Tunable electrochemical properties of liquid phase deposited TiO2 films

Titanium dioxide (TiO₂) films on glassy carbon (GC) electrode surface were prepared by the liquid phase deposition (LPD) process for different deposition times. The morphological structure, interfacial property and electrocatalytic activity of as-prepared LPD TiO₂ films on GC surface were studied by field-emission scanning electron microscopy (FE-SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The FE-SEM observation showed that the deposition time controlled the morphology of film on GC surface. With increasing deposition time, TiO₂ formed nanoparticles at the initial 5-h stage and compact thick films after 20 h. Due to the semiconducting properties of TiO₂, the LPD films inhibited the electron transfer process of [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ on GC by increasing the redox reaction peak potential separation of CV curve and electron transfer resistance of EIS. The inhibition was increased with TiO₂ film thickness. Nevertheless, the onset reduction potential of maleic acid decreased with increasing LPD TiO₂ film thickness while the cathodic and anodic currents increased, demonstrating the useful electrocatalytic activity of LPD TiO₂ films.     

Corrosion resistant TiO2 film formed on magnesium by liquid phase deposition treatment

Liquid phase deposition treatment (LPD) was applied to form a corrosion protective titanium dioxide (TiO₂) film on commercially available pure magnesium. Changing the solution pH, from acidic to highly alkaline, and with the addition of sucrose, it becomes possible to form a highly adhesive and thin TiO₂ film on commercially available pure magnesium without any heat treatment. The role of the sucrose may be attributed to the formation of tetrafluoroboric acid (BF₄)⁻ in the solution reducing the homogeneous nucleation of TiO₂ in the LPD solution. The film formed in the weak alkaline environment shows better corrosion resistance than at other LPD conditions, while the average rest potential is the same as that of as-polished specimens. This low rest potential may be due to micro-cracks in the formed film and high activity of the magnesium substrate.     

A Novel Method for Preparing V-doped Titanium Dioxide Thin Film Photocatalysts with High Photocatalytic Activity Under Visible Light Irradiation

The liquid phase deposition (LPD) method was successfully used for preparing V-doped TiO₂ thin film photocatalysts. In this simple and easily-controlled process, V-doped anatase TiO₂ thin films were directly deposited on a soda lime glass substrate placed in an aqueous solution containing Ti- and V-fluoro complex ions, followed by annealing. The thin films were analyzed by XRD, XPS, UV-vis. V⁴⁺ ions were introduced into the lattice of TiO₂ through in-situ substituting Ti⁴⁺. The absorption edge of V-doped TiO₂ films shifted to visible light region. The highly efficient photocatalytic activity was verified by the decomposition of methylene blue under visible light irradiation.     

Examining the use of TiO2 to enhance the NH3 sensitivity of polypyrrole films

Polypyrrole/Titanium dioxide (PPy/TiO₂) composite thin films were prepared by polymerizing the monomer pyrrole in aqueous solution containing a certain amount of TiO₂ particles at room temperature, and their response to ammonia (NH₃) gas was examined systematically. Compared with the pristine PPy film, which reached the saturation at the concentration of NH₃ beyond 200 ppm, the composite films showed more stable response and higher sensitivity. Furthermore, the PPy/TiO₂ composite thin films exhibited a low detection limit of 2 ppm. The film thickness, which had a strong influence on the film sensitivity to NH₃, could be controlled by varying the polymerization time. The sensitivity to NH₃ gas of the samples with different content of TiO₂ and different molar ratio of PPy/TiO₂/oxidant was studied. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Deposition and characterization of epitaxial Ta-doped TiO2 films for ultraviolet photoelectric detectors

Undoped and tantalum-doped titania (TiO₂:Ta) films were synthesized via metalorganic chemical vapor deposition (MOCVD). The crystallization qualities, surface morphologies and optical properties of the deposited films were systematically characterized. The results indicated that the films having low doping levels were epitaxial anatase titania along [001] orientation with high transparency in visible region. The optical band gap could be modulated from 3.38 to 3.52?eV by controlling Ta doping levels. Ultraviolet (UV) photoelectric detectors with metal-semiconductor-metal (MSM) structure were designed and fabricated based on the undoped and Ta-doped films. The maximum spectral response of 32.3?A/W was detected at about 315?nm for the 1% Ta-doped TiO₂ film-based detector. The detectors based on the undoped and 1% Ta-doped TiO₂ films also presented good temporal responses and visible-blind characteristics, showing excellent UV light detection performances.     

Microstructure development of hydrothermally grown TiO2 thin films with vertically aligned nanorods

TiO₂ (rutile) thin films were deposited via a hydrothermal process by adjusting the amount of ethanol, deposition time, and temperature. Especially, various amounts of ethanol generated different degrees of supersaturation in precursor solution. It allowed us to systematically change the width, lengths, and crystallinity of a vertically aligned 1‐D nanorod structure of TiO₂ films. The oriented attachment, confirmed by scanning electron microscopy and transmission electron microscopy, was shown to be responsible for their lateral growth of TiO₂ nanorods bundled by numerous well‐oriented nanowires and their vertical growth. TiO₂ nanorod thin films were also characterized via X‐ray diffraction and UV‐Vis‐NIR spectrophotometer to find a correlation between the process conditions and nanostructural evolution. Dye sensitized solar cells were assembled to relate the nanostructures of TiO₂ films with the effectiveness of its role as a photoelectrode.     

The Synthesis and Photocatalytic Properties of Nitrogen Doped TiO<Subscript>2</Subscript> Films Prepared Using the AC-PLD Method

Synthesis of N doped TiO₂ films were conducted by the atmospheric controlled pulsed laser deposition (AC-PLD) method to generate visible light active photocatalytic films. In this method, the anion doped TiO₂ films were synthesized on a quartz substrate by the irradiation of a pulsed Nd:YAG laser on a TiO₂ target in the presence of gaseous nitrogen containing reagents at reduced pressure. For nitrogen doping, the use of CH₃CN was found to be more effective than the use of NH₃. The visible light absorption properties of the films were very sensitive to the CH₃CN partial pressure during ablation. When using CH₃CN, nitrogen and an equal quantity of carbon was uniformly doped into the TiO₂ films. The resultant films showed better catalytic performance than those which were either un-doped or doped using NH₃. The formation of nitrogen doped TiO₂ is discussed by relating experimental results to thermodynamic considerations. It is also suggested that stronger reducing agents such as carbon are required for doping nitrogen into TiO₂ films.     

Preparation and characterization of TiO2 and polymer nanocomposite films with high refractive index

Novel nanocomposite films of TiO₂ nanoparticles and hydrophobic polymers having polar groups, poly (bisphenol‐A and epichlorohydrin) or copolymer of styrene and maleic anhydride, with high refractive indices, high transparency, no color, solvent‐resistance, good thermal stability, and mechanical properties were prepared by incorporating surface‐modified TiO₂ nanoparticles into polymer matrices. In the process of preparing colloidal solution of TiO₂ nanoparticles, severe aggregation of particles can be reduced by surface modification using carboxylic acids and long‐chain alkyl amines. These TiO₂ nanoparticles dispersed in solvents were found not to aggregate after mixing with polymer solutions. Transparent colorless free‐standing films were obtained by drying a mixture of TiO₂ nanoparticles colloidal solution and polymer solutions in vacuum. Transmission electronic microscopic studies of the films suggest that the TiO₂ nanoparticles of 3–6 nm in diameter were dispersed in polymer matrices while maintaining their original size. Thermogravimetric analysis results indicate that the nanocomposite film has good thermal stability and the weight fraction of observed TiO₂ nanoparticles in the film is in good accordance with that of theoretical calculations. The refractive index of nanocomposite films of TiO₂ and poly(bisphenol‐A and epichlorohydrin) was in the range of 1.58–1.81 at 589 nm, which linearly increased with the content of TiO₂ nanoparticles from 0 to 80 wt %. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Formation of Ti-Si composite oxide films on Mg-Al-Zn alloy by electrophoretic deposition and anodization

TiO₂ or SiO₂ nanoparticles dispersed in an acetone solvent containing iodine were deposited on Mg-Al-Zn alloy by electrophoretic deposition (EPD). Subsequently, the composite oxide films were formed on the substrate by anodization in KOH-Na₂SiO₃ aqueous solutions containing TiO₂ or SiO₂ nanoparticles. The films formed by EPD were improved binding with the substrate by anodization under high voltages with sparking, and then the anodic films consisted of Si-Mg or Ti-Si-Mg composite oxides. The film thicknesses of TiO₂ and SiO₂ on the alloy increased with anodization time. In polarization tests, the films anodized under high voltages with sparking in the alkaline solutions had high corrosion resistance. Thus, the composite oxide films formed in the present method were successful in providing corrosion resistance to Mg alloy.     

Thermal effect of carbamates based polymer on the TiO2 growth

We investigated the growth of TiO₂ on poly((tetrahydropyran‐2‐yl N‐(2‐methacryloxyethyl) carbamate)‐co‐(methyl 4‐(3‐methacryloyloxypropoxy) cinnamate) (THP‐polymer) using thermal heating, octyl isocyanate (OIC), and glutaraldehyde. It is found that TiO₂ can be grown on surfaces terminated with ? NH₂ and ? O? groups from aqueous solution. However, TiO₂ did not deposit on ? CH₃ terminated surfaces, due to the low surface energy of these surfaces. Fourier transform infrared spectroscopy and thermogravimetric analysis data showed that the ? THP functional group can be removed and the surface functional group converted to ? NH₂ by heating the material over 180°C. OIC can then be immobilized on the surface after heating, changing the surface functional group from ? NH₂ to ? CH₃. As TiO₂ can be deposited from solution on ? NH₂ terminated, but not ? CH₃ terminated surfaces, THP‐polymer can be used to switch the surface properties by thermal activation and subsequent reaction with OIC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Enhancing Photophysical Properties of MDMO-PPV-DMP Conjugated Polymer via Incorporation Anatase Titania Nanoparticles

Improving photophysical properties of poly[2-methoxy-5-(3,7-dimethyl-octyloxy)-1,4-phenylenevinylene]-end capped with dimethylphenyl, MDMO-PPV-DMP, was achieved via incorporation anatase titania nanoparticles (TiO₂ NPs). Various contents of TiO₂ NPs (up to 50 wt%) were dispersed into fixed concentration of the MDMO-PPV-DMP (5 mg/mL) via solution blending method followed by spin coating onto cleaned glass substrates to form their thin films. The formation of MDMO-PPV-DMP/TiO₂ nanocomposites was evidenced from the results of X-ray diffractograms and Fourier transform infrared spectra, while the homogeneity of the films was detected by field emission-scanning electron microscopy (FE-SEM). Increasing the contents of TiO₂ NPs resulted in a slight decrease (up to ~?0.07 eV) in both direct and indirect energy band gaps of the MDMO-PPV-DMP in the nanocomposite thin films. A higher degree of disorder in the electronic structure of the MDMO-PPV-DMP/TiO₂ nanocomposite and increasing the localized states density within the forbidden gap can be achieved by increasing the energy tail values and decreasing the steepness parameter with rising the TiO₂ NPs content. The enhancement in emission intensity and broadening of emission spectra with increasing the TiO₂ NPs content can be explained by the charge trapping effect and particle size distribution, respectively. Moreover, the incorporation of TiO₂ NPs into the MDMO-PPV-DMP led to tuning its emitted light color which is of distinct interest in optoelectronic devices.

     

Investigation of mixing performance in a semi-active T-micromixer actuated by magnetic nanoparticles: Characterization via Villermaux–Dushman reaction

A semi-active T-type micromixer is designed to intensify micromixing by actuating magnetic nanoparticles (MNPs). Five permanent magnets in a zig-zag arrangement are located next to the mixing channel of the micromixer to apply the magnetic field to the fluid flow. Micromixing performance is considered in terms of the segregation index (X_S) by the Villermaux/Dushman reaction test. The effects of magnetic flux intensity (B = 380–500 mT), the concentration of MNPs (φ = 0.002–0.01 [w/v]), and flow rate ratios on X_S and pressure drop are investigated. By increasing MNPs concentration from φ = 0.002–0.008 (w/v), X_S decreased and the rise in φ up to 0.008 (w/v) has not been significant on X_S. Maximum mixing efficiency (i.e., minimum X_S = 0.0088) is achieved for B = 500 mT and φ = 0.01 (w/v). By applying the magnetic field, the mixing performance increased due to the motion of MNPs, but its negative effect is an increase in the pressure drop along the micromixer reactor. Generally, with the formation of MNPs barriers inside the mixing channel, the main fluid flows through these layers and creates the sinusoidal flow paths compared to no magnetic field conditions, and thus, a superior mixing efficiency could be attained.     

Formation of double-surface-silvered polyimide films via a direct ion-exchange self-metallization technique: The case of BPADA/ODA and [Ag(NH3)2]+

Double-surface-silvered polyimide (PI) films have been successfully fabricated via a direct ion-exchange self-metallization method using silver ammonia complex cation ([Ag(NH₃)₂]⁺) as silver resource and bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride/4,4′-oxydianiline (BPADA/ODA)-based poly(amic acid) (PAA) as the PI precursor. The alkaline characteristic of the silver precursor dramatically improves the efficiency of the ion exchange and film metallization process. By using an aqueous [Ag(NH₃)₂]⁺ solution with a concentration of only 0.01M and an ion-exchange time of only 5 min, metallized films with desirable performance could be easily obtained by simply heating the silver(I)-doped PAA films to 300°C. The strong hydrolysis effect of the basic [Ag(NH₃)₂]⁺ cations on the flexible and acidic BPADA/ODA PAA chains was observed during the ion exchange process by the quantitative evaluation of the mass loss of PAA matrix. Nevertheless, under the present experimental conditions, the final metallized film essentially retained the basic structural, thermal, and mechanical properties of the pristine PI, which make it a truly applicable material. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Development of MgO:TiO2 thin films for gas sensor applications

In this study, structural, morphological and optical properties, and gas sensor performance of magnesium oxide (MgO) doped titanium dioxide (TiO₂) thin films were investigated in detail. Gas sensor metallic patterns were fabricated on Si substrate using traditional photolithographic technique. MgO doped TiO₂ thin films were deposited on formed Pt electrode surface by confocal sputtering (co-sputtering) system as the active layer. Thin film characterizations were realized by using secondary ion mass spectroscopy (SIMS), atomic force microscope (AFM) and UV–Vis Spectrometer (UV–Vis). Gas sensing measurements were performed by gas sensing test system against methane gas at working temperature of 300?°C. To evaluate deposition and thermal annealing effects on the sensing performance, sensors were tested under gas. The sensitivity and response/recovery time of gas sensors were measured in 1000?ppm. MgO doped TiO₂ based sensor at substrate temperature of 100?°C has high sensitivity and short response/recovery time.     

Sintered TiO2 powder containing metallic Co binder prepared via mechanical carbonization,and its mechanical properties

A TiO₂-Co-a composite powder was prepared via carbonizing and selective oxidation processing of a Ti-Co alloy. The conventionally mixed TiO₂-Co-c composite powder and pure TiO₂ were sintered at 1100, 1200, 1300, 1400?°C, respectively. The structural characterization was performed using X-ray diffraction, field emission scattering electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The sintered samples were more densified, and melted bonding occurred at temperature higher than 1300?°C. The flexural strength and fracture toughness of the TiO₂-Co-a sample were higher than those of the TiO₂ and TiO₂-Co-c sintered at temperature higher than 1300?°C, while the Vickers hardness of TiO₂-Co-a was the lowest at all sintering temperatures. The sintered TiO₂-Co-a sample was more ductile and strengthened than the TiO₂-Co-c sample with added metallic Co binder via mechanical mixing. The enhanced mechanical properties of the TiO₂-Co-a sample were due to the fine dispersion of the metallic Co binder wetted with a TiO₂ matrix.     

Properties of polyimide hybrids with mixed metal oxide

Polyimide/silica–titania (PI/SiO₂–TiO₂) hybrid films were prepared via an in situ sol–gel process. The PI precursor, poly(amic acid) (PAA), which contains 2,2'‐bis[4‐(4‐aminophenoxy)‐phenyl]propane (p‐BAPPP), 3,3',4,4'‐ benzophenetetracarboxylic anhydride (BTDA) and 3‐aminopropyltrimethoxysilane (APrTMOS), was first synthesized; this was followed by the addition of phenyltrimethoxysilane (PTMS) and/or tetraethyl orthotitanate (Ti(OEt)₄) to fabricate PI/SiO₂–TiO₂ films. The relative content of SiO₂ to TiO₂ has remarkable effects on the crosslink structure and resultant properties of the hybrids. XPS results confirm that the amount of Si on the surface of the hybrids is higher than that in the bulk. The distribution of Ti in the hybrid films is contrary to the above trend because of the formation of three‐dimensional Si? O? Si, Si? O? Ti, and Ti? O? Ti networks. The SiO₂ content of the hybrids containing only silica significantly affects their refractive index, contact angle, and dielectric constant. The films with added PTMS show higher contact angles than pure PI because nonpolar segments, ? C₂H₆ or benzene groups, tend to distribute on the surface. Upon the addition of (Ti(OEt)₄), some hydrophilic segments on the surface of the hybrids are induced because of the formation of a crosslinked structure. The denser crosslinked molecular structure, and consequently lower CTE and higher T_g are obtained from hybrids containing more TiO₂. By comparing the above properties and flexibility, the best composition of metal oxides (SiO₂/TiO₂) in hybrids is 20/80. That is, an optimum ratio of metal oxides in PI hybrids induces superior properties for advanced practical applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Photostabilization of cationic UV-cured coatings in the presence of nanoTiO2

The effect of TiO₂ nanoparticles for sun-weathering protection of UV-cured coatings is investigated. TiO₂ is either introduced in the form of nanoparticles in the photocurable formulations or generated in situ via sol–gel process. Cured films containing comparable amounts of TiO₂ were weathered for 800 h under UV irradiation and compared with free-TiO₂ coating. The TiO₂ presence induces a clear lower mass loss decrease during weathering as well as a lower gel content decrease. The TiO₂ screen effect is also confirmed by a lower alkyl-band reduction monitored by FT-IR during weathering. The TiO₂ generated in situ via sol–gel gives rise to transparent coatings without interfering with photopolymerization process and therefore without compromising UV-cured film properties.     

Self-organized TiO2 nanotubes in mixed organic–inorganic electrolytes and their photoelectrochemical performance

The formation of self-organized TiO₂ nanotube array films by electrochemical anodizing titanium foils was investigated in a developed organic–inorganic mixed electrolyte. It was found that the structure and morphology of the TiO₂ nanotube layer were greatly dependent upon the electrolyte composition, anodizing potential and time. Under the optimized electrolyte composition and electrochemical conditions, a controllable, well-ordered TiO₂ nanotube array layer could be fabricated in a short time. The diameters of the as-prepared TiO₂ nanotubes could be adjusted from 20 to 150 nm, and the thickness could be adjusted from a few hundred nanometers to several micrometers. The photoresponse and the photocatalytic activity of the highly ordered TiO₂ nanotube array films were also examined. The nanotube array film with a thickness of about 2.5 μm had the highest incident photon to photocurrent conversion efficiency (IPCE) (34.3%) at the 350 nm wavelength, and had better charge transfer ability under UV light illumination. The photocatalytic experimental results indicated that the 450 °C annealing samples have the highest photodegradation efficiency for methyl orange pollutant.     

Structural Modification of TiO2 Nanorod Films with an Influence on the Photovoltaic Efficiency of a Dye-Sensitized Solar Cell (DSSC)

TiO₂ nanorod films have been deposited on ITO substrates by dc reactive magnetron sputtering technique. The structures of these nanorod films were modified by the variation of the oxygen pressure during the sputtering process. Although all these TiO₂ nanorod films deposited at different oxygen pressures show an anatase structure, the orientation of the nanorod films varies with the oxygen pressure. Only a very weak (101) diffraction peak can be observed for the TiO₂ nanorod film prepared at low oxygen pressure. However, as the oxygen pressure is increased, the (220) diffraction peak appears and the intensity of this diffraction peak is increased with the oxygen pressure. The results of the SEM show that these TiO₂ nanorods are perpendicular to the ITO substrate. At low oxygen pressure, these sputtered TiO₂ nanorods stick together and have a dense structure. As the oxygen pressure is increased, these sputtered TiO₂ nanorods get separated gradually and have a porous structure. The optical transmittance of these TiO₂ nanorod films has been measured and then fitted by OJL model. The porosities of the TiO₂ nanorod films have been calculated. The TiO₂ nanorod film prepared at high oxygen pressure shows a high porosity. The dye-sensitized solar cells (DSSCs) have been assembled using these TiO₂ nanorod films prepared at different oxygen pressures as photoelectrode. The optimum performance was achieved for the DSSC using the TiO₂ nanorod film with the highest (220) diffraction peak and the highest porosity.     

The influence of anatase-rutile mixed phase and ZnO blocking layer on dye-sensitized solar cells based on TiO2nanofiberphotoanodes

High performance is expected in dye-sensitized solar cells (DSSCs) that utilize one-dimensional (1-D) TiO₂ nanostructures owing to the effective electron transport. However, due to the low dye adsorption, mainly because of their smooth surfaces, 1-D TiO₂ DSSCs show relatively lower efficiencies than nanoparticle-based ones. Herein, we demonstrate a very simple approach using thick TiO₂ electrospun nanofiber films as photoanodes to obtain high conversion efficiency. To improve the performance of the DSCCs, anatase-rutile mixed-phase TiO₂ nanofibers are achieved by increasing sintering temperature above 500°C, and very thin ZnO films are deposited by atomic layer deposition (ALD) method as blocking layers. With approximately 40-μm-thick mixed-phase (approximately 15.6?wt.% rutile) TiO₂ nanofiber as photoanode and 15-nm-thick compact ZnO film as a blocking layer in DSSC, the photoelectric conversion efficiency and short-circuit current are measured as 8.01% and 17.3?mA?cm^?2, respectively. Intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy measurements reveal that extremely large electron diffusion length is the key point to support the usage of thick TiO₂ nanofibers as photoanodes with very thin ZnO blocking layers to obtain high photocurrents and high conversion efficiencies.