Azo dyes decomposition on new nitrogen-modified anatase TiO2 with high adsorptivity
ABSTRACT New vis active photocatalyst was obtained by the modification of commercial anatase TiO2 (Police, Poland) in pressure reactor in an ammonia water atmosphere at 100 °C for 4 h. The photocatalytic activity of new material was tested during three azo dyes decomposition: monoazo (Reactive Read), diazo (Reactive Black) and poliazodye (Direct Green). Obtained photocatalyst had new bands at 1430–1440 cm−1 attributed to the bending vibrations of NH4+ and at 1535 cm−1 associated with NH2 groups or NO2 and NO. UV–vis/DR spectra of photocatalyst had also insignificant decrease in visible region. Fluorescence technique was used for studying the amount of hydroxyl radicals produced on TiO2 surface during visible light irradiation. The hydroxyl radicals produced react with coumarin present in the solution to form 7-hydroxycoumarin which has fluorescent capacity. Photocatalytic activity of modified TiO2 was compared with commercial titanium dioxide P25 (Degussa, Germany). The photocatalytic activity of TiO2/N was higher than that of unmodified material and P25 under visible light irradiation. The ability for dye adsorption (Reactive Red) on photocatalyst surface was also tested. Unmodified TiO2 and P25 has isotherm of adsorption by Freundlich model, and nitrogen-modified TiO2 by Langmuir model. The presence of nitrogen at the surface of TiO2 significantly increased adsorption capacity of TiO2 as well as OH radicals formation under visible radiation.
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ABSTRACT: The investigation on incorporating nitrogen group into titanium dioxide in order to obtain powdered visible light-active photocatalysts is presented. The industrial hydrated amorphous titanium dioxide (TiO2·xH2O) obtained directly from sulphate technology installation was modified by heat treatment at temperatures of 100–800°C for 4h in an ammonia atmosphere. The photocatalysts were characterized by UV–VIS–DR and XRD techniques. The UV–VIS–DR spectra of the modified catalysts exhibited an additional maximum in the VIS region (λ≈470nm, EG≈2.64eV) which may be due to the presence of nitrogen in TiO2 structure. On the basis of XRD analysis it can be supposed that the presence of nitrogen does not have any influence on the transformation temperature of anatase to rutile. The photocatalytic activity of the modified photocatalysts was determined on the basis of decomposition rate of phenol and azo-dye (Reactive Red 198) under visible light irradiation. The highest rate of phenol degradation was obtained for catalysts calcinated at 700°C (6.55%), and the highest rate of dye decomposition was found for catalysts calcinated at 500 and 600°C (ca. 40–45%). The nitrogen doping during calcination under ammonia atmosphere is a very promising way of preparation of photocatalysts which could have a practical application in water treatment system under broader solar light spectrum.
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ABSTRACT: The photocatalytic decolourisation of two azo dyes—Reactive Red 198 and Direct Green 99—in an aqueous solution by the artificial visible light radiation was investigated. The industrial metatitanic acid (H2TiO3) obtained directly from the sulphate technology installation was N-doped and used as photocatalyst. H2TiO3 was calcinated at different temperatures, ranging from 300 to 500 °C, for 4 or 20 h, respectively, in an ammonia atmosphere. The UV–vis/DR spectra of the modified catalysts exhibited an additional maximum in the vis region (λ ≈ 476.8 nm, EG = 2.60 eV for catalysts calcinated for 4 h and λ ≈ 479.5 nm, EG = 2.59 eV for catalysts calcinated for 20 h, which may be due to the presence of nitrogen in TiO2 particles. The chemical structure of the modified photocatalysts was investigated using FTIR/DRS spectroscopy and the presence of nitrogen was confirmed. A photocatalytic activity of the investigated catalysts was determined on the basis of a decomposition rate of azo dyes. The decomposition of Reactive Red 99 increased with increasing the calcination temperature of photocatalysts, whereas the activity of the prepared photocatalysts towards Direct Green 198 degradation was as follows: 300–20 h < 400–20 h < 500–20 h < 300–4h < 400–4 h < 500–4 h. Both, the calcination time and temperature had no influence on the amount of nitrogen-doped into TiO2 structure. The inversely proportional linear dependence between the decomposition rates of azo dyes and the intensity of the band attributed to the hydroxyl groups for both dissociated water and molecularly adsorbed water was observed. With increasing temperature of calcinations, the amount of the hydroxyl groups decreased, whereas the decomposition of azo dyes increased.Applied Catalysis B Environmental 01/2006; 62(1-2-62):150-158. DOI:10.1016/j.apcatb.2005.07.008 · 6.01 Impact Factor
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ABSTRACT: Parylene films loaded with TiO2 are reported as photocatalysts in azo dye discoloration processes. The TiO2 loading of the parylene film was 0.32% (w/w) and the amount of TiO2 on the film was about two orders of magnitude below the TiO2 added in suspension to discolore the same solution of Methyl Orange used as a probe. The parylene/TiO2 films showed a similar activity in the presence of O2 or H2O2 during the discoloration of dyes. This shows the efficient role of O2 as ecb− scavenger. The photonic efficiency of the parylene/TiO2 film during the Methyl Orange discoloration was 0.04. Based on X-ray photoelectron spectroscopy (XPS) data, the TiO2 particles loaded on the parylene film were shown to be at first encapsulated in the polymer. After the encapsulation is broken, the TiO2 particles are fully exposed to the dye solution. The lack of surface intermediates like C-residues, N and S-species after the photocatalytic process implies an efficient decomposition of the dye at the catalyst interface. During the dye degradation carbonates and carboxylates were detected by XPS and Fourier transform infrared spectroscopy (FTIR) disappearing at the end of the discoloration process. Evidence is presented during the photocatalysis for the formation of a composite parylene/TiO2 film. The formation of this composite involves surface modification of parylene (partial lost of chlorine) in the outermost surface layer with concomitant densification of the TiO2 particles on the parylene film. The parylene film presented a side with high rugosity and one with low rugosity attaching different amounts of TiO2 in each case as observed by transmission electron microscopy (TEM).Applied Catalysis B Environmental 02/2008; 79(1-79):63-71. DOI:10.1016/j.apcatb.2007.10.006 · 6.01 Impact Factor