6 research outputs found

    Polymorphic phase transformation of Degussa P25 TiO2 by the chelation of diaminopyridine on TiO6 2- octahedron: Correlation of anatase to rutile phase ratio on the photocatalytic activity

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    A series of nitrogen-doped Degussa P25 photocatalysts were synthesized successfully by grinding and calcination method using 2,6-diaminopyridine (DAP) as a nitrogen precursor. The prepared samples were characterized by various analytical methods. The phase contents of anatase and rutile in the Degussa P25 powders have been altered by simply changing the proportion of DAP. A mechanism involving chelated DAP molecule on TiO6 2- octahedron is discussed. The enhanced activity is attributed to synergistic effect in the two phase solid material. Due to the low activation barrier, the effective inter particle electron transfer between the two polymorphs is quite efficient only when they are in close proximity with similar crystallite sizes. The transfer of electrons from the rutile phase to lattice/electron trapping sites of anatase and also to the Ti3+-Vo defect level created by the dopant favors effective charge separation and enhance the photocatalytic activity under solar illumination. © 2013 Elsevier B.V. © 2013 Elsevier B.V. All rights reserved

    Preparation, characterization and enhanced photocatalytic activity of Ni2+ doped titania under solar light

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    Anatase TiO2 was prepared by sol-gel method through the hydrolysis of TiCl4. Ni2+ was doped into the TiO2 matrix in the concentration range of 0.02 to 0.1 at. and characterized by various analytical techniques. Powder X-ray diffraction revealed only anatase phase for all the samples, while diffuse reflectance spectral studies indicated a red shift in the band gap absorption to the visible region. The photocatalytic activities of these photocatalysts were probed for the degradation of methyl orange under natural solar light. The photocatalyst with optimum doping of 0.08 at. Ni2+, showed enhanced activity, which is attributed to: (i) effective separation of charge carriers and (ii) large red shift in the band gap to visible region. The influence of crystallite size and dopant concentration on the charge carrier trapping - recombination dynamics is investigated. © Versita Warsaw and Springer-Verlag Berlin Heidelberg

    Effect of chloride and sulfate ions on the advanced photo Fenton and modified photo Fenton degradation process of Alizarin Red S

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    The degradation of Alizarin Red S (ARS) was carried out by heterogeneous advanced photo Fenton processes (HAPFP) of the type Fe0/H 2O2/UV and heterogeneous modified photo Fenton process (HMPFP) of the type Fe0/ammonium persulfate (APS)/UV. The influence of various reaction parameters like pH, catalyst loading, concentration of the oxidants and the influence of inorganic anions such as Chloride (Cl-) and Sulfate (SO42-) ions on processes were investigated. Quenching of the hydroxyl radical by inorganic anions was confirmed by the decrease in the degradation rate constant for the HAPFP from 3.33 � 10-2 to 0.19 à 10-2 (for Cl- (1 M)) and 0.29 à 10-2 min-1 (for SO42- (1 M)). Similar decrease in rate constant for HMPFP is from 4.67 à 10 -2 to 0.41 à 10-2(for Cl- (1 M)) and 0.51 à 10-2 min-1 (for SO42- (1 M)) process. The combined effect of concentration of sulfate and chloride ions on the rate constant for the degradation of ARS with APS and H2O 2 as oxidants is investigated. The initial degradation mechanism involves the cleavage of a quinone group to catechol as detected by UV-visible and GC-MS analysis. © 2013 Elsevier B.V. All rights reserved

    Synergistic effect of Ag deposition and nitrogen doping in TiO 2 for the degradation of phenol under solar irradiation in presence of electron acceptor

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    Ag deposited nitrogen doped TiO 2 (Ag-TiO 2-xN x) was prepared using sol gel titania by grinding it with stoichiometric amount of Urea as nitrogen source followed by the photoreduction of Ag + to Ag 0. These samples were characterized by powder X-ray diffraction (PXRD), UV-visible absorption spectroscopy, Fourier transformed infrared spectroscopy (FTIR), photoluminescence (PL) and scanning electron microscope (SEM). PL analysis of the samples indicated that the electron-hole recombination has been effectively inhibited after the Ag deposition on TiO 2 and TiO 2-xN x. Ag-TiO 2-xN x exhibits much higher visible-light photocatalytic activity when compared with N-doped or pristine TiO 2. The catalysts along with the oxidants can accelerate electron transfer process and inhibit the fast electron-hole recombination. The observed high process efficiency (Φ λ) of Ag-TiO 2-xN x particles compared to TiO 2-xN x and pure TiO 2 photocatalyst can be accounted to the synergistic effect of Ag loading along with N doping. Strongly interacting electron accepting species such as hydrogen peroxide and ammonium persulphate chemisorbed at the photocatalyst surface are said to act like surface states enabling inelastic transfer of electrons from the conduction band to the oxidizing species. The electronic states of different energies within the band gap have a major role in enhancing the efficiency. © 2011 Elsevier B.V.

    Degradation mechanism of diazo dyes by photo-Fenton-like process: Influence of various reaction parameters on the degradation kinetics

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    The degradation of diazo dyes Brilliant Yellow (BY) and Bismark Brown (BB) was investigated by the photo-Fenton-like process Fe2+/aminonium persulphate (APS)/UV in acidic pH medium. The influence of various reaction parameters like pH, concentration of Fe2+ ions/APS, structure of the dye and effect of radical scavenger on the degradation kinetics is reported. The rate constant (k), catalytic efficiency (kc) and process efficiency (Φ) are evaluated at different concentrations of Fe2+ ions. It was found out that the BB degrades at a faster rate than BY. The degradation process was followed by GC-MS technique. The results show that the initial step in the degradation of BB involves direct oxidation of azo chromophore, while in the case of BY the initial step is oxidation of azo group followed by the oxidation of ethylenic chromophore. Based on the obtained intermediates, probable degradation mechanism has been proposed. The results show that photo-Fenton-like process could be a useful and efficient technology for the mineralization of diazo dyes at lower concentrations of iron in acidic medium. © 2009 Bulgarian Academy of Sciences, Union of Chemists in Bulgaria

    Photo-Fenton and photo-Fenton-like processes for the degradation of methyl orange in aqueous medium: Influence of oxidation states of iron

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    Degradation of methyl orange (MO) was carried out by the photo-Fenton process (Fe2+/H2O2/UV) and photo-Fenton-like processes (Fe3+/H2O2/UV, Fe2+/S2O8 2-/UV, and Fe3+/S2O8 2-/UV) at the acidic pH of 3 using hydrogen peroxide and ammonium persulfate (APS) as oxidants. Oxidation state of iron had a significant influence on the efficiency of photo-Fenton/photo-Fenton-like processes. It was found that a process with a source of Fe3+ ions as the catalyst showed higher efficiency compared to a process with the Fe2+ ion as the catalyst. H2O2 served as a better oxidant for both oxidation states of iron compared to APS. The lower efficiency of APS is attributed to the generation of excess protons which scavenges the hydroxyl radicals necessary for degradation. Further, the sulfate ions produced from S2O8 2- form a complex with Fe2+/Fe3+ ions thereby reducing the concentration of free iron ions in the solution. This process can also reduce the concentration of hydroxyl radicals in the solution. Efficiency of the various MO degradation processes follows the order: Fe3+/H2O2/UV, Fe3+/APS/UV, Fe2+/H2O2/UV, Fe2+/APS/UV. © 2009 Institute of Chemistry, Slovak Academy of Sciences