Hydrothermal synthesis of (Fe,N) co-doped TiO<Subscript>2</Subscript> powders and their photocatalytic properties under visible light irradiation

(Fe, N) co-doped titanium dioxide powders have been prepared by a quick, low-temperature hydrothermal method using TiOSO₄, CO(NH₂)₂, Fe(NO₃)₃, and CN₃H₅ · HCl as starting materials. The synthesized powders were characterized by XRD, TEM, BET, XPS, and UV–Vis spectroscopy. Experimental results show that the as-synthesized TiO₂ powders are present as the anatase phase and that the N and Fe ions have been doped into the TiO₂ lattice. The specific surface area of the powders is 167.8 m²/g by the BET method and the mean grain size is about 11 nm, calculated by Scherrer’s formula. UV–Vis absorption spectra show that the edge of the photon absorption has been red-shifted up to 605 nm. The doped titanium dioxide powders had excellent photocatalytic activity during the process of photo-degradation of formaldehyde and some TVOC gases under visible light irradiation.     

Preparation of nanocrystalline Fe-doped TiO<Subscript>2</Subscript> powders as a visible-light-responsive photocatalyst

Nanocrystalline Fe-doped TiO₂ powders were prepared using TiOSO₄, urea, and Fe(NO₃)₃ · 9H₂O as precursors through a hydrothermal method. The as-synthesized yellowish-colored powders are composed of anatase TiO₂, identified by X-ray diffraction (XRD). The grain size ranged from 9.7 to 12.1 nm, calculated by Scherrer’s method. The specific surface area ranged from 141 to 170 m²/g, obtained by the Brunauer–Emmett–Teller (BET) method. The transmission electron microscopy (TEM) micrograph of the sample shows that the diameter of the grains is uniformly distributed at about 10 nm, which is consistent with that calculated by Scherrer’s method. Fe³⁺ and Fe²⁺ have been detected on the surface of TiO₂ powders by X-ray photoelectron spectroscopy (XPS). The UV–Vis diffuse reflection spectra indicate that the light absorption thresholds of the Fe-doped TiO₂ powders have been red-shifted into the visible light region. The photocatalytic activity of the Fe-doped TiO₂ was evaluated through the degradation of methylene blue (MB) under visible light irradiation. The Fe-doped TiO₂ powders have shown good visible-light photocatalytic activities and the maximum degradation ratio is achieved within 4.5 h.     

Preparation of novel visible-light-driven In<Subscript>2</Subscript>O<Subscript>3</Subscript>–CaIn<Subscript>2</Subscript>O<Subscript>4</Subscript> composite photocatalyst by sol–gel method

Novel visible-light-activated In₂O₃–CaIn₂O₄ photocatalysts were developed in this paper through a sol–gel method. The photocatalytic activities of In₂O₃–CaIn₂O₄ composite photocatalysts were investigated based on the decomposition of methyl orange under visible light irradiation (λ > 400 nm). The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and UV–vis diffused reflectance spectroscopy (DRS). The results revealed that the In₂O₃–CaIn₂O₄ composite samples with different In₂O₃ and CaIn₂O₄ content can be obtained by controlling the synthesis temperature, and the composite photocatalysts extended the light absorption spectrum toward the visible region. The photocatalytic tests indicated that the composite samples demonstrated high visible-light activity for decomposition of methyl orange. The significant enhancement in the In₂O₃–CaIn₂O₄ photo-activity under visible light irradiation can be ascribed to the efficient separation of photo-generated carriers in the In₂O₃ and CaIn₂O₄ coupling semiconductors.     

Influence of NH<Subscript>3</Subscript>-treating temperature on visible light photocatalytic activity of N-doped P<Subscript>25</Subscript>-TiO<Subscript>2</Subscript>

The influence of NH₃-treating temperature on the visible light photocatalytic activity of N-doped P₂₅-TiO₂ as well as the relationship between the surface composition structure of TiO₂ and its visible light photocatalytic activity were investigated. The results showed that N-doped P₂₅-TiO₂ treated at 600°C had the highest activity. The structure of P₂₅-TiO₂ was converted from anatase to rutile at 700°C. Moreover, no N-doping was detected at the surface of P₂₅-TiO₂. There was no simply linear relationship between the visible light photocatalytic activity and the concentration of doped nitrogen, and visible light absorption. The visible light photocatalytic activity of N-doped P₂₅-TiO₂ was mainly influenced by the synergistic action of the following factors: (i) the formation of the single-electron-trapped oxygen vacancies (denoted as V_o^·); (ii) the doped nitrogen on the surface of TiO₂; (iii) the anatase TiO₂ structure.     

Photodegradation of dye pollutants on TiO<Subscript>2</Subscript> pillared bentonites under UV light irradiation

TiO₂ pillared bentonite samples dried under different conditions are used to degrade 2,4-dichlorophenol and orange II under UV light irradiation. The supercritical dried sample exhibits a high activity for the photodegradation of 2,4-dichlorophenol and orange II due to its structural features. TOC and COD are measured during the degradation of 2,4-dichlorophenol under UV light irradiation using P25 and TiO₂ pillared bentonite samples dried under different conditions. The clay-based catalysts can be readily separated by filtration or sedimentation.     

Effect of PEG with different <Emphasis Type="Italic">M</Emphasis><Subscript>W</Subscript> as template direction reagent on preparation of porous TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> with assistance of supercritical CO<Subscript>2</Subscript>

Titania–silica composite have been prepared using polyethylene glycol (PEG) with different molecular weights (M _w), PEG20000, PEG10000, and PEG2000, as template in supercritical carbon dioxide (SC CO₂). The composite precursors were dissolved in SC CO₂ and impregnated into PEG templates using SC CO₂ as swelling agent and carrier. After removing the template by calcination at suitable temperature, the titania–silica composite were obtained. The composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and nitrogen sorption–desorption experiment. Photocatalytic activity of the samples has been investigated by photodegradation of methyl orange. Results indicate that there are many Si–O–Ti linkages in the TiO₂/SiO₂ composite; the PEG template has a significant influence on the structure of TiO₂/SiO₂. In addition, the TiO₂/SiO₂ prepared with PEG10000 exhibited high photocatalytic efficiency. So this work supplies a clue to control and obtain the TiO₂/SiO₂ composite with different photocatalytic reactivity with the aid of suitable PEG template in supercritical CO₂.     

Sol–gel synthesis,characterization and photocatalytic activity of mesoporous TiO<Subscript>2</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3 </Subscript>granules

Mesoporous TiO₂/γ-Al₂O₃ composite granules were prepared by combining sol–gel/oil-drop method, using various titania solution. The product granules can be used as a photocatalyst or adsorbent in moving, fluidized bed reactors. The phase composition and pore structure of the granules can be controlled by calcination temperature and using different titania solution. In the photocatalysis of NH₃ decomposition, TiO₂/γ-Al₂O₃ granules using Degussa P25 powder treated thermally at 450 °C showed the highest catalytic ability. However, TiO₂/γ-Al₂O₃ granules using titania made by hydrothermal method had comparable performance in NH₃ decomposition.     

Effect of TiO<Subscript>2</Subscript> surface modification in Rhodamine B photodegradation

Commercial TiO₂ nanoparticles were superficially modified through polymeric resins obtained from polymerization of citrate complexes of Y³⁺ and Al³⁺ with ethylenglycol. The materials were treated at 450 °C for 4 h to obtain modified nanoparticles, which were characterized by HR-TEM, Zeta potential and surface area through N₂ fisisorption. Rhodamine B photodegradation by visible light irradiation and in presence of those modified nanoparticles was compared with the same process in presence of unmodified commercial TiO₂ nanoparticles. It was observed, by UV–visible spectroscopy, that the catalytic photoactivity in presence of modified nanoparticles was smaller than that observed with commercial TiO₂ nanoparticles. However, the surface modifier played an important role in the photodegradation kinetic process, showing a non-linear relation between modifier amount and photodegradation rate, presenting a maximum value at 0.8% (w/w).     

Microwave-assisted combustion synthesis of nanocrystalline La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript> oxide-ion conductor and its characterization

Nanocrystalline La₂Mo₂O₉ oxide-ion conductor has been successfully synthesized by microwave-assisted combustion method within a very short time duration using aspartic acid as the newer fuel in a domestic microwave oven. The synthesized nanocrystalline powder showed good sinterability and reached more than 97% of theoretical density even at low temperature of 800 °C for 5 h. The sintered La₂Mo₂O₉ sample exhibited a conductivity of 0.159 S/cm in air at 750 °C.     

Modeling the active centers of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/SiO<Subscript>2</Subscript> and V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> supported catalysts. DFT theoretical analysis of optical properties

Within the framework of the density functional theory (DFT), the electronic structure of monooxodioxovanadium functional groups in tetrahedral coordination, which model the active centers (ACs) of fine supported catalysts V₂O₅/SiO₂ and V₂O₅/TiO₂, has been analyzed. The optimal structures of three ACs as possible models of monomeric and polymeric oxovanadium forms on the carriers with low vanadium content were determined. The modified DFT method involving the time dependence of Kohn-Sham equation (TDDFT) was used for the adopted AC models to calculate the energies of the excited states, and optical spectra of the absorption in 25000–60000 cm^?1 region were reconstructed on their base. The spectrum in this region is due to O → V charge transfer. The features of electronic spectra with the charge transfer for V₂O₅/SiO₂ and V₂O₅/TiO₂ catalysts and the vibrational spectra of three AC models corresponding to the monomeric and dimeric oxovanadium forms of the supported catalysts V₂O₅/SiO₂ and V₂O₅/TiO₂ were defined. The detailed interpretation of normal vibration frequencies is given. The frequencies typical of the monomeric and dimeric oxovanadium forms on the carrier surface were identified.     

Direct analysis of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powders by total reflection X-ray fluorescence spectrometry

A direct analysis procedure for the determination of trace impurities of Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga in Al₂O₃ ceramic powders by total reflection X-ray fluorescence spectrometry (TXRF) is described. The powders were analysed in the form of slurries containing 1–10 mg mL^–1 of powder. The use of the procedure in the case of powders with differing grain size and for different slurry concentrations was investigated. Three different quantification possibilities were compared, namely the use of Al as a matrix component, the use of Fe as a trace element contained in the sample or of Co added in concentrations of 200 g g^–1 as internal standard. The homogeneity of elemental distributions in sample layers deposited on the TXRF quartz carriers by evaporating 5 L of the 10 mg mL^–1 slurries was studied by scanning the 4- to 5-mm-diameter spots of two samples by synchrotron radiation TXRF at Hasylab. For powders with differing graininess but mainly finer than about a few 10 m, no systematic influence of the grain size on the accuracy of the determinations of Ca, V, Fe, Ni, Cu and Zn could be observed. The measurement precision, however, seemed to be limited by inhomogeneous distributions of the trace elements in the samples as testified by the synchrotron radiation TXRF scans. Detection limits of the developed TXRF procedure for Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga were found to be in the 0.3–7 g g^–1 range and were shown to increase slightly with the grain size of the samples. Quantification using Al (matrix) as internal standard led to systematically higher values out of the accuracy required, whereas the other two approaches in all cases led to reliable results.Dedicated to the memory of Wilhelm Fresenius     

Preparation and characterization of highly photoactive nanocrystalline TiO<Subscript>2</Subscript> powders by solvent evaporationinduced crystallization method

Highly photoactive bi-phase nanocrystalline TiO₂ photocatalyst was prepared by a solvent evaporation-induced crystallization (SEIC) method, and calcined at different temperatures. The obtained TiO₂ photocatalyst was characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM) and BET surface areas. The photocatalytic activity was evaluated by the photocatalytic oxidation of acetone in air. The results show that solvent evaporation can promote the crystallization and phase transformation of TiO₂ at 100°C. When calcination temperatures are below 600°C, the prepared TiO₂ powders show bimodal pore size distributions in the mesoporous region. At 700°C, the pore size distributions exhibit monomodal distribution of the inter-aggregated pores due to the collapse of the intra-aggregated pores. At 100°C, the obtained TiO₂ photocatalyst by this method shows good photocatalytic activity, and at 400°C, its photocatalytic activity exceeds that of Degussa P25. This may be attributed to the fact that the prepared TiO₂ photocatalyst has higher specific surface areas, smaller crystallite size and bimodal pore size distribution.     

LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> and LiCoO<Subscript>2</Subscript> composite cathode materials obtained by mechanical activation

New composite cathode materials xLiMn₂O₄/(1 ? x) LiCoO₂(x = 0.7, 0.6, 0.5 и 0.4) were obtained by mechanical activation. According to scanning electron microscopy data, the process was accompanied by pronounced dispersion and fine mixing of the initial components. In the course of the preparation and electrochemical cycling of the composites, LiMn₂O₄ and LiCoO₂ partially reacted, leading to the replacement of manganese with cobalt in the structure of spinel, which was detected by powder X-ray diffraction (XRD), IR and X-ray photoelectron spectroscopy (XPS), and cyclic chronopotentiometry. The specific discharge capacity of composites was ～100 mAh/g.     

Photocatalytic reduction of CO<Subscript>2</Subscript> over TiO<Subscript>2</Subscript> based catalysts

At present, carbon dioxide is considered the largest contributor among greenhouse gases. This review covers the current state of problem of carbon dioxide emissions from industrial and combustion processes, the principle of photocatalysis, existing literature related to photocatalytic CO₂ reduction over TiO₂ based catalysts and the effects of important parameters on the process performance including light wavelength and intensity, type of reductant, metal-modified surface, temperature and pressure. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Quantum-chemical modelling of nanotubes of titanium silicocarbides Ti<Subscript>2</Subscript>SiC,Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript>, and Ti<Subscript>4</Subscript>SiC<Subscript>3</Subscript>

Atomic models are proposed for nanotubes of the titanium silicocarbides Ti₂SiC, Ti₃SiC₂, and Ti₄SiC₃, and their electronic structure and interatomic interactions are investigated by the density functional tight-binding method (DFTB) in comparison with the corresponding crystalline phases. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 2, pp. 88-92, March-April, 2009.     

Ionic conduction of a high-temperature modification of Lu<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>

A nanoceramic product of the composition Lu₂Ti₂O₇ is synthesized by a coprecipitation method with a subsequent sublimation drying and an annealing at 650–1650°C. The conduction of Lu₂Ti₂O₇ synthesized at 1650°C is ionic (10^–3 S cm^–1 at 800°C). Thus, a new material with a high ionic conduction has been discovered. The ordering in Lu₂Ti₂O₇ is studied by methods of RFA, RSA, IK spectroscopy, electron microscopy, and impedance spectroscopy. The existence of a low-temperature phase transition fluorite-pyrochlore at 800°C and a high-temperature conversion order-disorder at 1650°C are established.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 298–303.Original Russian Text Copyright © 2005 by Shlyakhtina, Ukshe, Shcherbakova.     

X-ray photoelectron study of the interaction of H<Subscript>2</Subscript> and H<Subscript>2</Subscript>+O<Subscript>2</Subscript> mixtures on the Pt/MoO<Subscript>3</Subscript> model catalyst

The effects of H₂ and H₂ + O₂ gas mixtures of varying composition on the state of the surface of the Pt/MoO₃ model catalyst prepared by vacuum deposition of platinum on oxidized molybdenum foil were investigated by X-ray photoelectron spectroscopy (XPS) at room temperature and a pressure of 5–150 Torr. For samples with a large Pt/Mo ratio, the XP spectrum of large platinum particles showed that the effect of hydrogen-containing mixtures on the catalyst was accompanied by the reduction of molybdenum oxide. This effect results from the activation of molecular hydrogen due to the dissociation on platinum particles and subsequent spill-over of hydrogen atoms on the support. The effect was not observed at low platinum contents in the model catalyst (i.e., for small Pt particles). It is assumed for the catalyst that the loss of its hydrogen-activating ability is a consequence of the formation of platinum hydride. Possible participation of platinum hydride as intermediate in hydrogen oxidation to H₂O₂ is discussed.     

Temperature dependence of the polarization resistance of the O<Subscript>2</Subscript>,Au/La<Subscript>0.88</Subscript>Sr<Subscript>0.12</Subscript>Ga<Subscript>0.82</Subscript>Mg<Subscript>0.18</Subscript>O<Subscript>2.85</Subscript> electrode system

The impedance of a porous gold electrode in contact with solid electrolyte La_0.88Sr_0.12Ga_0.82Mg_0.18O_2.85 and the effect of the manufacture conditions on its polarization resistance are studied at 600–800°C in air. The overall oxygen reaction rate on a gold electrode is described as the sum of two partial constituents, namely, the oxygen exchange at the gas/electrolyte interface at the gold/gas/electrolyte triple-phased boundary.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 190–197.Original Russian Text Copyright © 2005 by Shkerin, Sokolova, Khlupin, Beresnev.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Effects of Ni-ion doping on electrochemical characteristics of spinel LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> powders prepared by a spray-drying method

Spinel LiMn_2−x Ni _x O₄ compounds doped with a range of Ni (x=0–0.06) were synthesized by a spray-drying method. The structure and morphology characteristics of the powders were studied in detail by means of X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy. The XRD data reveal that all the samples have well-defined spinel structure, but, with the increase in Ni content, the doped lithium manganese spinels have smaller lattice constant. The undoped and doped spinel LiMn₂O₄ particles are fine, narrowly distributed, and well crystallized. The electrochemical characteristics of the samples are measured in the coin-type cells in a potential range of 3.2–4.35 V vs Li/Li⁺. All cyclic voltammogram curves exhibit two pairs of redox reaction peaks, but, among them, there are some differences about the peak split. With the increase in the Ni content, the specific capacities of the samples decrease slightly, but their cyclic ability increases.