Tetragonal Anatase Research Articles

Enhanced lithium ion storage in TiO2 nanoparticles, induced by sulphur and carbon co-doping

Abstract Sulphur and carbon codoped anatase nanoparticles are synthesized by one-step approach based on interaction between thiourea and metatitanic acid. Electron microscopy shows micrometer-sized randomly distributed crystal aggregates, consisting of many 25–40 nm TiO 2 nanoparticles. The obtained phase composition and chemical states of the elements in the structure are analyzed by means of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). XRD shows that after doping the tetragonal anatase structure is preserved. Further data assessment by Rietveld refinement allows detection of a slight increase of the c lattice parameter and volume related to incorporation of the doping elements. XPS confirms the coexistence of both elemental and oxide carbon forms, which are predominantly located on the TiO 2 particle surface. According to XPS analysis sulphur occupies titanium sites and the element is present in S 6+ sulfate environment. Analysis based on cyclic voltammetry and galvanostatic intermittent titration (GITT) suggests an accelerated Li + transport in the doped TiO 2 structure. The synthesized S and C co-doped anatase has an excellent electrochemical performance in terms of capacity and very fast lithiation kinetics, superior to the non-doped TiO 2 . The material displays 83% capacity retention for 500 galvanostatic cycles and nearly 100% current efficiency.

Microwave-assisted synthesis of CuO/TiO2 nanocomposite for humidity sensor application

Nowadays the sensors importance has been increased because of its various applications in almost all the existing fields. Present paper deals with CuO/TiO2 nanocomposites preparation, characterization and humidity sensor application. For this purpose, we report microwave-assisted synthesis of CuO/TiO2 nanocomposites using copper acetate, titanium tetra isopropoxide, sodium hydroxide and 1-ethyl-3-methyl-imidazolium-ethylsulfate (EMISE) as precursors. Structural properties of CuO/TiO2 was measured by X-ray diffractometer and it was found that the obtained nanocomposite contains monoclinic CuO and tetragonal anatase TiO2. Surface morphology of samples was observed by scanning electron microscope and transmission electron microscope. Cu–O and Ti–O–Ti bands were observed in Fourier transform infrared spectroscopy. The weight loss was investigated by thermo gravimetric analysis. The CuO/TiO2 pellets considered as sensing element, recorded resistance with respect to relative humidity. The sensitivity of sensing elements increased with annealed temperature.

Paramagnetic behavior of Co doped TiO2 nanocrystals controlled by self-purification mechanism

Doping in nanocrystals is a challenging process because of the self- purification mechanism which tends to segregate out the dopants resulting in a greater dopant concentration near the surface than at the interior of nanocrystals. In the present work nanocrystals of TiO2 doped with different atom % of Co were synthesized by peroxide gel method. XRD analysis confirmed the tetragonal anatase structure and HRTEM images showed the rod-like morphology of the samples. Raman modes of anatase phase of TiO2 along with weak intensity peaks of Co3O4 for higher Co dopant concentrations were observed for the samples. EPR measurements revealed the presence of cobalt in +2 oxidation state in the TiO2 matrix. SQUID measurements indicated paramagnetic behavior of the Co doped TiO2 nanocrystals. The paramagnetic behavior is attributed to an increased concentration of Co2+ ions and an increased presence of Co3O4 phase near the surface of the TiO2 nanocrystals due to self-purification mechanism.

Influence of sprayed nanocrystalline Zn-doped TiO2 photoelectrode with the dye extracted from Hibiscus Surattensis as sensitizer in dye-sensitized solar cell

Highly oriented Zn doped TiO2 thin films (0, 2, 4, 6 and 8at%) were deposited by spray pyrolysis technique. X-ray diffraction analysis showed a strong orientation along (101) direction for 6at% Zn with polycrystalline tetragonal anatase phase. Scanning electron microscopy observations revealed uniform distribution of spherical-shaped grains, whereas columnar arrangement of tetragonal-shaped grains with porous nature was revealed from atomic force microscopy. Transmittance spectra indicated a decrease in the energy band gap with increasing doping concentration; i.e. 3.55 up to 3.21eV, attributed to grain refinement to the nanoscale regime. The optical constants such as refractive index and extinction coefficient as a function of wavelength, were determined; the low extinction coefficient values confirmed the good quality of the thin films. Photoluminescence spectra showed strong emissions at 423 and 437nm with a weak emission at 505nm, which confirmed the lesser defect density in 6at% Zn film. The electrical properties studied by Hall Effect measurements revealed that the 6at% Zn led to an increase in the carrier concentration, as well as an increase in the mobility with a least resistivity. The efficiency of dye sensitized solar cells, assembled by using natural dye extracted from Hibiscus Surattensis as sensitizer and Zn-doped TiO2 nanocrystalline thin films as a photoelectrode, was found to be around 1.22%.

Effect of mixed valence state of titanium on reduced recombination for natural dye-sensitized solar cell applications

Nanocrystalline TiO2 was prepared using water-assisted hydrothermal technique. X-ray diffraction pattern confirms the formation of tetragonal anatase phase, and it was further confirmed with Raman results. Williamson-Hall (W-H) plot reveals an induced strain in the sample and the calculated crystallite size of 15 nm is in accordance with the XRD results. Strain induced in the sample is due to creation of oxygen vacancies (defect), and it is responsible for the mixed valence state of Ti atom (Ti3+ and Ti4+) which is confirmed by X-ray photoelectron spectroscopy. Impedance studies result in increased conductivity of oxygen defect-based TiO2 due to its fast electron hopping between the mixed valence states. High-resolution scanning electron microscopic (HR-SEM) image shows a well-agglomerated spherical-shaped nanoparticle with high surface area of 152 m2/g. Here, we report for the first time the effect of mono and co-sensitization of natural dyes on the prepared TiO2 photoanode for dye-sensitized solar cell (DSSC) applications. The interfacial charge transfer resistance, chemical capacitance and electron recombination lifetime of the devices were examined using electrochemical impedance spectroscopy (EIS) analysis, and the performance of the best photoanode was studied using standard solar simulator at 1 Sun intensity (AM 1.5 G).

Strain induced phase formation, microstructural evolution and bandgap narrowing in strained TiO2 nanocrystals grown by ball milling

Band gap narrowing in metal oxide semiconductor nanostructures is important and advantageous for various potential applications including visible light photocatalysis. We present a systematic study on the anomalous strain evolution, phase change and band gap narrowing in TiO2 nanocrystals (NCs) as a result of ball milling. In addition to the size reduction and strain evolution with milling time, we report the formation of a new phase of TiO2 with milling, as identified in the XRD pattern and Raman spectra for the first time. Besides the tetragonal anatase phase of TiO2 NCs, two additional peaks centered at 2θ = 31.28° and 41.60° evolve with milling, and it corresponds to the (1¯ 12) and (312) planes of Ti3O5, respectively. Further, our results show that the band gap of TiO2 NCs reduces with increasing strain and lowest band gap achieved in strained TiO2 is 2.71 eV, consistent with a recent theoretical calculation. The evolution of the crystallite size, strain, stress and energy density was evaluated from the line shape analysis of the XRD pattern using various models, such as uniform deformation model, uniform stress deformation model, uniform deformation energy density model and the results are compared with those obtained directly from HRTEM analyses. The increased d-spacing with milling time was attributed to the tensile strain in TiO2 NCs. Direct evidence of lattice strain and strain relaxation is provided from HRTEM imaging and differential scanning calorimetry analyses. Our results demonstrate strain engineering of TiO2 to achieve narrow bandgap in anatase TiO2 NCs, which are promising for visible light photocatalytic and other emerging applications.

Deposition of Co-doped TiO2 Thin Films by sol-gel method

Cobalt doped TiO2 thin films have been prepared by sol-gel method onto glass substrate at room temperature. in this present work, we are interesting to study the effect of Cobalt doped TiO2 thin films.the concentration of Co was varied from 0 to 6%at .The obtained films have been annealed at 500°C for 2 hours. X-ray diffraction patterns showed that Co: TiO2 films are polycrystalline with a tetragonal anatase and orthorhombic brookite types structures. The surface morphologies of the TiO2 doped with cobalt thin films were evaluated by Atomic Force Microscopy (AFM). The optical properties were studied by mean of UV-visible and near infrared spectroscopy.The calculated optical band gap decreases from 3.30 to 2.96 eV with increasing Co doping.

Truncated tetragonal bipyramidal anatase nanocrystals formed without use of capping agents from the supercritical drying of a TiO2sol

Titanium dioxide (TiO2) nanoparticles are extremely attractive materials for numerous applications, especially in the anatase form. We have made these shaped, <10 nm anatase nanoparticles (NPs) via the supercritical (SC) drying of a titania sol, made by a “green” aqueous sol–gel nanosynthesis route. The SC drying was carried out in alcohol at 255–260 °C, and no further heating or processing of the NPs was required. The true phase composition (crystalline and amorphous phases) and the microstructure of the NPs was thoroughly characterised by the advanced X-ray methods, such as Rietveld-reference intensity ratio (RIR) and the whole powder pattern modelling (WPPM) technique, and HR-TEM analysis. Furthermore, the NPs were also characterised by Raman, FT-IR and optical spectroscopy. These anatase NPs showed themselves to exhibit a truncated tetragonal bipyramidal shape, exposing the {101} (side) and {001} (top) faces. They had a euhedral crystal habit, with sharply defined and easily recognised faces, and were very homogeneous and monodisperse in both shape and size. The photocatalytic activity (PCA) of the samples was assessed in gas–solid phase by monitoring the degradation of nitrogen oxides (NOx), a major atmospheric pollutant. Results showed that the particular shape of these anatase NPs played a key role in their photocatalytic behaviour. In fact, these truncated tetragonal bipyramidal nanocrystals exhibited an enhanced photocatalytic activity, double that of spherical anatase NPs of a similar size reported previously by the authors. This was attributed to the exposure of mainly the {101} and, to a lesser extent, {001} crystal faces, which are more reactive under photocatalysis for redox reactions.

Synthesis of titanium dioxide (TiO2) nanofiber and nanotube using different chemical method

Abstract Titanium dioxide (TiO2) was prepared using chemical spray pyrolysis technique on glass substrate at 350 °C with a spray rate of 5 s/1 min, for a thickness of 350 nm. The material characterization of the TiO2 nanofiber was performed using X-ray diffraction (XRD), scanning electronic microscopy (SEM), and atomic force microscopy (AFM). The optical absorption of the fibers was measured using a UV – vis spectrophotometer. The X-ray diffraction measurements confirmed that the films grown by this technique have good crystalline tetragonal anatase phase structure and with the preferred orientation along the [1 0 1] direction. The surface morphology of the TiO2 fibers showed that the micrography of the nanofiber are extra-fine. UV – vis transmittance measurements have shown that TiO2 fibers are highly transparent (∼90 (%in the visible wavelength region. The optical band gap of TiO2 fiber is 3.32 eV. The diameters of titanium dioxide nanotubes are found to be 30 – 60 nm, retaining the size and near cylindrical shape of the pores.

Room temperature ferromagnetism in Cu2+ doped TiO2 nanocrystals: The impact of their size, shape and dopant concentration

Cu2+ doped TiO2 nanocrystals were synthesized using dispersions of titania nanotubes in the presence of Cu2+ ions as a precursors. The morphologies of nanotubular titania precursors and resulted Cu2+ doped TiO2 nanocrystals were characterized by TEM. Structural and optical properties were studied by XRPD analysis and UV–vis spectroscopy in reflectance mode, respectively. Their magnetic properties were investigated using SQUID magnetometer. Tetragonal anatase crystalline structure was confirmed in all synthesized samples. Polygonal (d∼15nm) and spheroid like (length, up to 90nm) Cu2+ doped TiO2 nanocrystals in samples synthesized at different pHs were observed by TEM. Ferromagnetic ordering with almost closed loop (Hc∼200Oe) was detected in all Cu2+ doped TiO2 nanoparticle films. The saturation magnetization values varied depending on the Cu2+ concentration, nanoparticles shape, size and consequently different number of oxygen vacancies. This study revealed possibility to control magnetic ordering by changing the shape/aspect ratio of Cu2+ doped TiO2 nanocrystals.

Antibacterial effect of Ag-doped TiO2 nanoparticles incorporated natural rubber latex foam under visible light conditions

Ag-doped TiO2 nanoparticles (Ag-TiO2 NPs) incorporated into natural rubber latex foam (NRLF) showed enhanced antimicrobial activities under visible light. Synthesis of Ag-TiO2 NPs and their incorporation into NRLF are investigated in this paper. Synthesized Ag-TiO2 nanopowder was evaluated by powder X-ray diffraction (XRD) technique, surface electron microscopy (SEM), and high-resolution transmission electron micrograph (HRTEM) coupled with energy dispersive X-ray (EDX) technique. The modified NRLF materials were also evaluated by SEM-EDX analysis, XRD analysis, and antibacterial susceptibility tests. It was found that the XRD peaks obtained for the Ag-TiO2 NP perfectly matched with the reference code of 98-010-5393 which was the tetragonal type anatase phase of TiO2. Most of XRD peaks obtained for the modified NRLF matched with those of Ag-TiO2 NPs which confirmed the presence of nano Ag-TiO2 NPs in the modified NRLF. The particle size analysis carried out by HRTEM images and the EDX mapping results showed that the Ag nanoparticles with a diameter of 5 nm were simply attached to the surface of TiO2 nanoparticles. Modified NRLF showed antimicrobial activity against Gram positive Staphylococcus epidermidis, Gram-positive methicillin-resistant Staphylococcus aureus and Gram-negative Escherichia coli (strain numbers HB101, DH5d) bacteria species.

Titanium Dioxide/Multi-Walled Carbon Nanotube Heterostructure Containing Single One Carbon Nanotube and Its Electromagnetic Properties

TiO 2@MWCNT heterostructure containing single one carbon nanotube has been successfully prepared via solvothermal method. X-ray diffration (XRD) analysis shows that TiO 2 nanocrystals only contain highly crystallized tetragonal anatase phase. Interestingly, scanning electron microscope (SEM) and transmission electron microscope (TEM) results show that most of the TiO 2 nanocrystals are perpendicular to the surface of multi-walled carbon nanotube (MWCNT) and only single one carbon nanotube is coated by TiO 2 crystals. The electromagnetic (EM) characteristics are investigated at 0.5–18.0 GHz range. The EM properties show that both the permittivity and the permeability present a typical resonance behavior at 11.0 GHz and 12.0 GHz, respectively. Besides, the TiO 2@MWCNT heterostructures exhibit a broadband absorption throughout the whole Ku wave bands (12.0–18.0 GHz). Interestingly, the reflection loss (RL) of the TiO 2@MWCNT heterostructures change slightly as the thickness of the heterostructures increase from 3.0 mm to 5.0 mm in the 8.0–13.0 GHz range.

Lithiation Confined in One Dimensional Nanospace of TiO2 (Anatase) Nanotube to Enhance the Lithium Storage Property of CuO Nanowires.

We have fabricated CuO@TiO2 nanocable arrays by a facile method involving in situ thermal oxidation of Cu foil and coating of tetrabutyl titanate solution. The structure of the nanocables has been investigated by various techniques to comfirm that the cores are mainly crystalline monoclinic CuO, and the shells are crystalline tetragonal anatase TiO2. When used as an anode material for lithium-ion batteries, the nanoconfinement effect plays an important role in improving the lithium-ion storage preformance: the lithiation will be confined in one-dimensional space of TiO2 nanotubes to limit the pulverization of CuO, and the phase interface will cause an interfacial adsorption to enrich more lithium ions at some level. Benefiting from the nanoconfinement effect and interfacial adsorption, the reversible capacity does not fade, but rather increases gradually to 725 mAh g(-1) after 400 cycles at a current density of 60 mA g(-1), superior to the theoretical capacity of CuO.

Influence of Sr doping on structural, optical and magnetic properties of TiO2 nanoparticles

Strontium (Sr) doped anatase TiO2 nanoparticles were synthesized by the method of hydrolysis and characterized for their structural, optical and magnetic properties. The crystalline nature and tetragonal anatase phase of undoped and Sr doped TiO2 nanoparticles were examined by XRD. The blue shifted band gap of the nanoparticles was studied by UV–vis analysis. Room-temperature (RT) photoluminescence (PL) spectra of Sr doped TiO2 nanoparticles exhibited a strong UV emission at 364nm and 381nm, and a weak emission at 406nm and 431nm. The PL spectra also showed an increase in concentration of the defects, due to doping. The room temperature ferromagnetism (RTFM) was observed from VSM measurement, for undoped and Sr doped TiO2 nanoparticles and the influence of Sr is discussed.

Novel hydrogen sensor based on p-type Ni:TiO2 nanorods fabricated on ITO substrate

In the present work, Ni-doped TiO2 nanorods were fabricated on indium tin oxide (ITO) coated glass substrate by a novel spray pyrolysis deposition route. The influence of pyrolytic temperature on the degree of crystallinity of the Ni:TiO2 films was clearly reflected in the X-ray diffractograms. The promoting effect of ITO seed layer on Ni:TiO2 film was reflected in the film prepared at 300 °C which show predominantly a (101) orientation corresponding to the c-axis of pure tetragonal anatase TiO2. The evaluated optical band gap (Eg) of the films prepared at different temperature was in the range of 3.3–3.62 eV. The high Eg values confirmed the existence of TiO2–Ni catalyst influence interaction. The morphology of the film optimized at 300 °C was almost rod shaped with large roughness favorable for sensing. The hydrogen sensing properties of the Ni:TiO2 nanorod sensor was investigated. The Ni doped TiO2 films exhibited a different p-type response to H2. It was found that the sensor based on Ni:TiO2 nanorod structure optimized at 300 °C exhibited good performance even at room temperature.

Preparation of TiO2–MWCNT core/shell heterostructures containing a single MWCNT and their electromagnetic properties

TiO2–MWCNT core/shell heterostructures containing a single MWCNT have been successfully prepared via solvothermal method. TiO2–MWCNT heterostructures with different morphologies and electromagnetic (EM) properties have obtained by adjusting the weight ratio of titanium dioxide (TiO2) and multi-walled carbon nanotubes (MWCNT) (weight ratio: 1:1, 5:1 and 10:1). EDS spectrum and X-ray diffraction analysis reveal that the product is composed of Ti, O, and C elements, and the crystal structure of TiO2 is tetragonal anatase phase. SEM and TEM images show that the MWCNTs are coated by a thin layer of TiO2 crystals, and the average diameters of the needle-like TiO2 nanocrystals are less than 100 nm. EM properties of the as-prepared TiO2–MWCNT heterostructures are investigated in the 0.5–18.0 GHz range. The permittivity and permeability of the TiO2–MWCNT heterostructures change obviously as the weight ratio of TiO2 and MWCNT increases. Moreover, the typical resonance–antiresonance phenomenon can be observed in the permittivity and permeability curves.

Spray pyrolysed microporous TiO2 thin films by optimisation of substrate temperature for ‘all sprayed’ solar cells

Titanium dioxide thin films were deposited on glass substrate at temperatures ranging from 300 °C to 500 °C by a simple, cost effective spray pyrolysis method using commercially available TiO2 powder (Degussa P25). Analyses using scanning electron microscopy (SEM) and atomic force microscopy (AFM) reveal the microporous nature of the films at 350 °C. X-ray diffraction (XRD) and Raman studies reveal that these films are amorphous in nature. The films were subsequently annealed at 500 °C for 2 h, resulting in crystallisation (the tetragonal anatase phase). XPS analysis was effectively used to study the chemical composition of the samples. Finally, optimized microporous TiO2 thin films were used for the fabrication of an ‘all-sprayed’ solar cell utilizing well-established CuInS2 as the absorber layer. The best device under this study has an open-circuit voltage of 409 mV and a short-circuit current density of 3.90 mA cm−2. The efficiency and fill factor were 0.61% and 38%, respectively.

Effect of Sprayed Solution Flow Rate on the Physical Properties of Anatase TiO2 Thin Films

Titanium dioxide (TiO2) thin films were synthesized on glass substrates by spray pyrolysis. The effect of solution flow rate on the physical properties of the films was investigated by use of x-ray diffraction (XRD), scanning electron microscopy, atomic force microscopy (AFM), and spectrophotometry techniques. XRD analysis revealed the tetragonal anatase phase of TiO2 with highly preferred (101) orientation. AFM images showed that grain size on top of TiO2 thin films depended on solution flow rate. An indirect band gap energy of 3.46 eV was determined by means of transmission and reflection measurements. The envelope method, based on the optical transmission spectrum, was used to determine film thickness and optical constants, for example real and imaginary parts of the dielectric constant, refractive index, and extinction coefficient. Ultraviolet and visible photoluminescence emission peaks were observed at room temperature. These peaks were attributed to the intrinsic emission and to the surface defect states, respectively.

Anatase supported nickel nanoparticles for catalytic hydrogenation of 4-nitrophenol

Nickel nanoparticles supported on titania were prepared by a combined sol–gel and chemical reduction procedure. XRD reveals face centred cubic structure of nickel nanoparticles; while tetragonal anatase type structure for the supporting titania phase. The structural and morphological properties showed well dispersion of nickel nanoparticles on the supported titania lattice. From TEM images, the average crystallite size of nickel nanoparticles was found to be ∼20nm. HRTEM images identified lattice fringes with spacing around 0.203nm, which matches with ‘d’ value for the (111) plane of cubic nickel. The saturation magnetization, remanent magnetization, and coercivity values of supported nickel/bare nickel nanoparticles were higher than that of bulk nickel. This enhanced magnetization property was helpful for its separation from the reaction mixture by magnetic field. The influence of titania support on the performance of nickel catalysts for the hydrogenation of 4-nitrophenol was investigated. The catalytic performance was higher for supported nickel nanoparticles as compared to that of bare nickel nanoparticles. Supported nickel catalyst was found to be superior, cost effective, magnetically separable and recyclable in hydrogenation reactions.

Synthesis of Nanoporous TiO2 Thin Films for Photocatalytic Degradation of Methylene Blue

This work reports a structure and photocatalytic activity of nanoporous titania (TiO2) thin films by an anodizing approach. Xray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) studies showed that tetragonal anatase was the main phase in the thin films that consisted of countless disordered nanopores in the order of 10 to 15 nm. In the photocatalytic degradation of methylene blue, the titania thin films showed a good photocatalytic activity. 82.2 % methylene blue could be photodegraded by titania thin films with UV radiation. XPS results indicate that during the degradation of methylene blue, some Ti3+ may be partially oxidized to Ti4+ in the TiO2 films and the surface hydroxyls directly participate in the reaction. Our nanoporous titania thin films is commensurable to Degussa-25 TiO2 powders because the latter requires filtration in each treatment; it is also much superior to the direct photolysis approach with respect to photoactivity.