L. Gomathi Devi

Bangalore University, Bengalūru, Karnataka, India

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Publications (45)115.93 Total impact

  • L. Gomathi Devi · R. Kavitha · B. Nagaraj
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    ABSTRACT: Sulfur ion (S6+) was incorporated into the TiO2 lattice (Ti0.85S0.15O2) using sulfur powder as precursor. 0.05% of silver was deposited on the surface of Ti0.85S0.15O2 by photoinduced deposition method. The photocatalytic reactivity of TiO2, Ag–TiO2, Ti0.85S0.15O2 and Ag–Ti0.85S0.15O2 photocatalysts were probed for the degradation of a model compound congo red (CR) dye under UV/solar light illumination. FTIR and XPS results suggested that the dopant sulfur ion (S6+) was incorporated into the TiO2 crystal lattice at Ti4+ lattice site and the sulfur ions on the surface were modified as active sites serving as electron withdrawing group. TEM and XPS analysis of Ag–Ti0.85S0.15O2 has confirmed the deposition of silver in the Ag0 state. Ag–Ti0.85S0.15O2 shows better photoactivty under solar light irradiation when compared to all the other photocatalysts. The enhanced photocatalytic activity of this catalyst is attributed to the synergetic effects of the incorporated dopant electronic energy level with the dual surface modifications of the type active centers and Schottky junctions created by metallic Ag0. Further the deposited Ag particles plays a dual role one as a sensitizer due to the Surface Plasmon Resonance (SPR) effect and also acts as an electron trapper under solar light illumination reducing the recombination of photogenerated charge carriers.
    No preview · Article · Dec 2015 · Materials Science in Semiconductor Processing
  • L. Gomathi Devi · R. Kavitha
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    ABSTRACT: The titania based nanomaterials are an attractive candidates for energy and environmental applications. TiO2 is one of the most important photocatalyst for its special multiple characteristics like high reactivity, low toxicity, low cost, high flexibility, long term stability especially in aqueous medium, shows relatively high energy conversion efficiency, easy to prepare several modifications with various morphologies, with good recycle ability, favorable band edge positions and superior physicochemical and optoelectronic properties. However, large band gap of titania and massive charge carrier recombination impairs its wide photocatalytic applications. As an alternative to various strategies reported extensively in literature, noble metal deposition on the titania surface seems to be effective and reliable method for increasing the life time of excitonic pairs and to extend the band gap absorption to visible range of the solar spectrum. In this focused review, we discuss the fundamental and critical issues in the photocatalytic activity of metal deposited titania taking into consideration the influence of various parameters like preparation methods, metal dispersion on titania, formation of heterojunctions and optimum metal loadings on the interfacial charge carrier dynamics. The metal deposition onto the varied hierarchical morphology, crystal structure, defective surface of titania along with extended modification like simultaneous doping and heterostructure coupling with other semiconductors is also highlighted. It was revealed that deposited metal is involved in multiple crucial roles like; (i) it serves as passive electron sink with high capacity to store electrons to suppress photogenerated charge carrier recombination; (ii) it facilitates rapid dioxygen reduction to generate reactive free radicals; (iii) visible light response for titania can be achieved through surface plasmon resonance effect; (iv) direct excitation of metal nanoparticles especially under visible light and vectorial electron transfer to the TiO2 CB. This review attempts to provide a comprehensive update of design and fabrication of metallization on the surface of TiO2 semiconductor particles highlighting some of the advancements made in the energy and environment applications.
    No preview · Article · Nov 2015 · Applied Surface Science
  • 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-TiO2via 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.
    No preview · Article · Nov 2014 · ChemInform
  • 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.
    No preview · Article · Sep 2014 · Journal of Molecular Catalysis A Chemical
  • B. Nagaraj · L. Gomathi Devi
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    ABSTRACT: Silver was deposited on manganese-doped titanates (Mn-TiO2) by photoinduced deposition method. The catalyst shows enhanced photocatalytic activity due to the synergistic effect of bicrystalline framework of anatase and rutile structures with high intimate contact due to the similarity in their crystallite sizes. The deposited metal nanostructures help in the formation of resonant surface plasmons in response to a photon flux, localizing the electromagnetic energy close to their surfaces. Better charge separation is achieved near the semiconductor surface due to the localized field. Silver deposition was varied from 0.1 to 1.5% on the surface of Mn-TiO2. The mechanism of interfacial electron transfer at heterojunctions in mixed phase induced by the plasmonic catalysis is explained. The extent of band bending, the variation of potential field in the space charge region with respect to the size of the deposited Ag metal particles is discussed. The photocatalytic activity of silver deposited Mn-TiO2 was evaluated by taking resorcinol (Rs) as the model compound along with oxidants such as hydrogen peroxide (H2O2) and ammonium per sulfate (APS) under UV/solar light illumination. The electronic level of the dopant, high intimate contact between the anatase and rutile phases along with efficient electron trapping by silver particles, plays a significant role in the photocatalytic process.
    No preview · Article · Aug 2014 · Journal of Molecular Catalysis A Chemical
  • R. Kavitha · L. Gomathi Devi
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    ABSTRACT: Visible light-sensitive carbon doped titanium dioxide (C-TiO2) was prepared by grinding anatase TiO2 with anhydrous D-glucose solution as carbon source followed by calcination. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET surface area measurements, scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), FTIR analysis and photoluminescence (PL) techniques. The results confirmed the interstitial incorporation of carbon atoms in the TiO2 lattice via O-Ti-C and Ti-O-C surface states. The calculation of valence band (VB) edge position of C-TiO2 by using electronegativity values shows cathodic shift with increase in the carbon concentration and this renders high oxidative power for photogenerated holes. The observed new electronic state above the VB edge was responsible for the electronic origin of band gap narrowing and visible light photoactivity of C-TiO2. The carbon atom was also present as carbonaceous species on the surface which acts as sensitizer. The photocatalytic activity of C-TiO 2 was evaluated for the degradation of 4-chlorophenol under both UV and solar irradiation. The undoped TiO2 showed better activity under UV light whereas C-TiO2 showed higher photocatalytic activity under visible light. The pretreatment of C-TiO2 with UV light reduced the visible light activity due to the removal of surface carbonaceous species. The synergistic effect of surface carbonaceous species along with interstitial carbon is discussed in detail and accounted for visible light activity.
    No preview · Article · Jun 2014 · Journal of Environmental Chemical Engineering
  • L. Gomathi Devi · R. Kavitha
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    ABSTRACT: Sulfur ion (S6+) was doped into the anatase TiO2 prepared by sol-gel method (SG-TiO2) using sulfur powder as a sulfur source (S-TiO2) and its photoreactivity was probed for the degradation of phenol under UV/solar light illumination. The S-TiO2 and SG-TiO2 were characterized by PXRD, UV-vis DRS, FTIR, SEM, XPS, BET and PL techniques. It was observed that S6+ ion was incorporated into the TiO2 crystal lattice at Ti4+ lattice site and the sulfur on the surface gets modified to SO42- due to the heat treatment under atmospheric conditions. The high photocatalytic activity of S-TiO2 compared to SG-TiO2 is attributed to the surface modification of sulfur as sulfate which plays a crucial role in trapping electrons. S-TiO2 shows significant increase in the surface area, reduced crystallite size, increased surface acidity, visible light absorption and prolonged lifetime of the photogenerated charge carriers. Hole scavengers like potassium iodide and tertiary butanol suggested the surface degradation mechanism rather than the bulk degradation pathway. Addition of oxidizing agents to the degradation reaction did not show any enhancement in the degradation rates since the presence of SO42- on the TiO2 surface itself acts as the efficient electron trapping centers. Both trapping and detrapping of the electron takes place more efficiently at SO42- centers. The enhanced activity of S-TiO2 is attributed to the synergistic effect between S6+ dopant with surface modified SO42-.
    No preview · Article · Feb 2014 · Materials Chemistry and Physics
  • 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.
    No preview · Article · Aug 2013 · Applied Catalysis B Environmental
  • 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.
    No preview · Article · Jul 2013 · Applied Surface Science
  • 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.
    No preview · Article · Mar 2013 · Journal of Molecular Catalysis A Chemical
  • 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.
    No preview · Article · Nov 2012 · Applied Surface Science
  • 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
    No preview · Article · Dec 2011 · Central European Journal of Chemistry
  • 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.
    No preview · Article · Nov 2011 · Journal of Sol-Gel Science and Technology
  • 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.
    No preview · Article · Sep 2011 · The Journal of Physical Chemistry A
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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.
    No preview · Article · Jul 2011 · Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy
  • 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).
    No preview · Article · May 2011 · Applied Surface Science
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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.
    No preview · Article · Apr 2011 · Desalination
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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
    No preview · Article · Mar 2011 · Journal of the Taiwan Institute of Chemical Engineers
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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.
    Preview · Article · Feb 2011 · The Journal of Physical Chemistry A
  • 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.
    No preview · Article · Jan 2011 · Applied Surface Science