Photocatalytic thin films containing TiO_2:N nanopowders obtained by the layer-by-layer self-assembling method

摘要

In this work, TiO_2-N powders were synthesized by high-energy ball milling, using commercial titanium dioxide (TiO_2) in the anatase phase and urea to introduce nitrogen into TiO_2 in order to enhance their photocatalytic properties in the visible spectral region. Several samples were prepared by milling a mixture of TiO_2-urea during 2,4,8,12 and 24 h and characterized by spectroscopic and analytical techniques. X-ray diffraction (XRD) results showed the coexistence of anatase and high-pressure srilankiteTiO_2 crystalline phases in the samples. Scanning electron microscopy (SEM) revealed that the grain size of the powder samples decreases to 200 nm at 24 h milling time. UV-Vis diffuse reflectance spectroscopic data showed a clear red-shift in the onset of light absorption from 387 to 469 nm as consequence of nitrogen doping in the samples. The photocatalytic activity of the TiO_2-N samples was evaluated by methylene blue degradation under visible light irradiation. It was found that TiO_2-N samples had higher photocatalytic activity than undoped TiO_2 samples, which could be assigned to the effect of introducing N atoms and XPS results confirm it. Using polyethylenimine (PEI), transparent thin films of TiO_2-N nanoparticles were prepared by layer-by-layer self assembly method. UV-visible spectrophotometry was employed in a quantitative manner to monitor the adsorbed mass of TiO_2 and PEI after each dip cycle. The adsorption of both TiO_2 and PEI showed a saturation dip time of 15 min.