Photosensitive nanostructured TiO2 grown at room temperature by novel “bottom-up” approached CBD method

The current paper incorporates with a “bottom-up” approached chemical bath deposition method to grow titanium dioxide (TiO₂) nanostructure at room temperature on glass and stainless steel substrates. The room temperature deposited TiO₂ films are heat treated at 673 K for 1 h in air and the corresponding change in structural, morphological and optical properties are studied by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and UV-VIS-NIR spectrophotometer. The heat-treated films are utilized as a photocathode in photoelectrochemical (PEC) cell in 1 M NaOH electrolyte. The experimental results show that, the CBD method allows formation of photosensitive, anatase TiO₂ thin film, which can be potentially tuned in many functional applications with feasibility.     

Photocatalytic performance of nano-photocatalyst from TiO2 and Fe2O3 by mechanochemical synthesis

Nano-particles of homogeneous solid solution between TiO₂ and Fe₂O₃ (up to 10 mol%) have been prepared by mechanochemical milling of TiO₂ and yellow Fe₂O₃/red Fe₂O₃/precipitated Fe (OH)₃ using a planetary ball mill. Such novel solid solution cannot be prepared by conventional co-precipitation technique. A preliminary investigation of photocatalytic activity of mixed oxide (TiO₂/Fe₂O₃) on photo-oxidation of different organic dyes like Rhodamine B (RB), Methyl orange (MO), Thymol blue (TB) and Bromocresol green (BG) under visible light (300-W Xe lamp; λ > 420 nm) showed that TiO₂ having 5 mol% of Fe₂O₃ (YFT1) is 3-5 times higher photoactive than that of P25 TiO₂. The XRD result did not show the peaks assigned to the Fe components (for example Fe₂O₃, Fe₃O₄, FeO₃, and Fe metal) on the external surface of the anatase structure in the Fe₂O₃/TiO₂ attained through mechanochemical treatment. This meant that Fe components were well incorporated into the TiO₂ anatase structure. The average crystallite size and particle size of YFT1 were found to be 12 nm and 30 ± 5 nm respectively measured from XRD and TEM conforming to nanodimensions. Together with the Fe component, they absorbed wavelength of above 387 nm. The band slightly shifted to the right without tail broadness, which was the UV absorption of Fe oxide in the Fe₂O₃/TiO₂ particle attained through mechanochemical method. This meant that Fe components were well inserted into the framework of the TiO₂ anatase structure. EPR and magnetic susceptibility show that Fe³⁺ is in low spin state corresponding to μ_B = 1.8 BM. The temperature variation of μ_B shows that Fe³⁺ is well separated from each other and does not have any antiferromagnetic or ferromagnetic interaction. The evidence of Fe³⁺ in TiO₂/Fe₂O₃ alloy is also proved by a new method that is redox titration which is again support by the XPS spectrum.     

Structural, optical and charge transport study of rutile TiO2 nanocrystals at two calcination temperatures

In this study the influence of two different calcination temperatures 80 °C and 450 °C on the structural, optical and charge transport properties of rutile TiO₂ nanocrystals has been investigated. TiO₂ nanocrystals have been prepared at low temperature by a simple hydrolysis method using titanium tetrachloride as starting precursor. The results of X-ray diffraction (XRD) showed that the prepared nanocrystals have a rutile tetragonal crystalline structure. Specific surface area of 80 °C and 450 °C calcinated rutile TiO₂ nanocrystals are 25.38 × 10⁵ cm²/g and 7.61 × 10⁵ cm²/g respectively, which has been calculated by X-ray diffraction data. Williamson-Hall plot results indicate the presence of compressive strain at 80 °C and tensile strain at 450 °C. Ultraviolet-visible (UV-vis) absorption spectroscopy is used to calculate the band gap of the material and the shift in absorption edge and it has been observed that the absorption spectra are strongly modified by the calcination temperature. The red-shift in photoluminescence (PL) is attributed to the change in strain from compressive to tensile. Photoconductivity (PC) measurements showed that capture cross-section of 80 °C (R1) and 450 °C (R2) calcinated rutile nanocrystals are 55.10 × 10⁻¹⁰ and 39.50 × 10⁻¹⁰ cm² respectively. High value of electron life-time, low value of radiative recombination and a four order increase in photogenerated charge carriers have been reported for the rutile TiO₂ nanocrystals calcinated at 450 °C.     

Fabrication and properties of p-type K doped Zn1−xMgxO thin film

A series of K doped Zn_1−xMg_xO thin films have been prepared by pulsed laser deposition (PLD). Hall-effect measurements indicate that the films exhibit stable p-type behavior with duration of at least six months. The band gap of the K doped Zn_1−xMg_xO films undergoes a blueshift due to the Mg incorporation. However, photoluminescence (PL) results reveal that the crystallinity decreased with the increasing of Mg content. The fabricated K doped p-type Zn_0.95Mg_0.05O thin film exhibits good electrical properties, with resistivity of 15.21 Ω cm and hole concentration of 5.54 × 10¹⁸ cm⁻³. Furthermore, a simple ZnO-based p-n heterojunction was prepared by deposition of a K-doped p-type Zn_0.95Mg_0.05O layer on Ga-doped n-type ZnO thin film with low resistivity. The p-n diode heterostructure exhibits typical rectification behavior of p-n junctions.     

In situ template polymerization of aniline on the surface of negatively charged TiO2 nanoparticles

The in situ oxidative template polymerization of aniline was performed successfully on the surface of negatively charged titania (TiO₂) nanoparticles with a mean diameter of 40 nm using ammonium persulfate and a Chem-Solv solution at pH 1 and 25 °C. SEM showed that the resulting polyaniline (PANI)/TiO₂ composites were well dispersed in solution due to the electrostatic repulsion force. Ultraviolet/visible spectroscopy, thermogravimetric analysis, Fourier-transform infrared spectroscopy, and cyclic voltammetry showed that the optical, thermal, and electrical properties of PANI/TiO₂ composites were quite different from those of pure PANI or TiO₂, which was attributed to the strong interaction between the two components. The conductivity of the PANI/TiO₂ composite was estimated to be 0.91 × 10⁻¹ S/cm at 25 °C in the range of semiconductor.     

Structural and dielectric properties of Bi2Zn2/3Nb4/3O7 thin films prepared by pulsed laser deposition at low temperature for embedded capacitor applications

Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited on Pt/TiO₂/SiO₂/Si(1 0 0) substrates at a room temperature under the oxygen pressure of 1-10 Pa by pulsed laser deposition. Bi₂Zn_2/3Nb_4/3O₇ thin films were then post-annealed below 200 °C in a rapid thermal process furnace in air for 20 min. The dielectric and leakage current properties of Bi₂Zn_2/3Nb_4/3O₇ thin films are strongly influenced by the oxygen pressure during deposition and the post-annealing temperature. Bi₂Zn_2/3Nb_4/3O₇ thin films deposited under 1 Pa oxygen pressure and then post-annealed at a temperature of 150 °C show uniform surface morphologies. Dielectric constant and loss tangent are 57 and 0.005 at 10 kHz, respectively. The high resolution TEM image and the electron diffraction pattern show that nano crystallites exist in the amorphous thin film, which may be the origin of high dielectric constant in the Bi₂Zn_2/3Nb_4/3O₇ thin films deposited at low temperatures. Moreover, Bi₂Zn_2/3Nb_4/3O₇ thin film exhibits the excellent leakage current characteristics with a high breakdown strength and the leakage current density is approximately 1 × 10⁻⁷ A/cm² at an applied bias field of 300 kV/cm. Bi₂Zn_2/3Nb_4/3O₇ thin films are potential materials for embedded capacitor applications.     

TiO2 nanotube-supported amorphous Ni-B electrode for electrocatalytic oxidation of methanol

Amorphous Ni-B/TiO₂ electrodes were successfully prepared by electroless plating. Highly ordered TiO₂ nanotube arrays fabricated by anodic oxidation were employed as substrate and loaded with Ni-B alloy by electroless plating. The phase formation, microstructures and catalytic activity of electrodes were investigated by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and electrochemistry analyzer, respectively. The results show that Ni-B/TiO₂ electrodes with an average particle size of 200 nm present a typical amorphous structure of Ni and B, and have high catalytic activity for methanol electrooxidation in alkaline medium. The peak current density in cyclic voltammetry (CV) curves reaches 360 mA cm⁻² in the solution with 0.5 mol L⁻¹ methanol, much higher than that of Ni-B/Ti electrode. With the methanol concentration increasing to 1.5 mol L⁻¹, the peak current density increases to 488 mA cm⁻², after which it remains almost constant. The Ni-B/TiO₂ electrodes are relatively stable according to catalytic lifetime test; the peak current density remains 72.1% of the original value after 1300 times cycles. The amorphous Ni-B/TiO₂ electrode should be a promising candidate for direct methanol fuel cell.     

Deposition of TiO2 thin films on steel using a microwave activated chemical bath

Microwave activated chemical bath deposition (MW-CBD) is a simple and novel technique in which the substrate is heated directly by microwaves and very well adhered layers are obtained. It has not been used previously for TiO₂ deposition on metals. We show that it is possible to coat stainless steel with TiO₂ using MW-CBD. Two different precursor solutions are used for TiO₂ deposition on steel grade 316. TiO₂ thin films on steel substrates were characterized using SEM and Raman spectroscopy. Raman analysis showed that amorphous TiO₂ is obtained using the precursor solution based on TiOSO₄; however, films show anatase crystal structure when using the precursor solution based on (NH₄)₂TiF₆. Thermal treatment of the films improved crystallinity and also allowed iron diffusion from the steel substrate into the film. Crystalline phases that appeared due to heat treatment were identified from Raman spectra. MW-CBD allows simple low temperature coating of a metal substrate with TiO₂ and this should be useful for a number of different applications.     

Synthesis of CeO2/TiO2 nanoparticles by laser ablation of Ti target in cerium (III) nitrate hexahydrate (Ce(NO3)3·6H2O) aqueous solution

A new synthesis process, laser ablation in an aqueous solution of target material, was applied to synthesize nanostructured CeO₂/TiO₂ catalyst particles. Reactivity within the laser plume (plasma) can be used to synthesize CeO₂ from an aqueous solution, 2 M cerium (III) nitrate hexahydrate (Ce(NO₃)₃·6H₂O) aqueous solution, and to fabricate TiO₂ from Ti target. CeO₂/TiO₂ nanoparticles were successfully synthesized by the laser ablation of Ti target in 2 M cerium (III) nitrate hexahydrate (Ce(NO₃)₃·6H₂O) aqueous solution. Laser ablation of Ti in a liquid environment and chemical reactions of the solution within a plasma plume are discussed.     

Piezoelectric and dielectric properties of Dy2O3-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ + x wt% Dy₂O₃ with x = 0-0.3 ceramics were synthesized by conventional solid-state processes. The effects of Dy₂O₃ on the microstructure, the piezoelectric and dielectric properties were investigated. X-ray diffraction pattern confirmed that the coexistence of tetragonal and rhombohedral phases in the (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ composition was not changed by adding 0.05-0.3 wt% Dy₂O₃. SEM images indicate that all the ceramics have pore-free microstructures with high density, and that doping of Dy₂O₃ inhibits the grain growth of the ceramics. The addition of Dy₂O₃ shows the double effects on decreasing the piezoelectric and dielectric properties for 0 < x < 0.15 when Dy³⁺ ions substitute B-site Ti⁴⁺ ions, and increasing the properties for 0.15 < x < 0.3 when Dy³⁺ ions enters into A-site of the perovskite structure. The optimum electric properties of piezoelectric constant d₃₃ = 170 pC/N and the dielectric constant ?_r = 1900 (at a frequency of 1 kHz) are obtained at x = 0.3.     

Controlled synthesis of TiO2 mesoporous microspheres via chemical vapor deposition

Anatase titanium dioxide (TiO₂) mesoporous microspheres with core-shell and hollow structure were successfully prepared on a large scale by a one-step template-free chemical vapor deposition method. The effects of various reaction conditions on the morphology, composition and structure of the products were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) technique and photoluminescence (PL) method. The results indicate that the product near the source was composed of core-shell structure TiO₂ microspheres with diameters from 3 to 5 μm. With increasing the distance between the source materials and the substrate, the hollow TiO₂ spheres with 1-2 μm dominant the products. A localized Ostwald ripening can be use to explain the formation of core-shell and hollow structures, and the size of the initial TiO₂ solid nanoparticles plays an important role in determining the evacuation manner of the solid in the ripening-induced hollowing process. The surface area of TiO₂ hollow microspheres determined by the adsorption isotherms was measured to be 74.67 m²/g. X-ray photoelectron spectroscopy (XPS) analysis revealed that the O-H peaks of hollow structures have a chemical shift compared with the core-shell structures. The optical property of the products was also discussed.     

Modification of TiO2 nanorods by Bi2MoO6 nanoparticles for high performance visible-light photocatalysis

In this work, TiO₂ nanorods were prepared by a hydrothermal process and then Bi₂MoO₆ nanoparticles were deposited onto the TiO₂ nanorods by a solvothermal process. The nanostructured Bi₂MoO₆/TiO₂ composites were extensively characterized by X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy and UV-vis diffuse reflectance spectroscopy. The photocatalytic activity of the Bi₂MoO₆/TiO₂ composites was evaluated by degradation of methylene blue. The Bi₂MoO₆/TiO₂ composites exhibit higher catalytic activity than pure Bi₂MoO₆ and TiO₂ for degradation of methylene blue under visible light irradiation (λ > 420 nm). Further investigation revealed that the ratio of Bi₂MoO₆ to TiO₂ in the composites greatly influenced their photocatalytic activity. The experimental results indicated that the composite with Bi₂MoO₆:TiO₂ = 1:3 exhibited the highest photocatalytic activity. The enhancement mechanism of the composite catalysts was also discussed.     

Preparation of large scale photocatalytic TiO2 films by the sol-gel process

Nanocrystalline titanium dioxide films were formed on frosted and clear borosilicate glass with a large surface area (12 × 22 cm) using doctor blade and spray coating techniques. The films were subjected to a high temperature treatment at 550 °C. X-ray diffraction (XRD) analysis indicated that the TiO₂ films contain only the anatase phase. Optical microscopy was used to determine the morphology changes after the deposition of each layer. Scanning electron microscopy (SEM) was used to study the films surface morphology. The large scale TiO₂ films produced showed a high photocatalytic activity which was evaluated by the degradation of methyl orange (MO) in aqueous solution (10 mg L^− 1) under illumination of a UV light source with an overall irradiance of 0.9 mW cm^− 2. UV-visible spectrophotometry was used to monitor the degradation of MO through the decrease of the main absorbance peak at 464 nm. The results demonstrated that a complete decomposition of MO could be achieved after 2 h of UV irradiation.     

Low temperature growth of nanocrystalline TiO2 films with Ar/O2 low-field helicon plasma

TiO₂ thin films were deposited on silicon wafer substrates by low-field (1 < B < 5 mT) helicon plasma assisted reactive sputtering in a mixture of pure argon and oxygen. The influence of the positive ion density on the substrate and the post-annealing treatment on the films density, refractive index, chemical composition and crystalline structure was analysed by reflectometry, Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD). Amorphous TiO₂ was obtained for ion density on the substrate below 7 × 10¹⁶ m^− 3. Increasing the ion density over 7 × 10¹⁶ m^− 3 led to the formation of nanocrystalline (~ 15 nm) rutile phase TiO₂. The post-annealing treatment of the films in air at 300 °C induced the complete crystallisation of the amorphous films to nanocrystals of anatase (~ 40 nm) while the rutile films shows no significant change meaning that they were already fully crystallised by the plasma process. All these results show an efficient process by low-field helicon plasma sputtering process to fabricate stoichiometric TiO₂ thin films with amorphous or nanocrystalline rutile structure directly from low temperature plasma processing conditions and nanocrystalline anatase structure with a moderate annealing treatment.     

Oxidation behavior of Ti3AlC2 at 1000-1400 °C in air

The isothermal oxidation behavior of bulk Ti₃AlC₂ has been investigated at 1000-1400 °C in air for exposure times up to 20 h by means of TGA, XRD, SEM and EDS. It has been demonstrated that Ti₃AlC₂ has excellent oxidation resistance. The oxidation of Ti₃AlC₂ generally followed a parabolic rate law with parabolic rate constants, k_p that increased from 4.1×10⁻¹¹ to 1.7×10⁻⁸ kg² m⁻⁴ s⁻¹ as the temperature increased from 1000 to 1400 °C. The scales formed at temperatures below 1300 °C were dense, adherent, resistant to cyclic oxidation and layered. The inner layer of these scales formed at temperatures below 1300 °C was continuous α-Al₂O₃. The outer layer changed from rutile TiO₂ at temperatures below 1200 °C to a mixture of Al₂TiO₅ and TiO₂ at 1300 °C. In the samples oxidized at 1400 °C, the scale consisted of a mixture of Al₂TiO₅ and, predominantly, α-Al₂O₃, while the adhesion of the scales to the substrates was less than that at the lower temperatures. Effect of carbon monoxide at scale/substrate was involved in the formation of the continuous Al₂O₃ layers.     

Evaluation of physico-chemical properties of plasma treated PS-TiO2 nanocomposite film

In this work, we use TiO₂ nanoparticles with average particle size 30 nm and polystyrene for production nanocomposite thin films. After polystyrene was dissolved in toluene, then TiO₂ nanoparticles was added to the solution with different percentage. The obtained solutions were coated on quartz substrate using spin coater. The effect of argon RF plasma (13.6 MHz, with treatment time 30-120 s) on the optical properties, crystallinity, and the surface energy of PS-TiO₂ nanocomposite has been investigated. Some characterization techniques viz., X-ray diffraction analysis (XRD), UV-visible spectroscopy and contact angle measurement were used to study the induced changes on the properties of the treated PS-TiO₂ nanocomposite. Crystalinity and optical properties remained unchanged at the same conditions. Moreover, the surface energy of treated sample varied comparing to the respective untreated samples.     

Efficient dual functionality of highly porous nanocomposites based on TiO2 and noble metal particles

Porous nanocomposites based on TiO₂ aerogels and Au and, respectively, Ag particles were synthesized and their dual functionality to decontaminate water, via photocatalysis, and to detect low concentrations of pollutants from water, via SERS technique, was evaluated using model pollutants. The apparent photodegradation rate constants of a standard pollutant molecule revealed a considerable improvement of the composites photocatalytic performances (even better than one order of magnitude) in comparison with the commercial product Degussa P25. The essential role of the contact between TiO₂ and Au nanoparticles was demonstrated and the potential of all synthesized porous composites for photocatalytic experiments with visible light was pointed out. The lowest concentrations of contaminants adsorbed on the noble metal particles detectable by SERS were found to depend on the composite and pollutant species type and were determined to be between 10⁻³ and 5 × 10⁻⁶ M, and 10⁻⁸ and 10⁻¹⁰ M for off and under resonant excitation, respectively. The morphological (BET, pore size distribution, TEM) and structural (Raman, XRD, diffuse reflectance) particularities of the obtained porous composites were also discussed.     

Microwave dielectric properties of (1 − x)ZnMoO4-xTiO2 composite ceramics

(1 − x)ZnMoO₄-xTiO₂ (x = 0.0, 0.05, 0.158, 0.25, and 0.35) composite ceramics were synthesized by the conventional solid state reaction process. The sintering behavior, phase composition, chemical compatibility with silver, and microwave dielectric properties were investigated. All the specimens can be well densified below 950 °C. From the X-ray diffraction analysis, it indicates that the triclinic wolframite ZnMoO₄ phase coexists with the tetragonal rutile TiO₂ phase, and it is easy for silver to react with ZnMoO₄ to form Ag₂Zn₂(MoO₄)₃ phase and hard to react with TiO₂. When the volume fraction of TiO₂ (x value) increasing from 0 to 0.35, the microwave dielectric permittivity of the (1 − x)ZnMoO₄-xTiO₂ composite ceramics increases from 8.0 to 25.2, the Q_f value changes in the range of 32,300-43,300 GHz, and the temperature coefficient τ_f value varies from −128.9 to 157.4 ppm/°C. At x = 0.158, the mixture exhibits good microwave dielectric properties with a ?_r = 13.9, a Q_f = 40,400 GHz, and a τ_f = +2.0 ppm/°C.     

High transmittance and superhydrophilicity of porous TiO2/SiO2 bi-layer films without UV irradiation

In order to obtain the TiO₂ films with high transmittance and superhydrophilicity without UV irradiation, porous TiO₂/SiO₂ bi-layer films were prepared by spin coated SiO₂ sol and TiO₂ sol including polyethylene glycol 2000 (PEG 2000) onto glass and subsequent calcination at 550 °C. Meanwhile, factors that affect the TiO₂/SiO₂ bi-layer films transmittance and superhydrophilicity were investigated in details by observing their surface morphologies and measuring their water contact angles (WCAs), spreading time and transmittances. The results indicated that the as-prepared TiO₂/SiO₂ bi-layer film showed superhydrophilicity without UV irradiation when 0.5 wt.% PEG 2000 was added in TiO₂ sol. At the same time, its maximum transmittance was as high as 92.3%. The spreading time was only about 0.16 s. More importantly, the resultant film had an excellent stability of the superhydrophilic property.     

Photogenerated cathodic protection of flower-like, nanostructured, N-doped TiO2 film on stainless steel

Flower-like, nanostructured, N-doped TiO₂ (N-TiO₂) films were fabricated using a low-temperature hydrothermal method. The morphology, crystalline phase, and composition of these flower-like nanostructured films were characterized systematically by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV-vis spectroscopy. The photoelectrochemical properties of N-TiO₂ films in 0.5 M NaCl solution were evaluated under illumination and in the dark through electrochemical measurements. Flower-like nanostructured TiO₂ films exhibited a drastically enhanced photocurrent in the UV light region and a notable absorption in the visible light region (600-700 nm). The negative shifts of the electrode potentials of 316L stainless steel coupled with N-doped TiO₂ photoanodes are 470 and 180 mV under UV and visible light irradiation, respectively. The flower-like, nanostructured, N-doped TiO₂ films were able to function effectively as photogenerated cathodic protection for metals under UV and visible light illumination. Such photogenerated cathodic protection could last a period of 5.5 h even in darkness.