L. Gomathi Devi

Bangalore University, Bengalūru, Karnataka, India

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Publications (39)100.8 Total impact

  • L. Gomathi Devi, R. Kavitha
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    ABSTRACT: Titanium dioxide photocatalyst has witnessed considerable interest for use in water and air cleanup owing to its fascinating properties like non-toxicity, ease of preparation, favorable band edge positions, water insolubility, multifaceted electronic properties, surface acid-base properties, and super hydrophilicity. Although it possesses much functionality, large bandgap and massive charge carrier recombination limits its wide utility under natural solar light. These drawbacks were overcome through nitrogen doping in titania matrix (N-TiO2), which alters the surface-bulk structure for visible light absorption with high quantum efficiency. In this review, we highlight the recent progress of N-TiO2 towards pollutant degradation, hydrogen evolution and its use in organic synthesis under ambient conditions. The preparation of N-TiO2 via different methods (physical and chemical methods) with diverse morphologies, nature of chemical dopants, induced defects and fundamental reaction parameters governing efficient photoinduced reactions are explored in this review. Further improvements in the photoefficiency of N-TiO2 were achieved through co-doping with foreign ions, heterostructuring with other semiconductors, metal deposition and the tuning of N-TiO2 with reactive exposed facets. The resultant improvement from each of the modification is discussed in the light of charge carrier generation-separation-transfer-recombination dynamics together with pollutant adsorption and their reactions with reactive oxygenated species in the liquid or gaseous regime. This review attempts to give an overview of the research highlights concerned with N-TiO2. Although it is impossible to cover all of the research articles in the literature, several milestones in the pathway towards highly applicable N-TiO2 are explored. It is hoped that this review article will trigger further research in synthesizing N-TiO2 with multifunctional features to enhance its capacity for green energy applications.
    ChemInform 11/2014; 45(44). DOI:10.1002/chin.201444239
  • L.Gomathi Devi, M. L. ArunaKumari
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    ABSTRACT: The synergistic effects between alpha-Sulfur (alpha-S) and TiO2 photocatalysts is studied under UV/solar light. An enhancement in photocatalytic activity was observed under UV light, due to formation of sulfate anions in the reaction mixture and these ions get adsorbed on TiO2 surface by electrostatic force of attraction or it may react with holes/hydroxyl radicals to generate sulfate radical anion. An increase in quantum efficiency is observed with sulfated TiO2 due to reduction in electron-hole recombination rate. The extended response of alpha-S under visible region is due to non-vertical absorption process, which paved a new way for elemental photocatalysis.
    Journal of Molecular Catalysis A Chemical 09/2014; 391. DOI:10.1016/j.molcata.2014.04.012 · 3.68 Impact Factor
  • R. Kavitha, L. Gomathi Devi
    Journal of Environmental Chemical Engineering 06/2014; DOI:10.1016/j.jece.2014.02.016
  • L. Gomathi Devi, R. Kavitha
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    ABSTRACT: The multifunctional and advanced semiconductor titania with superior physicochemical and opto-electronic properties is extensively investigated in wastewater purification mainly due to its non-toxicity, favorable band edge positions, water insolubility, multifaceted electronic properties, surface acid–base properties, super hydrophilicity and so on. However, large band gap and massive photogenerated charge carrier recombination hinders its wide application under natural solar light. Thus, altering the surface-bulk structure of titania is a major goal in the area of both materials and environmental chemistry for its better applications. The substitution of p block elements (B, C, N, F, S, P, and I) either at Ti4+ and O2− sites is a promising approach to overcome the aforementioned drawbacks. This review focuses on the photocatalytic activity of non metal doped titania for a wide variety of pollutants degradation under UV/visible light, with special emphasis on nitrogen doped TiO2. Further improvement in photoactivity of N–TiO2 is achieved via depositing with noble metals, co-doping with foreign ions, sensitization, surface modifications and heterostructuring with other semiconductors. The mechanism governing the photocatalytic reactions is discussed in the light of charge carrier generation–separation–transfer–recombination dynamics together with pollutant adsorption and their reactions with reactive oxygenated species in liquid or gaseous regime. We are positive that this review article will further stimulate our research interest on this intriguing hot topic.
    Applied Catalysis B Environmental 08/2013; s 140–141:559–587. DOI:10.1016/j.apcatb.2013.04.035 · 6.01 Impact Factor
  • L. Gomathi Devi, M. L. ArunaKumari
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    ABSTRACT: TiO2 was prepared by sol–gel method through the hydrolysis of TiCl4 and its surface derivatization was carried out with molecular catalyst like Hemin (chloro(protoporhyinato)iron(III)). Catalyst was characterized by various analytical techniques like UV–vis spectroscopy, FT-IR, FE-SEM and XRD.The anchoring of Hemin on titania surface is confirmed by FT-IR spectra through the linkage of OCOTi bond and also by TGA–DSC and elemental analysis. The photocatalytic activity of the surface modified catalyst is tested for the degradation of methyl orange (MO) as a model compound under UV light. The Hemin impregnated TiO2 (H-TiO2) in presence of H2O2 shows an excellent photocatalytic activity compared to pristine TiO2, Hemin, H2O2, TiO2/H2O2, and Hemin/H2O2 systems. The enhancement in the photocatalytic activity is attributed to the presence of iron (III) porphyrin ring on the TiO2 surface, which reduces the electron–hole recombination rate and also by acting as a mediator for continuous production of enriched concentration of hydroxyl radicals along with various other reactive free radicals.
    Applied Surface Science 07/2013; 276:521–528. DOI:10.1016/j.apsusc.2013.03.127 · 2.54 Impact Factor
  • K. Eraiah Rajashekhar, L. Gomathi Devi
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    ABSTRACT: 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 TiO62− 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.
    Journal of Molecular Catalysis A Chemical 03/2013; 374. DOI:10.1016/j.molcata.2013.02.009 · 3.68 Impact Factor
  • L. Gomathi Devi, S. Girish Kumar
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    ABSTRACT: The degradation of structurally different anionic dyes like Alizarin Red S (ARS) Amaranth (AR), Brilliant Yellow (BY), Congo Red (CR), Fast Red (FR), Methyl Orange (MO), and Methyl Red (MR) were carried out using Ln3+ (Ln3+ = La3+, Ce3+ and Gd3+) doped TiO2 at different pH conditions under UV/solar light. All the anionic dyes underwent rapid degradation at acidic pH, while resisted at alkaline conditions due to the adsorptive tendency of these dyes on the catalyst surface at different pH conditions. Gd3+ (0.15 mol%)-TiO2 exhibited better activity compared to other photocatalyst ascribed to half filled electronic configuration of Gd3+ ions. It is proposed that Ln3+ serves only as charge carrier traps under UV light, while it also act as visible light sensitizers under solar light. Irrespective of the catalyst and excitation source, the dye degradation followed the order: AR > FR > MO > MR > ARS > BY > CR. The results suggest that pre-adsorption of the pollutant is vital for efficient photocatalysis which is dependent on the nature of the substituent's group attached to the dye molecule.
    Applied Surface Science 11/2012; 261:137–146. DOI:10.1016/j.apsusc.2012.07.121 · 2.54 Impact Factor
  • L. Gomathi Devi, S. Girish Kumar
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    ABSTRACT: The modification of titania by metal / non metal ion doping, coupling with narrow band gap sensitizer, surface flourination, metal deposition, and together with recent ventures on application of {001} facets of anatase titania for visible light response with enhanced charge carrier separation are briefly overviewed. KeywordsTitania–Doping with metal / non metal ion–Surface fluorination–Metallization–{001} anatase facet
    Central European Journal of Chemistry 12/2011; 9(6):959-961. DOI:10.2478/s11532-011-0084-9 · 1.33 Impact Factor
  • L. Gomathi Devi, K. Eraiah Rajashekhar
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    ABSTRACT: Nitrogen doped TiO2 (TiO2−xNx) with a homogenous anatase phase was synthesized, using β-alanine as a nitrogen precursor and ethanol as a oxygen depriving agent in the concentration range of 0.05, 0.10, 0.15 and 0.2 at % and were characterized by Powder X-ray Diffraction (PXRD), X-ray Photoelectron Spectra (XPS), Scanning Electron Microscope (SEM), Fourier Transform Infrared (FT-IR) and UV-visible Diffused Reflectance Spectroscopic (DRS) techniques. Ethanol deprives the surface oxygen, thereby generating oxygen defects whose concentration was evaluated by FTIR, Photoluminescence (PL) and Electron Spin Resonance (ESR) studies. FTIR analysis reveal that concentration of oxygen vacancies / defects (Vo) decreases as the nitrogen concentration increases leading to the reduction in the Ti-O bond length. This results in a shift of the IR absorption peak towards a low wave number as predicted by simple physical harmonic oscillator model. The Ti 2p 3/2 XPS spectra of TiO2−xNx shifts to lower binding energies due to the increase in the electron densities around the Ti atoms indicating the formation of Ti3+ in the doped samples. N2 adsorption-desorption isotherms measurements show a slight increase in the Brunner-Emmet–Teller (BET) surface area, pore diameter, mesopore volume, while the crystallite size and the morphology were also effected by the nitrogen doping. The equilibrium adsorption of Toluene molecules on the photocatalyst surface follows Langmuir theory and the rate controlling step could be the surface reaction of the adsorbed Toluene molecules.
    Journal of Sol-Gel Science and Technology 11/2011; 60:144-158. DOI:10.1007/s10971-011-2570-0 · 1.55 Impact Factor
  • S Girish Kumar, L Gomathi Devi
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    ABSTRACT: Titania is one of the most widely used benchmark standard photocatalysts in the field of environmental applications. However, the large band gap of titania and massive recombination of photogenerated charge carriers limit its overall photocatalytic efficiency. The former can be overcome by modifying the electronic band structure of titania including various strategies like coupling with a narrow band gap semiconductor, metal ion/nonmetal ion doping, codoping with two or more foreign ions, surface sensitization by organic dyes or metal complexes, and noble metal deposition. The latter can be corrected by changing the surface properties of titania by fluorination or sulfation or by the addition of suitable electron acceptors besides molecular oxygen in the reaction medium. This review encompasses several advancements made in these aspects, and also some of the new physical insights related to the charge transfer events like charge carrier generation, trapping, detrapping, and their transfer to surface are discussed for each strategy of the modified titania to support the conclusions derived. The synergistic effects in the mixed polymorphs of titania and also the theories proposed for their enhanced activity are reported. A recent venture on the synthesis and applications of anatase titania with a large percentage of reactive {001} facets and their band gap extension to the visible region via nonmetal ion doping which is a current hot topic is briefly outlined.
    The Journal of Physical Chemistry A 09/2011; 115(46):13211-41. DOI:10.1021/jp204364a · 2.78 Impact Factor
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    ABSTRACT: The coordinating behavior of a new dihydrazone ligand, 2,6-bis[(3-methoxysalicylidene)hydrazinocarbonyl]pyridine towards manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) has been described. The metal complexes were characterized by magnetic moments, conductivity measurements, spectral (IR, NMR, UV-Vis, FAB-Mass and EPR) and thermal studies. The ligand crystallizes in triclinic system, space group P-1, with α=98.491(10)°, β=110.820(10)° and γ=92.228(10)°. The cell dimensions are a=10.196(7)Å, b=10.814(7)Å, c=10.017(7)Å, Z=2 and V=1117.4(12). IR spectral studies reveal the nonadentate behavior of the ligand. All the complexes are neutral in nature and possess six-coordinate geometry around each metal center. The X-band EPR spectra of copper(II) complex at both room temperature and liquid nitrogen temperature showed unresolved broad signals with g(iso)=2.106. Cyclic voltametric studies of copper(II) complex at different scan rates reveal that all the reaction occurring are irreversible.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 07/2011; 79(2):348-55. DOI:10.1016/j.saa.2011.03.011 · 2.13 Impact Factor
  • L. Gomathi Devi, K. Mohan Reddy
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    ABSTRACT: Nano-sized silver deposits on the surface of Degussa P25 TiO2 (Ag-DP25) particles act as sites of electron accumulation where the reduction of adsorbed species takes place. Electrons can be transferred from Degussa P25 TiO2 (DP25) to Ag particles because of the difference in the work functions of the two materials. The efficiency of the electron transfer depends on the size and the distribution of metal deposits. A significant photocatalytic oxidation enhancement by metal deposit will only be observed if the metal deposits play a more dominant role than just increasing the life time of charge carriers. The properties of metal deposits like, loaded amount, oxidation state of the deposit and its size will influence the performance. Further, a decrease in band-gap in DP25 and Ag-DP25 was observed due to the carbide ion substitution for the oxide ion in TiO2. Such unintentional carbon incorporation is expected mostly in combustion synthesized materials. Silver metal deposits and unintentional incorporation of the carbon shows the beneficial effect by specific mechanism in the photocatalytic degradation of Congo Red (CR).
    Applied Surface Science 05/2011; 257(15):6821-6828. DOI:10.1016/j.apsusc.2011.03.006 · 2.54 Impact Factor
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    ABSTRACT: The photo degradation of Amaranth (AR) dye by advanced photo Fenton process in the presence of symmetrical peroxides like hydrogen peroxide (H2O2) and ammonium persulfate (APS) are investigated. The influence of various reaction parameters like the effect of iron dosage, concentration of H2O2/APS, initial dye concentration, effect of pH and the influence of various aromatic derivativeswere studied and optimumconditions are reported. The efficiency of the oxidant was strongly influenced by the nature of aromatic photoproducts formed during the course of the degradation reaction. To study their effect on the rate of degradation these aromatic derivatives were added in known concentration (10 ppm). The influence of various aromatic derivatives on the degradation kinetics shows the following order: hydroquinonesNchlorophenolNdichlorobenzeneNaromatic carboxylic acidsNanilidineNnitrophenol. The addition of these derivatives did not influence the degradation pathway although it altered the reaction rate. The percentage COD and TOC removal were determined in presence of aromatic derivatives to evaluate the complete removal of the pollutant. Based on the intermediates obtained in the UV–vis and GC-MS spectroscopic techniques probable degradation mechanism has been proposed.
    Desalination 04/2011; 270(1-3):31-39. DOI:10.1016/j.desal.2010.11.017 · 3.96 Impact Factor
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    ABSTRACT: The present research work has demonstrated the usage of zero valent metallic iron (ZVMI) in the photo- Fenton process under UV light as a promising and novel technique for the complete degradation of di azo dye Bismarck Brown (BB) in aqueous medium. The influence of various reaction parameters like concentration of oxidants/dye/iron powder and pH of the solution was investigated and optimum conditions are reported. Ammonium persulfate (APS) proved to be better oxidant in comparison with hydrogen peroxide for enhancing the degradation rate and effectively inhibited the precipitation of iron hydroxides at higher dosages of iron powder which is attributed to the acidity provided by APS which is crucial for Fenton process. The rate constant for the kinetics of degradation using various oxidation processes follows the order: Fe0/APS/UV > Fe0/H2O2/UV > Fe0/APS/dark > Fe0/UV > Fe0/H2O2/ dark > Fe0/dark > H2O2/UV > APS/UV. The effects of inorganic anions that are commonly found in the industrial effluents like NaCl, KNO3, Na2SO4, Na2CO3 and NaHCO3 at different concentrations on the degradation rate were studied in detail. The degradation was followed by UV–vis and GC–MS techniques
    Journal of the Taiwan Institute of Chemical Engineers 03/2011; 42(2):341–349. DOI:10.1016/j.jtice.2010.05.010 · 2.64 Impact Factor
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    L. Gomathi Devi, G Krishnamurthy
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    ABSTRACT: Investigation of the photocatalytic activity of BaTiO(3), a perovskite wideband gap semiconductor has been done in comparison with a widely used photocatalyst TiO(2) for the degradation of 4-chlorophenol (4-CP), 4-chloroaniline (4-CA), 3,4-dichloronitrobenzene (3,4-DCNB), and 2,4,5-trichlorophenol (2,4,5-TCP). BaTiO(3)/TiO(2) nanoparticles were prepared by gel-to-crystalline conversion method. BaTiO(3) has exhibited better catalytic efficiency and process efficiency compared with TiO(2) in most of the cases. The present research focuses mainly on two aspects: first the photocatalytic activity of BaTiO(3), as there are very few reports in the literature, and second the reactivity/orientation effects of substituent groups of the pollutant molecules on the degradation rate. The above chloroorganic compounds have at least one chlorine substituent in common, along with other functional groups such as -OH, -NH(2), and -NO(2). Furthermore, the effect of electron acceptors and pH on the rate of degradation is presented. The reactions follow first-order kinetics. The degradation reaction was followed by UV-vis, IR, and GC-MS spectroscopic techniques. On the basis of the identification of the intermediates, a probable degradation reaction mechanism has been proposed for each compound.
    The Journal of Physical Chemistry A 02/2011; 115(4):460-9. DOI:10.1021/jp103301z · 2.78 Impact Factor
  • L. Gomathi Devi, S. Girish Kumar
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    ABSTRACT: To understand the role of dopant inside TiO2 matrix, anatase TiO2 was doped with transition metal ions like Mn2+, Fe3+, Ru3+ and Os3+ having unique half filled electronic configuration and their photocatalytic activity was probed in the degradation of Indigo Carmine (IC) and 4-nitrophenol (NP) under UV/solar light. For comparison, TiO2 was also doped with V5+, Ni2+ and Zn2+ metal ions having d0, d8 and d10 electronic configuration respectively. Irrespective of excitation source UV/solar light and nature of the organic pollutant, photocatalytic activities of doped photocatalysts followed the order: Mn2+-TiO2 > Fe3+-TiO2 > Ru3+-TiO2 ≥ Os3+-TiO2 > Zn2+-TiO2 > V5+-TiO2 > Ni2+-TiO2 at an optimum concentration of dopant. Based on the experimental results obtained, it is proposed that the existence of dopant with half filled electronic configuration in TiO2 matrix which is known to enhance the photocatalytic activity is not universal! Rather it is a complex function of several physicochemical–electronic properties of doped titania. Enhanced photocatalytic activity of Mn2+ (0.06 at.%)-TiO2 was attributed to the combined factors of high positive reduction potential of Mn2+/Mn3+ pairs, synergistic effects in the mixed polymorphs of anatase and rutile, smaller crystallite size with high intimate contact between two phases and favorable surface structure of the photocatalyst. Despite the intense research devoted to transition metal ion doped TiO2, it is rather difficult to make unifying conclusion which is highlighted in this study.
    Applied Surface Science 01/2011; 257(7-257):2779-2790. DOI:10.1016/j.apsusc.2010.10.062 · 2.54 Impact Factor
  • L. Gomathi Devi, K. Eraiah Rajashekhar
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    ABSTRACT: Nitrogen was doped into the TiO2 matrix in the concentration range of 0.05–0.20 at.% and the photocatalytic activities were tested for the degradation of phenol (Ph) under UV/solar light using hydrogen peroxide (HP) and ammonium persulfate (APS) as electron acceptors. The prepared photocatalysts characterized by various analytical techniques confirm the incorporation of nitrogen in the TiO2 lattice. The 0.15 at.% dopant concentration shows higher photocatalytic activity compared with sol–gel TiO2 (SG) and Degauss P25 TiO2 (P25) for the degradation process. Photoluminescence technique was used for studying the extent of hydroxyl radicals produced on TiO2 and TiO2−xNx (NT) surface in the presence of oxidants under UV/solar light irradiation. The kinetic rate equation obtained for the best system TiO2−xNx (x = 0.15 at.%)/APS/under solar irradiation is found to be: rap,solar = 0.0041[NT]0.54[APS]0.71[Ph]−0.70. A kinetic/mathematical model was developed based on the nonlinear regression analysis for the various processes and the validity of the model was tested by comparing the experimental values with the theoretically calculated data as a function of variable parameters like catalyst dosage, concentration of electron acceptors and initial concentration of Ph.
    Journal of Molecular Catalysis A Chemical 01/2011; 334(1-2):65–76. DOI:10.1016/j.molcata.2010.10.025 · 3.68 Impact Factor
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    ABSTRACT: Ag deposited nitrogen doped TiO2 (Ag–TiO2−xNx) was prepared using sol gel titania by grinding it with stoichiometric amount of Urea as nitrogen source followed by the photoreduction of Ag+ to Ag0. 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 TiO2 and TiO2−xNx. Ag–TiO2−xNx exhibits much higher visible-light photocatalytic activity when compared with N-doped or pristine TiO2. The catalysts along with the oxidants can accelerate electron transfer process and inhibit the fast electron-hole recombination. The observed high process efficiency (˚�) of Ag–TiO2−xNx particles compared to TiO2−xNx and pure TiO2 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.
    Chemical Engineering Journal 01/2011; 181. DOI:10.1016/j.cej.2011.11.076 · 4.06 Impact Factor
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    ABSTRACT: Anatase TiO2 was doped with divalent transition metal ions like Mn2+, Ni2+ and Zn2+ and characterized by various analytical techniques. Powder X-ray diffraction revealed stabilization of anatase phase for Ni2+ and Zn2+ doped samples, while phase transformation from anatase to rutile was promoted due to Mn2+ inclusion. The rutile fraction increased with Mn2+ concentration due to the creation of surface oxygen vacancies. All the doped catalysts showed red shift in the band gap absorption to the visible region. The photocatalytic activities of these catalysts were evaluated in the degradation of Aniline Blue (AB) under UV/solar light. Among the photocatalysts, Mn2+ (0.06 at.%)–TiO2 showed enhanced activity, which is attributed to the synergistic effect in the bicrystalline framework of anatase and rutile. Further the unique half filled electronic structure of Mn2+ serves as a shallow trap for the charge carriers to enhance the photocatalytic activity. An insight to the mechanism of interfacial charge transfer in the mixed phase of anatase and rutile is explored, taking into consideration the theories of previous models.
    Journal of Molecular Catalysis A Chemical 08/2010; 328(1-2):44-52. DOI:10.1016/j.molcata.2010.05.021 · 3.68 Impact Factor
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    ABSTRACT: The degradation of Methyl Orange was carried out using Photo Fenton process (Fe2+ / H2O2 / UV) and Photo Fenton like processes (Fe3+ / H2O2 / UV, Fe2+ / S2O82- / UV and Fe2+ / S2O82- / UV) at acidic pH 3 using hydrogen peroxide and ammonium persulfate (APS) as oxidants. The oxidation state of the iron had a significant influence on the efficiency of photo Fenton / photo Fenton like processes. It was found that the process with a source of Fe3+ ion as the catalyst showed higher efficiency compared to the process with Fe2+ ion as the catalyst. H2O2 served as a better oxidant for both the oxidation state of iron compared to APS. The lower efficiency of APS is attributed for the generation of excess protons which scavenges the hydroxyl radicals necessary for degradation. Further the sulfate ions produced from S2O82- forms complex with Fe2+ / Fe3+ ions thereby reducing the concentration of free iron ions in the solution. This process reduces the concentration of hydroxyl radicals in the solution. The higher efficiency of Fe3+ for both the oxidants is attributed to the enhanced generation of hydroxyl radicals.
    Chemical Papers- Slovak Academy of Sciences 06/2010; 64:378–385. DOI:10.2478/s11696-010-0011-0 · 1.19 Impact Factor