Hydrophobic TiO2 Research Articles

Self-assembly and photocatalysis of mesoporous TiO2 nanocrystal clusters

Mesoporous nanocrystal clusters of anatase TiO2 with large surface area and enhanced photocatalytic activity have been successfully synthesized. The synthesis involves the self-assembly of hydrophobic TiO2 nanocrystals into submicron clusters, coating of these clusters with a silica layer, thermal treatment to remove organic ligands and improve the crystallinity of the clusters, and finally removing silica to expose the mesoporous catalysts. With the help of the silica coating, the clusters not only maintain their small grain size but also keep their mesoporous structure after calcination at high temperatures (with BET surface area as high as 277 m2/g). The etching of SiO2 also results in the clusters having high dispersity in water. We have been able to identify the optimal calcination temperature to produce TiO2 nanocrystal clusters that possess both high crystallinity and large surface area, and therefore show excellent catalytic efficiency in the decomposition of organic molecules under illumination by UV light. Convenient doping with nitrogen converts these nanocrystal clusters into active photocatalysts in both visible light and natural sunlight. The strategy of forming well-defined mesoporous clusters using nanocrystals promises a versatile and useful method for designing photocatalysts with enhanced activity and stability.

Photocatalytic degradation of dichloroacetyl chloride adsorbed on TiO2

Dichloroacetyl chloride (DCAC) attracted our attention as an intermediate product of the photocatalytic degradation of trichloroethylene (TCE). The adsorption and photocatalytic reaction of DCAC on TiO2 have been investigated by FTIR spectroscopy. The influence of the surface structure of several TiO2s on the reaction mechanism was discussed in order to understand the complete degradation mechanism of TCE as well as DCAC. DCAC was transformed into dichloroacetic acid (DCAA) on the relatively hydrophobic TiO2 surface by the small amount of the water molecules weakly adsorbed on the surface. This DCAA was degraded to phosgene, CO2, and CO during UV irradiation. For the hydrophilic TiO2, DCAC was mainly transformed into the dichloroacetate anion. UV irradiation allowed this species to produce chloroform in addition to phosgene, CO2, and CO. It is suggested that DCAC easily reacts with the Ti–OH group on the hydrophilic TiO2 and forms the bidentate titanium chelate of dichloroacetate, which efficiently degrades into chloroform.

Corrosion behavior of anodic oxidized TiO2 film in seawater

TiO2 films were formed on metallic titanium substrates by the anodic oxidation method in H2SO4 solution under the 80V D.C.. Phase component and microstructure were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Water contact angles on titanium oxide film surface were measured under both dark and sunlight illumination conditions. Corrosion tests were carried out in seawater under different illumination conditions by electrochemistry impedance spectrum (EIS) and polarization curves. The result showed that the TiO2 film prepared by the anodic oxidation method was anatase with a uniform structure and without obvious pores or cracks on its surface. The average water contact angle of the film was 116.4° in dark, in contrast to an angle of 42.7° under the UV illumination for 2 hours, which demonstrates good hydrophobic property. The anti-corrosion behavior of the TiO2 film was declining with the extended immersion time. Under dark conditions, however, the hydrophobic TiO2 film retarded the water infiltrating into the substrate. The impedance changed slowly and the corrosion current density was 2 orders of magnitude lower than that with the film illuminated by sunlight. All of those mentioned above indicate that the TiO2 film possesses much better performance under dark condition, and it can be applied as an engineering material under dark seawater environment.

<i>In Situ</i> Growth of Hydrophobic TiO<sub>2</sub> on <i>Calocedrus macrolepis</i> Kurz Wood Surface Using a Cosolvent-Controlled Hydrothermal Method

This paper examined the in situ growth of hydrophobic anatase TiO2 coating on wood surface using a cosolvent-controlled hydrothermal method. EDXA, FTIR and XRD analysis confirmed that the growth of TiO2 coating on wood surface was bonded to hydrocarbon chains. The relative contact angle of before and after treated wood sample was changed from 46.5o to 136.8o with the examination of contact angle analyzer, which induced a change of the untreated wood surface from hydrophilic to hydrophobic. As observed on SEM image, some slippery TiO2 spheres with about 300-600 nm in diameter evenly dispersed on treated wood surface.

Structural Degradation at the Surface of a TiO2-Based Nanomaterial Used in Cosmetics

A number of commercialized nanomaterials incorporate TiO(2) nanoparticles. Studying their structural stability in media mimicking the environment or the conditions of use is crucial in understanding their potential eco-toxicological effects. We focused here on a hydrophobic TiO(2) nanoparticle-based formulation used in cosmetics: T-Lite SF. It is composed of a TiO(2) core, coated with two successive protective layers of Al(OH)(3), and polydimethylsiloxane. Soon after contact with water (pH = 5, low ionic strength), the T-Lite SF becomes hydrophilic and form aggregates. During this aging, 90%wt of the total Si of the organic layer is desorbed, and the PDMS remaining at the surface is oxidized. The Al(OH)(3) layer is also affected but remains sorbed at the surface. This remaining Al-based layer still protects from the production of superoxide ions from the photoactive/phototoxic TiO(2) core in our experimental conditions.

Particle Coating of Talc with TiO2Nanoparticles Using Ultrasonic Irradiation in Liquid CO2

We describe particle coating using ultrasonic irradiation in liquid carbon dioxide (CO2). Talc (Mg3Si4O10(OH)2) microparticles were coated with hydrophilic and hydrophobic TiO2 nanoparticles. Shock waves generated by collapsing cavitation bubbles induced with ultrasonic irradiation accelerated the deagglomeration and dispersion of TiO2 nanoparticles and achieved dry particle coating in liquid CO2. Talc particles coated with TiO2 nanoparticles were observed using scanning electron microscopy (SEM). This revealed that the talc was completely coated with TiO2 nanoparticles, and a smooth coating surface was obtained. The flowability and wettability of the talc was improved by TiO2 nanoparticle coating. A comparative study was also conducted with conventional hand mixing and ultrasonic irradiation in water as a coating media. Effects of the experimental conditions (depressurizing method, ultrasonic intensity, TiO2 concentration, and TiO2 particle size) on the morphology and properties of the composite micropar...

Characteristics modification of TiO2 thin films by doping with silica and alumina for self-cleaning application

Self-cleaning hydrophilic and hydrophobic properties of TiO2-based thin films on glass substrates have been investigated in this study. The addition of SiO2 into TiO2 can increase the wettability of films and maintain the hydrophilic state for a long time even in the dark. The contact angle of water on deposited films containing 15% SiO2 is less than 2° after 2 h of UV illumination. These TiO2–SiO2 films exhibit excellent antifogging characteristics. Meanwhile, TiO2–Al2O3 films possess high water repellent ability and the photo-induced self-cleaning can take place even in visible light. The TiO2 thin film containing 33% of Al2O3 shows a high hydrophobic state with a water contact angle of 73° after being irradiated with sunlight for 2 h. A comparison of hydrophilic TiO2–SiO2 and hydrophobic TiO2–Al2O3 films demonstrates the ability to modify the TiO2 thin film properties for self-cleaning applications.

EIS analysis of hydrophobic and hydrophilicTiO 2 film

Titanium oxide films were formed on metallic titanium substrates by employing a thermal treatment at 800 °C under air atmosphere. Component and microstructure of the oxide films were characterized by XRD and SEM method. Water contact angles on titanium oxide film surface were measured in both dark and sunlight illumination condition. Corrosion tests were carried in seawater solution under different illuminate conditions. Electrochemical impedance spectroscopy (EIS) techniques were used to study the changes on TiO 2 film. Results indicated that: hydrophilic TiO 2 film suffered a severe photo-corrosion effect in seawater due to their semiconductor properties under sunlight condition, but the hydrophobic TiO 2 film under dark condition exhibited a good corrosion resistance.

Preparation and characterization of hydrophobic TiO 2 pillared clay: The effect of acid hydrolysis catalyst and doped Pt amount on photocatalytic activity

Titanium hydrate sols were prepared using different acid hydrolysis catalysts, i.e., acetic acid and hydrochloric acid. The platinum-doped TiO 2 sol–gels were also synthesized by adding K 2PtCl 6 into the titanium hydrate sols. The hydrophobic montmorillonite clay, treated with organic cationic surfactant, i.e., hexadecyltrimethylammonium bromide, was used as a template to prepare TiO 2 pillared photocatalyst with the above sols. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX) were employed to characterize the resulting photocatalysts. The adsorption performance and photoactivity of prepared pillared clays were studied by using methyl orange as a model organic pollutant. The preliminary results indicated that the hydrophobic TiO 2 pillared clay prepared with acetic acid as the acid hydrolysis catalysts possessed higher photocatalytic activity than that with hydrochloric acid. Due to the excellent sedimentation property of the clay, the resulting pillared photocatalyst is easily recovered and reused in the postrun treatment. Also the doping of platinum into the hydrophobic photocatalyst can increase the photocatalytic activity significantly.

Hydrophilicity transition of the clean rutile TiO 2 (1 1 0) surface

We present contact angle measurements of water on single-crystal rutile TiO 2 (1 1 0) surfaces, exposed to ambient air, or protected in dry air. Our measurements indicate that the surfaces exposed to ambient air are hydrophobic, with a contact angle of θ = 61(5)°. However, the well-protected dry surface also exhibits some hydrophobic tendency, with θ = 32(5)°. It is known that UV irradiation transforms both surfaces superhydrophilic, with θ = 0° [R. Wang, K. Hashimoto, A. Fujishima, M. Chikuni, E. Kojima, A. Kitamura, M. Shimohigoshi, T. Watanabe, Nature 388 (1997) 431–432]. We also present preliminary X-ray crystal truncation rod measurements on the hydrophobic TiO 2 (1 1 0) surface, and of the effect of UV illumination on the surface.

Photocatalytic degradation of dimethyl phthalate ester using novel hydrophobic TiO2 pillared montmorillonite photocatalyst

TiO2 pillared montmorillonites were prepared by introducing Ti4+ into a layer of montmorillonite modified with or without cetyltrimethylammonium bromide. The components and texture of the prepared composites were characterized by thermogravimetric analysis, X-ray powder diffraction and scanning electron misroscopy. The adsorption and photocatalytic degradation performance of a model environmental endocrine disruptor, dimethyl phthalate ester, were investigated using this newly prepared hydrophobic TiO2 pillared montmorillonite photocatalyst. The adsorption of dimethyl phthalate ester from water varied from 9% to 28% on the prepared hydrophobic photocatalyst. Although the experimental results showed that the photocatalytic activity of the hydrophobic photocatalyst was slightly lower than that of hydrophilic one, electron spin resonance verified that hydroxyl radicals were also generated in hydrophobic TiO2 pillared montmorillonite photocatalyst under UV irradiation. To elucidate the decomposition mechanism of dimethyl phthalate ester, 12 main photocatalytic intermediates were identified during the photocatalytic degradation process, and a plausible degradation mechanism was also proposed.

Effect of Surface Hydrophilicity on Charging Mechanism of Colloids in Low-Permittivity Solvents

Electrophoretic mobilities of TiO2 colloids in an apolar solvent, toluene, were measured by differential-phase optical coherence tomography (DP-OCT). An electrode spacing of 0.18 mm, made possible by optical coherence tomography with transparent electrodes, enables measurement of the electrophoretic mobility with small samples (20 μL) of highly turbid colloids at low applied electric potential to avoid electrohydrodynamic instability and electrochemical reactions. In the presence of Aerosol-OT reverse micelles, which stabilized the countercharges, the zeta potential was positive for hydrophilic TiO2 (13 mV at 90 mM AOT) and negative for hydrophobic TiO2. The magnitudes of the zeta potentials were very similar for these two types of TiO2 and decreased at the same rate with AOT concentration. For both hydrophilic and hydrophobic TiO2, a general mechanism is presented to describe the zeta potential in terms of preferential partitioning of cations and sulfosuccinate anions between the particle surface and reverse micelle cores in bulk. This preferential partitioning is governed by the hydrophilicities and extents of the particle surfaces and reverse micelle cores, as a function of surfactant and water concentration. The emerging understanding of the complex charging and stabilization mechanisms for colloids in apolar solvents will be highly beneficial for the design of novel materials.

Super-hydrophilic amorphous titanium dioxide thin film deposited by cathodic electrodeposition

A super-hydrophilic amorphous titanium dioxide (TiO2) thin film was prepared by simple electrodeposition method from aqueous peroxo-titanium complex solution. The surface structure was characterized by scanning electron microscopy (SEM). The hydrophobic amorphous TiO2 film was converted into super-hydrophilic by the irradiation of ultraviolet (UV) light. The super-hydrophilicity of the films was controlled reversibly by alternate UV irradiation and storage in the dark.

ｎ‐ブチルトリメトキシシランを用いるＴｉＯ２粉末の疎水化に及ぼすｐＨ調節剤の影響

ｎ‐ブチルトリメトキシシランを用いるＴｉＯ２粉末の疎水化に及ぼすｐＨ調節剤の影響

Modified TiO2–SiO2 mixed oxides: 1. Effect of manganese concentration and activation temperature towards catalytic combustion of volatile organic compounds

Catalytic combustion of acetone, methanol and 2-propanol as model volatile organic compounds (VOCs) has been measured over manganese-modified, hydrophobic TiO2–SiO2 mixed oxides in the temperature range 373–573K. The complete decomposition of VOCs at relatively low temperature range and no loss of catalytic activity in time-on-stream study depends on the surface area, surface oxygen and hydrophobic properties of the samples. CO2 and H2O are detected as the only combustion products of acetone and methanol at all reaction temperatures. In case of 2-propanol, acetone and di-isopropylether are detected as by-products. It is observed that manganese-modified, hydrophobic TiO2–SiO2 mixed oxides are effective enough for the destruction of VOCs and can be considered as low-temperature oxidation catalysts.

Effect of Temperature and Pressure in the Photocatalytic Oxidation of n-Octanol on Partially Desilanized Hydrophobic TiO2 Suspended in Aerated Supercritical CO2

Reaction temperature and CO2 pressure affect the rate of reaction in photocatalytic oxidations in supercritical (sc) CO2 on partially silanized TiO2. In supercritical CO2, the photocatalytic oxidation of octanol appeared to follow pseudo-first-order kinetics, with octanal being produced as the initial product. At 309 K, the pseudo-first-order rate constant kdis decreased upon increasing CO2 pressure from 8 to 20 MPa, giving rise to an increased yield of octanal. When the temperature was raised within the range from 299 to 319 K at constant CO2 pressure (10 MPa), kdis increased while the net yield of octanal decreased. These changes are rationalized as being caused by changes in near-surface CO2 density and, hence, in efficiency of mass transport of octanal to and from the catalytically active site. The observed dependence of the photoactivity of hydrophobic T805 TiO2 in scCO2 on temperature and pressure likely varies with surface conditions promoted by irradiation, which effects partial desilanization photocatalytically active sites. When scCO2 density was very low, T805 TiO2 did not suspend well into the scCO2 fluid; that is, almost all of the T805 TiO2 precipitated on a window or inner wall of the cell. At scCO2 densities between 8 and 20 MPa, T805 TiO2 was efficiently dispersed under stirring. At very low pressures near the critical point, the kinetic analysis was complicated by incident light scattering caused by suspended particles which act as inhibitory inner filters.

Highly hydrophobic TiO 2 pillared clay for photocatalytic degradation of organic compounds in water

Four kinds of TiO 2 pillared clays were prepared from different raw clays (montmorillonite, saponite, fluorine hectorite and fluorine mica), and their surface hydrophobicities and performances in adsorption–photocatalytic degradation of phthalate esters (di- n-butyl phthalate and dimethyl phthalate) were investigated. It was found that surface hydrophobicity of TiO 2 pillared clays largely varied with the host clay: it increased in the order saponite < fluorine hectorite < montmorillonite < fluorine mica. The order of performance in adsorption and successive photocatalytic degradation of phthalate ester was consistent with that of surface hydrophobicity. It was clarified that employing the host clay that enhances surface hydrophobicity of the TiO 2 pillared clay, such as fluorine mica, is quite an efficient way to obtain highly active photocatalysts for photodegradation of organic compounds in water.

Adsorption and Photocatalytic Degradation of Toluene Vapor in Air on Highly Hydrophobic TiO2 Pillared Clay

Abstract Hydrophobicity of TiO2 pillared clay prepared from different raw clays increased with the order of the raw clay; saponite &amp;lt; montmorillonite &amp;lt; fluorine mica. This order agreed with that of performance in both adsorption and photocatalytic degradation of toluene vapor in humid air.

アルキルトリメトキシシランを用いた湿式カップリング処理によるＴｉＯ２の疎水化

The preparation of Hydrophobic TiO2 by the wet coupling treatment method was investigated using compounds of the alkyltrimethoxysilane series. Additionally, wet treatment of TiO2 using preliminarily treated n-PTMS and n-BTMS solutions was examined for the effectiveness of the use of preliminarily treated silane coupling agent in the wet process. The main results obtained are as follows : (1) The adsorption amount of n-PTMS dissolved in pure water onto TiO2 treated by the wet method was negligibly small, resulting in an M value that indicated the degree of hydrophobicity was zero. In contrast, M values of TiO2 treated by the wet method using i-BTMS, n-BTMS and n-HTMS increased with the increase in elapsed time. However the increase in carbon number resulted in the acceleration of increase of M values, causing an increase in maximum M value. A large amount of fixed ATMS does not necessarily signify maximum M value. (2) The maximum M value of TiO2 treated by the wet method using different pH solutions containing n-BTMS appeared to be 60%. Retention time required to increase of M value was shortened according to the sequence of pure water, pH 9.0, pH 4.0 and pH 3.3, and this finding suggested that the sequence was directly related to hydrolysis and condensation reaction rates of n-BTMS in those solutions. The amount of n-BTMS required to provide sufficient hydrohobicity to TiO2 at pH value, under which coupling treatment proceeds quickly, is larger than for slower treatment. The minimum amount of fixed n-BTMS providing maximum M value to TiO2 was found to be about 1 mg per 1 g TiO2, which was 27% of the theoretical amount of n-BTMS addition. In aqueous ammonia solution of pH 10.0, n-BTMS exhibits white turbidity to form an emulsion. Using this emulsion, wet coupling treatment of TiO2 proceeds quickly compared to those at lower pHs. (3) Wet treatment of TiO2 using preliminarily treated n-PTMS or n-BTMS was able to provide hydrophobicity faster than that using n-BTMS solution without preliminary treatment.

Photocatalytic oxidation of n-octanol in aerated supercritical CO2 on hydrophobic TiO2

Supercritical CO2 (scCO2) has been used as a reaction medium for the photocatalytic oxidative degradation of n-octanol on a partially desilanized hydrophobic suspension of TiO2 as photocatalyst. Hydrophobic sites on the catalyst surface are necessary to maintain a sustained suspension, and hence surface-mediated interfacial electron exchange, in this non-polar medium. The reaction rates for photooxidative degradation, ultimately to complete mineralization, depend only weakly on temperature and pressure of the supercritical fluid near the critical point. Product distributions were monitored in situ by on-line gas chromatographic analysis, which provides a convenient and rapid method for comparisons and optimization of the reaction conditions.