TiO2 nanotube, nanowire, and rhomboid-shaped particle thin films fixed on a titanium metal plate

Titanium dioxide thin films having various nanostructures could be formed by various treatments on sodium titanate nanotube thin films approximately 5 μm thick fixed on titanium metal plates. Using an aqueous solution with a lower hydrochloric acid concentration (0.01 mol/L) and a higher reaction temperature (90 °C) than those previously employed, we obtained a hydrogen titanate nanotube thin film fixed onto a titanium metal plate by H⁺ ion-exchange treatment of the sodium titanate nanotube thin film. Calcination of hydrogen titanate nanotube thin films yielded porous thin films consisting of anatase nanotubes, anatase nanowires, and anatase nanoparticles grown directly from the titanium metal plate. H⁺ ion-exchange treatment of sodium titanate nanotube thin films at 140 °C resulted in porous thin films consisting of rhomboid-shaped anatase nanoparticles.     

Adsorption and surface complexation of trimesic acid at the alpha-alumina-electrolyte interface

Adsorption kinetics, adsorption isotherms and surface complexation of trimesic acid onto alpha-alumina surfaces were investigated. Adsorption kinetics of trimesic acid with an initial concentration of 0.5 mM onto alpha-alumina surfaces were carried out in batch method in presence of 0.05 mM NaCl (aq) at pH 6 and 298.15, 303.15 and 313.15 K. Adsorption isotherms were carried out at 298.15 K, pH 5-9, and 0.05 mM NaCl (aq) by varying trimesic acid concentration from 0.01 to 0.6 mM. Three kinetics equations such as pseudo-first-order, pseudo-second-order and Ho equations were used to estimate the kinetics parameters of the adsorption of trimesic acid on the alpha-alumina surfaces. Ho equation fits the experimental kinetics data significantly better and the estimated equilibrium concentration is in excellent agreement with the experimental value. The adsorption data were fitted to Freundlich and Langmuir adsorption model and the later best fits the adsorption isotherms. Comparison of adsorption density of trimesic acid with that of benzoic and phthalic acids follows the sequence: benzoic acid < trimesic acid < phthalic acid. The negative activation energy and the Gibbs free energy for adsorption indicate that the adsorption of trimesic acid onto alpha-alumina is spontaneous and facile. DRIFT spectroscopic studies reveal that trimesate forms outer-sphere complexes with the surface hydroxyl groups that are generated onto alpha-alumina surfaces in the pH range of the study.     

热处理气氛对 TiO2 纳米管阵列薄膜光电催化性能的影响

 采用原位阳极氧化法在 Ti 基底上制备了高度有序的 TiO₂ 纳米管阵列薄膜, 分别在 O₂, 空气, Ar 和 H₂ 气氛中于 500 oC 进行结晶热处理, 考察了热处理气氛对 TiO₂ 纳米管阵列薄膜光电催化降解亚甲基蓝 (MB) 反应性能的影响. 结果表明, 在这些气氛中热处理得到的锐钛矿晶型的纳米管阵列薄膜对 MB 降解满足一级反应, 其速率常数分别为 4.967, 3.127, 1.989 和 1.625 h^-1 (0.5 V). 电化学阻抗分析表明, TiO₂ 纳米管的光电催化性能受控于光生电荷的传递特性. 在 O₂ 中热处理, TiO₂ 纳米管的光吸收及激发性能得以改善, 且电荷传递阻抗降低, 因而其光电催化性能最好.     

Mesostructured Dye‐Doped Titanium Dioxide for Micro‐Optoelectronic Applications

Optically transparent, mesostructured titanium dioxide thin films were fabricated using an amphiphilic poly(alkylene oxide) block copolymer template in combination with retarded hydrolysis of a titanium isopropoxide precursor. Prior to calcination, the films displayed a stable hexagonal mesophase and high refractive indices (1.5 to 1.6) relative to mesostructured silica (1.43). After calcination, the hexagonal mesophase was retained with surface areas >300 m² g^?1. The dye Rhodamine 6G (commonly used as a laser dye) was incorporated into the copolymer micelle during the templating process. In this way, novel dye‐doped mesostructured titanium dioxide films were synthesised. The copolymer not only directs the film structure, but also provides a solubilizing environment suitable for sustaining a high monomer‐to‐aggregate ratio at elevated dye concentrations. The dye‐doped films displayed optical thresholdlike behaviour characteristic of amplified spontaneous emission. Soft lithography was successfully applied to micropattern the dye‐doped films. These results pave the way for the fabrication and demonstration of novel microlaser structures and other active optical structures. This new, high‐refractive index, mesostructured, dye‐doped material could also find applications in areas such as optical coatings, displays and integrated photonic devices.     

Synthesis of photocrosslinkable hyperbranched polyesters and their film properties

Hyperbranched polyesters with terminal methacryloyl groups (HBPEAc) were synthesized by the one‐pot polyaddition of bisphenol A diglycidyl ether and trimesic acid in the presence of methacrylic acid with a number‐average molecular weights of 5100–7700 in 70–83% yields. The photoradical polymerization of HBPEAc was examined in the presence of 2‐methyl‐1‐[4‐(methylthio)phenyl]‐2‐morpholinopropan‐2‐one (Irgacure 907®) as a photoinitiator in the film state upon UV irradiation to afford the corresponding cured films quantitatively. The crosslinking densities of the cured films of HBPEAc were higher than those of the corresponding linear ones, and birefringence cannot be detected for the cured films of HBPEAc because of their random structures. Furthermore, an alkaline‐developable hyperbranched polyester containing pendant carboxyl groups (HBPEAc‐COOH) was prepared by the addition reaction of HBPEAc with cis‐1,2,3,6‐tetrahydrophthalic anhydride, and its patterning properties were examined to give the resolution of a 55‐μm‐line and 275‐μm‐space pattern by UV irradiation with 700 mJ/cm². © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4642–4653, 2005     

Time-resolved light scattering studies of Spin-coated titanium dioxide

Spin coating of titanium alkoxides is a fast and straightforward method of forming compact and durable titanium dioxide thin films. In this report, an optical interference technique is used to understand the dynamics of titanium dioxide thin film formation during the spin coating process of titanium (IV) ethoxide sols, and a 4-stage thinning model is proposed. Optical monitoring of interference fringes as a function of time enables determination of the time-dependent film thickness through measurement of the interference fringe separation while the sol to gel transition can be monitored by analyzing the fringe visibility. For films that are spun at 2,000 rpm or faster, a spin duration of 5 s is sufficient for the film to reach its final thickness. At a given spin speed, spin times longer than 5 s do not affect the final film thickness. However, thinner final film thicknesses can be achieved by increasing the spin speed. All films were found to densify on annealing with an annealed thickness approximately 0.4 times that of the pre-anneal thickness regardless of spin speed. Spin-coated titanium dioxide films are expected to play an important role in low-cost and scalable next generation solar cells employing dyes and quantum dots as the light harvesting agents.     

Preparation and characterization of thin TiO2-films on gold/mica

Flat and highly (111) oriented gold and silver films were prepared by physical vapour deposition (PVD) using optimized deposition parameters. On these films, which were characterized with atomic force microscopy (AFM), scanning tunneling microscopy (STM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), titanium dioxide films were deposited by electron beam evaporation and dip coating. Dip coating from titanium tetraisopropoxide solutions resulted in films with different morphology and coverage depending on the alkoxide concentration (0.009 mol/L – 0.60 mol/L) and the post-treatment. Scanning electron microscopy (SEM) and AFM revealed that the deposited TiO₂ consists of amorphous, highly porous islands when the applied alkoxide concentration is high (0.05 mol/L – 0.6 mol/L). At higher temperatures these amorphous TiO₂ islands sintered significantly and crystallized to anatase. In contrast, transparent TiO₂ films were obtained from low concentrated alkoxide solutions (< 0.01 mol/L) which covered the whole substrate, similar to electron beam evaporated thin films. Sputter profiles with ion scattering spectroscopy (ISS) indicated that the film thickness is in the range of 2 nm when alkoxide solutions with a concentration of 9 mmol/L are used. The deposition of TiO₂ by electron beam evaporation normally resulted in significantly reduced TiO₂ films, completely oxidized ones were obtained when deposition was performed at elevated oxygen partial pressures (p(O₂) > 2 × 10^–5 mbar).     

Substrate temperature influenced physical properties of silicon MOS devices with TiO2 gate dielectric

DC reactive magnetron sputtering technique was employed for deposition of titanium dioxide (TiO₂) films. The films were formed on Corning glass and p‐Si (100) substrates by sputtering of titanium target in an oxygen partial pressure of 6×10^?2 Pa and at different substrate temperatures in the range 303 – 673 K. The films formed at 303 K were X‐ray amorphous whereas those deposited at substrate temperatures ≥ 473 K were transformed into polycrystalline nature with anatase phase of TiO₂. Fourier transform infrared spectroscopic studies confirmed the presence of characteristic bonding configuration of TiO₂. The surface morphology of the films was significantly influenced by the substrate temperature. MOS capacitor with Al/TiO₂/p‐Si sandwich structure was fabricated and performed current–voltage and capacitance–voltage characteristics. At an applied gate voltage of 1.5 V, the leakage current density of the device decreased from 1.8 × 10^?6 to 5.4 × 10^?8 A/cm² with the increase of substrate temperature from 303 to 673 K. The electrical conduction in the MOS structure was more predominant with Schottky emission and Fowler‐Nordheim conduction. The dielectric constant (at 1 MHz) of the films increased from 6 to 20 with increase of substrate temperature. The optical band gap of the films increased from 3.50 to 3.56 eV and refractive index from 2.20 to 2.37 with the increase of substrate temperature from 303 to 673 K. Copyright © 2012 John Wiley & Sons, Ltd.     

TiO2‐modified Carbon Paste Electrode as a Sensor for the Assay of Weak Organic Acids/Bases and Complex Matrix Samples

The construction, general performance characteristics and analytical application of a titanium dioxide–modified carbon paste electrode sensitive to hydrogen ions, based on incorporation of titanium dioxide in a carbon paste matrix, is described. The proposed electrochemical sensor exhibits a linear response in the pH range from 2 to 10, at 25 °C, with a sub‐Nernstian slope. The value of a slope is in a direct correlation with the electrode composition – the optimum content of a titanium dioxide in carbon paste is 30 %. Titanium dioxide‐modified carbon paste electrode shows fast response time and reproducibility, confirmed by different compounds determination in both, individual and complex material, namely, in synthetic and real samples. Besides, the electrode shows high selectivity in the presence of the alkali and the alkaline earth ions as Na⁺, K⁺, Ca²⁺ or Mg²⁺. The standard deviation of the investigated acids (acetic, oxalic, 5‐sulfosalicylic, p‐toluensulfonic acid, and amino acid‐glycine) and bases (N,N′‐diphenylguanidine and collidine) is less than 1.3 %. The obtained data are compared with those obtained by using a conventional glass pH‐electrode under the same experimental conditions and indicate a high correlation between them.     

Photoelectrochemical properties of TiO2 films obtained by electrical explosion

The electrical explosion of wires was used to prepare titanium dioxide nanopowders alloyed with silver nanoparticles. The photoelectrochemical properties and electronic structure of these materials were studied. The quantum yield for the photoelectrochemical current η and the flat band potential E _fb for TiO₂/Ag films were found to be proportional to the content of the Ag⁰ phase on the electrode surface.     

Improving titanium dioxide dispersion in water through surface functionalization by a dicarboxylic acid

In this work, we show evidence of improving the dispersion of titanium dioxide particles in water. This is observed in the titanium dioxide-water colloid by the shear-thinning flow behavior in rheological measurements induced by the functionalization of a glutaric acid layer on the surface of titanium dioxide particles. The characterization of the layer was achieved by using infrared spectroscopy and ^13?C nuclear magnetic resonance. Rheological measurements corroborated that functionalization of TiO₂ particles decreases the rheological properties such as viscosity measurements at a constant shear rate in two orders of magnitude compared with the pure TiO₂ in suspensions. We present the results as a novel strategy to limit the formation of agglomerates in these colloidal suspensions, and this will be of great use in applications in the paints field and printing technologies.     

Molecular Conformations of Shape Anisometrically Variant Mesogens in Liquid Crystalline Phase Studied by 13C NMR Spectroscopy

Mesogens that vary in shape anisometry have been investigated by ¹³C solid-state NMR in the liquid crystalline phase to inspect the conformations. The molecules examined comprise of (i) rod-like mesogen with three-phenyl ring core and terminal hexyloxy chains, (ii) three-ring core linked to the fourth phenyl ring via a spacer, and (iii) trimesic acid connected to three side arms core units through a spacer. The order parameter (S_zz) values for the phenyl rings of the rod-like mesogen are 0.65–0.68, while the mesogen with a three-ring core linked to a phenyl ring via spacer showed dissimilarity. Consequently, for the core unit phenyl rings, S_zz is ~0.70, and the terminal phenyl ring showed a low value of 0.12. For the trimesic acid based mesogen, the S_zz value for the side arm phenyl rings is ~0.53, and for the central phenyl ring, a very low value of 0.11 is witnessed. By considering the ordering of the rod-like mesogen as a yardstick and employing the ratios of S_zz values of the phenyl rings, the average conformations of other mesogens are arrived. Accordingly, for the trimesic acid based mesogen, a tripod-like conformation instead of λ shape is proposed in the liquid crystalline phase.     

核-壳和中空多面体二氧化钛制备、表征及光催化

本文采用水热法控制制备了具有特殊纳米结构的核-壳和中空多面体二氧化钛, 以进一步提高具有特定暴露面多面体二氧化钛的比表面积, 达到更优异的光催化效果。用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)等技术对所制备特殊结构二氧化钛的物相和微/纳结构进行表征分析, 结果表明所得核-壳和中空结构多面体二氧化钛具有一个类似隧道结构的(001)/(001)洞开的截顶双金字塔型壳层。这两种特殊结构的形成可能是源于配位/弱酸性腐蚀原理的共同作用。用核-壳和中空结构二氧化钛对亚甲基蓝进行光降解实验, 结果表明:所得两种新颖结构二氧化钛的光催化效率得到明显提高, 尤其是在添加过氧化氢条件下。可能原因是:两种特殊结构二氧化钛大比表面积正面作用抵消了(001)晶面消失或减少所产生的副作用, 以及过氧化氢在光催化反应中提供的活性氢氧根自由基使得光辐照二氧化钛产生的电子-空穴对在催化剂表面得到有效分离。     

Preparation of TiO2 Sol Using TiCl4 as a Precursor

A titanium dioxide sol with narrow particle size distribution was synthesized using TiCl₄ as the starting material. The sol was prepared by a process where HCl was added to a gel of hydrated titanium oxide to dissolve it. The resulting aqueous titanic acid solution was heated to form titanium dioxide sol. The effects of preparation parameters were investigated. TiCl₄ was slowly added to distilled water at 5°C. Aqueous solution of sodium hydroxide was added to adjust the pH of the system to 8–12. After aging for a period of time, the peptized sol was filtered and sufficiently washed. The filtered cake was repulped in water. Hydrochloric acid was slowly added to the solution with stirring. After condensation reaction and crystallization, a transparent sol with suspended TiO₂ was formed. XRD results show that the crystalline phase was anatase. The suspended TiO₂ particles were rhombus primary particles with the major axis ca. 20 nm and the minor axis ca. 5 nm. The TiO₂ particles prepared at pH 8 had the largest surface area of 141 cm³/g and it was microporous. The compositions of the solution which yielded the smallest suspended TiO₂ particles were TiO₂:HCl (35% HCl) = 1:1 (molar ratio), concentration of TiO₂ = 10%. Hydroxypropyl cellulose with viscosity of 150–400 cps was added as a dispersant. The sol was excellent in dispersibility and long-term stability. Transparent thin films could be obtained through dip-coating glass substrate in the sol. The dip-coating on glass can be less than three times to have one monolayer TiO₂. The transparent TiO₂ thin film had strong hydrophilicity after being illuminated by UV light.     

Electrochemical behavior of benzenepolycarboxylic acids on solid electrodes in aqueous and mixed solutions

Electrochemical behavior of biologically active benzenepolycarboxylic (trimellitic, trimesic, pyromellitic, mellitic) acids is studied by a voltammetry method on Pt, Cu, Ta, and Cu-Hg in aqueous media and water mixtures with ethanol and pyridine. In all cases, voltammograms for the acids display waves corresponding to the discharge of hydrogen ions. In the case of Cu-Hg, voltammograms for trimellitic, trimesic, and pyromellitic acids additionally exhibit poorly pronounced prewaves. Concentrations of ionized and non-ionized forms in dilute solutions of the acids are calculated. Apparent dissociation constants K _a ^II and K _a ^III for mellitic acid are calculated from the voltammetry data.     

核-壳和中空多面体二氧化钛制备、表征及光催化

本文采用水热法控制制备了具有特殊纳米结构的核-壳和中空多面体二氧化钛,以进一步提高具有特定暴露面多面体二氧化钛的比表面积,达到更优异的光催化效果。用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)等技术对所制备特殊结构二氧化钛的物相和微/纳结构进行表征分析,结果表明所得核-壳和中空结构多面体二氧化钛具有一个类似隧道结构的(001)/(001)洞开的截顶双金字塔型壳层。这两种特殊结构的形成可能是源于配位/弱酸性腐蚀原理的共同作用。用核-壳和中空结构二氧化钛对亚甲基蓝进行光降解实验,结果表明:两种新颖结构二氧化钛具有优异的光催化性能,尤其是在添加过氧化氢条件下。可能原因是:两种特殊结构二氧化钛大比表面积正面作用抵消了(001)晶面消失或减少所产生的副作用,以及过氧化氢在光催化反应中提供的活性氢氧根自由基使得光辐照二氧化钛产生的电子-空穴对在催化剂表面得到有效分离。     

Interaction of pigments with polystyrene latex prepared using a zwitterionic emulsifier

An emulsion polymerization of styrene in the presence of a zwitterionic emulsifier,N,N-dimethyl-n-laurylbetaine (LNB), was carried out at pH 7.0. The stability of mixed dispersions composed of latex particles prepared with the emulsifier (LNB) and titanium dioxide particles was studied as a function of pH. The zeta potential of the synthesized latex particles was significantly dependent on the pH and showed the existence of an isoelectric point. In the pH range of 3.0–8.3, where the latices are positively charged while titanium dioxide pigment particles are negatively charged, the mixed suspensions of the latices and titanium dioxide particles were dispersed but exhibited heterocoagulation with increasing particle number of the latices. Furthermore, titanium dioxide particles were restabilized with further addition of the latices. The mechanisms of these processes are discussed. A similar experiment was conducted with silica particles.     

Effect of micron and nano-grade titanium dioxides on the efficiency of hindered piperidine stabilizers in a model oxidative reaction

Polymer additives often show many side reactions during the ageing of polymers which change the useful life-time of the materials. In this regard nano-grade titanium dioxide additives with high surface areas and nano-particle sizes appeared in recent years to be used in polymers where the side reactions have been found to markedly influence mechanisms of ageing. The interaction between titanium dioxide pigments and stabilizers therefore is proposed as a field of great importance.In this paper the influence of nano and micron particle grade anatase and rutile titanium dioxide pigments on the efficiency of a hindered amine stabilizer, Chimassorb 119FL and Chimassorb 119 has been investigated in the system comprising the model radical reaction of cumene initiated (2,2′-azobisisobutyronitrile, AIBN) oxidation. This model reaction was designed to simulate the thermo-oxidative processes in polymers.Kinetic measurements of oxidation rates in the absence of the pigments showed strong retarding activity of the stabilizers under conditions of the model experiments. The rates depend linearly on the reciprocal square root of the concentration of the stabilizers over a sufficiently wide range thereby fitting the mechanism of addition of cumylalkyl R radicals to the Chimassorb molecules. The rate constants for the addition of cumyl R radicals to Chimassorb 119FL and Chimassorb 119 were determined to be k_(333 K) = (1.4 ± 0.2) × 10⁸ and (1.2 ± 0.2) × 10⁸ M⁻¹ s⁻¹, respectively. Hence the Chimassorb 119 family is relatively powerful retarders of thermal oxidation.Further measurements of oxidation rates in the presence of titanium dioxide particles showed that there is a significant reduction in the retarding action of the stabilizers in the presence of titanium dioxides. It occurs as a result of the initiating action of titanium additives producing an additional concentration of free radicals and inducing an additional oxidation rate which may weaken the initial inhibiting efficiency of the added hindered piperidine stabilizers. The titanium nano-samples added at a 1-wt.% into the oxidized condensed system are able to completely decrease the initial inhibiting efficiency of the stabilizers. In terms of the degree of the sensitising action the titanium dioxides can be ordered as: nano-rutile > nano-anatase treated hydroxyapatite > nano-anatase untreated > micro-anatase > micro-rutile.The behaviour of titanium dioxide particles incorporated with hindered piperidine HAS stabilizers in condensed systems may thus be used for the assessment of their performance during the thermo-oxidative degradation of polymers.     

Adsorption of cadmium(II) onto goethite and kaolinite in the presence of benzene carboxylic acids

The effect of benzene carboxylic acids on the adsorption of Cd(II) (5×10⁻⁵ M) by goethite and kaolinite has been studied in 0.005 M NaNO₃ at 25°C. The concentrations of phthalic (benzene-1,2-dicarboxylic acid), hemimellitic (1,2,3), trimellitic (1,2,4), trimesic (1,3,5), pyromellitic (1,2,4,5) and mellitic (1,2,3,4,5,6) acids varied from 2.5×10⁻⁵ to 1×10⁻³ M. Mellitic acid complexes Cd(II) strongly above about pH 3, but the other acids only at higher pH, phthalic acid forming the weakest complexes. Phthalic, trimesic and mellitic acids adsorbed strongly to goethite at pH 3, but adsorption decreased at higher pH; however, mellitic acid was still about 50% adsorbed at pH 9, by which the other two were almost entirely in solution. At 10⁻³ M all the acids enhanced the adsorption of Cd(II) to goethite, the higher members of the series being the most effective. The higher members of the series suppressed Cd(II) adsorption onto kaolinite, but phthalic and trimesic acids caused slight enhancement. The effects of mellitic acid on Cd(II) adsorption depended strongly on its concentration. The maximum enhancement of Cd(II) adsorption onto goethite was at 10⁻⁴ M. The greatest suppression of Cd(II) adsorption onto kaolinite was at 10⁻³ M, and at 2.5×10⁻⁵ M mellitic acid enhanced Cd(II) adsorption onto kaolinite at intermediate pH. The results are interpreted in terms of complexation between metal and ligand (acid), metal and substrate, ligand and substrate, and the formation of ternary surface complexes in which the ligand acts as a bridge between the metal and the surface.     

Photoelectrochemical cells based on nanocrystalline TiO2 synthesized by high temperature hydrolysis of ammonium dihydroxodilactatotitanate(IV)

Photoelectric parameters of dye-sensitized solar cells (DSSC) based on nanocrystaline titanium dioxide synthesized by several methods are studied. The lifetime of charge carriers (electrons) is shown to be 10 ms for DSSC with anodes of TiO₂ synthesized by hydrolysis of ammonium dihydroxodilactatotitanate(IV) (DLTA) and about 7 ms for anodes of commercial titanium dioxide (AEROXIDE®, TiO₂, P 25, Evonik), which points to the lower recombination losses for anodes of DLTA. The transition times for both cell versions are close to one another and equal to 10 ms; under these conditions, the diffusion coefficient of electrons is assessed to be ca. 10^?5 cm² s^?1. The comparable transition times and lifetimes of electrons in DSSCs under study suggest that a part of photogenerated electrons is lost at the diffusion to the conducting substrate.