A facile route to a highly stabilized hierarchical hybrid of titania nanotube and gold nanoparticle

A hierarchical hybrid of gold nanoparticles and titania nanotubes with high metal loading was prepared by a one-pot approach using a natural cellulosic substance as template. Gold nanoparticles were uniformly anchored onto titania nanotubes, and particle fusion at high temperature was suppressed by surface coating with an ultrathin titania layer.     

Strategies developed on the modification of titania for visible light response with enhanced interfacial charge transfer process: an overview

The modification of titania by metal / non metal ion doping, coupling with narrow band gap sensitizer, surface flourination, metal deposition, and together with recent ventures on application of {001} facets of anatase titania for visible light response with enhanced charge carrier separation are briefly overviewed.     

Review on modified TiO2 photocatalysis under UV/visible light: selected results and related mechanisms on interfacial charge carrier transfer dynamics

Titania is one of the most widely used benchmark standard photocatalysts in the field of environmental applications. However, the large band gap of titania and massive recombination of photogenerated charge carriers limit its overall photocatalytic efficiency. The former can be overcome by modifying the electronic band structure of titania including various strategies like coupling with a narrow band gap semiconductor, metal ion/nonmetal ion doping, codoping with two or more foreign ions, surface sensitization by organic dyes or metal complexes, and noble metal deposition. The latter can be corrected by changing the surface properties of titania by fluorination or sulfation or by the addition of suitable electron acceptors besides molecular oxygen in the reaction medium. This review encompasses several advancements made in these aspects, and also some of the new physical insights related to the charge transfer events like charge carrier generation, trapping, detrapping, and their transfer to surface are discussed for each strategy of the modified titania to support the conclusions derived. The synergistic effects in the mixed polymorphs of titania and also the theories proposed for their enhanced activity are reported. A recent venture on the synthesis and applications of anatase titania with a large percentage of reactive {001} facets and their band gap extension to the visible region via nonmetal ion doping which is a current hot topic is briefly outlined.     

Sol–gel titania coating on unmodified and surface-modified polyimide films

Sol–gel coating of metal oxides on polymer substrates is a useful process to fabricate various organic–inorganic hybrid materials under mild conditions. However, this process is hardly applicable to pristine polyimide (PI) films because their surfaces do not display effective functional groups for metal oxide coatings. In this study, we firstly examined direct sol–gel coating of titania thin layers on unmodified PI film surfaces. The results confirmed homogeneous, ultrathin titania layer coating and showed that the thickness and microscopic morphology of the titania layers were affected by titanium alkoxide concentrations in the spin coating solutions. We next investigated titania layer coating on surface-modified PI films that prepared using alkaline hydrolysis, which generated carboxylic acid groups on the film surfaces. Optimal hydrolysis time was determined using FT-IR spectroscopy and contact angle measurements. After sol–gel titania coating on the hydrolyzed PI film surfaces, the Scotch tape test was conducted to evaluate adhesion strength between the titania layers and PI film surfaces. Morphological observations of the sample surfaces after the tests clearly showed that surface modification of PI films increased titania layer adhesions. Effect of hydrothermal treatments on film formability and adhesion strength between titania-PI film interfaces was also evaluated.     

Features of composites prepared by radical graft-polymerization of styrene to a hydrophilic macromer adsorbed on ultrafine colloidal particles

Polymer modifications of ultrafine monodispersed colloidal metal oxide particles, smaller than 80 nm in diameter, by the graft-polymerization of styrene to a hydrophilic macromer adsorbed on the surface were investigated. The polymerization in ethanolic silica and titania colloid solution, which had negatively larger ζ-potentials, ?30 and ?42 mV in neutral aqueous solution respectively, gave poly(styrene)–silica or titania composite, being of nonspherical shape. The modifications of colloidal particles, having lower surface energy, such as Al(OH)₃ and CeO₂–TiO₂–SiO₂ complex, led to the formation of spherical composites, ranging in size from 500 to 3000 nm, of scattered metal oxide or hydroxide particles.     

Surface electric and titration behaviour of fumed oxides

Adsorption of Pb(II), Sr(II), and Cs(I) on fumed silica, alumina, titania, silica/titania (ST), silica/alumina (SA), and alumina/silica/titania (AST) reveals that mixed oxides containing titania have a greater adsorptive capability in respect to metal cations than individual and SA oxides. Pyrocarbon deposits on fumed oxides enhance the adsorption of metal ions. Calculations of electrophoretic potential (ζ) with consideration for the porosity of aggregates of primary particles of AST show a significant influence of surface alumina (at pH<8) and titania and silica (at pH>8) on the ζ values. The effective diameter of particles (D_ef) of fumed oxides in aqueous media depends on pH for AST stronger than for ST (between isoelectric points (IEPs) of titania and alumina). A significant difference in the pH values of IEP and point of zero charge is observed for AST samples. A pyrocarbon influence on the ζ potential depends on the type of oxide matrix, since ζ increases for certain samples but for others it decreases. These changes depend nonlinearly on pH as well as the secondary particle size distributions (SPSDs) and D_ef.     

Effect of UV and visible light on photocatalytic reduction of lead and cadmium over titania based binary oxide materials

Uniform sized silica and zirconia mixed titania samples were prepared in presence of a surfactant (CETAB) using controlled hydrolysis of corresponding metal alkoxides. Photocatalytic activity towards reduction of lead and cadmium metal in aqueous solution was evaluated both in UV and visible light in a 100 ml capacity reactor. In particular mixing of 10 wt% silica with titania not only increases the surface area of the material but also increases the photocatalytic activity in UV light. Whereas mixing of zirconia with titania proved to be beneficial for visible light reaction. However, addition of hole scavenger increases the activity many folds and complete removal of Pb(2+) and Cd(2+) was possible in 60 min of reaction using synthesized catalysts. Among all the organic hole scavengers used, sodium formate is found to be the most active one. Interestingly quite high metal removal (89%) is also observed in presence of visible light within 60 min of reaction. Thus the above study indicates that the presence of certain oxides in low quantity (10 wt%) with titania can facilitates the photocatalytic process selectively in UV as well as visible light.     

Surface Hydroxyls and Chemisorbed Hydrogen on Titania and Titania Supported Cobalt

The dehydroxylation and rehydroxylation properties of titania (Degussa P-25) were investigated. FTIR and TPD-MS data indicate that hydroxyl groups are not completely removed at 500 °C in vacuo, and rehydration/rehydroxylation occur under helium (water content < 1 ppm) flow at room temperature. In addition, repeating dehydroxylation/rehydroxylation treatments for ten times does not significantly modify the dehydroxylation/rehydroxylation property of titania surface. Desorption of hydrogen from titania was observed at 535 °C after titania was reduced above 400 °C. The maximum surface density of hydrogen was determined to be 0.75 H atom/nm². TPD data show four types of hydrogen on 3% titania supported cobalt catalysts: hydrogen adsorbed on cobalt metal (desorption temperature around 100 °C), reverse spillover hydro gen (150-250 °C), hydrogen from H-TiO_2-x- Co interacting species (-330 °C), and recombined hydrogen from Ti³⁺-H on titania (-535 °C). The absence of hydrogen desorption peak at 535 °C for titania supported cobalt reduced above 400 °C can be explained in terms of the migration of H-TiO_2-x moieties onto cobalt metal surface during reduction. Removal of hydroxyl groups by thermal treatment before reduction enhanced the amount of hydrogen desorption from normal cobalt surface. This indicates that the hydroxyl groups play a role in the surface migration of H-Ti_2-x.     

Preparation of metallodielectric composite particles with multishell structure

In this article, we demonstrated the synthesis of metallodielectric composite particles comprising a metal shell on a dielectric core and an outer coating of an insulating dielectric layer by depositing silver on silica supporting cores followed by coating of titania. A combination of surface reaction and surface seeding techniques is exploited for the formation of a complete silver shell on silica spheres. The additional outer coating of titania on silver shell particles is then performed by hydrolyzing tetra-n-butyl titanate in ethanol at room temperature. The morphologies of silver shells and titania coating are studied with electron microscopy, and their existences are confirmed with X-ray diffraction and energy-dispersive X-ray measurement.     

Patterning of sol gel thin films by capillary force assisted soft lithographic technique

Patterning of sol gel based silica and silica–titania films has been developed at room temperature by soft lithographic technique. Corresponding metal alkoxides have been utilized for the preparation of precursor sols. Elastomeric stamps of polydimethylsiloxane (PDMS) are used to emboss patterns of a master grating on the as-prepared silica and silica–titania films obtained by sol gel process. Pressure-less capillary force lithography has been used to fabricate both 1-D and 2-D ordered structures of simple stripe patterns. A modified solvent assisted lithography and micro-molding in capillaries yielded stable and high fidelity 1-D structures for silica and silica–titania films over a large area.     

Reactive landing of gas-phase ions as a tool for the fabrication of metal oxide surfaces for in situ phosphopeptide enrichment

Zirconium, titanium, and hafnium oxide-coated stainless steel surfaces are fabricated by reactive landing of gas-phase ions produced by electrospray ionization of group IVB metal alkoxides. The surfaces are used for in situ enrichment of phosphopeptides before analysis by matrix-assisted laser desorption ionization (MALDI) mass spectrometry. To evaluate this method we characterized ZrO₂ (zirconia) surfaces by (1) comparison with the other group IVB metal oxides of TiO₂ (titania) and HfO₂ (hafnia), (2) morphological characterization by SEM image analysis, and (3) dependence of phosphopeptide enrichment on the metal oxide layer thickness. Furthermore, we evaluated the necessity of the reactive landing process for the construction of useful metal oxide surfaces by preparing surfaces by electrospray deposition of Zr, Ti, and Hf alkoxides directly onto polished metal surfaces at atmospheric pressure. Although all three metal oxide surfaces evaluated were capable of phosphopeptide enrichment from complex peptide mixtures, zirconia performed better than hafnia or titania as a result of morphological characteristics illustrated by the SEM analysis. Metal oxide coatings that were fabricated by atmospheric pressure deposition were still capable of in situ phosphopeptide enrichment, although with inferior efficiency and surface durability. We show that zirconia surfaces prepared by reactive landing of gas-phase ions can be a useful tool for high throughput screening of novel phosphorylation sites and quantitation of phosphorylation kinetics.     

Separation of xanthines in hydro‐organic and polar‐organic elution modes on a titania stationary phase

Hydrophilic interaction LC was investigated in hydro‐organic and nonaqueous elution modes on a titania column by using a set of N‐methyl xanthines as neutral polar probes. To get information regarding the mechanisms that are behind the discrimination of these analytes in hydrophilic interaction, we focused our study on the type and amount of organic modifier as a critical yet rarely explored mobile phase parameter. Several alcohols such as methanol, ethanol, and isopropanol were studied as substitutes to acetonitrile in hydro‐organic elution mode. Compared to silica, the investigation of the eluotropic series of these alcohols on titania highlighted a different implication in the retention mechanism of the xanthine derivatives. At low amounts of protic solvents, the adsorption mainly characterized the retention of analytes on bare silica; whereas mixed interactions including adsorption and ligand exchange were identified on native titania. To investigate the peculiar behavior of alcohols on the metal oxide, methanol, ethanol, and ethylene glycol were tested in replacement of water in polar‐organic elution mode. Distinctive effects on the chromatographic retention and selectivity of xanthines were noticed for the dihydric alcohol, which was found to be a stronger eluting component than water on titania.     

Catalytic incineration of benzene over titania/vanadia/tungsten oxide catalysts

Catalytic decomposition of benzene was carried out on various metal oxides. Pure titania is not effective in decomposing 99% of benzene even at temperature of 600°C. Addition of vanadia improves its ability to decompose benzene. Titania-vanadia catalyst can decompose 99% of benzene at 410°C. The combination of titania/vanadia/tungsten oxide is more effective. It can decompose 99% of benzene at as low as 355°C.     

TiO2光催化剂可见光化研究进展

TiO2在光催化和光电转换方面应用前景十分广阔,而阻碍其应用的是它的大禁带宽度(E_g=3.2_eV),不能有效地利用太阳能,因此研究开发可见光响应的TiO₂就成为当前光催化剂研究的关键课题.目前TiO₂可见光化的研究取得了一定进展,金属离子掺杂、非金属离子掺杂、离子注入以及染料光敏化等方法都不同程度地实现了TiO₂可见光化.本文综述了目前的研究现状,并对今后的研究提出了展望.     

Synthesis of titania-supported platinum catalyst: the effect of pH on morphology control and valence state during photodeposition

Solid-supported metal catalysts have been widely used in industrial processes. The morphology of coated metal on the support is usually an important factor affecting the efficiency of the catalyst. In this study, a photocatalytic process is utilized to control the morphology of platinum particles deposited on titania (Degussa P-25). More specifically, the effect of pH on the morphology and the valence state of platinum nanoparticles was systemically investigated. It is found that, via a simple pH-controlled process, various states of platinum (Pt0, PtIIO, or PtIVO2) can be deposited onto the support directly at will. In this paper, the mechanism of morphology control and the key influencing factors at different pH regimes will be discussed. Followed by photodeposition, a H2 thermal treatment process was employed to convert the oxides into metal platinum with narrow size distribution and even coverage on the supporting titania. Various techniques such as transmission electron microscopy, high-resolution transmission electron microscopy, energy-dispersive analysis of X-rays, and X-ray photoelectron spectroscopy were employed to characterize the prepared titania-supported platinum particles.     

Titania Nanomaterials Produced from Ti-Salt Flocculated Sludge in Water Treatment

Titania is the most widely used metal oxide for the applications of pigments, paper, solar cells and environmental purification. In order to meet the demand of a large amount of titania, our group has developed a novel process which could significantly lower the cost of waste disposal in water treatment, protect the environment and public health and yield economically valuable titania. Titanium tetrachloride (TiCl₄) or titanium sulfate (Ti(SO₄)₂) as an alternative coagulant in water treatment has been explored for the removal of various pollutants from contaminated water or wastewater. Flocculation efficiencies of the Ti-salts were superior to those of Al- and Fe- salts with additional benefits in that a large amount of titania can be produced by calcinating the flocculated floc. The produced titania showed high photocatalytic activity for the removal of volatile organic compounds. The large amount of titania can be applied to pigments, environment and construction materials which require a lot of titania usages. This review paper presents an historical progress from fundamental to application in terms of the detailed production process, characterization, photoactivity of titania produced from Ti-salt flocculated sludge, and its various applications.     

Phosphopeptide-selective column-switching RP-HPLC with a titania precolumn.

A methodology of phosphopeptide-selective analysis coupled with column-switching HPLC utilizing titania as precolumn media is presented. Phosphopeptides were selectively enriched on titania packing within a protein/peptide mixture without any additional procedure, and analyzed by column-switching high-performance liquid chromatography. First, phospho-compounds were separated from complex mixtures by trapping them under acidic conditions on a titania packing, where non-phosphorylated compounds were effused out of the precolumn. Subsequently, phospho-compounds were desorbed from the titania column under a specific condition and analyzed. The behavior of phospho-compounds on a titania surface, especially adsorption/desorption, was precisely examined and optimized. A phosphoric buffer was successively employed for the elution of phosphopeptides on a titania surface by competition with the free phosphate group. From the successes of a selective concentration/analysis of phosphopeptides with column-switching HPLC with a titania precolumn, a novel phosphopeptide-selective RP-HPLC analysis has been shown to have an application possibility as a tool for phosphoproteomics.     

Evaluation of titania as an ion-exchanger and as a ligand-exchanger in HPLC

Summary The chromatographic properties of titania have been compared with those of zirconia and alumina, by comparison of their relative Lewis acidities whenp-substituted benzoic acids were chromatographed with aqueous mobile phases. The retention behavior ofp-substituted benzoic acids on titania was found to be similar to that on zirconia; the slopes of plots of retention factors against solute pK _a were approximately parallel for all pH values and the slopes obtained were similar to the average slope for zirconia. The shapes of solute peaks on titania were more symmetrical than on alumina and zirconia. The effect of calcination temperature on the chromatographic properties of titania was examined by use of titania prepared at different temperatures. The results obtained clearly showed that the preparation temperature affected the chromatographic properties of titania. It seemed, for example, that titania dried at 40°C behaved as a cation-exchanger, titania heated at 200°C behaved as an amphoteric exchanger, and titania calcined at 600°C behaved as an anion-exchanger in the pH range 4.1–6.5 It was found that the control of the preparation temperature enabled us to make effective use of titania.