Ishihara ST-01 Research Articles

Influence of carbon-functional groups with less hydrophilicity on a TiO 2 photocatalyst for removing low-level elemental mercury

Abstract A carbon-containing titanium dioxide (C-TiO 2 ) photocatalyst was prepared via ethanol impregnation using commercial Ishihara ST-01 TiO 2 powder as the precursor. Scanning Electron Microscopy and X-ray Diffractometry results indicated that raw ST-01 and C-TiO 2 had similarly globular shapes and presented in anatase phase. N 2 adsorption isotherms suggested that carbon impregnated on the TiO 2 surface could slightly reduce the total surface area and pore volume. X-ray Photoelectron Spectroscopy and Fourier Transform Infrared Spectroscopy examinations further supported the formation of various C-functional groups on the C-TiO 2 surface. Removal of low-concentration Hg 0 by raw and C-TiO 2 was enhanced with increasing O 2 concentration. Furthermore, because the existence of C-functional groups on the C-TiO 2 surface, the photoinduced hydrophilicity resulted from light irradiation appears to decrease, causing less adsorption competition from H 2 O for Hg 0 adsorption at higher temperature. The reemission of adsorbed Hg species could thus be significantly decreased by carbon impregnation.

Influence of lattice distortion and oxygen vacancies on the UV-driven/microwave-assisted TiO2 photocatalysis

The influence of lattice distortions on TiO2 photocatalysis produced by subjecting commercially available P25 titania samples to a heat treatment in the temperature range 645–800 °C was examined; it caused the initial anatase-to-rutile ratio of 81/19 to decrease to 1/99 at the highest temperature. The photoactivities of these heat-treated samples were established through the photodegradation of 4-chlorophenol (4-CP) exposed to UV irradiation alone, UV/microwave irradiation (2.45 GHz), and to UV irradiation accompanied with conventional heating at a temperature otherwise identical to that under UV/MW irradiation. Raman band intensities of pure anatase (143 cm−1), pure rutile (446 cm−1) and of the heat-treated P25 specimens were examined in situ after being exposed to microwave irradiation for about 4 min. Changes are attributed to a microwave non-thermal effect involving oxygen vacancies that affect the specimens’ photoactivities as determined by subjecting samples of Evonik P25 titania (AEROXIDE® TiO2 P25) and Ishihara ST-01 TiO2 to a heat treatment in the presence of molecular hydrogen. Such treatment caused lattice distortions of both systems that affected the kinetics of degradation of the chlorophenol under various irradiation conditions. UV/visible absorption spectra of the heat/H2-treated specimens displayed a broad unresolved absorption envelope at wavelengths above 400 nm that has been attributed to oxygen vacancies and thus to F-type color centers in accord with an earlier study by Kuznetsov and Serpone. The presence of such defects, particularly in the heat/H2-treated samples, and the influence of the microwaves caused the photodegradation kinetics for the 4-CP to be enhanced significantly.

Characteristics of microwaves on second generation nitrogen-doped TiO 2 nanoparticles and their effect on photoassisted processes

Characteristics of 2.45-GHz microwave radiation were examined on two second generation nitrogen-doped TiO 2 nanomaterials prepared by annealing Degussa P-25 TiO 2 and Ishihara ST-01 TiO 2 at 400 °C and 500 °C, respectively, in air in the presence of urea, and for comparison on the undoped pristine samples. Band gaps of all four samples were determined by diffuse reflectance spectroscopy. Both the sizes and the BET specific surface areas of the TiO 2 particles were determined, together with dielectric constants and dielectric loss factors. Nitrogen doping caused the size to increase and surface area to decrease. Temperature–time profiles showed that the heating efficiency of the N-doped specimens by the microwaves was greater, particularly significant for the N-doped P25 sample, but rather small for the N-ST01 sample. The effect of microwaves on the surface optical phonons of the samples, with and without UV–vis irradiation, was examined by an in situ Raman spectroscopic technique; for the undoped P-25 and nitrogen-doped N-P25 TiO 2 systems the effect was negligible. By contrast, microwave irradiation of Ishihara ST-01 and nitrogen-doped N-ST01 TiO 2 samples showed significant changes in the 144-cm −1 optical phonons. Results infer a microwave thermal effect on the Ishihara ST-01 and N-ST01 specimens, whereas for the Degussa P-25 samples the microwaves also imparted a specific effect as the microwaves influenced the N-dopant sites in contrast to the ST-01 systems where the dopant sites were unaffected as evidenced by temperature–time profiles. The microwave-/photo-assisted degradation of 4-chlorophenol under various conditions of UV–vis irradiation and conventional heating, as opposed to microwave heating, confirms the specific microwave effect for the P-25 systems.

Photocatalytic Activity for Hydrogen Evolution of Electrospun TiO2 Nanofibers

We report herein a simple procedure for the fabrication of TiO2 nanofibers by the combination of electrospinning and sol-gel techniques by using poly(vinylpyrrolidone) (PVP), titanium(IV) butoxide, and acetylacetone in methanol as a spinning solution. TiO2 nanofibers (260-355 nm in diameter), with a bundle of nanofibrils (20-25 nm in diameters) aligned in the fiber direction, or particle-linked structures were obtained from the calcination of as-spun TiO2/PVP composite fibers at temperatures ranging from 300 to 700 degrees C. These nanofibers were utilized as photocatalysts for hydrogen evolution. The nanofiber photocatalyst calcined at 450 degrees C showed the highest activity among the TiO2 nanofibers tested such as ones prepared by the hydrothermal method and anatase nanoparticles (Ishihara ST-01). These results indicate that one-dimensional electrospun nanofibers with highly aligned bundled nanofibrils are beneficial for enhancement of the crystallinity, large surface area, and higher photocatalytic activity.

Sol–gel modified TiO 2 powder films for high performance dye-sensitized solar cells

Techniques in TiO 2 film fabrication process are a very important aspect in construction of efficient dye-sensitized solar cells (DSSCs). Among fundamental factors in high efficiency solar cells is the development of a highly porous nanocrystalline film in a relatively thick and mechanical stable TiO 2 network. In present work, two types of commercial titania powders with high loading (74% (wt.%) in the final films), Degussa P25 powders and Ishihara ST-01 powders, have been successfully incorporated into a mesoporous structured TiO 2 crystalline network. The good mechanical stability of both types of films involves the presence of a titanium alkoxide solution mixed with non-ionic surfactant Tween 20 as a suitable binder precursor to immobilize commercial titania nanoparticles on a SnO 2:F conductive glass via a dip coating sol–gel process. The results of photoelectrochemical characterization of the films in a dye-sensitized solar cell showed that both films presented high conversion efficiency (about 6%) with only a slight difference on their photovoltaic behavior, when a quasi-solid state electrolyte was employed. The crystalline structure of the foreign titania particles, the particle size and the existence of any agglomeration, as well as the surface area and the pore structure of these films made of different titania powder sources were examined in detail and are discussed in relation to the relatively high solar to electrical energy conversion efficiency obtained in such quasi-solid state DSSCs.

Visible-light-induced oxidative removal of nitrogen oxides in air by metal chloride-modified titanium (IV) oxide nanoparticles

Various metal chloride-modified titanium(IV) oxide (TiO2) (MCMT) samples were prepared by loading metal chloride on commercial TiO2 nanoparticles (Ishihara ST-01) having a large specific surface area and used for photoinduced oxidative removal of nitrogen oxides (NO x ) in air under irradiation of visible light and/or ultraviolet (UV) light. The NO x removal activity of MCMT samples under photoirradiation from a blue fluorescent lamp (BFL) with a UV cut filter decreased in the following order: RhCl3/ST-01>H2PtCl6/ST-01>RuCl3/ST-01>ST-01>IrCl4/ST-01>HAuCl4/ST-01, indicating that RhCl3. H2PtCl6 and RuCl3 fixed on TiO2 effectively worked as photosensitizers for NO x removal. NO x was almost quantitatively fixed as nitrate on RhCl3/ST-01 photoirradiated with BFL or blue light-emitting diodes. Under irradiation of both visible light and UV light from a white fluorescent lamp, RhCl3/ST-01 exhibited a higher level of removal of NO x and a much lower level of release of nitrogen dioxide than did bare ST-01, indicating that RhCl3/ST-01 effectively utilized both visible light and UV light and that two types of reaction (photosensitization by fixed RhCl3 and photocatalysis by TiO2) occurred over RhCl3/ST-01.

Single Nanocrystals of Anatase-Type TiO2 Prepared from Layered Titanate Nanosheets: Formation Mechanism and Characterization of Surface Properties

Anatase-type TiO2 single nanocrystals with boatlike, comblike, sheetlike, leaflike, quadrate, rhombic, and wirelike particle morphologies were prepared by hydrothermal treatment of a layered titanate nanosheet colloidal solution. The formation reactions and surface properties of the TiO2 nanocrystals were investigated using XRD, TEM, TG-DTA analyses, and measurements of BET specific surface area, photocatalytic activity, and ruthenium dye (N719) adsorption. The crystal morphology can be controlled by reaction temperature, pH value of reaction solution, and exfoliating agent. The titanate nanosheets were transformed to the TiO2 nanocrystals by two types of reactions. One is an in situ topotactic structural transformation reaction, and the other is a dissolution-deposition reaction on the surface. The anatase nanocrystals formed by the in situ topotactic structural transformation reaction retain the sheetlike particle morphology of the precursor, and they preferentially expose the (010) plane of anatase structure. The crystal surface of anatase nanocrystals prepared in this study showed higher photocatalytic activity and higher ruthenium dye adsorption capacity than did the Ishihara ST-01 sample, a standard anatase nanocrystal sample. The results indicated the (010) plane of the anatase structure has high photocatalytic activity and high ruthenium dye adsorption ability.

Synthesis and photocatalytic activity for water-splitting reaction of nanocrystalline mesoporous titania prepared by hydrothermal method

Nanocrystalline mesoporous TiO 2 was synthesized by hydrothermal method using titanium butoxide as starting material. XRD, SEM, and TEM analyses revealed that the synthesized TiO 2 had anatase structure with crystalline size of about 8 nm. Moreover, the synthesized titania possessed a narrow pore size distribution with average pore diameter and high specific surface area of 215 m 2/g. The photocatalytic activity of synthesized TiO 2 was evaluated with photocatalytic H 2 production from water-splitting reaction. The photocatalytic activity of synthesized TiO 2 treated with appropriate calcination temperature was considerably higher than that of commercial TiO 2 (Ishihara ST-01). The utilization of mesoporous TiO 2 photocatalyst with high crystallinity of anatase phase promoted great H 2 production. Furthermore, the reaction temperature significantly influences the water-splitting reaction.

Photocatalytic oxidation of NO x by Pt-modified TiO 2 under visible light irradiation

Photooxidation of NO x has been studied using titanium dioxide (Ishihara ST-01) treated with H 2PtCl 6. The experimental results indicate that Pt-modified TiO 2 with different ligand structures can be synthesized according to the Pt treating procedure. TiO 2 photocatalysts with certain Pt complexes produced significantly high photocatalytic activity under visible light irradiation without decreasing photoactivity under UV light irradiation. The visible-light-induced photocatalytic activity depended on the amount of Pt, but not greatly on the coordination number of Cl ions. It was suggested that the surface complex formation associated with Ti–O–Pt chemisorption dominated the visible light reactivity.

Synthesis, characterization, and photocatalytic activity for hydrogen evolution of nanocrystalline mesoporous titania prepared by surfactant-assisted templating sol–gel process

Nanocrystalline mesoporous titania was synthesized via a combined sol–gel process with surfactant-assisted templating method, treated under various calcination conditions, and evaluated for its photocatalytic activity through photocatalytic hydrogen evolution from an aqueous methanol solution. In this synthetic method, applied surfactant template molecules functioned as both mesopore-forming and gelation-assisting agents. The resulting products were methodically characterized by TG-DTA, XRD, N 2 adsorption–desorption, diffuse reflectance UV-Vis spectra, SEM, and TEM analyses. The partial phase transformation from anatase to rutile occurred beyond calcination temperature of 600 °C and anatase–rutile transition kinetics was also investigated. The calcination conditions and crystalline phases existing in the products exerted significant effect on the photocatalytic hydrogen evolution activity. The activity of the synthesized titania treated under appropriate calcination conditions was considerably higher than that of commercial titania powders, Ishihara ST-01 and Degussa P-25. It is clearly seen that the introduction of mesopore into titania photocatalyst substantially improved the photocatalytic performance.

Photocatalytic evolution of hydrogen over nanocrystalline mesoporous titania prepared by surfactant-assisted templating sol–gel process

Nanocrystalline mesoporous titania was synthesized via a combined sol–gel process with surfactant-assisted templating route and evaluated for photocatalytic activity of hydrogen evolution from an aqueous methanol solution. In this proposed method, applied surfactant template molecules advantageously behaved as both mesopore-forming and gel formation-assisting agent. The activity of the mesoporous titania thermally treated under appropriate conditions, i.e., at calcination temperature of 600 °C for 4 h, was considerably higher than that of commercial titania powders, Ishihara ST-01 and Degussa P-25. It is clearly revealed that introducing mesoporous framework into TiO 2 by this synthetic system provided much better photocatalytic performance.

Solvothermal syntheses of semiconductor photocatalysts of ultra-high activities

Thermal treatment of titanium(IV) butoxide dissolved in 2-butanol at 573 K under autogenous pressure (alcohothermal treatment) yielded microcrystalline anatase-type titanium(IV) oxide (TiO 2). Thermal treatment of oxobis(2,4-pentanedionato-O,O′)titanium (TiO(acac) 2) in ethylene glycol (EG) in the presence of sodium acetate and a small amount of water at 573 K yielded microcrystalline brookite-type TiO 2. Tungsten(VI) oxide (WO 3) powders of monoclinic crystal structure with high crystallinity were synthesized by hydrothermal treatment (HTT), at 523 or 573 K, of aqueous tungstic acid (H 2WO 4) solutions prepared from sodium tungstate by ion-exchange (IE) with a proton-type resin. Anatase and brookite TiO 2 products were calcined at various temperatures and then used for photocatalytic mineralization of acetic acid in aqueous solutions under aerated conditions and dehydrogenation of 2-propanol under deaerated conditions. Almost all the anatase-type TiO 2 samples showed the activities more than twice higher than those of representative active photocatalysts, Degussa P-25 and Ishihara ST-01 in both reactions. A brookite sample with improved crystallinity and sufficient surface area obtained by calcination at 973 K exhibited the hydrogen evolution rate almost equal to P-25. HTT WO 3 powders with various physical properties were used as photocatalyst for evolution of oxygen (O 2) from an aqueous silver sulfate solution. WO 3 powder of high crystallinity, e.g., IE-HTT-WO 3 synthesized at 573 K, gave much higher O 2 yield than commercially available WO 3 samples.

Photocatalytic redox-combined synthesis of l-pipecolinic acid from l-lysine by suspended titania particles: effect of noble metal loading on the selectivity and optical purity of the product

Photocatalytic (>300 nm) conversion of l-( S)-lysine ( l-Lys), in its neutralized aqueous solution, into l-pipecolinic acid ( l-PCA) under deaerated conditions at 298 K was investigated in detail using suspended TiO 2 powders (Degussa P-25, Ishihara ST-01, and HyCOM TiO 2) loaded with platinum (Pt), rhodium (Rh), or palladium (Pd). A common feature of the results of experiments using a wide variety of metal-loaded TiO 2 photocatalysts is that the rate of PCA formation ( r PCA) was greatly reduced when higher optical purity of PCA (OP PCA), i.e., enantio excess of the l-isomer of PCA, was obtained; higher r PCA was achieved by the use of Pt-loaded TiO 2 powders, while these powders gave relatively low OP PCA. Selectivity of PCA yield ( S PCA), i.e., amount of PCA production based on l-Lys consumption, also tended to increase with decrease in OP PCA, giving a master curve in the plots of OP PCA versus S PCA. Among the TiO 2 powders used in this study, HyCOM TiO 2 showed relatively high OP PCA and S PCA but not optimum S PCA and OP PCA simultaneously. In order to interpret such relations, the mechanism of stereoselective synthesis of the l-isomer of PCA ( l-PCA) was investigated using isotope-labeled α- 15N- l-lysine with quantitative analysis of incorporation of 15N in PCA and ammonia (NH 3), a by-product. It was observed for several photocatalysts that the 15N proportion ( P 15) in PCA was almost equal to OP PCA, suggesting that oxidative cleavage by photogenerated positive holes of the ε-amino moiety of l-Lys gave optically pure l-PCA through retention of chirality at the α-carbon in the presumed intermediate, a cyclic Schiff base ( α-CSB), which undergoes reduction by photoexcited electrons into PCA. From P 15 in NH 3 and PCA, the selectivity of oxidation between α and ε-amino groups in l-Lys by photoexcited positive holes ( h +) and the efficiency of reduction of α-CSB (produced via ε-amino group oxidation to give optically pure PCA) and ε-CSB (produced via α-amino group oxidation to give racemic PCA) by photoexcited electrons ( e −) were calculated. The former was found to be independent of the kind of photocatalyst, especially the loaded metal, while the latter was influenced markedly only by the loaded metal. It was clarified that OP PCA and S PCA obtained for various TiO 2 powders used in the present study were strongly governed by the reduction stage, i.e., the efficiency of reduction of two types of CSB. When S PCA was relatively low, photocatalysts, favoring the reduction of α-CSB rather than ε-CSB, gave higher OP PCA but lower S PCA, since some ε-CSB remained unreduced to give racemic PCA. In contrast, at higher S PCA, both CSBs were reduced nonselectively and OP PCA was found to be determined mainly by the selectivity in the oxidation stage. The relatively low yield of molecular hydrogen (H 2) when higher S PCA was achieved is consistent with the mechanism in which H 2 liberation occurs instead of the reduction of CSBs by e −. Thus, the general tendency of plots between OP PCA and S PCA could be explained by the above-described redox-combined mechanism of photocatalysis.

Role of Synthesis Method and Particle Size of Nanostructured TiO 2 on Its Photoactivity

TiO 2 prepared by different methods was used to obtain anatase powders with particle sizes ranging from 5 to 165 nm. Powders were prepared using two methods: (i) a flame aerosol process in which nanoparticles of TiO 2 were synthesized in a flame on oxidation (combustion) of an organotitanium precursor, and (ii) calcination of commercially available nanostructured TiO 2 (Ishihara ST-01, 5 nm, as received). For comparison, Degussa P25 and Aldrich anatase TiO 2 powders were also used as received. The TiO 2 powders were characterized using XRD to determine crystal phase and crystal size, BET surface area analyses, uv–vis absorbtion spectroscopy to determine the band gap, and experiments in which the photoxidation rate of phenol in water was used as a measure of photoactivity. A model was developed based on the mechanistic steps in photocatalysis to elucidate the role of particle size on the apparent photoactivity of TiO 2 for the photooxidation of organic substrates in water. The model was used to explain the trends in the experimental data for four different sets of photoactivity experiments with TiO 2 powders. The results of this study elucidate a strong effect of particle size on photoactivity. The effects of particle size on the efficiency of light absorption and scattering and charge-carrier dynamics at particle sizes less than 25 nm dominate the apparent photoactivity of TiO 2, and an optimum particle size of 25 to 40 nm exists within all sets of photocatalysis experiments conducted with TiO 2 powders in this study. The optimum particle size is a result of competing effects of effective particle size on light absorption and scattering efficiency, charge-carrier dynamics, and surface area.

TiO2 assisted photocatalytic degradation of 4-chlorobenzoic acid in water: effect of type of catalyst, catalyst loading, initial contaminant concentration and solution characteristics

Photocatalytic degradation of 4chlorobenzoic acid in water was studied using different TiO2 catalysts (Degussa P-25, Ishihara ST01 and Hombikat UV-100) and solution characteristics. Mineralization of 4chlorobenzoic acid was achieved in all the experiments and total recovery of the chlorine as free Cl- was obtained. The catalyst concentration influenced the photocatalytic rates and the optimum loading concentration was determined to be different for Degussa P-25 and Ishihara ST01, mainly due to the difference in their adsorption and scattering characteristics. Comparison between the catalysts for their photocatalytic activity revealed that other factors must influence the photocatalytic reaction rates beside the surface area of the catalysts. The photocatalytic reaction rates were found to obey the Langmuir-Hinshelwood adsorptionreaction model. At pH = 7.0, the presence of Cl did not inhibit the reaction rates. At pH = 3.0, however, the photocatalytic reaction rates were higher for the solution containing NO-3 instead of Cl- at the same molar concentration.

Synthesis of titanium(IV) oxide of ultra-high photocatalytic activity: high-temperature hydrolysis of titanium alkoxides with water liberated homogeneously from solvent alcohols

Thermal treatment of titanium(IV) alkoxides dissolved in alcohols at temperature of 523–573 K under autogenous pressure yielded microcrystalline anatase titanium(IV) oxide (TiO 2) with diameter of 11–31 nm and surface area of 42–138 m 2 g −1. Similar treatment in hydrocarbons such as toluene gave no solid products, indicating that both hydrolysis of alkoxides with water liberated homogeneously from solvent alcohols and crystallization of anatase phase occurred simultaneously. These TiO 2's were thermally stable, e.g., BET surface area of TiO 2 synthesized at 573 K, 63 m 2 g −1, was reduced only 30% (45 m 2 g −1) even by calcination at 973 K. Their photocatalytic activity was examined in mineralization of acetic acid in aqueous solutions under aerated conditions and dehydrogenation of 2-propanol under deaerated conditions; almost all the samples showed the activity more than twice higher than those of representative active photocatalysts, Degussa P-25 and Ishihara ST-01. The superior activity of the present TiO 2 photocatalysts was attributable to compatibility of high crystallinity and large surface area owing to the newly developed synthetic procedure.

Novel synthesis of microcrystalline titanium(IV) oxide having high thermal stability and ultra-high photocatalytic activity: thermal decomposition of titanium(IV) alkoxide in organic solvents

Thermal decomposition of titanium(IV) tetra-tert-butoxide (TTB) in inert organic solvents at 573 K yielded microcrystalline anatase (titanium(IV) oxide, TiO2) powders with a crystallite size of ca. 9 nm and a surface area of <100 m2 g-1. Primary and secondary alkoxides of titanium(IV), however, were not decomposed under similar conditions, indicating that the thermal stability of C-O bonds in the alkoxides was a decisive factor for their decomposition. The TiO2 prepared from TTB by this manner was thermally stable upon calcination in air and retained high surface area of ca. 100 m2 g-1 even after calcination at 823 K. The as-prepared TiO2 powders, without calcination, exhibited much higher rate of carbon dioxide formation than any other active photocatalysts such as Degussa P-25 and Ishihara ST-01 in the photocatalytic mineralization of acetic acid in aerated aqueous solutions. The higher activity of the present TiO2 photocatalysts is attributed to both high crystallinity and large surface of the present product. The calcination of the as-prepared TiO2 in air reduced the photocatalytic activity, but it was still higher than the other commercially available TiO2's.

Photocatalytic Mineralization of Acetic Acid in Aerated Aqueous Suspension of Ultra-highly Active Titanium(IV) Oxide Prepared by Hydrothermal Crystallization in Toluene

Abstract Anatase titanium(IV) oxide synthesized by high-temperature hydrolysis of titanium(IV) tetrabutoxide in toluene was used for photocatalytic mineralization of acetic acid in aerated aqueous solutions, and showed the rate of carbon dioxide production much higher than representative active photocatalysts (Degussa P-25 and Ishihara ST-01). The catalyst of the larger crystallite size showed the higher activity, suggesting the importance of reduction of crystal defects.