Search

Rutile TiO2 nanorods with lengths greater than 600 nm and aspect ratios greater than ca. 16 were synthesized through a one-pot hydrothermal method using lactic acid (LA) as a structure-directing agent. Under the hydrothermal treatment at 200 °C, the LA concentration higher than 1.6 mol dm–3 and the hydrothermal time of 72 h were needed to obtain 100% rutile nanorods. The length and the width of the nanorods increased with the increasing LA concentration. The photocatalytic activity of the synthesized nanorods was evaluated for the oxygen evolution in aqueous AgNO3 solutions under ultraviolet irradiation. Calcination of the synthesized nanorods at 400 °C was required to decompose residual organic compounds on the surface and improve the oxygen evolution. The highest oxygen evolution rate was obtained with the nanorods after being calcined at 800 °C. It is worth noting that the nanorods retained their shape (aspect ratio of 8.8) at 800 °C. Selected area electron diffraction patterns indicated that the side or the end surface of the nanorods was attributable to the {110} or {111} facet, respectively. Deposition of Pt or PbO2 on the nanorods revealed that the {110} or {111} facet acted as reductive or oxidative sites. For comparison, near-spherical TiO2 nanoparticles were synthesized by a sol–gel method. Furthermore, using glycolic acid as the structure-directing agent, we synthesized small rutile TiO2 nanorods (aspect ratio of 9) and changed the shape to near-spherical (aspect ratio of 1.3) by calcining at 800 °C. Time-resolved diffuse reflectance spectra were measured to determine the lifetime of the photogenerated electrons. The photocatalytic activity of the nanorods was much lower than that of the near-spherical TiO2 nanoparticles. However, the nanorods synthesized with LA are useful as catalyst support or platforms for various applications because of their unique morphology and high heat resistance.

Transition metal oxide nanoparticles have been extensively studied for the development of smart windows which are expected to be a promising technology to save energy in buildings. However, most of them turn blue under UV irradiation. Since the blue coloration affects the color of objects through the windows, the development of materials with a neutral color which hardly disturbs the view is more beneficial. In this work, we prepared a colorless-transparent TiO

Photocatalysis is a promising technique for developing sustainable and environmentally friendly materials to improve indoor air quality. Visible-light-responsive TiO2 has been widely investigated but there are inconsistent results because photocatalytic properties depend strongly on synthetic methods. Herein, we synthesize TiO2 doped with 10 different metal ions (M–TiO2) by conducting a dialysis in a sol–gel method to obtain the best photocatalyst for the degradation of acetaldehyde under LED irradiation. Purification of a sol by dialysis enables us to discuss pure effects of dopants on the photocatalytic activity because impurities such as counter ions of metal salts are removed before sintering. Only Cr–, Pt–, V–, and Fe–TiO2 show photocatalytic activity and the optimal doping amounts are 0.50–1.7, 0.10, 1.0, and 0.10 atom%, respectively. Such differences in the optimal amounts can be explained in terms of the dopant ions having different valence states, suggesting the formation of oxygen vacancies. The Cr–TiO2 powder exhibits high activity even at the doping amount of 4.2 atom%. We also demonstrate that the Cr–TiO2 film prepared on a glass substrate can be used to degrade acetaldehyde by changing the film thickness and the LED intensity depending on the degree of the indoor contamination.

TiO2 nanorods have been widely investigated for various applications as catalyst support, photoanode, bioanalytical platform, and photocatalyst because of their unique properties due to the high le...

Porous titanium dioxide pellets modified with copper(II) ion (Cu-TiO2) were synthesized by sol-gel method with dialysis for photocatalytic degradation of gaseous trichloroethylene (TCE) under visible light (VL) irradiation. TCE was completely degraded by passing the gas stream (mole fractions of oxygen and TCE were 0.2 and 1.75 × 10−4, respectively) at the flow rate of 25 mL min−1 through 0.2 g of the Cu-TiO2 pellets (Cu content: 0.1 atom%) calcined at 200 °C. TCE was converted mainly to carbon dioxide, dichloroacetic acid (DCAA), and inorganic chlorine species. Relatively small quantities of pentachloroethane (PCA) and trichloroacetaldehyde (TCAH) were detected as products on the Cu-TiO2 surface. Comparison with porous TiO2 pellets under ultraviolet irradiation revealed that more chlorinated products and less carbon dioxide were formed on Cu-TiO2 under VL irradiation. The mineralization of TCE to carbon dioxide was calculated to be only ca. 30.0%. It is noted that DCAA, PCA and TCAH were accumulated on the surface and were extracted with ethyl acetate. The porous Cu-TiO2 pellets show promise as the photocatalyst acting under VL irradiation for converting TCE gas to chlorinated compounds which can be used in industries.

There are many factors affecting TiO2 photocatalysis, such as specific surface area, crystal phase, crystallite size, and crystallinity. However, there is controversy regarding the most important factor among them. In this chapter, we prepared TiO2 by conducting dialysis in a sol–gel synthesis and investigated the photocatalytic activity. Purification of TiO2 sol by dialysis minimizes the effect of impurities originating from raw materials on the crystallization of TiO2 during the thermal treatment. As a result, we reveal that fine anatase powder with high crystallinity is the most appropriate for the degradation of 4-chlorophenol in water, whereas the crystallite size is the key factor determining the oxygen evolution from water. In the case of visible light–responsive TiO2 doped with metal ions, the photocatalytic activity is controlled by the metal ion dopants having different valence states. These factors are related to the efficiency to suppress the recombination of the photogenerated charge carriers.

We synthesized rutile TiO2 nanorods with high crystallinity, i.e., degree of crystallinity greater than ca. 90%, by using a hydrothermal method and studied the effect of the morphological change from rod shape to subsphere by the subsequent thermal treatment. The photocatalytic activity was estimated for O2 evolution from water oxidation because this reaction was hardly affected by the specific surface area of photocatalysts. Thermal desorption and gas chromatography–mass spectrometry measurements suggested the decomposition of residual glycolic acid in TiO2 nanorods at 272 and 590 °C. Observation with scanning electron microscopy and physical properties such as specific surface area and crystallite size indicated deformation of the rod shape to subsphere by the calcination above 600 °C. Time-resolved microwave conductivity measurements have revealed that the TiO2 nanorods possess the longest lifetime of photogenerated electrons among all samples. However, the O2 evolution rate of the TiO2 nanorods was mu...

Titanium dioxide doped with Cr ions (Cr–TiO2) was synthesized by a sol–gel method, with only water as the solvent, and dialysis. For Cr–TiO2 sintered at 200 °C, ca. 90% of 4-chlorophenol (4-CP) was degraded at Cr doping amounts of 0.68–1.3 atom% under visible light irradiation. At doping amounts above 1.7 atom%, the 4-CP degradation ratio increased for Cr–TiO2 sintered at 300–500 °C. X-ray photoelectron spectroscopy and X-ray absorption near edge structure measurements showed that only Cr(III) was present on the surfaces of Cr–TiO2 samples sintered at 200 or 400 °C and some of the Cr(III) in the bulk was oxidized to Cr(VI) by sintering at 400 °C. The 4-CP degradation was enhanced with increasing Cr(VI)/Cr(III) ratio in the bulk, suggesting the spatial separation of Cr(III) on the surface under visible light irradiation: electrons are excited from Cr(III) to the conduction band of TiO2 and then trapped at the doped Cr(VI) whereas the photogenerated Cr(IV) oxidizes 4-CP. Time-resolved diffuse reflectance spectroscopy was used to evaluate the lifetimes of the photogenerated electrons. The highest photocatalytic activity was obtained with ca. 0.8 atom% Cr–TiO2 sintered at 200 °C. This high activity is ascribed to the presence of oxygen vacancies, which act as electron-trapping sites.

The present paper reports the development of TiO2 photocatalysts adsorbed with squaraine dyes for the utilization of visible light. We synthesized 1,3-bis(3,3-dimethyl-2-methylene indolenine)squaraine (ISQ) and its derivatives having two COOH (ISQ-(COOH)2), COOH and COOC4H9 (ISQ-COOHCOOBu) and two COOC4H9 groups (ISQ-(COOBu)2) at both ends. We used porous TiO2 which was synthesized by a sol–gel method and possessed a specific surface area of 229 m2 g−1. ISQ without an anchoring group of COOH hardly adsorbed and the number of the adsorbed ISQ-(COOH)2 or ISQ-COOHCOOBu per gram of TiO2 was estimated to be (5.53 ± 0.74) × 10-5 or (5.93 ± 0.68) × 10-5 mol g−1, respectively. Photocatalytic degradation of methyl orange (MO) was performed on TiO2 adsorbed with ISQ-(COOH)2 or ISQ-COOHCOOBu in the range of (0.12–5.4) × 10-5 or (0.15–6.2) × 10-5 mol g−1. The degradation rate increased drastically with an increase in the adsorbed amounts of these dyes less than 1.7 × 10-5 mol g−1 but then increased gradually up to ca. 6 × 10-5 mol g−1. The electrochemical measurements revealed that the photogenerated electron was transferred from these dyes to the conduction band of TiO2. No MO was degraded on TiO2 adsorbed with ISQ-(COOH)2 in the nitrogen atmosphere under VL irradiation. We proposed the degradation mechanism of MO on TiO2 adsorbed with ISQ-(COOH)2 or ISQ-COOHCOOBu.

Titanium dioxide doped with the Pt ion (Pt–TiO2) was synthesized by a sol–gel method using only water as the solvent and conducting dialysis. The photocatalytic activity for the degradation of 4-chlorophenol (4-CP) on Pt–TiO2 was not affected by the Brunauer–Emmett–Teller specific surface area under visible light (VL) irradiation. X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure measurements revealed that only the Pt(IV) ion existed in the TiO2 bulk and both Pt(II) and Pt(IV) were present near the Pt–TiO2 surface. Pt(IV) is most likely substituted in the Ti(IV) site of the TiO2 lattice because of their similar ionic sizes. Quantitative analysis of Pt(II) was performed in the XPS measurements, indicating that the amount of Pt(II) on the surface increased with an increase in the doping amount from 0.2 to 1.0 atom %. We synthesized 0.5 atom % Pt–TiO2 with various Pt(II)/Pt(IV) ratios by changing the Ti(OC3H7)4 concentration used in the sol–gel synthesis. The 4-CP conversion on Pt–TiO2 increased linearly with an increase in the Pt(II)/Pt(IV) ratios. A similar relationship was obtained with Pt–TiO2, which was prepared by a conventional sol–gel method in ethanol–water mixed solvent. Therefore, the Pt(II)/Pt(IV) ratio is a key factor affecting the photocatalytic activity of Pt–TiO2 under VL irradiation. Our results indicate that controlling the mixed valence states of the doped metal ions is a new strategy to developing highly active metal-ion-doped TiO2 under VL irradiation.

Porous platinum ion-doped TiO2 (Pt–TiO2) was prepared by a sol–gel method and demonstrated to have superior photocatalytic activity for the photodegradation of gaseous trichloroethylene (TCE) under visible light (VL) irradiation from a xenon lamp equipped with 422-nm cut-off filter. Kinetic studies were performed to clarify the effect of the doping amounts, space times, VL intensity, and mole fractions of TCE, O2, and H2O on the degradation of TCE. Under ultraviolet (UV) irradiation, the photocatalytic activity of Pt–TiO2 was the same as that of TiO2, indicating that the doped Pt ion did not act as a recombination center for the photogenerated holes and electrons. Based on the kinetic data and reaction products, we conclude that the photocatalytic degradation of TCE on Pt–TiO2 under VL irradiation proceeds similarly to TiO2 under UV irradiation. We also performed the photocatalytic degradation of TCE at the space time of 7.5 × 107 g s mol−1 in a tubular reactor packed with the Pt–TiO2 pellets which are more suitable than the Pt–TiO2 powder for the practical remediation of the contaminated gas. TCE was completely degraded, i.e. 100% conversion was achieved under VL irradiation but only a small quantity of CO2 was formed with the stoichiometric ratio of [CO2]formed/[TCE]degraded of ca. 0.33. By switching the gas stream containing TCE to humid air, more CO2 was formed, indicating that the dichloroacetates accumulated on the Pt–TiO2 surface are photodegradable to CO2 under VL irradiation.

TiO 2 modified with Cu 2+ or Cr 3+ ion (M-TiO 2 , M-grafted TiO 2 ) was synthesized by a sol-gel method using Ti(OC 3 H 7 ) 4 as a starting material or a graft method by impregnation of rutile TiO 2 . In the sol-gel method, the Brunauer-Emmett-Teller (BET) surface area of M-TiO 2 was varied by preparing with or without dialysis of TiO 2 sol (M-TiO 2 (D) or M-TiO 2 (ND), respectively). Even by using the sol-gel method, Cu 2+ whose ionic size is larger than Ti 4+ cannot be doped but is incorporated in TiO 2 due to relatively weak interaction. Dissolution of Cu 2+ ion was observed when Cu-TiO 2 (D), Cu-TiO 2 (ND) or Cu-grafted TiO 2 was immersed into the acidic solution of 0.1 mol dm −3 HCl. The photocatalytic activity for the degradation of 4-chlorophenol (4-CP) under visible light irradiation was the following order: Cu-grafted TiO 2 > Cu-TiO 2 (ND) > Cu-TiO 2 (D). We have revealed that the photocatalytic activity of Cu-grafted TiO 2 decreases linearly with an increase in the number-density of Cu 2+ ion on the TiO 2 surface. On the other hand, in the case of Cr 3+ ion which has a similar size as Ti 4+ , the photocatalytic activity increased remarkably by doping Cr 3+ in TiO 2 by the sol-gel method. An increase in the BET surface area by conducting dialysis enhanced the photocatalytic activity. This paper demonstrates from the viewpoint of the higher photocatalytic activity as well as the chemical stability in acidic conditions that Cr-doped TiO 2 prepared by the sol-gel method gives an advantage over Cu-grafted TiO 2 for the degradation of 4-CP which is one of the non-degradable organic contaminants in water.

The effect of physicochemical properties such as specific surface area, crystalline phase, crystallite size, and crystallinity of TiO2 on photocatalytic water oxidation was investigated. Two types of polycrystalline TiO2 samples which have different physicochemical properties were prepared by a sol–gel method. The photocatalytic activities of the TiO2 samples for water oxidation were evaluated by the O2 evolution rate from an aqueous silver nitrate solution under ultraviolet light irradiation. Comparison of the two types of TiO2 samples revealed that the specific surface area and crystalline phase were not related to the O2 evolution rate. In contrast, a linear relationship between the crystallite sizes and the O2 evolution rates was observed for most of the TiO2 samples. Crystal face selective Pt and PbO2 depositions on the TiO2 samples were observed by photocatalytic reduction of PtCl62− and oxidation of Pb2+ ions, respectively, indicating that the oxidation and reduction sites are separated on the surface. An increase in the crystallite size of the TiO2 promotes a spatial separation of the redox sites and suppresses the electron–hole recombination, leading to the enhancement of the photocatalytic activity.

Tungsten oxide-based photochromic films which changed reversibly in air between colorless- transparent in the dark and dark blue under UV irradiation were prepared by using methylcellulose as a film matrix and polyols such as ethylene glycol (EG), propylene glycol (PG), and glycerin (Gly) as dispersing agents. Influence of the dispersing agents and water in the films on the photochromic behavior was systematically studied. Under UV irradiation, absorption bands around 640 and 980 nm increased and the coloring rate was the following order: Gly > EG > PG. An increase in the amounts of dispersing agents or water accelerated the coloring rate. By increasing the water content of the film, a new absorption peak appeared at ca. 775 nm and the Raman spectra indicated a shift of W-O-W stretching vibration to lower wavenumber which was due to the formation of hydrogen bonding. All absorption spectra were fit by three Lorentz functions, whose bands were ascribed to various packing of WO6 octahedra. After the light was turned off, the formation of W(5+) was stopped and bleaching occurred by the reaction with O2 in air to recover its original transparent state. We anticipate that the biodegradable photochromic films developed in this study can be applied in recyclable display medium and especially in detachable films for glass windows whose light transmission properties are changed by sunlight, i.e., for usage as an alternative of smart windows without applying voltage.

Tungsten oxide (WO3) based photochromic films consisting of methyl cellulose (MC), hydroxyethyl cellulose, carboxymethyl cellulose (CMC) or cellulose nanofiber (CNF) are fabricated for monitoring ultraviolet (UV) light. The opaque WO3/MC film becomes transparent by adding ethylene glycol (EG) whereas the WO3/CMC and WO3/CNF are transparent without EG. The WO3/EG/MC film possesses much higher sensitivity to the UV light than the WO3/CNF film. Visually, the blue color of the WO3/CNF film after UV irradiation for 8 h is almost equivalent to that of the WO3/EG/MC film after irradiation for 1 min. The color change of the WO3/CNF and the WO3/EG/MC film can be used to monitor UV from the sun light. We also demonstrated that the WO3/EG/MC film can be used to measure the UV intensity quantitatively up to 6 mW cm−2.

We fabricated 5,10,15,20-tetra(4-pyridyl)porphyrinatozinc(II) (ZnTPyP) fibers by utilizing surfactant-assisted method with cetyltrimethylammonium bromide (CTAB). The ZnTPyP fibers became longer as molar ratio of CTAB to ZnTPyP (γ) increased. In the case of γ ≥ 50, the Soret band of ZnTPyP monomer was observed after stirring for 1 h and was split into two peaks after the aging at 40 °C for more than 5 days. On the other hand, such split peaks were observed without the aging when the γ value was 10 or 20. These findings suggest that CTAB interacts with the ZnTPyP monomer in aqueous solution to form micelles, and the fibers are gradually constructed by self-assembling the stabilized ZnTPyP monomer. Photocatalytic activity of the ZnTPyP fibers was evaluated for the degradation of rhodamine B (RhB) in water under visible light (VL) irradiation. The highest photocatalytic activity was obtained at γ = 150–300, indicating that the fibers with 1.3–2.0 μm were the most suitable as photocatalyst. When air was bubbled in the reaction solution, the photocatalytic activity was higher than that under N2 bubbling. However, absorption peak attributed to the ZnTPyP fibers decreased under air bubbling although it remained almost constant under N2 bubbling. These results suggest that the ZnTPyP fibers can act as photocatalyst and active oxygen species such as O2•− radical might decompose the ZnTPyP fibers. Kinetic studies were performed to clarify the degradation mechanism of RhB under the experimental condition where the decomposition of the ZnTPyP fibers was negligible.

Tungsten oxide-based photochromic films that change reversibly in air between colorless-transparent in the dark and dark blue under UV irradiation were prepared by using methylcellulose as a film matrix and various dispersants. Alpha-hydroxyl acid such as glycolic acid (GA) or glyceric acid (GlyA) is the best dispersant because it can make the film transparent by adding a small quantity much less than that of 3-hydroxypropionic acid or ethylene glycol. Fourier-transform infrared spectra and Raman spectra indicate that a strong interaction exists between WO3 and GA or GlyA. The coloration and bleaching processes of the prepared films were investigated to clarify the effect of the dispersants and the moisture contents. The bleaching rate remarkably decreased in the films containing GA or GlyA but accelerated by increasing the contact with O2. Measurements of electron-spin resonance reveals that GA and GlyA as dispersants stabilize the W5+ state. This paper shows that the coloring rate and the period for keeping the blue-colored state are tunable by changing the dispersants. The photochromic films containing α-hydroxyl acid as the dispersant have the potential for application as rewritable film on which information displayed with blue-colored state can be clearly readable for longer times compared with other dispersants.

Aiming at developing a highly active photocatalyst to decompose organic compounds under visible light irradiation, we have prepared metal ion doped TiO 2 (M-TiO 2 ) by conducting dialysis in sol–gel method. Dialysis leads to the formation of mesoporous materials with surface area larger than 200 m 2 g −1 but the metal ions should be added into the TiO 2 sol at pH 3 in order to avoid their losses during dialysis. Among seven metal ions tested as dopants, Pt-TiO 2 and Cr-TiO 2 showed higher photocatalytic activity for the degradation of 4-chlorophenol under visible light irradiation. The photocatalytic activity of Cr-TiO 2 was strongly affected by the doping amount of Cr ion and the optimal value was evaluated to be 0.68–1.30 atom%. X-ray photoelectron spectroscopy analyses showed the Cr ion was present mainly in Cr(III). The Cr-TiO 2 can be used safely for a practical application to remediate environmental contamination instead of expensive Pt-TiO 2 .

The surface interactions between xanthene (XN) dyes, including rhodamine B, rhodamine 3B, rhodamine 19, rhodamine 6G, rhodamine 110, and rhodamine 123, and tungsten(VI) oxide (WO3) colloid particles were investigated. These XN dyes were strongly adsorbed as a monolayer onto the WO3 surface via the electrostatic interaction between their peripheral cationic amino substituents and negatively surface-charged WO3 colloid particles, and most of the ones adsorbed eventually formed stable π-stacked dimers. The geometry of dimers formed on the WO3 colloid surface is discussed on the basis of the molecular exciton theory framework. Cationic XN dyes formed the approximately ideal face-to-face H-dimers on the WO3 colloid surface, whereas zwitterionic ones had a higher tendency to form the oblique J-dimers. Additionally, we have experimentally demonstrated the possibility of pH-induced switching between H- and J-aggregation modes of the XN dye’s dimers formed on the WO3 colloid surface. The findings lead to a better ...

The adsorption and aggregation behaviors of the cationic porphyrin derivatives such as 5,10,15,20-tetrakis(4-pyridyl)porphyrin [TPyP], 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin [TMPyP], 5,10,15,20-tetrakis(N-ethyl-4-pyridyl)porphyrin [TEPyP], and 5,10,15,20-tetrakis(N-n-propyl-4-pyridyl)porphyrin [TPPyP] (hereafter called "TPyP derivatives") in the tungsten(VI) oxide (WO3) colloid aqueous solution at weak acidic pH were studied by UV-vis spectroscopy. The TPyP derivatives were strongly adsorbed as monolayer onto the WO3 surface via the electrostatic interaction between their peripheral cationic substituents and negatively surface-charged WO3 colloid particles, and most of the ones adsorbed eventually formed J-type dimers aligned in the head-to-tail fashion. These different dimerization states were effectively analyzed by the change of ratios among the intensities of exciton split Soret bands (H- and J-bands). Judging from the exciton coupling theory and adsorption measurements, we concluded that the J-dimer geometry of the TPyP derivatives adsorbed on the WO3 colloid particle surface is strongly dependent on the presence and difference of peripheral substituents. The results described here indicate a new and promising way of designing surface supramolecular structures combination of two principles, the self-association of organic dyes, and the steric repulsive interaction between the peripheral substituents and the inorganic semiconductor surfaces.

Photocatalysis of a transparent aqueous WO 3 sol was investigated for the color-fading of Orange II. Dependence of the degradation rate of Orange II on pH and ionic strength of the WO 3 sol was explained in terms of the electrostatic interaction between Orange II and the WO 3 colloid particles. The degradation rate follows the first-order kinetics with respect to the concentration of Orange II. It was demonstrated that the photogenerated electron in WO 3 reduced O 2 effectively since the photochromism of the WO 3 sol observed under nitrogen atmosphere did not occur under air-saturated condition. The photocatalytic activity of WO 3 was lower than that of TiO 2 by a factor of 0.5 and was enhanced by mixing with the TiO 2 sol. The best photocatalytic performance for the degradation of Orange II was obtained by using the mixed sol with WO 3 :TiO 2 molar ratio of 1:2. Similar enhancement in the photocatalytic activity was confirmed for the degradation of 4-chlorophenol.

Kinetic studies on the photocatalytic degradation of trichloroethylene (TCE) were performed in TiO 2 or WO 3 aqueous sol which consisted of anatase nanocrystalline TiO 2 of ca. 3.9 nm or WO 3 spherical particles of ca. 17.6 nm. Photocatalytic activity of TiO 2 colloid is higher than that of WO 3 by a factor of 2.1. Kinetic analyses for both sols give a similar rate law containing γ value which represents a ratio of the reaction rate of the photogenerated electrons with O 2 against the total disappearance rate of the photogenerated electrons. Reaction temperature did not affect the TiO 2 photocatalysis whereas higher temperature increased the oxidation rate of TCE in the WO 3 sol. Such a difference in the temperature effect was explained in terms of the γ values. The photocatalytic degradation of TCE was enhanced by mixing the WO 3 and the TiO 2 sol and the best performance was obtained by using the mixed sol with WO 3 :TiO 2 molar ratio of 1:2. In the mixed sol, the similar temperature dependence as in the WO 3 sol was obtained. Reaction mechanism and the rate law are proposed to account for the obtained kinetic data.

Silicon oxycarbide/silica composites with well-dispersed tungsten(VI) oxide (WO3) nanoparticles were obtained as transparent hybrid xerogels via an acid-catalyzed sol-gel process (hydrolysis/condensation polymerization) of 3-(triethoxysilyl)propyl methacrylate (TESPMA) and tetraethoxysilane (TEOS). The self-diffusion mechanism of alkali-metal cations and the kinetics of the photochromic coloration process in the WO3/TESPMA/TEOS hybrid xerogel systems have been systematically investigated. Under continuous UV illumination, a gradual color change (colorless → blue) corresponding to the reduction of W(6+) into W(5+) states in WO3 nanoparticles can be confirmed from the WO3/TESPMA/TEOS hybrid xerogels containing alkali-metal sulfates, although no coloration of the hybrid xerogel without alkali-metal sulfate was observed. The coloration behavior depended exclusively on a variety of alkali-metal cations present in the hybrid xerogel system. Furthermore, a detailed analysis of the self-diffusion mechanism confirmed that the alkali-metal cations electrostatically interact with a layer of unreacted silanol groups on the TESPMA/TEOS matrix surface, and subsequently pass through the interconnected pore network of the hybrid xerogel. More interestingly, in the context of an Arrhenius analysis, we found a good coincidence between the activation energies for alkali-metal cation self-diffusion and UV-induced coloration in the WO3/TESPMA/TEOS hybrid xerogel system containing the corresponding alkali-metal sulfate. It is experimentally obvious that the photochromic properties are dominated by the diffusion process of alkali-metal cations in the WO3/TESPMA/TEOS hybrid xerogel system. Such hybrid materials with cation-controlled photochromic properties will show promising prospects in applications demanding energy-efficient "smart windows" and "smart glasses".

Porous platinum-ion-doped TiO2 (Pt-TiO2) with BET surface area higher than 200 m2 g−1 was prepared by using water as solvent and conducting dialysis in a sol–gel method and demonstrated to have superior photocatalytic activity for the photodegradation of 4-chlorophenol (4-CP) under both ultraviolet and visible light (VL) irradiation. During dialysis, 76.5% of Cl− was removed and mesopores were formed in Pt-TiO2. Measurements of pore-size distribution indicated a peak at ca. 3 nm after the calcination of Pt-TiO2 at 200 °C. Optimal conditions to prepare Pt-TiO2 acting under VL were 0.5 at.% as the Pt-doping content and 200 °C as the calcination temperature in the range of 200–500 °C. Kinetic studies were performed to clarify the effect of the amount of Pt-TiO2, initial concentration of 4-CP, intensity and wavelength of the incident light, pH and temperature on the reaction rate and to obtain the rate law under VL irradiation. Formation of benzoquinone and hydroquinone as intermediates was observed. They were further photodegraded on Pt-TiO2 and 90.7% of 4-CP was completely mineralized at the VL irradiation of 390 min.

Photochromism of a WO3 aqueous sol has been investigated in a nitrogen atmosphere under controlled temperature. Effects of ageing of the WO3 sols, concentrations of WO3 sols or Cl− ion and temperature on the coloring rate were examined. The coloring rate was the first-order with respect of the WO3 concentration. The coloring process was accelerated by an addition of TiO2 aqueous sols. Spectral changes were measured using the mixing sol with various molar ratios (γ) of WO3 and TiO2. The absorption spectra changed from those having the single peak at 775 nm to those with two peaks at 640 and 980 nm. Such spectral transformation was ascribed to the structural change of the WO3 nanoclusters, depending on the γ value and the concentration of Cl− ion.

The vinyltrimethoxysilane-grafted ethylene-propylene copolymer/trifunctional methoxysilane (EPR-g-VTMS/RTMS) composites were prepared via in situ silica sol–gel reactions. Five trifunctional methoxysilane compounds (n-hexyltrimethoxysilane, n-decyltrimethoxysilane, n-tetradecyltrimethoxysilane, n-octadecyltrimethoxysilane, and phenyltrimethoxysilane) have been selected for this study. The water-cross-linked EPR-g-VTMS/RTMS composites were characterized by attenuated total reflectance-Fourier transform infrared spectroscopy, gel content, solid-state 29Si CP/MAS NMR, wide-angle x-ray scattering, tensile strength, and field emission scanning electron microscopy measurements. The type of RTMS additive has a substantial influence on the nature of siloxane band networks and eventually the mechanical tensile properties. This finding suggests that the interaction and/or entanglement between the EPR-g-VTMS matrix and the substituent of the RTMS additives are crucial for the modifying mechanical properties. Moreover, for the water-cross-linked EPR-g-VTMS/CnTMS (n = 6, 10, 14, and 18) composites, the joint evidence provided by attenuated total reflectance-Fourier transform infrared spectroscopy, 29Si CP/MAS NMR, and wide-angle x-ray scattering results suggested the formation of ladder-type poly(n-alkyl silsesquioxane)s and the presence of the highly ordered structure with a thickness equal to the length of two n-alkyl groups in all-trans conformation. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.

Cu-deposited TiO2 films were prepared by photoreduction of Cu(II) in the presence of sodium formate. With the initial Cu(II) concentrations more than 100 mg L−1, induction periods were observed before the transmittance decreased. Scanning electron microscopy indicated that Cu particles of 2.6 ± 0.5 μm were deposited isolatedly with much open space in the induction periods. The films prepared by changing the irradiation time within the induction periods showed a higher photocatalytic activity than a pure TiO2 for the degradation of methylene blue under the reaction condition without purging air.

TiO2 particles encapsulated in hollow silica shells with controlled shell thicknesses were fabricated. Compared to naked TiO2 without coverage by a hollow silica shell, all of these composites showed low levels of photocatalytic activity for gas-phase decomposition of acetone into CO2. The activities over these composites tended to decrease with increase in thickness of the lateral silica shell. These results can be explained by a decrease in the diffusion of acetone with increase in thickness of the silica shell, leading to hampering of supply of the substrate to the surfaces of core TiO2 particles. In contrast, for the overall photodecomposition of gaseous 2-propanol into CO2, the presence of the lateral silica shell was found to be beneficial, i.e., the composite induced a high level of activity compared to the activity of naked TiO2. The enhancement of activity for this reaction was likely to be due to condensation of the intermediate product of acetone in the void spaces, leading to an increase in the collision probability between acetone and the surface of the TiO2 core.

The monomer-aggregate equilibrium of four phenothiazine (PN) dyes, containing thionine (TH), methylene blue (MB), new methylene blue (NMB), and 1,9-dimethylmethylene blue (DMB), in the tungsten(VI) oxide (WO(3)) nanocolloid solution has been investigated by means of UV-vis spectroscopy. Addition of PN dye into the WO(3) nanocolloid solution brought about significant changes in the absorption spectrum, suggesting the formation of H-type (face-to-face fashion) trimer on the WO(3) nanocolloid surface. The adsorptivity of PN dyes onto the WO(3) nanocolloid surface was diminished by the raising the ionic strength, indicating the evidence of the electrostatic interaction between cationic PN dye and negatively charged WO(3) nanocolloids. The detail analysis of each spectral data provided insight into the effect of molecular structure of PN dyes on the adsorption and aggregation behaviors on the WO(3) nanocolloid surface. Moreover, in situ measurement of PN dye aggregation using the centrifugal liquid membrane (CLM) technique revealed that the aggregation of PN dyes on the WO(3) nanocolloid surface proceeded in a two-step three-stage (monomer --dimer --trimer) formation. The aggregation mechanism of PN dyes on the WO(3) nanocolloid surface was discussed on the basis of Kasha's exciton theory.

The thermal treatment of TiO2 pellets prepared by the sol–gel method decreased the photocatalytic activity. The activity divided by the specific surface area of the pellets for the complete mineralization of ethylene or chloroform was maximized at the firing temperature of 400°C. For the photocatalytic degradation of trichloroethylene (TCE), most of them were converted to chlorinated by-products, such as dichloroacetic acid, chloroform, and phosgene, and the stoichiometric ratio of [CO2]formed/[TCE]degraded showed a maximal value at 400°C. The electron spin resonance (ESR) spin-trapping with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) in the flow injection system indicated that firing at 400°C gave the highest signal intensity of DMPO–OH adducts. These findings indicated that the OH radical was produced most effectively on the TiO2 fired at 400°C, which would be related to the content of anatase and rutile. Concerning the formation of chlorinated by-products from TCE, more dichloroacetic acid (DCAA) were detected and less CHCl3 and COCl2 were formed at lower firing temperatures, suggesting that the branching ratio of chloroethoxy radicals to the formation of DCAA or CHCl3 and COCl2 by C–C bond scission depended on the firing temperature.

Photocatalytic degradation of 4-( tert -octyl)phenol (4-OP) has been investigated by recirculating the aqueous solution through a packed bed reactor with TiO 2 . The first-order rate constant k for the degradation of 4-OP was evaluated to be 5.40 × 10 −3 min −1 and an activation energy of 18.6 kJ mol −1 was obtained. The rate constant k was not dependent of the flowrate but a decrease in total organic carbon (TOC) became smaller as the flowrate increased. Under the illumination for 6 h at the flowrate of 28.5 ml min −1 , 83.2% of 4-OP was degraded but 60.7% of the initial TOC was remained. Measurements of LC/MS using electrospray ionization revealed the formation of byproducts having molecular weights of 136, 178, 192, 220 and 222. Possible candidates for these byproducts were proposed. The degradation rate of 4-OP was remarkably accelerated by addition of K 2 S 2 O 8 : 4-OP was completely disappeared under irradiation of 4 or 2 h, respectively, in the presence of 4 × 10 −3 or 2 × 10 −2 mol dm −3 K 2 S 2 O 8 . In the latter case, the TOC decreased to 34.6% by continuing the irradiation even after 4-OP was disappeared. In the presence of S 2 O 8 2− , 4-OP was degraded without TiO 2 , which is attributable to the reaction by SO 4 − radicals. We demonstrated that the UV/TiO 2 /S 2 O 8 2− system was more appropriate than the UV/S 2 O 8 2− for decontamination of 4-OP in water.

Photocatalysis of a transparent aqueous sol, which was prepared by peptizing titanium tetraisopropoxide in nitric acid for 7 days followed by dialysis was examined for the color-fading of methylene blue (MB) and Orange II and for the degradation of 4-chlorophenol (4-CP). Measurements of XRD patterns of the powders obtained by drying the sol indicated the formation of anatase. Under argon-bubbling, MB was degraded via the formation of colorless leuco form and the color of the sol returned to original by bubbling air in the dark. Reaction rates for oxidative degradation of MB under air-bubbling showed maximum at the 0.013 mol-Ti dm −3 in the sol and at pH 4.2. Reaction rates for color-fading of Orange II were higher by a factor of 6.8 than that of MB. The dependence of rates on the concentrations of MB or Orange II in the sol was discussed with the rate law. For the degradation of 4-CP in the sol under the irradiation for 6 h, 92.7% of 4-CP was completely dechlorinated and 69.5% of the initial TOC was decreased.

Few general chemistry textbooks of high schools, colleges and universities introduce the corrosion of iron into the oxidation-reduction (redox) section, although the corrosion is very popular phenomena for students. Besides, no description appears about conductive polymers as anti-corrosion materials. The corrosion is a redox reaction proceeding through the local cell mechanism : the iron oxidation half-cell reaction at the local anode and the reduction of oxygen at the local cathode. To prepare a teaching tool for understanding of the mechanism, the visualization of the corrosion was attempted using phenolphthalein and potassium hexacyanoferrate (III) as color couplers for the anodic and cathodic products : Fe2+ and OH-. The local anode and cathode were obviously shown as gradual blue and red coloration when commercial nails were soaked in 4% NaCl aqueous solution containing phenolphthalein and potassium hexacyanoferrate (III) . On the other hand, no coloration occurred for the nail covered with a conductive polymer polyaniline. To know the anti-corrosion mechanism, the open-circuit potential of the nail was measured. The fact that the potential was kept at the potential range where iron was passivated implied that polyaniline acted as an in-situ oxidant. The visualization was experimentally performed at an actual chemistry class and the utility value was estimated. As a result, the visualization is expected to be a useful teaching tool for the corrosion and the understanding of the role of polyaniline as the anti-corrosion material.

1,4-Dioxane in hexane as a solvent was adsorbed on TiO2 due to an electrostatic interaction. The porous TiO2 pellets (SG) prepared by sol–gel method were superior adsorbent to ST-B21 and Degussa P-25. Effects of firing temperature of the pellets and the initial concentrations of 1,4-dioxane on the adsorption percents were examined. Photocatalytic degradation of aqueous 1,4-dioxane gave 1,2-ethanediol diformate and formic acid as intermediates. Analysis of total organic carbon indicated that 1,4-dioxane was mineralized effectively in the following order: P-25 > ST-B21 > SG. The photocatalytic degradation of 1,4-dioxane adsorbed on the TiO2 pellets in air showed that ST-B21 had a higher activity than SG. These facts indicate that SG pellet acts as a good adsorbent because of its high specific surface area but the internal region of the pores is not illuminated and acts only as a support.

Photocatalytic degradation of trichloroethylene (TCE) was investigated using a tubular photoreactor packed with TiO2 powders prepared by sol–gel techniques. Powders of the following metals: Cr, Fe, Ni, Cu and Pt, or Ca(OH)2 were uniformly mixed with the TiO2 powders and then their effect on the formation of COCl2, CHCl3, and CHCl2COCl as by-products was examined. Concentrations of COCl2 and CHCl3 were determined in a product gas stream by GC/MS while CHCl2COCl accumulated on the catalyst surface. When the catalysts were immersed in water after TCE photodegradation, the formation of Cl- and CHCl2COO− ions was confirmed by ion-chromatography. Of the chemicals tested, only Cu and Ca(OH)2 inhibited the formation of the chlorinated by-products. With increasing Cu and Ca(OH)2 content, TCE conversion decreased while the stoichiometric ratio ([CO2]formed/[TCE]degraded) increased. Concentrations of COCl2, CHCl3, and CHCl2COCl decreased with increasing Cu and Ca(OH)2 content. Especially, the formation of COCl2 was remarkably suppressed with Ca(OH)2.

The photocatalytic degradation of chloroform was studied in a tubular photoreactor packed with TiO2 pellets prepared by sol–gel method. Concentrations of chloroform and CO2 in the gas stream and Cl− ion which was dissolved from the pellets into water after the photodegradation experiments were detected quantitatively. Chloroform was completely mineralized to CO2 and HCl but the conversion decreased drastically with an increase in the irradiation time. Such a decrease in the catalytic activity was attributable to the accumulation of Cl− on the TiO2 surface and was recovered by washing the pellets with water. The presence of Cu and Ca(OH)2 increased the concentration of Cl− accumulated on the surface. The deterioration of the catalytic activity was suppressed with Ca(OH)2 whereas no appreciable effect was observed with Cu. The TiO2 prepared by sol–gel method exhibited a higher catalytic activity than commercially available Degussa P-25.

The photoassisted catalytic degradation of chloroethylene was studied in a tubular photoreactor packed with TiO2 pellets prepared by a sol−gel method. The experiments were performed in a noncirculating mode. Kinetic data and the reaction products were compared with those for the photodegradation of ethylene, trichloroethylene, and tetrachloroethylene. The theoretical calculations at the MP4/6-31G**//B3LYP/6-31G** level indicated that the addition of OH radicals to chlorinated ethylenes is more exothermic than that of Cl radicals by 14.6−29.5 kcal mol-1. Examination of Cl mass balance indicated that the concentration of Cl- collected from the TiO2 surface was higher than that from the product gas stream. When the photodegradation of ethylene was performed on the TiO2 pellets which had been used for that of TCE or which were pretreated with HCl, the formation of chloroacetaldehyde was confirmed by the GC/MS. We proposed that during the photodegradation of the chlorinated ethylenes, the Cl-, as one of the re...

An aramid resin, poly(p-phenylene terephtalamide) (PPTA) was precoated on an ITO electrode as a stable matrix film. Iridium oxide could be electrodeposited on the electrode because the PPTA film was permeable to dissolved species. Although the cyclic voltammogram (CV) pattern of the PPTA–iridium oxide film was almost the same as that of the original iridium oxide film, the color change differed a little. In the oxidized state, the PPTA–iridium oxide film showed greenish blue. The XPS-biding energy of Ir 4f5/2 and Ir 4f7/2 electrons was shifted to about 2 eV higher energy. The maximum absorption wavelength of the original iridium oxide film was about 650 nm, while that of the PPTA–iridium oxide film was about 600 nm. The color change was probably due to donating of the lone pair electrons of PPTA to the indium. The electrodeposition of Au on the PPTA–iridium oxide film was carried out. The obtained PPTA–iridium oxide–Au film showed quite different electrochromic properties. New redox current peaks appeared in the CV of the film. The film was colored vermilion in the reduced state and greenish blue in the oxidized state. The XPS-biding energy of Ir 4f5/2 and Ir 4f7/2 electrons was shifted to about 2 eV lower energy, implying that the electrodeposition of Au transformed the electronic state and structure structure of iridium oxide, suggesting the formation of a –Au–Cl–Ir– binuclear Cl-bridged complex. Keywords: Iridium oxide, Electrochromism, Electrodeposition of gold, Poly(p-phenylene terephtalamide), Vermilion color

Photoreductive deposition of Cu2+ on TiO2 thin film prepared by sol–gel method has been investigated by measuring a change of transmittance of the film. The transmittance decreased with irradiation time, corresponding to a decrease of the Cu2+ concentration in the solution. Removal percent of Cu2+ ions from the solution was obtained to be 80–98%. On the other hand, the transmittance change (ΔT) was greatly affected by experimental conditions: the ΔT value increased when the thicker films or films fired at higher temperature were used or when the same film was employed repeatedly. With the initial concentrations of Cu2+ more than 100 ppm, induction periods (I.P.) of 45–240 min were observed before the transmittance decreased. When Na2C2O4 was used as a sacrificial donor instead of HCOONa, the decrease rate for Cu2+ concentration in the solution became slightly lower. However, with Na2C2O4, no induction period was observed and the ΔT values were two times as high as those with HCOONa.