Síntese, otimização e caracterização da atividade fotocatalítica de TIO2 dopado com nitrogênio

Abstract

The optimization of the synthetic route of titanium dioxide nanoparticles doped with nitrogen was carried out in order to obtain photocatalysts with improved photocatalytic activity. Thereby, from the synthesized photocatalysts was possible to reach about 100% discoloration and 64% mineralization of Ponceau 4R (P4R) dye. Both doped (with largest and smallest photocatalyitc activity) and undoped catalysts were analyzed by X-ray diffraction showing the predominance of the crystalline anatase phase. Besides, using the Rietveld method, the results showed 17.3% of brookite phase in the undoped oxides. By further analysis of diffuse reflectance spectroscopy was observed that doped catalysts presented slight shift on absorption band to the visible region, highlighting the best photocatalyitc activity of the oxide with a band gap of 3,29 eV. This oxide (K1) exhibited specific area of 63.03 g/m2 while the oxide with lower photocatalytic activity (K2) exhibited a specific area of 12.82 g/m2. The Raman spectroscopy analysis showed that doped samples are more ordered than no doped, and vibrational modes related to nitrogen was not observed. Infrared spectra showed that calcination of the doped oxides leads to considerable loss in nitrogen content, and this is corroborated by the XPS measurements. Photocatalytic assays were carried out on laboratory scale using K1 catalyst in order to optimize the mineralization of P4R. Thus, the substrate concentration, catalyst concentration and pH of reaction medium were evaluated and the best result was 85% mineralization using 15 mg/L of P4R, 100 mg/L of catalyst and pH 6.4. Additional photocatalytic tests were conducted under solar radiation showing that doping increases photocatalytic activity under UV-A and visible irradiation, since 600 kJ of accumulated UV-A radiation (referring to 9 minutes of reaction time in bench scale) proved to be enough to reach 100% mineralization of dye using doped catalyst against 77% mineralization using undoped catalyst.