Nanocrystalline Titania Films Research Articles

Modeling Weakly Scattering Random Media: A Tool to Resolve the Internal Structure of Nanoporous Materials

Nanoporous media scatter a small fraction of the light propagating through them, even if pore sizes are significantly smaller than the characteristic visible wavelengths. The disordered spatial modulation of the refractive index at the few or few tens of nanometers length scale, resulting from the presence of randomly distributed air bubbles or solid aggregates within a continuous solid background, gives rise to these weak scattering effects. However, standard theoretical approaches to describe this kind of media use effective medium approximations that do not account for diffuse, ballistic, and specular components. Herein, all spectral components and the angular distribution of the scattered light are captured through optical modeling. A Monte Carlo approach, combining scattering Mie theory and Fresnel equations, implemented within a genetic algorithm, allows us to decode the void and aggregate size distribution and hence the internal structure of a nanocrystalline titania (TiO2) film chosen as a paradigmatic example. The approach allows to generically describe the scattering properties of nanoporous materials which, as shown herein, may be used to decipher their internal structure from the fitting of their far‐optical field properties.

Enhanced photocatalysis and photohydrophilicity in TiO2–W5O14 nanocomposite thin films grown by in-lay sputtering

Investigation on the photocatalytic and photoinduced hydrophilic properties of pure and nitrogen doped TiO2–W5O14 nanocomposite thin films grown by in-lay sputtering process is reported. For comparison, similar properties of reactively sputtered nanocrystalline titanium dioxide (TiO2) and nanowire tungsten oxide (W18O49) thin films are studied as well. Structurally, TiO2–W5O14 thin films are highly crystalline and strongly multiphased while TiO2 and W18O49 thin films are anatase, monoclinic, respectively. The band gap of nitrogen doped TiO2–W5O14 thin film is ∼2.82 eV while that of TiO2 and W18O49 thin films are ∼3.27 eV. Surface morphology of TiO2–W5O14 and TiO2 films show nanocrystalline particulates of sizes 15–70 nm, 20–50 nm, respectively while W18O49 films show randomly dispersed nanowires with average diameter of ∼50 nm and maximum length of ∼30 μm. Owing to bandgap shift in visible range, porous surface structures and crystallinity, the nitrogen doped TiO2–W5O14 nanocomposite thin films are found to exhibit better (i) photohydrophilicity with water contact angle of ∼7° in 2 h under UV-A irradiation and (ii) photocatalytic efficiency with methylene blue degradation rate of −1.12μmol/(l.d), −0.78 μmol/(l.d) under ultraviolet and visible light sources, respectively.

Utilizing Spectroscopy and Optical Microscopy to Characterize Titanium Dioxide Thin Films

This paper presents the surface electronic structure and morphological characteristics of the nano-crystalline titanium dioxide (nc TiO2) films derived from the two different sol-gels. Using Scanning tunneling microscopy/spectroscopy (STM/S), it was found that the particles of nc-TiO2 produced from batch A have a surface band gap of ~3.3 eV while the particles of nc-TiO2 produced from batch B have a surface band gap of ~2.6 eV. On other hand, the small particles have aggregated together to form larger particles ranging from ~120 nm to 150 nm in size and distributed randomly over the surface of the batch A nc-TiO2 films. For batch B nc-TiO2films, the small particles have formed larger particles but with their size ranging from 200 nm to 225 nm. That is ascribed to differences between sol-gels used to prepare nc-TiO2 films. As a result of that, the electric power of batch A nc-TiO2/P3HT solar cells is enhanced by more than 8 times in comparison with batch B solar cells.

Comparative study of Ag, Sn or Zn doped TiO2 thin films for photocatalytic degradation of methylene blue and methyl orange

Nanocrystalline titania (TiO2) films with high optical transmittance and appropriate type and level of metal dopants offer promise for use in photocatalysis and environmental remediation purposes. In this study, a facile, cost-efficient sol-gel reflux synthesis route was devised to obtain smooth, nanocrystalline anatase TiO2 thin films doped with silver (Ag), tin (Sn) or zinc (Zn) with up to 5 mole percent. The microstructure, surface morphology and phase composition were determined using scanning electron microscope, atomic force microscope and x-ray diffraction techniques. The films were found to be nanocrystalline with average crystallite size of the order of ∼11 nm. Upon Ag or Sn doping, the films became superhydrophilic due to generation of surface defects and enhanced absorption via incident light scattering. The low extinction coefficient confirmed low surface roughness and uniform dispersion of the metal dopants into the TiO2 lattice. There was a decrease in the refractive index values of the Zn-doped films. The band gap values, as computed using Tauc plots, indicated a maximum reduction from 3.66 eV for the updoped TiO2 to 3.25 eV for Ag-doped TiO2 film. When assessed for photocatalytic degradation of methylene blue (MB) and methyl orange (MO), all the films were found to follow pseudo first-order kinetics in accordance with the Langmuir-Hinshelwood model. The apparent rate constant values were found to increase by 2 to 3 fold (4.30 × 10−3 s–1 for MB; 5.34 × 10−3 s–1 for MO) upon doping with 5 mole percent ZnO, presumably due to dual role of Zn as a reductant causing Ti3+ formation and a stabilizer of the oxygen vacancies.

Compressive stress in nano-crystalline titanium dioxide films by aerosol deposition

Aerosol deposition is a kinetic energy, particle impacting process to produce dense ceramic films or coatings at room temperature, and thus results in high residual compressive stress. The purpose of this work was to determine the stress and its thickness dependence in titanium dioxide, TiO2, films. Aerosol deposition was used to produce films, 1 to 22 μm thick, on glass substrates. A scanning interferometric optical profiler was used to generate surface maps and measure curvature values of the substrates before and after deposition. The Stoney equation was used to calculate average film stress from the measured thickness and radius of curvature. The effect of substrate shape was also investigated by using square and beam substrates in the deposition experiments. Surface maps of the square and beam substrates after deposition showed an increasing trend towards spherical curvature as the film thickness increased. Average (compressive) stress measured for square samples was 0.37 GPa, while the average for beams was 0.52 GPa. The beam-shaped sample data showed good linearity between curvature and film thickness, and fitting to the simple Stoney formula resulted in an intrinsic stress value of 0.50 GPa.

Effect of Rare-Earth Metal Oxide Nanoparticles on the Conductivity of Nanocrystalline Titanium Dioxide: An Electrical and Electrochemical Approach

Doping of rare-earth metal oxides into nanocrystalline titanium dioxide (NTD) films is known to improve performance for photovoltaic and photocatalytic applications; however, the reasons for this improvement are not well understood. To explore the enhancement mechanism, an electrical and electrochemical study of rare-earth oxide-doped NTD films was performed. Doped films were found to be 40–50 times more conductive than undoped films, with linear current–voltage characteristics and decreased light sensitivity. Cyclic voltammograms of doped samples show an enhanced scan rate dependence in the deep trap regime due to a slower charge trapping rate. Finally, electrochemical impedance measurements reveal a decrease in space charge density and a shift in the flat-band potential. Taken together, these results suggest that charge transfer from the rare earth oxide neutralizes the deep trap states in the NTD film, decreasing charge scattering, and improving the NTD performance as an electron acceptor and electron ...

One-Step Electrodeposition of Nanocrystalline TiO2 Films with Enhanced Photoelectrochemical Performance and Charge Storage

With the rapid development of renewable energy technologies there is an urgent need to find synthesis routes that address the needs of materials in a reproducible and affordable way. In this study, we present a one-step electrochemical method for the deposition of nanocrystalline titanium dioxide films on different carbon substrates. By optimizing the synthetic conditions, electrodeposition of nanocrystalline and porous titanium dioxide layers was achieved in only a few minutes. To deconvolute the complex effect of the solution pH and temperature, as well as the deposition potential, a set of systematic experiments was carried out on glassy carbon electrodes. The robustness and general applicability of this synthetic approach is demonstrated by extending it to graphene film electrodes. The phase composition of TiO2 was controlled by varying the solution composition. The photoelectrochemical performance of the electrodeposited titanium dioxide films was better than, or at least comparable to the benchmark...

Dye sensitized solar cell based on TiO2 nanoparticles and chlorophyll from Pandanus amaryllifolius Roxb. leaves

Dye sensitized solar cell (DSSC) is a low-cost photo electrochemical solar cell, that belongs to third generation solar cells and known for its easy fabrication procedures. Its working is based on the interfacial kinetics between a photo-sensitized nanocryastalline anode and an electrolyte, with a counter electrode to complete the cell configuration. A lot of research has been conducted due to their interesting potential for low-cost, lightweight, with reasonably good photovoltaic efficiency. Present work reports the dye sensitized solar cells using TiO2 nanoparticles with Pandanus amaryllifolius chlorophyll as an absorber. P. amaryllifolius leaves are rich in chlorophyll and widely used as natural colorant to impart deep green colour to food products. Moreover, the leaves are rich in basmati aroma volatiles. In the present investigation, chlorophyll pigment was extracted from P. amaryllifolius leaves and nanocrystalline Titanium dioxide (TiO2) film was prepared by doctor blade method. The Titania films were immersed overnight in the chlorophyll extract for sensitization. An electrolyte solution consisting of Polyiodide was injected into the cell before sealing it. Pt coated FTO was used as counter electrode to assemble the cell configuration before it was characterized for its photovoltaic performance. The photoelectrochemical performance of the fabricated DSSC based on this dye showed 0.14 mA/cm2 short circuit current (JSC) and 0.125 V open circuit voltage (VOC).

Photocatalytic and photoelectrocatalytic degradation of the drug omeprazole on nanocrystalline titania films in alkaline media: Effect of applied electrical bias on degradation and transformation products

Photocatalytic and photoelectrocatalytic degradation of the drug omeprazole has been studied in the presence of nanocrystalline titania films supported on glass slides or transparent FTO electrodes in alkaline environment. Its photocatalytic degradation rate was assessed by its UV absorbance and by HPLC, while its transformation products were analyzed by HR-LC–MS. Based on UV absorbance, omeprazole can be photocatalytically degraded at an average rate of 6.7×10−4min−1 under low intensity UVA irradiation of 1.5mWcm−2 in the presence of a nanoparticulate titania film. This corresponds to degradation of 1.4mg of omeprazole per gram of the photocatalyst per liter of solution per hour. The photodegradation rate can be accelerated in a photoelectrochemical cell by applying a forward bias. In this case, the maximum rate reached under the present conditions was 11.6×10−4min−1 by applying a forward bias of +0.6V vs. Ag/AgCl. Four major transformation products were successfully identified and their profiles were followed by HR-LC–MS. The major degradation path includes the scission of the sulfoxide bridge into the corresponding pyridine and benzimidazole ring derivates and this is accompanied by the release of sulfate anions in the reaction mixture.

Growth and Optical Properties of Nanocrystalline Titania Films for Optoelectronics and Photovoltaics

Growth and Optical Properties of Nanocrystalline Titania Films for Optoelectronics and Photovoltaics

Photocatalytic and photoelectrocatalytic degradation of the antibacterial agent ciprofloxacin.

Photocatalytic and photoelectrocatalytic degradation of the antibacterial fluoroquinolone drug, ciprofloxacin, has been studied in the presence of nanocrystalline titania films supported on glass slides or transparent electrodes. The degradation has been examined either in pure water or in the presence of NaOH or NaCl. Titania films can photocatalytically or photoelectrocatalytically degrade ciprofloxacin. In the presence of NaOH, the degradation rate was lower than in pure water and this is explained by the fact that at high pH values attraction of ciprofloxacin to the titania surface is discouraged. In the presence of NaCl, the degradation rate was the highest, thanks to Cl-based radicals which can be photocatalytically created by interacting with photogenerated holes. Application of a forward (anodic) bias increased the photodegradation rate in the presence of both electrolytes while a reverse (cathodic) bias decreased the photodegradation rate. Electrocatalytic effects, i.e. degradation of ciprofloxacin in the dark or in the absence of a photocatalyst under an applied bias of up to ±1.0 V vs. Ag/AgCl, were not detected in the case of NaOH and were of limited importance in the case of NaCl.

Multifunctional alumina/titania hybrid blocking layer modified nanocrystalline titania films as efficient photoanodes in dye sensitized solar cells

A facile way of fabricating efficient blocking layer on mesoporous TiO2 film of dye-sensitized solar cells (DSSCs) is demonstrated here for the first time. Al2O3 and TiO2 are combined together to form a blocking layer. A simple spin coating technique is employed which is a versatile and low-cost method over the atomic layer deposition (ALD) technique. Multifunctional alumina/titania (Al2O3/TiO2) hybrid overlayer is prepared on traditional TiO2 nanocrystalline thin film surface, through sequential deposition of AlCl3·6H2O and TiCl4 precursor solutions followed by sintering at 500 °C for 30 min. Al2O3 effectively plays its role in retarding interfacial recombination of electrons and improving open circuit potential (Voc), while the tiny TiO2 clusters synthesized from TiCl4 treatment act as electron transporting channels to facilitate electron diffusion which leads to enhanced photocurrent (Jsc). Compared to the device without blocking layer, the DSSCs assembled with Al2O3/TiO2 hybrid blocking layer showed improvement in Jsc (from 13.09 mA/cm2 to 16.90 mA/cm2) as well as in Voc (from 0.72 V to 0.73 V) resulting a much better conversion efficiency of 8.60%.

Modelling and Validation of Transmittance from Nanocrystalline Titania film for Photoanodic Action in Dye-Sensitized Solar Cells

AbstractA four phase model air/glass/indium doped tin oxide/TiO2 has been studied by modifying Rouard’s model to calculate the final transmittance from TiO2 layer to be used as photoanode in dye-sensitized solar cells. An optical simulation for the reflectance and transmittance has been executed for the constructed nanocrystalline TiO2 films. To validate the theoretical results TiO2 film has been deposited onto indium doped tin oxide (ITO) layer by sol-gel dip coating technique. It has been found that the incident light suffers losses by 5-15% on passage through TiO2 coated ITO layer. Experimentally it has been observed on the basis of efficiency value that meso-nano combination is the best candidate to be used as photoanode in a dye-sensitize solar cell.

Photoelectrocatalytic degradation of potential water pollutants in the presence of NaCl using nanocrystalline titania films

AbstractBACKGROUNDPhotocatalytic degradation using nanoparticulate titania films does not provide sufficiently high specific surface area for fast pollutant degradation. This deficiency can be corrected by electrocatalytic and photoelectrocatalytic processes.RESULTSNanocrystalline titania films have been deposited on transparent conductive electrodes and were used for photocatalytic and photoelectrocatalytic discoloration of the anionic Acid Orange 7 and the cationic Rhodamine 6G under simulated solar radiation. Experiments have been conducted in the presence of either NaCl, as a natural active species, or Na2SO4, as a relatively inert electrolyte. Photocatalytic discoloration was relatively slow but the process was highly accelerated by applying an electric bias, both in the forward and the reverse direction, particularly in the presence of NaCl. Application of forward bias assisted photogenerated electron–hole separation and affected attraction or repulsion of the charged dyes towards the photocatalyst. However, both effects were masked by the strong electrocatalytic effect produced in the presence of NaCl when Cl‐based oxidative species could be created on either of the two electrodes under any electric bias. As expected, such electrocatalytic effects were much slower in the presence of SO42‐ instead of the highly active Cl‐ anions.CONCLUSIONSDegradation of model pollutants can be accelerated in a photoelectrochemical cell using the same quantity of photocatalyst. The natural electrolyte NaCl additionally allows for strong electrocatalytic effects, which were obtained at moderate applied electric bias. © 2014 Society of Chemical Industry

Influence of TiCl4 post-treatment condition on TiO2 electrode for enhancement photovoltaic efficiency of dye-sensitized solar cells.

Titanium tetrachloride (TiCl4) treatment processed by chemical bath deposition is usually adopted as pre- and post-treatment for nanocrystalline titanium dioxide (TiO2) film deposition in the dye-sensitized solar cells (DSSCs) technology. TiCl4 post-treatment is a widely known method capable of improving the performance of dye-sensitized solar cells. In this work, the effect of TiCl4 post-treatment on the TiO2 electrode is proposed and compared to the untreated film. A TiO2 passivating layer was deposited on FTO glass by RF magnetron sputtering. The TiO2 sol prepared sol-gel method, nanoporous TiO2 upper layer was deposited by screen printing method on the passivating layer. TiCl4 post-treatment was deposited on the substrate by hydrolysis of TiCl4 aqueous solution. Crystalline structure was adjusted by various TiCl4 concentration and dipping time: 20 mM-150 mM and 30 min-120 min. The conversion efficiency was measured by solar simulator (100 mW/cm2). The dye-sensitized solar cell using TiCl4 post-treatment was measured the maximum conversion efficiency of 5.04% due to electron transport effectively. As a result, the DSSCs based on TiCl4 post-treatment showed better photovoltaic performance than cells made purely of TiO2 nanoparticles. The relative DSSCs devices are characterized in terms of short circuit current density, open circuit voltage, fill factor, conversion efficiency.

Effect of the Nature of Cadmium Salts on the Effectiveness of CdS SILAR Deposition and Its Consequences on the Performance of Sensitized Solar Cells

Nanocrystalline titania films deposited on FTO transparent electrodes were sensitized by CdS nanoparticles synthesized in situ by the SILAR method. Three precursor solutions were employed for adsorption of Cd2+ ions: nitrate, sulfate, and acetate. The CdS load and the size of CdS nanoparticles varied a lot from one precursor to the other. The highest load and the largest nanoparticles were obtained in the case of cadmium acetate, the smallest in the case of nitrate, while sulfate gave intermediate values. Ultraviolet photoelectron spectroscopy was employed to measure the ionization potential (and valence band potential) for pure titania and for sensitized titania in the three cases. The obtained values were 7.4 eV for pure titania and 6.7, 6.6, and 5.7 eV for CdS-sensitized titania made by using cadmium nitrate, sulfate, and acetate precursors, respectively. The corresponding band gap values ranged between 2.5 and 2.3 eV. The thus characterized photoanodes were employed to make Quantum Dot Sensitized Sola...

A modified cryostat for photo-electrical characterization of porous materials in controlled atmosphere at very low gas dosage

We developed an integrated system for photo-electrical characterization of materials for sensing applications in strictly controlled environment conditions. The peculiar aspect of this setup is the capability of a fine-tuned gas dosage and a fast dynamic chamber pressure control, coupled with current and voltage sensing within a modified cryostat. To illustrate the capabilities of our system we have characterised both p+-type mesoporous silicon (meso-PS) membranes and nano-crystalline mesoporous titanium dioxide (nc-TiO2) films. In particular, as a main topic is presented a well-resolved characterization of mesoporous silicon electrical conductivity changes induced by presence of ethanol. At low pore filling level adsorbate-shunted conduction is avoided, while dielectric screening effects on frozen doping centres are observable. Beside we presented observation of mesoporous titanium dioxide photo-conductivity as a function of different gas pressure reporting opposite effects of relatively low- and high-pressure regimes. High reproducibility provided by the system is discussed as a final remark.

Effect of Heat Treatment on Structural and Electronic Transition of Nano-Crystalline Titanium Dioxide Film

Nanocrystalline of titanium dioxide nano films were deposited by spin coating method on silicon and ITO-glass substrates at 2000 rpm, in which starting material of Titanium Isopropoxide (C12H28O4Ti).X-ray diffraction (XRD) patterns confirmed thatpolycrystalline TiO2 anatase phase formation. The intensity of XRD peaks increases with the increase in heat treatment and better crystallinity takes place at higher temperature. The morphology of deposited films were characterized by atomic force microscope (AFM); with increasing heat treatment, both the particle size and surface roughness increased .The particle size value were 2.184,2.374,4.834,5.125, and 8.336 nm and RMS roughness values were 0.161, 0.223,0.552,0.810 and 1.494 nm for films deposited at 250, 350, 450, 550 and 650 o C respectively. Optical properties measurements (Transmittance ,T , and Absorptance , A ,) of (TiO2) films showed high transparency. It is observed that maximum transmittance at 250 o C for wavelength range 320-900 nm. The optical band gap of the films has been found to be in the range 3.28-3.62 eV for the forbidden direct electronic transition and 3.45-3.75 eV for the allowed direct transition for the different heat treatment. Keywords - Nanoanatase TiO2, Sol-Gel, XRD,AFM,Transmittance, Absorptance

Nano Crystalline TiO2 Thin Films as Negative Electrodes for Lithium Ion Batteries

In this study, rutile (tetragonal, P42/mnm), anatase (tetragonal, I41/amd) polymorphs of titanium dioxide films were synthesized successfully magnetron sputtering of titanium films on stainless steel substrates followed by in situ direct current plasma oxidation. The as-prepared titanium dioxide thin films were oxidized at 75 W, 100 W and 125 W plasma powers in order to optimize the system with best electrochemical performance. The mean grain sizes of the deposited films were found to be in the range of 14.2-12.9 nm as revealed by the scanning electron microscopy and X-ray diffractometer studies. The electrochemical studies were performed with pure metallic lithium foil cathode with the best performing nano structured titanium dioxide as anode. The specific capacity of the nanocrystalline titanium dioxide films oxidized at 125 W direct current was 207 mA h g(-1) even after 20 cycles in the 0.02-2 V region, indicating excellent cycling stability and reversibility.

Photocatalytic activity and reusability study of nanocrystalline TiO2 films prepared by sputtering technique

The photocatalytic activity of nanocrystalline titanium dioxide (TiO2) films deposited on unheated glass substrates by DC reactive magnetron sputtering at different oxygen partial pressures was tested on the decolorization of Rhodamine 6G (Rh6G) aqueous solutions. The dye photodecolorization process was studied considering the influence of the crystallinity and preferred orientation of growth of the prepared films. It was found that the higher photocatalytic activity was achieved by the film with preferred orientation of growth along the (101) crystal direction and showing a vestigial rutile phase in a mainly anatase phase. The recycling catalytic ability of the TiO2 films was also evaluated and a promising photocatalytic performance has been revealed with a very low variation of the decay rate after five consecutive usages. Structural and morphological characterization revealed high photochemical stability of the films after successive photodegradations assays.