Synthesis and nanostructural investigation of TiO<Subscript>2</Subscript> nanorods doped by SiO<Subscript>2</Subscript>

TiO₂ Nano rods can be used as dye-sensitized solar cells, various sensors and photocatalysts. These nanorods are synthesized by a hydrothermal corrosion process in NaOH solution at 200°C using TiO₂ powder as the source material. In the present work, the synthesis of TiO₂ nanorods in anatase, rutile and Ti₇O₁₃ phases and synthesis of TiO₂ nanorods by incorporating SiO₂ dopant, using the sol–gel method and alkaline corrosion are reported. The morphologies and crystal structures of the TiO₂ nanorods are characterized using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) study. The obtained results show not only an aggregation structure at high calcination temperatures with spherical particles but also Ti–O–Si bonds having four-fold coordination with oxygen in SiO^4 −.     

Thermostable photocatalytically active TiO<Subscript>2</Subscript> anatase nanoparticles

Anatase is the low-temperature (300–550 °C) crystalline polymorph of TiO₂ and it transforms to rutile upon heating. For applications utilizing the photocatalytic properties of nanoscale anatase at elevated temperatures (over 600 °C) the issue of phase stabilisation is of major interest. In this study, binary TiO₂/SiO₂ particles were synthesized by a flame aerosol process with TiCl₄ and SiCl₄ as precursors. The theoretical Si/Ti ratio was varied in the range of 0.7–1.3 mol/mol. The synthesized TiO₂/SiO₂ samples were heat treated at 900 and 1,000 °C for 3 h to determine the thermostability of anatase. Pyrogenic TiO₂ P25 (from Evonik/Degussa, Germany) widely applied as photocatalyst was used as non-thermostabilized reference material for comparison of photocatalytic activity of powders. Both the non-calcinated and calcinated powders were characterized by means of XRD, TEM and BET. Photocatalytic activity was examined with dichloroacetic acid (DCA) chosen as a model compound. It was found that SiO₂ stabilized the material retarding the collapse of catalyst surface area during calcination. The weighted anatase content of 85% remains completely unchanged even after calcination at 1,000 °C. The presence of SiO₂ layer/bridge as spacer between TiO₂ particles freezes the grain growth: the average crystallite size increased negligibly from 17 to 18 nm even during the calcination at 1,000 °C. Due to the stabilizing effect of SiO₂ the titania nanoparticles calcinated at 900 and 1,000 °C show significant photocatalytic activity. Furthermore, the increase in photocatalytic activity with calcination temperature indicates that the titania surface becomes more accessible either due to intensified cracking of the SiO₂ layer or due to enhanced transport of SiO₂ into the necks thus releasing additional titania surface.     

Fabrication and characterization of CdS-sensitized TiO<Subscript>2</Subscript> nanotube photoelectrode

CdS quantum dot (Qd)-sensitized TiO₂ nanotube array photoelectrode is synthesised via a two-step method on tin-doped In₂O₃-coated (ITO) glass substrate. TiO₂ nanotube arrays are prepared in the ethylene glycol electrolyte solution by anodizing titanium films which are deposited on ITO glass substrate by radio frequency sputtering. Then, the CdS Qds are deposited on the nanotubes by successive ionic layer adsorption and reaction technique. The resulting nanotube arrays are characterized by scanning electron microscopy, X-ray diffraction (XRD) and UV–visible absorption spectroscopy. The length of the obtained nanotubes reaches 1.60 μm and their inner diameter and wall thickness are around 90 and 20 nm, respectively. The XRD results show that the as-prepared TiO₂ nanotubes array is amorphous, which are converted to anatase TiO₂ after annealed at 450 °C for 2 h. The CdS Qds deposited on the TiO₂ nanotubes shift the absorption edge of TiO₂ from 388 to 494 nm. The results show that the CdS-sensitized TiO₂ nanotubes array film can be used as the photoelectrode for solar cells.     

Poly(vinyl chloride)-<Emphasis Type="Italic">graft</Emphasis>-poly(<Emphasis Type="Italic">N</Emphasis>-vinyl caprolactam) graft copolymer: synthesis and use as template for porous TiO<Subscript>2</Subscript> thin films in dye-sensitized solar cells

Poly(N-vinyl caprolactam) (PNVCL) side chains were grafted to a poly(vinyl chloride) (PVC) backbone via atom transfer radical polymerization. The synthesized PVC-g-PNVCL graft copolymer was templated for the preparation of porous TiO₂ thin films, which involved a sol–gel reaction and calcination process. The interaction of the carbonyl groups in the PVC-g-PNVCL with the titania was revealed by FT-IR spectroscopy. X-ray diffraction and transmission electron microscopy analysis showed the formation of porous TiO₂ thin films with the anatase phase. A series of porous TiO₂ thin films with different pore sizes and porosities was prepared by varying the solution compositions and were used as photoelectrodes in dye-sensitized solar cells (DSSC) with a polymer electrolyte. The DSSC performed best when using the TiO₂ film with higher porosity, lower interfacial resistance, and longer electron life time. The highest energy conversion efficiency, photovoltage (V _oc), photocurrent density (J _sc), and fill factor (FF) were 1.2%, 0.68 V, 3.2 mA/cm², and 0.57 at 100 mW/cm², respectively, for the quasi-solid state DSSC with a 730-nm-thick TiO₂ film.     

Preparation of nanosized Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript> using different content of starting materials and their photoactivities

A series of nanosized Bi₂WO₆ catalysts was synthesized using various starting materials, and they were characterized by X-ray diffractometry, transmission electron microscopy, and diffuse reflectance spectroscopy. Rhodamine-B (RhB) photodegradation in aqueous medium was employed as a probe reaction to test the photoactivity of the as-prepared samples. Dependence of the photocatalytic activities on different contents of the starting materials was examined under visible irradiation (λ > 400 nm). The sample prepared in the following conditions: reaction time 24 h, the pH of the solution 7, the Bi³⁺ amount in the start precipitates 5 mmol — exhibited the highest photochemical activity when the hydrothermal temperature was settled at 180°C. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 243–249, Martch–April, 2009.     

Biotemplate fabrication of SnO<Subscript>2</Subscript> nanotubular materials by a sonochemical method for gas sensors

A sonochemical method is developed to fabricate SnO₂ nanotubular materials from biological substances (here, it is cotton). The cotton fibers in SnCl₂ solution were first treated with ultrasonic waves in air, followed by calcinations to give nanotubular materials that faithfully retain the initial cotton morphology. The microstructure and morphology of the obtained SnO₂ nanotubules were characterized by the combination of field-emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and N₂ adsorption/desorption measurements. The thermal behavior and crystalline properties were examined in the temperature range of 450–700 °C. The nanocrystals composing of SnO₂ nanotubules were estimated about 8.5, 13.2, and 14.2 nm corresponding to calcination temperatures of 450, 550, and 700 °C, respectively. The sensor performance of biomorphic SnO₂ nanotubules calcined at 700 °C was investigated in the atmosphere of ethanol, formaldehyde, carbinol, carbon monoxide, hydrogen, ammonia, and acetone, respectively, which exhibited a good selectivity for acetone at a working temperature of 350 °C. The sensitivity to 20 ppm acetone, S, was 6.4 at 350 °C with rapid response and recovery (around 10–9 s). These behaviors were well explained in relation to the morphology of the nanotubules thus produced.     

Synthesis and photocatalytic activity of polyaniline–TiO<Subscript>2</Subscript> composites with bionic nanopapilla structure

Polyaniline (PANI)–TiO₂ nanocomposites possessing both nano and microscale structures were prepared through a facile hydrothermal route in the presence of PANI. The nanopapilla particles were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectra, X-ray diffraction, FTIR spectra, UV–Vis spectroscopy, and N₂ adsorption analysis, etc. The results show that the composites possess both nano and microscale structures. The TiO₂ nanorods are dispersed on PANI with one end fixed to the surface. The photocatalytic properties of the powders were verified by the photodegradation of gaseous acetone under UV (λ = 254 nm) and visible-light irradiation (λ > 400 nm). In fact, the photocatalytic effects exhibited by the composite particles were superior to that of pure TiO₂ and P25 samples. This excellent behavior is attributed to the structural features of PANI–TiO₂ microspheres and the synergistic effect between PANI and TiO₂ which facilitates a larger amount of surface active sites. This in turn causes a faster charge separation and slower charge recombination which results in a more efficient decomposition of gaseous pollutants.     

Effect of ethylene carbonate plasticizer and TiO<Subscript>2</Subscript> nanoparticles on 49% poly(methyl methacrylate) grafted natural rubber-based polymer electrolyte

The effect of plasticizer and TiO₂ nanoparticles on the conductivity, chemical interaction and surface morphology of polymer electrolyte of MG49–EC–LiClO₄–TiO₂ has been investigated. The electrolyte films were successfully prepared by solution casting technique. The ceramic filler, TiO₂, was synthesized in situ by sol-gel process and was added into the MG49–EC–LiClO₄ electrolyte system. Alternating current electrochemical impedance spectroscopy was employed to investigate the ionic conductivity of the electrolyte films at 25 °C, and the analysis showed that the addition of TiO₂ filler and ethylene carbonate (EC) plasticizer has increased the ionic conductivity of the electrolyte up to its optimum level. The highest conductivity of 1.1 × 10⁻³ Scm⁻¹ was obtained at 30 wt.% of EC. Fourier transform infrared spectroscopy measurement was employed to study the interactions between lithium ions and oxygen atoms that occurred at carbonyl (C=O) and ether (C-O-C) groups. The scanning electron microscopy micrograph shows that the electrolyte with 30 wt.% EC posses the smoothest surface for which the highest conductivity was obtained.     

Surface photovoltage properties and photocatalytic activities of nanocrystalline CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> particles with porous superstructure fabricated by a modified chemical coprecipitation method

In this study, nanocrystalline CoFe₂O₄ particles with porous timber-like superstructure were synthesized by a modified chemical co-precipitation route with calcination temperatures of 573, 673, 773, 873, and 973 K, respectively. The structural properties of the samples were systematically investigated by X-ray powder diffraction, scanning electronic microscopy, energy-dispersive X-ray spectra, UV–Vis diffuse reflectance spectroscopy, and Fourier transform infrared spectroscopy techniques. The photo-induced charge separation in the samples was demonstrated by surface photovoltage (SPV) measurement. The photocatalytic performances of the CoFe₂O₄ samples were comparatively studied by the degradation of 4-chlorophenol under Xe lamp irradiation. The results indicated that the sample calcined at 673 K exhibited the highest photocatalytic efficiency among the five samples.     

Synthesis of large surface area LaFeO3 nanoparticles by SBA-16 template method as high active visible photocatalysts

Nanosized LaFeO₃ with large specific surface area has been successfully synthesized by an impregnation process, with mesoporous silica SBA-16 as hard template and corresponding metal nitrates as La and Fe resources, and the resulting LaFeO₃ is also characterized by thermogravimetry–differential thermal analysis (TG–DTA), X-ray diffraction (XRD), N₂ adsorption–desorptions, Brunauer Emmett Teller (BET) technique, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–visible diffuse reflection spectrum (UV–Vis DRS), and surface photovoltage spectroscopy (SPS). It is found that, compared with that prepared by the conventional citrate method, the as-prepared LaFeO₃ with 20-50 nm particle size has remarkable large specific surface area, even still with the surface area as large as about 85 m² g⁻¹ after calcination at 800 °C, which is attributed to its mesoporous structure as well as the small particle size. During the photocatalytic degradation of Rhodamine B solution under visible irradiation, all the LaFeO₃ samples obtained are superior to P25 TiO₂, and the activity becomes high with increasing calcination temperature. It is revealed that the excellent photocatalytic performance is mainly ascribed to the large surface area and high photogenerated charge separation rate.     

Preparation and investigation of composite SiO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> films

SiO₂-TiO₂ films [Si:Ti = 1:(0.06–2.3)] are obtained by the sol-gel method. The structural and photoluminescent properties of the films and powders heat-treated at different temperatures are studied. It is shown that after 700°C the composite consists of TiO₂ crystallites that are structurally similar to anatase and distributed in an amorphous SiO₂ matrix. The photoluminescence spectra have maxima at 450–500 nm. The photoluminescence intensity depends on the treatment temperature and TiO₂ content. __________ Translated from Zhurnal Prikladnoi Spektroskopii Vol. 74, No. 3, pp. 357–361, May–June, 2007.     

Efficient visible light-induced photoelectrocatalytic degradation of rhodamine B by polyaniline-sensitized TiO<Subscript>2</Subscript> nanotube arrays

Self-organized anodic TiO₂ nanotube arrays were sensitized with polyaniline by a simple electrodeposite method. The morphological and structural properties studied by scanning electron microscopy and fourier transform infrared spectroscopy reveal the successful deposition of polyaniline on the nanotube arrays. The polyaniline-sensitized TiO₂ nanotube arrays exhibit a distinguishable red shift on the absorption spectrum. Electrochemical impedance investigation attested to a significant improvement of the interfacial electron-transfer kinetics for promoted electron–hole effective separation. The as-prepared samples showed a high efficiency for the photoelectrocatalytic degradation of rhodamine B under visible-light irradiation (λ > 400 nm). The enhanced photoelectrocatalytic activity could be attributed to the extended absorption in the visible-light region by the polyaniline and the effective separation of photogenerated carriers driven by the photoinduced potential difference generated at the polyaniline/TiO₂ nanotube arrays interface.     

Preparation of TiO<Subscript>2</Subscript>-coated LiCo<Subscript>1/3</Subscript>Ni<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> by electrostatic self-assembly method and its properties

A precursor of TiO₂–LiCo_1/3Ni_1/3Mn_1/3O₂ was prepared by electrostatic self-assembly method. The final product was obtained by heating the precursor at 400–450 °C for 4–6 h in air. X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical tests were used to examine the structural, morphology, elementary valence, and electrochemical characteristics. XRD indicated that the TiO₂-coated material can be indexed by α-NaFeO₂ layered structure, which belongs to hexagonal-type space group R3m. XPS results confirmed the existence of TiO₂ compound on the surface of the coated sample. The SEM image showed that the material had spherically porous morphology with the uniform size about 6 μm. The initial charge–discharge capacity of the TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ material was 168.8/160.0 mAh/g. After 60 cycles, the discharge capacity of the TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ sample was 147.0 mAh/g, and the coulombic efficiency was 94.0%. Compared with the uncoated sample, the electrochemical performance of TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ was improved.     

Structural characterization of the V2O5/TiO2 system obtained by the sol–gel method

The influence of the vanadium load and calcination temperature on the structural characteristics of the V₂O₅/TiO₂ system was studied by X-ray diffraction and X-ray absorption spectroscopy (XAS) techniques. Samples of the V₂O₅/TiO₂ system were prepared by the sol–gel method under acid conditions and calcined at different temperatures. The rutile phase was found to predominate in pure TiO₂ calcined at 450 °C as a result of the reduction of phase transition temperature promoted by the sol–gel method under acid conditions. The anatase phase became predominant at 450 °C as the amount of vanadium increased from 6 to 9 wt%. A structural change in the TiO₂ phase from predominantly anatase to totally rutile with increased calcination temperature was observed in 6 wt% samples. An analysis of the vanadium X-ray Absorption Near Edge Structure (XANES) spectra showed that the oxidation state of vanadium atoms in the samples containing 6 and 9 wt% of vanadium and calcined at 450 °C was predominantly V⁴⁺. However, the presence of V⁵⁺ atoms cannot be ruled out. A qualitative analysis of extended X-ray absorption fine structure (EXAFS) spectra of the samples containing 6 and 9 wt% of vanadium calcined at 450 °C showed that the local structure around vanadium atoms is comparable to that of VO₂ crystalline phase, in which vanadium atoms are fourfold coordinated in a distorted structure. For the sample after calcination at 600 °C, the EXAFS and XANES results showed that a significant portion of vanadium atoms were incorporated in the rutile lattice with a V_xTi_(1−x)O₂ solid solution formation. The conditions of sample preparation used here to prepare V₂O₅/TiO₂ samples associated with different amounts of vanadium and calcination temperatures proved to be useful to modifying the structure of the V₂O₅/TiO₂ system.     

Preparation and characterization of Fe-doped TiO2 on fly ash cenospheres for photocatalytic application

Fe³⁺-doped TiO₂ film deposited on fly ash cenosphere (Fe-TiO₂/FAC) was successfully synthesized by the sol-gel method. These fresh photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analyses (TGA). The XRD results showed that Fe element can maintain metastable anatase phase of TiO₂, and effect of temperature showed rutile phase appears in 650 °C for 0.01% Fe-TiO₂/FAC. The SEM analysis revealed the Fe-TiO₂ films on the surface of a fly ash cenosphere with a thickness of 2 μm. The absorption threshold of Fe-TiO₂/FACs shifted to a longer wavelength compared to the photocatalyst without Fe³⁺-doping in the UV-vis absorption spectra. The photocatalytic activity and kinetics of Fe-TiO₂/FAC with varying the iron content and the calcination temperatures were investigated by measuring the photodegradation of methyl blue (MB) during visible light irradiation. Compared with TiO₂/FAC and Fe³⁺-doped TiO₂ powder (Fe-TiO₂), the degradation ratio using Fe-TiO₂/FAC increased by 33% and 30%, respectively, and the best calcined temperature was 450 °C and the optimum doping of Fe/Ti molar ratio was 0.01%. The Fe-TiO₂/FAC particles can float in water due to the low density of FAC in favor of phase separation to recover these photocatalyst after the reaction, and the recovery test shows that calcination contributes to regaining photocatalytic activity of Fe-TiO₂/FAC photocatalyst.     

Photoconductivity studies on amorphous and crystalline TiO<Subscript>2</Subscript> films doped with gold nanoparticles

In this work, amorphous and crystalline TiO₂ films were synthesized by the sol–gel process at room temperature. The TiO₂ films were doped with gold nanoparticles. The films were spin-coated on glass wafers. The crystalline samples were annealed at 100°C for 30 minutes and sintered at 520°C for 2 h. All films were characterized using X-ray diffraction, transmission electronic microscopy and UV-Vis absorption spectroscopy. Two crystalline phases, anatase and rutile, were formed in the matrix TiO₂ and TiO₂/Au. An absorption peak was located at 570 nm (amorphous) and 645 nm (anatase). Photoconductivity studies were performed on these films. The experimental data were fitted with straight lines at darkness and under illumination at 515 nm and 645 nm. This indicates an ohmic behavior. Crystalline TiO₂/Au films are more photoconductive than the amorphous ones.     

EPR Monitoring of BaTiO<Subscript>3</Subscript> Formation

BaCO₃ and anatase-type TiO₂ were adopted as initial materials to prepare BaTiO₃ powder by the solid-state reaction method at a heating rate of 350°C/h. The electron paramagnetic resonance (EPR) technique was employed to monitor the formation of BaTiO₃. TiO₂ showed a series of complicated EPR signals associated primarily with Fe impurities. The formation of BaTiO₃ can be monitored in terms of the evolution of EPR signals associated with Fe impurities with calcination and measurement temperatures. The activation of the g = 2.004 signal above the Curie point of BaTiO₃ and the disappearance of the other EPR signals in the BaCO₃/TiO₂ mixture at room temperature are characteristic of the formation of BaTiO₃.     

Application of photocatalytic technology for NO<Subscript>x</Subscript> removal

Materials that contain a photocatalyst have a semi-permanent capacity for removing harmful gases from the ambient air. It is the purpose of this study to investigate the photocatalytic activity of commercial paints containing TiO₂ nanoparticles towards NO and NO₂. Experiments were carried out in a stainless steel (30 m^-3) walk-in type environmental chamber (Indoortron), under “real world setting” conditions of temperature, relative humidity, irradiation and pollutant concentrations. Two types of nanoparticle TiO₂-containing paints were tested for their depolluting properties: a mineral silicate paint and a water-based styrene acrylic paint. The results showed a significant effect of TiO₂-materials in reducing NO_x. It was found that up to 74% of NO and 27% of NO₂ were photo-catalytically degraded by the mineral silicate paint, while degradation percentage using the styrene acrylic paint reached 91% and 71% for NO and NO₂, respectively. The photo-catalytic rate of NO on the mineral and styrene acrylic paint was calculated to 0.11 μg m^-2 s and 0.18 μg m^-2 s, respectively, indicating higher photocatalytic performance of the organic based material. The effect of relative humidity (RH) was also investigated. An increase of RH from 20% to 50% inhibited the NO_x photocatalysis on the surface of the samples. PACS 81.16.Hc; 81.65.Mq; 82.33.Tb; 82.50.Hp; 82.65.+r     

Effect of sintering conditions on the properties of sol-gel-derived Li<Subscript>1.3</Subscript>Al<Subscript>0.3</Subscript>Ti<Subscript>1.7</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Solid electrolyte Li_1.3Al_0.3Ti_1.7(PO₄)₃ was prepared by sol-gel method under different sintering conditions. The structural identification, surface morphology, electrochemical window, ionic conductivity, and activation energy of the Li_1.3Al_0.3Ti_1.7(PO₄)₃ sintered pellets were investigated by X-ray diffraction, scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. It is found that the sintering temperature and time have considerable effect on the properties of the Li_1.3Al_0.3Ti_1.7(PO₄)₃ sintered pellets. The Li_1.3Al_0.3Ti_1.7(PO₄)₃ pellet sintered at 900 °C for 2 h is denser than the pellets sintered at other conditions. Different sintering conditions result in the sintered pellet with different porosity. However, the sintering conditions have little effect on the electrochemical window of Li_1.3Al_0.3Ti_1.7(PO₄)₃. Among the Li_1.3Al_0.3Ti_1.7(PO₄)₃ pellets sintered at various conditions, the pellet sintered at 900 °C for 2 h shows the highest ionic conductivity of 3.46 × 10⁻⁴ S cm⁻¹ and the lowest activation energy of 0.2821 eV.     

Nanosized IrO<Subscript>2</Subscript> electrocatalysts for oxygen evolution reaction in an SPE electrolyzer

Nanosized IrO₂ electrocatalysts (d ~ 7–9 nm) with specific surface area up to 100 m² g⁻¹ were synthesized and characterized for the oxygen evolution reaction in a solid polymer electrolyte (SPE) electrolyzer. The catalysts were prepared by a colloidal method in aqueous solution and a subsequent thermal treatment. An iridium hydroxide hydrate precursor was obtained at ~100 °C, which was, successively, calcined at different temperatures from 200 to 500 °C. The physico-chemical characterization was carried out by X-ray diffraction (XRD), thermogravimetry–differential scanning calorimetry (TG–DSC) and transmission electron microscopy (TEM). IrO₂ catalysts were sprayed onto a Nafion 115 membrane up to a loading of 3 mg cm⁻². A Pt catalyst was used at the cathode compartment with a loading of 0.6 mg cm⁻². The electrochemical activity for water electrolysis of the membrane-electrode assemblies (MEAs) was investigated in a single cell SPE electrolyzer by steady-state polarization curves, impedance spectroscopy and chrono-amperometric measurements. A maximum current density of 1.3 A cm⁻² was obtained at 1.8 V and 80 °C for the IrO₂ catalyst calcined at 400 °C for 1 h. A stable performance was recorded in single cell for this anode catalyst at 80 °C. The suitable catalytic activity and stability of the most performing catalyst were interpreted in terms of proper combination between nanostructure and suitable morphology.