Photo(electro)catalytic Activity of Cu-Modified TiO2 Nanorod Array Thin Films under Visible Light Irradiation

In the present study, a two-step method was applied to synthesise Cu²⁺-modified TiO₂ nanorod array thin films for photocatalytic processes. TiO₂ nanorod array thin films were synthesised by a hydrothermal method and then modified with an ultrasonic-assisted sequential cation adsorption method. The samples were characterised by X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (DRS), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy and inductively coupled plasma mass spectroscopy (ICP-MS) analysis. The photoelectrochemical properties of the samples were evaluated by linear sweep voltammetry and Mott–Schottky analysis; photocatalytic activities were tested by methylene blue degradation under visible light. The photocurrent density of the TiO₂/FTO sample modified with 50 mM Cu²⁺ solution was 26 times higher than that of the unmodified TiO₂/FTO sample. Additionally, methylene blue degradation efficiency under visible light was increased 40% with respect to the efficiency of the unmodified sample. The mechanism of the photocatalytic activity enhancement of Cu²⁺-modified TiO₂ nanorod films was discussed.     

Applications of vertically oriented TiO2 micro-pillars array on the electrode of dye-sensitized solar cell

In this research, dye-sensitized solar cells based on TiO₂ micro-pillars fabricated by inductive couple plasma etcher were investigated by analyses of X-ray diffraction (XRD), scanning electron microscopy (SEM), contact angle, ultraviolet-visible absorption spectra (UV-vis), and current-voltage characteristics. X-ray diffraction patterns show that the TiO₂ anatase phase forms while sintering at 450 °C for 30 min. The SEM images reveal that the diameter and height of TiO₂ micro-pillars are about 3 and 0.8 μm, respectively. The measurements of contact angle between TiO₂ micro-pillars and deionized water (DI water) reveal that the TiO₂ micro-pillars is super-hydrophilic while annealed at 450 °C for 30 min.The absorption spectrum of TiO₂ micro-pillars is better than TiO₂ thin film and can be widely improved in visible region with N3 dye adsorbed. The results of current-voltage (I-V) characteristics analysis reveal that dye-sensitized solar cell with TiO₂ micro-pillars electrode has better I-V characteristics and efficiency than TiO₂ film electrodes. This result may be due to the annealed TiO₂ micro-pillars applied on the electrode of dye-sensitized solar cell can increase the contact area between TiO₂ and dye, resulting in the enhancement of I-V characteristics and efficiency for dye-sensitized solar cell.     

A nano-porous TiO2 thin film coating method for dye sensitized solar cells (DSSCs) using electrostatic spraying with dye solution

The dye coloring process on a nano-porous TiO₂ thin film for DSSCs was studied using an electrostatic spraying (ESS) method. In this study, dye coating experiments were performed using homemade ESS equipment. The coating patterns on the TiO₂ thin film are changed by adjusting the applied voltages of the ESS system. The geometry of the coating patterns is observed by a charge-coupled device (CCD) camera. The TiO₂ thin film is fabricated by controlling the electric field which allows a uniform color distribution to be obtained with a high dyeing capacity. The colored TiO₂ thin films are compared with those obtained using a conventional immersed dye solution by means of an UV–vis spectrometer. The performance of this novel coloring process was confirmed by measuring I–V curve characteristics.     

Understanding the solar photo-catalytic activity of TiO2-ITO nanocomposite deposited on low cost substrates

In this work, we report on the photo-catalytic properties of TiO₂-ITO nanocomposite deposited on low cost conventional clay ceramic substrates. The nanocomposite was formed by spraying a solution prepared from the P25 TiO₂ powder (Degussa) mixed with an organometallic paste of a dissolved combination of indium and tin. A TiO₂-ITO powder-like nanocomposite was prepared for X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterization. The mean particle size of the TiO₂-ITO nanocomposite was found to be larger than that of pure TiO₂. The optical features of TiO₂-ITO-based layers (deposited on glass substrates) were investigated using UV-vis spectroscopy. The TiO₂-ITO nanocomposite deposited layers were found to have higher light absorption than the P25 TiO₂ powder. The photo-catalytic properties of the TiO₂-ITO nanocomposite (deposited on low cost clay ceramic substrates) were tested under solar irradiation using a well-known polluting dye. It was shown that the TiO₂-ITO nanocomposite exhibits higher degradation rates towards the pollutant dye than the P25 TiO₂ powder. The optical band gap of the TiO₂-ITO nanocomposite (2.79 eV) was found to be lower than that of pure TiO₂ (3.1 eV), while ITO (indium tin oxide) has a band gap of about 4.2 eV. ITO was found to be entirely transparent to sun light, while it exhibits a slight photo-catalytic activity, signifying the possible existence of an indirect photo-catalysis phenomenon (sensitized semiconductor photocalysis) and potential degradation (oxidation) of the pollutant through electron transfer from the dye to conduction band of the semiconductor. All photo-catalytic activity results were discussed in light of the optical band gap of the various compounds.     

Thin film transistors based on TiO2 fabricated by using radio-frequency magnetron sputtering

This study demonstrates that nanocrystalline TiO₂ thin films were deposited on ITO/glass substrate by radio-frequency magnetron sputtering. Field-emission scanning electron microscope (FE-SEM) and atomic force microscopic (AFM) images showed the morphology of TiO₂ channel layer with grain size and root-mean-square (RMS) roughness of 15 and 5.39 nm, respectively. TiO₂ thin-film transistors (TFTs) with sputter-SiO₂ gate dielectric layer were also fabricated. It was found that the devices exhibited enhancement mode characteristics with the threshold voltage of 7.5 V. With 8-μm gate length, it was also found that the I_on/off ratio and off-state current were around 1.45×10² and 10 nA, respectively.     

TiO2表面质子化对染料敏化太阳能电池性能及吸附染料稳定性的影响

采用致密平整TiO₂薄膜作为染料敏化太阳能电池光电极,并研究了HCl处理表面质子化对电池性能的影响. 结果表明,HCl处理后电池的短路电流显著提升,电池的开路电压则有轻微的下降,电池电流提升了31%,而能量转化效率则提升了25%. 这是因为TiO₂的表面质子化增强了吸附染料与TiO₂间的电学耦合,提高了染料中激发电子向TiO₂导带的注入速率. 而电压的下降,一方面是由于质子化会引起TiO₂导带能级     

Enhanced photocatalytic activity of TiO2 nano-structured thin film with a silver hierarchical configuration

TiO₂ sol-gels with various Ag/TiO₂ molar ratios from 0 to 0.9% were used to fabricate silver-modified nano-structured TiO₂ thin films using a layer-by-layer dip-coating (LLDC) technique. This technique allows obtaining TiO₂ nano-structured thin films with a silver hierarchical configuration. The coating of pure TiO₂ sol-gel and Ag-modified sol-gel was marked as T and A, respectively. According to the coating order and the nature of the TiO₂ sol-gel, four types of the TiO₂ thin films were constructed, and marked as AT (bottom layer was Ag modified, surface layer was pure TiO₂), TA (bottom layer was pure TiO₂, surface layer was Ag modified), TT (pure TiO₂ thin film) and AA (TiO₂ thin film was uniformly Ag modified). These thin films were characterized by means of linear sweep voltammetry (LSV), X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy and transient photocurrent (I_ph). LSV confirmed the existence of Ag⁰ state in the TiO₂ thin film. SEM and XRD experiments indicated that the sizes of the TiO₂ nanoparticles of the resulting films were in the order of TT > AT > TA > AA, suggesting the gradient Ag distribution in the films. The SEM and XRD results also confirmed that Ag had an inhibition effect on the size growth of anatase nanoparticles. Photocatalytic activities of the resulting thin films were also evaluated in the photocatalytic degradation process of methyl orange. The preliminary results demonstrated the sequence of the photocatalytic activity of the resulting films was AT > TA > AA > TT. This suggested that the silver hierarchical configuration can be used to improve the photocatalytic activity of TiO₂ thin film.     

Luminescence properties from erbium oxide nanocrystals dispersed in titania/organically modified silane composite sol–gel thin films

Luminescence properties from erbium (III) oxide nanocrystals dispersed in titania/organically modified silane composite thin films were studied. Erbium oxide nanocrystals were prepared by an inverse microemulsion technique. A strong room-temperature photoluminescence was observed at 1.531 μm, with the full width at half maximum (FWHM) of 22 nm due to intra-atomic transitions between ⁴ I _13/2 and ⁴ I _15/2 levels in the erbium (III) ion. The shape, peak position, and FWHM of the photoluminescence signals from the composite thin films were quite comparable to those prepared by other methods. The photoluminescence peak of the composite thin films showed a maximum intensity at the heat-treatment temperature of 300 °C. A room-temperature green up-conversion emission at 543 nm (⁴ S _3/2?⁴ I _15/2) was observed for the composite thin films with different heat-treatment temperatures upon excitation at 993 nm. The up-conversion emission mechanism was explained by means of an energy-level diagram and the lifetime of the visible up-conversion emission was measured. Received: 10 July 2000 / Accepted: 11 July 2000 / Published online: 5 October 2000     

Hydrodynamic cavitation degradation of Rhodamine B assisted by Fe3+-doped TiO2: Mechanisms,geometric and operation parameters

In this paper, a novel method, hydrodynamic cavitation (HC) combined with Fe³⁺-doped TiO₂, for the degradation of organic pollutants in aqueous solution is reported. The venturi tubes with different geometric parameters (size, shape and half divergent angle) are designed to obtain a strong HC effect. The structure, morphology and chemical composition of prepared Fe³⁺-doped TiO₂ as catalyst are characterized via using XRD, SEM, TEM, XPS, UV-vis DRS and PL methods. The effects of added TiO₂ (heat-treated at different temperatures for different times) and Fe³⁺-doped TiO₂ (with different mole ratios of Fe and Ti) on the HC catalytic degradation of RhB are discussed. The influences of operation parameters including inlet pressure, initial RhB concentration and operating temperature on the HC catalytic degradation of RhB are studied by Box-Behnken design (BBD) and response surface methodology (RSM). Under 3.0 bar inlet pressure for 10 mg/L initial concentration of RhB solution at 40 °C operating temperature in the presence of Fe³⁺-doped TiO₂ with 0.05:1.00 M ratio of Fe and Ti, the best HC degradation ratio can be obtained (91.11%). Furthermore, a possible mechanism of HC degradation of organic pollutants in the presence of Fe³⁺-doped TiO₂ is proposed. Perhaps, this study may provide a feasible method for a large-scale treatment of dye wastewater.     

Tunable photocatalytic selectivity of fluoropolymer PVDF modified TiO2

Fluoropolymer poly-vinylidene-fluoride modified TiO₂ (PVDF/TiO₂) were prepared via a simple chemisorption approach and characterized by thermo gravimetric analyse, transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy and photoluminescence spectra. The modified mechanism and the photocatalytic selectivity of the PVDF/TiO₂ were studied. The existence of Ti-F coordination bond on the interface between TiO₂ and PVDF was confirmed. For the PVDF modification, the photocatalytic degradation (PCD) of cationic dye was greatly enhanced, and the PCD of anionic dye was obviously inhibited. PVDF/TiO₂ shows high photocatalytic selectivity than that of TiO₂ by degrading mixed solution of cationic dyes MB and anionic dyes MO. The selectivity can be tuned by changing the PVDF modification amount.     

Structural and optical properties of electrohydrodynamically atomized TiO2 nanostructured thin films

In this paper, we report an alternate technique for the deposition of nanostructured TiO₂ thin films using the electrohydrodynamic atomization (EHDA) technique using polyvinylpyrrolidone (PVP) as a stabilizer. The required parameters for achieving uniform TiO₂ films using EHDA are also discussed in detail. X-ray diffraction results confirm that the TiO₂ films were oriented in the anatase phase. Scanning electron microscope studies revealed the uniform deposition of the TiO₂. The purity of the films is characterized by using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS), confirming the presence of Ti–O bonding in the films without any organic residue. The optical properties of the TiO₂ films were measured by UV-visible spectroscopy, which shows that the transparency of the films is nearly 85% in the visible region. The current–voltage (I–V) curve of the TiO₂ thin films shows a nearly linear behavior with 45 mΩ?cm of electrical resistivity. These results suggest that TiO₂ thin films deposited via the EHDA method possess promising applications in optoelectronic devices.     

Titanium Dioxide/Germanium Core–Shell Nanorod Arrays Grown on Carbon Textiles as Flexible Electrodes for High Density Lithium‐Ion Batteries

Three‐dimensional (3D) titanium dioxide@germanium (TiO₂@Ge) core–shell nanorod arrays on carbon textiles are fabricated by a facile two‐step method and further investigated as flexible electrode for Li‐ion batteries (LIBs). The synthesis of TiO₂@Ge composite involves the hydrothermal growth of TiO₂ nanorod arrays on carbon textiles and a subsequent coat with a thin layer of germanium with radio frequency (RF) magnetron sputtering. The TiO₂ nanorod arrays can effectively not only increase the unit mass loading as a role of skeleton but also remarkably enhance the electrical conductivity via control the lithiation/delithiation voltage in the range of 0.01–1.0 V, where TiO₂ can be in situ lithiated to Li_xTiO₂ after the first discharge cycle. Moreover, each TiO₂@Ge nanorod has enough space to accommodate the large volume expansion of Ge during charge and discharge cycles. Benefiting from unique electrode architectures, this additive free, self‐supported electrode exhibits the high reversible capacity, outstanding rate capability, and the extremely long cycling stability even at a high rate (700.3 mAh g^?1 is still retained at 5 A g^?1 after 600 cycles).     

TiO2/MgAl layered double hydroxides mechanical mixtures as efficient photocatalysts in phenol degradation

MgAl layered double hydroxides (MgAl LDH) were synthesized by the sol-gel method using ultrasound irradiation in the crystallization step. The interlayer anions were nitrate and acetylacetonate-ethoxide. The solids were characterized by XRD, N₂-physisorption and TEM. TiO₂/MgAl LDH mixtures were prepared by mixing the MgAl LDH (as prepared) or the calcined sample with TiO₂ (Aldrich, 99.9% anatase) in different weight ratios. Photocatalytic activities of the TiO₂/MgAl LDH mixtures were evaluated through the degradation of phenol as model pollutant. TiO₂/MgAl LDH mixture (1:1) was more photocatalytically active for the degradation of phenol than pure TiO₂. The synergy effect was attributed to a higher production of ^•OH radicals, which were formed from the structural hydroxides. Also, the hydrotalcite phase enhanced the phenol adsorption and transfer to the TiO₂ sites where the phenol was photocatalytically degradated.     

Mechanism of enhanced photocatalysis of TiO2 by Fe in suspensions

In this work, the mechanism of enhanced photocatalysis of TiO₂ with Fe³⁺ was studied using Sulfadiazine (SD) as the model compound. Results indicated that degradation rate of SD was enhanced by the addition of Fe³⁺ in TiO₂ suspension. The crystalline structure of TiO₂ particles was stable in suspensions. The hydroxyl radical generated by TiO₂/Fe³⁺ (both TiO₂ and Fe³⁺) photocatalysis was in a higher yield. Moreover, Fe²⁺ was found not to give an obvious impact on the SD degradation in TiO₂ suspension, whereas Fe³⁺ had a notable effect. The adsorption amount of TiO₂ was greatly enhanced by the addition of Fe³⁺ in suspensions. Finally, an interaction model of SD degradation in TiO₂ suspension containing Fe³⁺ was also proposed by investigating of surface behaviors of TiO₂ particles. It will be beneficial to use Fe³⁺ as the electron acceptors on the surface of TiO₂ particles, which helps to improve the yield of hydroxyl radical.     

Effect of 10 MeV electron irradiation on dye-sensitized solar cells

The effect of 10?MeV electrons’ irradiation on dye-sensitized solar cells (DSSCs) has been studied in this paper. J–V characteristics measurements were carried out in order to investigate the degradation of the cells in electron radiation environments. The short-circuit current (J_sc) and maximum power density (P_max) of cells decrease significantly after the electron irradiation. When the irradiation dose increases to 10?kGy, the initial maximum power decreases nearly by 50%. The influences of the electron irradiation on FTO, dye sensitizer and anode were studied to investigate the degradation mechanism of DSSC, respectively. The ultraviolet–visible spectra of FTO show that the absorption peaks of dye decrease, resulting in a decline of the FTO transmittance. According to the X-ray diffraction measurement results, it was found that the particle size of nano-crystalline TiO₂ had changed after the electron irradiation. With the help of SEM, the conglomeration of TiO₂ nano-particles appears after the electron irradiation.     

Electrical characteristics of p-Si/TiO2/Al and p-Si/TiO2-Zr/Al Schottky devices

Electrical devices involve different types of diode in prospective electronics is of great importance. In this study, p-type Si surface was covered with thin film of TiO₂ dispersion in H₂O to construct p-Si/TiO₂/Al Schottky barrier diode (D1) and the other one with TiO₂ dispersion doped with zirconium to construct p-Si/TiO₂-Zr/Al diode (D2) by drop-casting method in the same conditions. Electrical properties of as-prepared diodes and effect of zirconium as a dopant were investigated. Current–voltage (I–V) characteristics of these devices were measured at ambient conditions. Some parameters including ideality factor (n), barrier height (Φ_B0), series resistance (Rs) and interface state density (Nss) were calculated from I–V behaviours of diodes. Structural comparisons were based on SEM and EDX measurements. Experimental results indicated that electrical parameters of p-Si/TiO₂/Al Schottky device were influenced by the zirconium dopant in TiO₂.     

Photosensitized growth of TiO2 nanoparticles improved the charge transfer dynamics of a bichromophoric dye

Nanostructured TiO₂ particles utilized in dye-sensitized solar cells (DSSCs) provide a large surface area, which facilitates the adsorption of sensitizing dye and charge recombination due to the high density of surface traps. In this article, a modified surface of TiO₂ nanoparticles was successfully synthesized in the presence of (1-hydroxycyclohexyl)(phenyl)methanone (HCPM) as a sensitizer to control formation in a toluene/ethanol medium via a photolytic process. A particle-size analysis showed that the oxides which had fully oxidized to TiO₂ were 20～35 nm in diameter. The structure of the TiO₂ particles being of an amorphous nature and the nearly defect-free distributions of Ti⁴⁺ and O^2- energy levels imply that the grain boundaries and surface trap sites were effectively suppressed. TiO₂ particles were subsequently blended with the bichromophoric dye, AMIP, to study fluorescence decay dynamics between AMIP/TiO₂ interfaces. Fluorescence lifetime measurements gave the rate constant for the charge-transfer process from the excited singlet of AMIP to the conduction band of TiO₂ as 1.2×10⁹ s^?l. When PL quenching measured as the TiO₂ contents of these composites reached a 2.5 wt% level, the maximum enhanced charge-transfer dynamics occurred. Structural properties and photophysical behaviors of composites of AMIP bound to TiO₂ were extensively demonstrated.     

Preparation of transparent conductive TiO2:Nb thin films by pulsed laser deposition

This study investigated the optical and electrical properties of Nb-doped TiO₂ thin films prepared by pulsed laser deposition (PLD). The PLD conditions were optimized to fabricate Nb-doped TiO₂ thin films with an improved electrical conductivity and crystalline structure. XRD analyses revealed that the deposition at room temperature in 0.92 Pa O₂ was suitable to produce anatase-type TiO₂. A Nb-doped TiO₂ thin film attained a resistivity as low as 6.7 × 10⁻⁴ Ω cm after annealing at 350 °C in vacuum (<10⁻⁵ Pa), thereby maintaining the transmittance as high as 60% in the UV-vis region.     

The surface of TiO2 gate of 2DEG-FET in contact with electrolytes for bio sensing use

In order to apply two-dimensional electron-gas-field-effect-transistors (2DEG-FETs) for cell-viability sensors, we investigated the chemical/electrical properties of TiO₂ thin films (13-17 nm) prepared with the sol-gel technique on the gate surface of AlGaAs/GaAs 2DEG-FETs. Photochemical/electrochemical reactions on GaAs surface in electrolytes, which induce the degradation of 2DEG-FET performance, are effectively suppressed by introducing a TiO₂ thin film on the gate area of 2DEG-FETs. Compared to conventional ion-selective FETs (ISFETs), the TiO₂/2DEG-FETs in this study exhibit a high sensitivity (410 mV/mM) for H₂O₂ detection. TiO₂ surfaces show better biocompatibility than GaAs surfaces as demonstrated by direct cell culture on these surfaces.     

Enhancing the efficiency of TiO2–perovskite heterojunction solar cell via evaporating Cs2CO3 on TiO2

In a TiO₂–perovskite heterojunction solar cell (TiO₂–PHSC), besides the perovskite CH₃NH₃PbX₃, TiO₂ as one side of the TiO₂/CH₃NH₃PbX₃ heterojunction also plays an important role in the photovoltaic effect. In order to improve the performance of the TiO₂–PHSC with the structure of glass/FTO/compact TiO₂/mesoporous TiO₂/CH₃NH₃PbI_3–xCl_x /poly‐TPD (poly(N,N ′‐bis(4‐butylphenyl)‐N,N ′‐bis(phenyl)benzidine))/Au, a 2 nanometer thick Cs₂CO₃ layer is thermally evaporated on the mesoporous TiO₂ layer. The short‐circuit current density (J_sc) raises from 17.7 mA cm^–2 to 18.9 mA cm^–2, the open‐circuit voltage (V_oc) from 0.81 V to 0.87 V, and the fill factor (FF) from 55.2% to 67.3%; as a result, the power conservation efficiency (PCE) increases from 8.0% to 11.1% under AM 1.5G solar illumination (100 mW cm^–2). Moreover, in a TiO₂–PHSC free of mesoporous TiO₂, where Cs₂CO₃ is evaporated on the compact TiO₂ layer, the J_sc, V_oc, FF and PCE values increase from 16.0 mA cm^–2, 0.83 V, 50.8% and 6.7% to 17.9 mA cm^–2, 0.90 V, 59.3%, and 9.5%, respectively. The reasons of the PCE increase for either the first kind of TiO₂–PHSC or the mesoporous‐TiO₂‐free TiO₂–PHSC with a nanometer‐thick Cs₂CO₃ layer on mesoporous TiO₂ or compact TiO₂ are discussed. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)