Titania Shell Research Articles

Photocatalytic activity of TiO2-capped ZnO nanoparticles

Using a combined hydrothermal and sol–gel route, TiO2 -capped ZnO nanoparticles with an average size of 60 nm were prepared. The titania shell was amorphous with a thickness of ~10 nm. Formation of Zn2TiO4 phase at higher calcination temperature was noticed. Effects of Ti/Zn molar ratio and coating time on the thickness of TiO2 shell and the photoactivity of the particles for decolorization of Methylene Blue (MB) under UV lamp irradiation (3 mW/cm2) were investigated. The nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, fourier-transform infrared spectrometry (FTIR), diffuse reflectance spectroscopy (DLS), and atomic absorption spectroscopy. Analysis of the photoactivity results according to Langmuir–Hinshelwood model revealed a two-step decolorization process with a high kinetics rate at the early stage followed by a slower step. The capped nanoparticles synthesized under specific conditions exhibited higher photodecolorization yield and faster kinetics in comparison to the uncoated ZnO and P25-Degussa TiO2 nanoparticles.

Titania shells with single crystallites layer thickness and the photocatalysis properties

TiO2 shells comprised of single-layer nanocrystallites were synthesised using sulphonated polystyrene (SPS) nanospheres as hard templates. The assembling of titania gel-based particles during the hydrolysation process caused the formation of SPS–titania gel core–shell spheres, the dissolution of SPS and the condensation process by calcination resulting in single-layer crystallites-connected TiO2 shells with a rough surface. The prepared TiO2 shells showed considerable photocatalytic activity on the degradation of Rhodamine B.

Synthesis of soluble polyimide/silica–titania core–shell nanoparticle hybrid thin films for anti-reflective coatings

In this study, researchers prepared polyimide/silica–titania core–shell nanoparticle hybrid thin films (PI/SiO 2–TiO 2) from soluble fluorine-containing polyimide, colloidal silica, and titanium butoxide. The soluble polyimide with carboxylic acid end groups (6FDA–6FpDA–4ABA–COOH) could condense with titanium butoxide to provide organic–inorganic bonding, and thus prevent macrophase separation. TGA and DSC analysis showed that the decomposition temperature of hybrid materials increased with an increase in the content of silica–titania nanoparticles within the hybrid films. FTIR spectra indicated that the imidization was complete and the cross-linking Ti–O–Ti network formed. HRTEM and HRSEM images showed that the size of the core–shell nanoparticles were 18–20 nm. The thickness of titania shell on the silica is about 2.5 nm. The n&k and UV–Vis analysis showed that the prepared hybrid films had good optical properties and a high refractive index of 1.735. Researchers applied the prepared PI/SiO 2–TiO 2 hybrid thin films to develop a three layer antireflective (AR) coating on the glass and PMMA substrate. Results showed that the reflectance of the AR coating on the glass and PMMA substrate at 550 nm was 0.356 and 0.495%, respectively. The transparency was greater than 90% for both AR coatings on the glass and PMMA substrates.

Widely tuning optical properties of nanoporous gold-titania core-shells

Widely shifting localized surface plasmon resonance (LSPR) bands of nanoporous metals is essential for light manipulation within small volumes. In this work, nanoporous gold-titania core-shells fabricated by atomic layer deposition exhibit tunable LSPR of gold skeletons in comparison with nanoporous gold-alumina developed before. Extremely large red-shift of LSPR band in nanoporous gold-titania from 537 to 751 nm results from high refractive index of titania and its dielectric medium dependence of LSPR, and the well-controlled thickness of titania shell at the nanometer scale will benefit to integrate optical nanodevices with supreme performances.

Ultrasound-Triggered Smart Drug Release from Multifunctional Core−Shell Capsules One-Step Fabricated by Coaxial Electrospray Method

Multifunctional core-shell capsules that triggered release by ultrasound stimulus were one-step fabricated by the coaxial electrospray method. The TiO(2) shell suppressed the initial burst release of the paclitaxel. Fe(3)O(4) and graphene quantum dots inside the oil core functioned successfully for magnetic targeting and fluorescence imaging, respectively. Paclitaxel was trigger released when the dual layer of titania shell cracked under the ultrasound stimulation, and the releasing profile could be controlled by the length of applied ultrasound time.

Template-Assisted Fabrication of Magnetically Responsive Hollow Titania Capsules

This study reports on the fabrication of magnetically responsive hollow titania capsules by confining the superparamagnetic Fe(3)O(4) nanoparticles within a hollow and porous titania (TiO(2)) shell. The employed protocol involves precipitation of titania shell on the magnetite (Fe(3)O(4)) encapsulated polystyrene beads followed by the calcination of resulting composite particles at elevated temperature. Scanning electron microscopy and transmission electron microscopy reveal the presence of a thick, complete but irregular titania shell on the magnetic polystyrene beads after the templating process. Electron energy loss mapping image analysis has been employed to investigate the spatial distribution of titania and magnetite phases of magnetic hollow titania capsules (MHTCs). Magnetic characterization indicates that both titania-coated magnetic polystyrene beads (TMPBs) and MHTCs are superparamagnetic in nature with the saturated magnetizations of 5.6 and 8.1 emu/g, respectively. X-ray diffraction (XRD) analysis reveals that titania shell of these capsules is composed of photoactive anatase phase. Nitrogen adsorption-desorption analysis has been employed to estimate the specific surface area and the average pore diameter of the fabricated hollow structures. Photocatalytic activity of the fabricated MHTCs for the photodegradation of rhodamine 6G dye has been demonstrated and compared with that of bulk titania nanoparticles.

ZnO and TiO 2 1D nanostructures for photocatalytic applications

ZnO and TiO 2 1D nanostructures (nanorods and nanotubes) were prepared by low-cost, low-temperature, solution-based methods and their properties and photocatalytic performance were studied. ZnO nanorod samples with titania and alumina shells were also prepared by solution-based methods, and their properties and photocatalytic performance were compared to that of bare ZnO nanorods. We found that ZnO and TiO 2 exhibited comparable photocatalytic performance. Faster dye degradation under simulated solar illumination was observed for ZnO, while under UV illumination faster degradation was observed for TiO 2. ZnO nanorods with titania shells exhibited inferior photocatalytic performance, while for alumina shells the performance was similar to bare ZnO. Reasons for observed differences are discussed, and the effect of the shell on photocatalytic activity is attributed to the changes in native defects at the ZnO surface/shell interface.

Association of Titania with Nonionic Block Copolymers in Ethanol: The Early Stages of Templating and Film Formation

We have prepared self-supporting, free-standing titania-surfactant mesostructured films via spontaneous growth on the surface of ethanolic solutions, as an alternative synthetic route to evaporation induced self-assembly. The initial stages of surfactant templating and interfacial film formation in alcoholic solutions of titania with a polyethylene−poly(ethylene glycol) surfactant have been observed by small angle neutron scattering and Brewster angle microscopy. Variation of parameters including the titania precursor concentration, acid concentration, and surfactant concentration allowed formation times and pathways to be probed. These time-resolved observations of titania development represent a novel achievement in formation studies and have allowed a formation mechanism for titania−surfactant films to be proposed. Micelles in solution undergo an initial slow accumulation of titania, followed by rapid growth of a titania shell, followed again by a slow growth period, and these species accumulate at the...

The preparation of TiO2/SiO2 composite hollow spheres with hydrophobic inner surface and their application in controlled release

Abstract The TiO 2 /SiO 2 composite hollow spheres (CHSs) with hydrophobic inner surface have been successfully synthesized by using carboxyl-functionalized polystyrene spheres as templates. The inner titania shell was selectively modified with stearic acid (SA). The morphologies, structures, drug loading amounts and release rates were characterized and investigated by SEM, TEM, XRD, N 2 adsorption–desorption isotherms, FT-IR, TG and HPLC analysis. Due to the hydrophobic interaction, the modified inner surface slowdown the release of the hydrophobic drug into the aqueous environment. The SA modified CHSs displayed higher drug loading amounts as well as lower release rates than that of unmodified spheres. The studies demonstrate that composite hollow spheres are promising for the multifunctional controlled release.

A General Method to Coat Colloidal Particles with Titania

We describe a general one-pot method for coating colloidal particles with amorphous titania. Various colloidal particles such as silica particles, large silver colloids, gibbsite platelets, and polystyrene spheres were successfully coated with a titania shell. Although there are several ways of coating different particles with titania in the literature, each of these methods is applicable to only one type of material. The present method is especially useful for giving the opportunity to cover many types of colloidal particles with titania and forgoes the use of a coupling agent or a precoating step. We can produce particles with a smooth titania layer of tunable thickness. The monodispersity, which improves during particle growth, and the high refractive index of titania make these particles potential candidates for photonic crystal applications. We also describe various ways of fabricating hollow titania shells, which have been intensively studied in the literature for their applications in electronics, catalysis, separations, and diagnostics. Note that our method initially produces amorphous shells on the particles, but these can be easily turned into crystalline titania by a calcination step. We also find that the growth of titania is a surface-reaction-limited process.

Preparation and characterization of sol–gel derived Er 3+–Yb 3+ codoped SiO 2/TiO 2 core–shell nanoparticles

The Er 3+–Yb 3+ codoped silica/titania core–shell nanoparticles were prepared by hydrolysis of titanium alkoxide precursors in the presence of lanthanide ions via sol–gel method. The structure of the particles was characterized by field emission scanning electron microscopy and transmission electron microscopy. The diameter of the silica core is about 50 nm. The thickness of the titania shell is about 4 nm. A typical doping density of Er 3+ in the titania shell is 4.51 at.%, and the one of Yb 3+ is 12.20 at.%. The UV–vis–NIR absorption spectra and the photoluminescence spectra were also investigated.

Synthesis and characterization of anatase TiO2 nanolayer coating on Ni–Cu–Zn ferrite powders for magnetic photocatalyst

In the current research, we successfully prepared TiO2/Ni–Cu–Zn ferrite composite powder for magnetic photocatalyst. The core Ni–Cu–Zn ferrite powder was synthesized using the steel pickling liquor and the waste solution of electroplating as the starting materials. The shell TiO2 nanocrystal was prepared by sol-gel hydrolysis precipitation of titanium isopropoxide [Ti(OC3H7)4] on the Ni–Cu–Zn ferrite powder followed by heat treatment. From transmission electron microscopy (TEM) image, the thickness of the titania shell was found to be approximately 5 nm. The core of Ni–Cu–Zn ferrite is spherical or elliptical shape, and the particle size of the core is in the range of 70–110 nm. The magnetic Ni–Cu–Zn ferrite nanopowder is uniformly encapsulated in a titania layer forming core-shell structure of TiO2/Ni–Cu–Zn ferrite powder. The degradation efficiency for methylene blue (MB) increases with magnetic photocatalyst (TiO2/Ni–Cu–Zn ferrite powder) content. When the magnetic photocatalyst content is 0.40 g in 150 mL of MB, the photocatalytic activity reached the largest value. With a further increase in the content of magnetic photocatalyst, the degradation efficiency slightly decreased. This occurs because the ultraviolet (UV) illumination is covered by catalysts, which were suspended in the methylene blue solution and resulted in the inhibition in the photocatalytic reaction. The photocatalytic degradation result for the relationship between MB concentration and illumination revealed a pseudo first-order kinetic model of the degradation with the limiting rate constant of 1.717 mg/L·min and equilibrium adsorption constant 0.0627 L/mg. Furthermore, the Langmuir–Hinshelwood model can be used to describe the degradation reaction, which suggests that the rate-determining step is surface reaction rather than adsorption is in photocatalytic degradation.

Synthesis of ellipsoidal hematite/polymer/titania hybrid materials and the corresponding hollow ellipsoidal particles

Ellipsoidal tri-layer hematite/poly(N,N′-methylenebisacrylamide-co-methacrylic acid)/titania (Fe2O3/P(MBA-co-MAA)/TiO2) hybrid materials were prepared by a three-stage reaction process, which included the combination of the controlled hydrolysis of inorganic salt to afford ellipsoidal hematite core and titania shell layer and distillation precipitation copolymerization of N,N′-methylenebisacrylamide (MBA) and methacrylic acid (MAA) in acetonitrile for the formation of a P(MBA-co-MAA) sandwiched mid-layer. The corresponding hollow ellipsoidal hematite-sphere-in-titania-spheres were afforded by selective removal of the sandwiched P(MBA-co-MAA) mid-layer viacalcination. Hollow titania ellipsoids were further obtained by selectively etching the hematite core in aqueous hydrofluoric acid (HF) solution from the ellipsoidal hematite-sphere-in-titania-sphere. The resultant ellipsoidal tri-layer Fe2O3/P(MBA-co-MAA)/TiO2 and the corresponding hollow ellipsoidal particles were confirmed by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, X-ray diffraction (XRD), thermogravimetric (TGA) analysis and vibrating sample magnetometery (VSM).

Magnetic (γ-Fe2O3@SiO2)n@TiO2 Functional Hybrid Nanoparticles with Actived Photocatalytic Ability

An easy chemical route for the synthesis of (γ-Fe2O3@SiO2)n@TiO2 functional hybrid nanoparticles is reported in this paper. The hybrid nanoparticles are composed of spherical nanoparticles about 100 nm in diameter, with several γ-Fe2O3 fine particles about 15 nm in diameter as cores distributing within the titania matrix and silica as coatings and barrier layers between the magnetic cores and titania shells. The (γ-Fe2O3@SiO2)n@TiO2 hybrid nanoparticles show good magnetic response and got together within 20 s in a magnetic field. Photodegradation examination of the magnetic hybrid nanoparticles was carried out in methylene blue solutions illuminated under UV light in a photochemical reactor. It is shown that the (γ-Fe2O3@SiO2)n@TiO2 functional hybrid nanoparticles are photocatalytically actived. About 80% of methylene blue decomposed in 80 min in the presence of magnetic hybrid nanoparticles under illumination of UV light. The synthesized magnetic hybrid nanoparticles display high photocatalytic efficienc...

A general protocol to coat titania shell on carbon-based composite cores using carbon as coupling agent

We present herein a general protocol to coat titania shell on carbon-based composite cores via the hydrolysis of titanium tetrabutoxide in a mixed solvent with the catalysis of ammonia. As coupling agent, their carbonaceous component can adsorb counter-charged NH 4 +, and then the negatively charged ≡TiO − species are adsorbed via electrostatic interaction to form TiO 2 shell. Various carbon-based cores with different functional components, such as Ag/C core/shell spheres, Ag/C nanocables, as well as magnetic (C–Fe 3O 4) hollow spheres can be coated with titania shell to form corresponding core/shell composites. Their optical or magnetic property is also investigated. Finally, anatase-phase titania shell with rough surface can be generated via hydrothermal treatment of aforementioned titania coated composites, which can further introduce the properties of anatase-phase titania to the composites.

Synthesis, characterization and photodegradation study of mixed-phase titania hollow submicrospheres with rough surface

Titania hollow submicrospheres with mixed phase (anatase–brookite or anatase–rutile) were synthesized via the combination of hydrothermal treatment and calcination of submicrospheres consisting of a polystyrene core and an amorphous TiO 2 shell. After hydrothermal treatment, amorphous titania shell could be transformed to anatase–brookite shell consisting of loose packed titania nanocrystals, which could be further converted to anatase–brookite (below 700 °C) or anatase–rutile titania (700–800 °C) hollow spheres with rough surface via calcination. The loose packing of titania nanocrystals not only inhibited the transformation temperature from anatase to rutile, but also provided titania hollow submicrospheres with high photodegradation activity of Rhodamine B. The photocatalytic activity of titania hollow spheres increased firstly then decreased when the calcination temperature was varied in the range of 450–800 °C, while hollow spheres obtained via calcinating at 700 °C exhibited the highest photocatalytic activity, which was five times higher than that of counterpart without hydrothermal treatment.

Facile preparation of titania hollow spheres by combination of the mixed solvent method and the sol–gel process and post-calcination

Polystyrene (core)–titania (shell) composite spheres consisting were readily prepared by a sol–gel process of titanium tetrabutoxide (TBOT) in a mixed solvent of ethanol/acetonitrile (3:1, v/v). Smooth and homogeneous titania coatings formed when the mixed solvent was dehydrated by anhydrous sodium sulfate. The thickness and surface roughness of titania coating increase with increase of the TBOT concentration. By adjusting the TBOT concentration in the range of 5.8–29.0 mM, the size of titania-coated PS spheres could be varied from 990 to 1125 nm. Calcination at elevated temperature gave dense, homogeneous, robust shells of anatase titania. The sizes of titania hollow spheres are 11.3–16.9% smaller than those of the titania-coated PS spheres as a result of calcination-induced shrinkage. The composite and hollow spheres were characterized by scanning electron microscopy, transmission electron microscopy and electron diffraction measurements. These core–shell organic–inorganic spheres and hollow ceramic spheres may have wide applications in catalysts, adsorbents, lightweight fillers, capsules, etc.

Multi-functional microcapsules produced by aerosol reaction

Multi-functional microcapsules with an n-octadecane (C18) core and a titania shell were prepared by a rapid aerosol process with a hydrothermal post-treatment. They had a high core loading of nearly 80% and a nanocrystalline shell of mostly anatase. Upon heating to induce C18 melting the enthalpy change was 92–97 J/g. They were found to have a photocatalytic activity to eliminate bacteria and react with mercaptans. They also provided UV-blocking. When applied to clothing by coating they are expected to promote wearer's comfort and skin health.

The effects of sonification and TiO 2 deposition on the micro-characteristics of the thermally treated SiO 2/TiO 2 spherical core–shell particles for photo-catalysis of methyl orange

SiO 2/TiO 2 core–shell particles were prepared to decompose methyl orange (MO) in a laboratory scale study prior to its use in the treatment of waste containing azo dyes that might potentially pose adverse environmental consequences and health hazard to human. The preparation of silica cores produced perfectly spherical and smooth surfaces, but when TiO 2 shell/film was deposited using titanium butoxide (TBOT) precursor at concentration >0.24 mol L −1, the resulting shell was rougher and loose, giving rise to Ostwald ripening that caused the core–shell particles to agglomerate. The use of sonification improved the dispersion at the expense of thin shell. When multi-step shell coating was applied to increase the shell thickness, loose titania shells were observed despite increasing surface coverage at higher number of coating step. The isoelectric point of the core–shell particles was equivalent to that of pure titania (4.5) due to the complete encapsulation of silica cores by titania. The silica core crystals exhibited highly amorphous structures, whereas titania covered silica cores demonstrated pure anatase phase that grew in size upon heat treatment at 900 °C. Rutile phase started to develop at 5 coatings, suggesting that anatase crystallite size was attainable for as long as the critical crystalline size smaller than ca. 30 nm was sustained or equivalently, 3 coatings were applied. Complete decomposition of MO was achieved in less than 370 min using core–shell particles prepared from triple coating.

Simple Route to Monodispersed Silica−Titania Core−Shell Photocatalysts

A monodispersed silica-titania core-shell photocatalyst was synthesized via a sol-gel route without the need of pH adjustment, cationic polyelectrolytes, or surfactants in a process where silica spheres were impregnated with hydrolyzed titanium tetrabutoxide, incubated at room temperature, and then condensed using an ethanol/water (1:1) solvent. Four coating cycles in a 10% v/v titania sol produced homogeneous titania shells. The quality of catalysts was assessed quantitatively using Rietveld analysis of powder X-ray diffraction patterns combined with X-ray fluorescence spectrometry. During calcination, the anatase-to-rutile transformation was delayed to 1000 degrees C, which is approximately 300 degrees C higher than usually observed. The thermal stability and surface area of titania were enhanced through the slow crystal growth of anatase. The photocatalytic activity of the core-shell photocatalysts calcined at 400-600 degrees C was found to be proportional to the thickness of titania but did not directly correlate with the surface area.