that the bigger specific surface area, the stronger absorption in visible region and the lower banding energy of PPy/TiO₂ nanocoposites had an effect on the photocatalytic activities of nanoparticles.The mechanism of the degradation of contamination with PPy/TiO₂ was discussed. It can be thought that PPy played a role as photosensitizer in the process, and this effect can make PPy inject electron to the conducting band of TiO₂ which resulted in higher photocatalytic activities.