Thickness Of TiO2 Shell Research Articles

A modified sol–gel method using acetone–ethanol mixed solvent for fast constructing nanometric TiO2 shells

We successfully constructed uniform and complete TiO2 shells on SiO2 cores in a short reaction time (2h) and obtained the core–shell particles with high dispersibility. In this modified sol–gel method, the adopting of ethanol–acetone mixed solvent was critical and advantageous for the fast formation of TiO2 shells. When acetone was controlled at an optimum fraction in solvent (acetone:ethanol=1.2:1v/v), it not only increased the hydrolysis rate of precursor (i.e., titanium (IV) tetrabutoxide) and the condensation rate of titanium oligomers, but also regulated these two sub-reactions of TiO2 formation to be in balance – and thus suppressed the occurrence of agglomeration during TiO2 coating. In addition, the influence of the concentration of catalyst NH3 and precursor titanium (IV) tetrabutoxide was also investigated. Furthermore, the thickness of TiO2 shells on 366nm SiO2 cores was varied from 30 to 107nm by simply adjust the addition volume of precursor, as the regulation role of acetone was widely applicable for different concentration of precursor. Finally, the obtained TiO2 shells were proved to be able to crystallize to anatase shells by calcination, while the core–shell structure showed high stability at high temperature.

Visible Photoelectrochemical Water Splitting Based on a Ru(II) Polypyridyl Chromophore and Iridium Oxide Nanoparticle Catalyst

Preparation of Ru(II) polypyridyl–iridium oxide nanoparticle (IrOX NP) chromophore–catalyst assemblies on an FTO|nanoITO|TiO2 core/shell by a layer-by-layer procedure is described for application in dye-sensitized photoelectrosynthesis cells (DSPEC). Significantly enhanced, bias-dependent photocurrents with Lumencor 455 nm 14.5 mW/cm2 irradiation are observed for core/shell structures compared to TiO2 after derivatization with [Ru(4,4′-PO3H2bpy)2(bpy)]2+ (RuP2) and uncapped IrOX NPs at pH 5.8 in NaSiF6 buffer with a Pt cathode. Photocurrents arising from photolysis of the resulting photoanodes, FTO|nanoITO|TiO2|−RuP2,IrO2, are dependent on TiO2 shell thickness and applied bias, reaching 0.2 mA/cm2 at 0.5 V vs AgCl/Ag with a shell thickness of 6.6 nm. Long-term photolysis in the NaSiF6 buffer results in a marked decrease in photocurrent over time due to surface hydrolysis and loss of the chromophore from the surface. Long-term stability, with sustained photocurrents, has been obtained by atomic layer depos...

Template-assisted synthesis of hollow TiO2@rGO core–shell structural nanospheres with enhanced photocatalytic activity

Reduced graphene oxide (rGO) wrapped hollow TiO2 nanospheres have been synthesized successfully via a simple two-step method, which involves preparation of SiO2@TiO2@GO core/shell structures without any modified agents and subsequently etching of the SiO2 core materials. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray and detector (EDX), X-ray photoelectron spectroscopy (XPS), respectively. The photocatalytic activity of the as-prepared samples was evaluated by photocatalytic decolorization of Rhodamine B (Rh B) both under ultraviolet and visible light irradiation. SEM and TEM images revealed that the diameter of the reduced graphene oxide wrapped hollow TiO2 nanospheres (HRGT NSs) is about 350–400nm, while the thickness of TiO2 and graphene shell is about 15nm and 5nm, respectively. The photocatalytic degradation results indicated that the HRGT NSs showed an enhanced photocatalytic activity than pure hollow TiO2 nanospheres (HT NSs) and P25 both under ultraviolet and visible light irradiation. And the excellent photocatalytic ability of the HRGT NSs could be mainly attributed to its enhanced absorption performance for organic pollutants and separation efficiency for photogenerated electron–hole pairs both under ultraviolet and visible light irradiation condition.

Study on enhanced photocatalytic activity of magnetically recoverable Fe3O4@C@TiO2 nanocomposites with core–shell nanostructure

A novel and simple approach for the fabrication of Fe3O4@C@TiO2 nanocomposites with a good core–shell structure has been successfully constructed. The as-synthesized core–shell structure is composed of a magnetic core, an interlayer of carbon, and an outer TiO2 shell. In this method, the carbon middle layer could provide negatively charged for the TiO2 coating without the surfactants. The as-obtained core–shell structure composites were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray photoelectron spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TG), N2 adsorption–desorption isotherm analyses and the magnetization measurement (SQUID). The TEM images showed that the thickness of TiO2 shell could be controlled by varying tertrabutyl titanate (TBOT) content in the ethanol/acetonitrile mixed solvents. Photocatalytic property of Fe3O4@C@TiO2 nanocomposites were evaluated by photodegradation methylene blue (MB). The results showed that the well-designed nanocomposites exhibited a higher photoactivity than Fe3O4@TiO2 nanocomposites. Moreover, this photocatalyst can be easily recovered by an external magnetic field and remain stable photocatalytic activity after five cycles. The presence of carbon interlayer can avoid the occurrence of photodissolution. Therefore, the photocatalytic activity of titania would not deteriorate seriously, which played key role for the enhanced photocatalytic activity.

Preparation and Optical Property of ZnS:Mn/XO<sub>2</sub> (X=Ti, Si) Nanoparticles with Core/Shell Structure

In this paper, Mn2+ doped ZnS (ZnS:Mn) nanoparticles were prepared by co-precipitation method. And then different thickness of TiO2 and SiO2 inorganic shell were coated on prepared ZnS:Mn through the hydrolysis reaction of tetrabutyl titanate (TBOT) and tetraethyl orthosilicate (TEOS). ZnS:Mn crystal and core/shell structure were described by X-ray diffraction (XRD) and scanning electron microscope (SEM). Optical property of all ZnS:Mn/XO2 (X=Ti, Si) nanoparticles were investigated by photoluminescence (PL) spectrometer. The effect of Mn2+ concentration and XO2 (X=Ti, Si) shell thickness on luminescence intensity of ZnS:Mn/XO2 was studied. The results showed that with TiO2 and SiO2 shell thickening, Mn2+ emission of ZnS:Mn/XO2 samples increased first and then decreased. When the thickness of inorganic shell (molar ratio of shell and core amount) reached to 0.5 (TiO2) and 1.0 (SiO2), the optimal luminescence intensity was obtained. The emission of ZnS:Mn/TiO2 and ZnS:Mn/SiO2 was 2.0 and 1.5 times more in intensity than that of uncoated ZnS: Mn, respectively.

General strategy to synthesize uniform mesoporous TiO2/graphene/mesoporous TiO2 sandwich-like nanosheets for highly reversible lithium storage.

Uniform oxide deposition on graphene to form a sandwich-like configuration is a well-known challenge mainly due to their large lattice mismatches and poor affinities. Herein, we report a general strategy to synthesize uniform mesoporous TiO2/graphene/mesoporous TiO2 sandwich-like nanosheets (denoted as G@mTiO2), which cannot be achieved by conventional one-pot synthetic methods. We show that by rational control of hydrolysis and condensation of Ti precursors in a slow way, GO sheets can be conformably coated by amorphous TiO2 shells, which then can be facilely transformed into the well-defined G@mTiO2 nanosheets by annealing. This amorphous-to-crystalline strategy conveniently allows bypassing strain fields that would inevitably arise if direct growth of mesoporous anatase shells on graphene. As distinct from the most common structures of graphene-based composites (mixed, wrapped, or anchored models), the resultant materials display a uniform sandwich-like configuration: few-layer graphene conformably encapsulated by mesoporous TiO2 shells. This new G@mTiO2 nanosheet exhibits ultrathin nature (∼34 nm), small size and high crystalline nanocrystals (∼6 nm), high surface areas (∼252 m(2)/g) and uniform mesopores (∼3.4 nm). We further show that the thickness of mesoporous TiO2 shells can be facilely adjusted as desired by controlling the ammonia content, and this facile strategy can be easily extended to design other oxide/graphene/oxide sandwich-like materials. More importantly, we showcase the benefits of the resultant G@mTiO2 nanosheets as anodes in lithium ion batteries: they deliver an extra high capacity, an excellent high-rate capability, and long cycle life.

Fabrication of Mono-dispersed Hollow Titania Nanospheres with Enhanced Photocatalytic Property

Abstract The mono-dispersed hollow TiO2 nanospheres were fabricated by calcining the polystyrene-titania composite microspheres prepared via a sol-gel process of titanium tetrabutoxide (TBOT) using cationic polystyrene (PS) spheres as template. The microstructure, the photocatalytic activity of the composite microspheres and the hollow nanospheres were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and UV-VIS DRS. The results indicate that the diameter of hollow titania spheres is ca.100 nm and the sizes of titania hollow spheres are about 25% smaller than those of the titania-coated PS spheres as a result of calcination-induced shrinkage. The thickness of TiO2 shell is finely tuned by varying the amount of titania precursor. The TiO2 shell is composed of many phase separated anatase/rutile mixed nanocrystallite. The prepared samples show much better photocatalytic activity in the degradation of methyl orange aqueous solution than commercial P25.

Atomic layer deposition of TiO2 on mesoporous nanoITO: conductive core-shell photoanodes for dye-sensitized solar cells.

Core-shell structures consisting of thin shells of conformal TiO2 deposited on high surface area, conductive Sn-doped In2O3 nanoparticle. Mesoscopic films were synthesized by atomic layer deposition and studied for application in dye-sensitized solar cells. Results obtained with the N719 dye show that short-circuit current densities, open-circuit voltages, and back electron transfer lifetimes all increased with increasing TiO2 shell thickness up to 1.8-2.4 nm and then decline as the thickness was increased further. At higher shell thicknesses, back electron transfer to -Ru(III) is increasingly competitive with transport to the nanoITO core resulting in decreased device efficiencies.

Preparation of Gold/Silver/Titania Trilayered Nanorods and Their Photocatalytic Activities

Gold/silver/titania trilayered nanorods have been prepared by the successive deposition of silver and titania layers on gold nanorod cores, and their photocatalytic activities were investigated under visible-light illumination (λ > 420 nm). The photocatalytic activity of the trilayered nanorods in the oxidation of 2-propanol depends on both the Au/Ag composition and the thickness of the TiO2 shell. It increases with increasing Ag content up to [Au]/[Ag] = 1:5 (molar ratio) and then decreases with further increasing Ag content. The photocatalytic activity also increases with increasing TiO2 shell thickness up to 10 nm and then decreases with further increases in the shell thickness. These effects were explained by electron-transfer and energy-transfer mechanisms.

Hybrid Ag@TiO2 core–shell nanostructures with highly enhanced photocatalytic performance

A new synthetic approach has been developed to prepare silver@titanium dioxide (Ag@TiO2) core–shell nanostructures with controllable size, shape, crystal phase and function at ambient conditions (e.g. in water, ≤100 ° C). This approach shows a few unique features, including short reaction time (a few minutes) for forming core–shell nanostructures, no requirement of high temperature calcinations for generating TiO2 (e.g. at ∼100 ° C in our case), tunable TiO2 shell thickness, high yield and good reproducibility. The experimental results show that the Ag@TiO2 core–shell nanostructures exhibit excellent photocatalytic activity compared to the commercial TiO2 (P25) and Ag-doped TiO2 nanocomposite in the degradation of organic dye molecules (e.g. methyl orange) with ultraviolet (UV) irradiation. This could be attributed to the large surface area of TiO2 nanoparticles for maximum harvesting of UV light, mixed anatase and rutile crystalline phases in the TiO2 shell and the effective charge separation between Ag and TiO2 that can reduce the possible recombination of electron–hole (e−–h+) pairs within TiO2 generated under UV radiation. To further understand the charge separation situation within Ag–TiO2 composites, theoretical simulation (e.g. density functional theory, DFT) was employed in this study. The DFT simulation results indicate that for the Ag@TiO2 core–shell nanostructures, photo-generated electrons transfer readily from the external TiO2 layer to the internal Ag layer with heavy accumulation compared to those doping Ag on TiO2 surfaces, which may reduce the recombination of e−–h+ pairs and thus enhance the photocatalytic efficiency. The findings may open a new strategy to synthesize TiO2-based photocatalysts with highly enhanced efficiency for environmental remediation applications.

Facile synthesis of silica–titania core–shell microsphere and their optical transmission spectra

SiO2–TiO2 core–shell microspheres are prepared by the liquid-phase deposition method, in which anatase TiO2 are shells and SiO2 sphere as cores. The positions of the transmittance peak of the water suspension for SiO2–TiO2 core–shell microspheres are moving toward the long wave number. The red-shift is maybe caused by the variation in the TiO2 shell thickness.

AgBr@Ag/TiO2 core–shell composite with excellent visible light photocatalytic activity and hydrothermal stability

[email protected]/TiO2 core–shell photocatalysts were fabricated by a facile green route. TiO2 was uniformly coated on the surface of cubic AgBr, making [email protected]/TiO2 core–shell photocatalyst show excellent hydrothermal stability. Beneficial from that Ag nanoparticles and AgBr can respond to visible light and core–shell structure can effectively separate the photogenerated electrons and holes, [email protected]/TiO2 core–shell composites exhibited outstanding visible light photocatalytic activity for the degradation of acid orange 7. The activity of [email protected]/TiO2 is related to the thickness of TiO2 shell, and the optimal shell thickness for obtaining the highest activity is 10 nm.

Effect of TiO2 shell layer prepared by wet-chemical method on the photovoltaic performance of ZnO nanowires arrays-based quantum dot sensitized solar cells

TiO2 shell layer on the surface of ZnO nanowires (NWs) was synthesized by a layer by layer adsorption and reaction (LBLAR) method. Scanning electron microscopy image shows that the prepared ZnO–TiO2 core–shell NW arrays have a similar morphology with the well-aligned ZnO core NW arrays, providing the LBLAR cycles is controlled within a certain number. The prepared ZnO–TiO2 core–shell NW arrays were sensitized with CdS quantum dots to assemble quantum dots sensitized solar cells. Results indicate that a dramatic increase in open-circuit voltage and fill factor is achieved with an introduction of the TiO2 shell layer with a thickness of about 7nm, resulting in a substantial improvement of the overall energy conversion efficiency. A rapid electron transfer from the CdS QDs to the ZnO NWs and a reduced electron recombination rate due to the energy barrier occurred at the interface between the ZnO core and the TiO2 shell are believed to contribute to the improved performance of the solar cells based on the ZnO–TiO2 core–shell NW arrays. In addition, effects of the TiO2 shell thickness on the performance of the as-fabricated devices are also discussed in detail.

Dye-sensitized Solar Cells Employing a SnO2-TiO2 Core-shell Structure Made by Atomic Layer Deposition

This paper describes the synthesis and characterization of core-shell structures, based on SnO2 and TiO2, for use in dye-sensitized solar cells (DSC). Atomic layer deposition is employed to control and vary the thickness of the TiO2 shell. Increasing the TiO2 shell thickness to 2 nm improved the device performance of liquid electrolyte-based DSC from 0.7% to 3.5%. The increase in efficiency originates from a higher open-circuit potential and a higher short-circuit current, as well as from an improvement in the electron lifetime. SnO2-TiO2 core-shell DSC devices retain their photovoltage in darkness for longer than 500 seconds, demonstrating that the electrons are contained in the core material. Finally core-shell structures were used for solid-state DSC applications using the hole transporting material 2,2',7,7',-tetrakis(N, N-di-p-methoxyphenyl-amine)-9,9',-spirofluorene. Similar improvements in device performance were obtained for solid-state DSC devices.

Facile Synthesis of ZnO/TiO<SUB>2</SUB> Core–Shell Nanostructures and Their Photocatalytic Activities

We reveal a new strategy for synthesizing ZnO/TiO2 core-shell nanostructures with different TiO2 shell thickness by wet chemical method. This is a facile and rapid process, requires inexpensive precursors with excellent fidelity. The thickness of a typical core-shell nanostructure ranges from 20-50 nm in size with TiO2 shell thickness of 3-6 nm which were confirmed by Transmission electron microscopy (TEM). X-ray diffraction peaks intensity of TiO2 gradually increased while we increase precursor ratio which confirmed the increase of shell thickness. X-ray photoelectron spectroscopy (XPS) results indicated that zinc ions did not enter TiO, lattice and more likely to bonded with oxygen atoms to form TiO2 coupled on the surface of ZnO. However, the PL intensity gradually increased with the increase of the TiO2 shell thickness, indicating charge transfer between the two materials of the ZnO/TiO2 core-shell nanostructures. Further investigation, revealed that the core-shell nanostructures possessed significantly higher solar light photocatalytic activity which was twice than that of original 1-D ZnO nanostructures. The mechanism of the optimal TiO2 shell thickness to reach the maximum photocatalytic activity in the ZnO/TiO2 core-shell nanostructures are proposed and discussed. It is believed that this facile, rapid wet chemical process is scalable and can be applied to synthesize other (oxide/oxide) core-shell nanostructures for various applications.

Synthesis of thermally stable Ag@TiO2 core–shell nanoprisms and plasmon–enhanced optical properties for a P3HT thin film

We develop a facile method to synthesize Ag@TiO2 core–shell nanoprisms (NPs) with a tunable shell thickness through a simple sol–gel route. The thickness of the TiO2 shell can be precisely tuned from 1 to 15 nm via changing the reaction time and amount of TiO2 sol–gel precursor. The localized surface plasmon resonance (LSPR) absorption band shows a red-shift of over a hundred nanometers with the increasing TiO2 shell thickness. The thermal stability of the Ag NPs is significantly improved due to the introduction of the TiO2 shell. We investigate the enhanced absorption and fluorescence of poly(3-hexylthiophene) (P3HT) via coating bare Ag and Ag@TiO2 core–shell NPs with P3HT. A similar absorption enhancement indicates that the LSPR absorption enhancement is not affected by the ultra-thin TiO2 shell. Weak and significant fluorescence enhancements are observed for the P3HT hybrid film with bare Ag NPs and Ag@TiO2 core–shell NPs, respectively. The bare Ag NPs work as both an enhancement element and a recombination center, which quench the P3HT fluorescence to some degree. The recombination of the charge carriers is effectively depressed by introducing the ultra-thin TiO2 shell, which blocks the hole transfer to the Ag NPs.

Enhanced visible light photocatalytic activity of interlayer-isolated triplex Ag@SiO2@TiO2 core–shell nanoparticles

Herein, we demonstrate the design and fabrication of a well dispersed triplex Ag@SiO2@TiO2 core-shell photocatalyst, which shows enhanced visible light photocatalytic activity due to the plasmonic field of the inner Ag core. The SiO2 interlayer is coated on the Ag core by a sol-gel process to prevent oxidation of Ag and adjusting the plasmonic field. The Ag@SiO2@TiO2 nanoparticles with systematic variation of the SiO2 interlayer thickness of 2, 4, 8, 20 nm and TiO2 shell thickness of 2, 10, 20, 40 nm are prepared. The enhancement of the photocatalytic efficiency increases with decreased SiO2 thickness. Nanoparticles with a 2 nm SiO2 interlayer and a 20 nm TiO2 shell exhibited the best photocatalytic performance, ca. 31 times larger in photocatalytic activity and ca. 38 times larger in photocurrent density than P25 under visible light. A brief mechanism relating the plasmon resonance energy transfer from Ag to TiO2 and scattering is proposed. Such an intriguing photocatalyst may find significant applications in various fields.

Effect of the TiO2 shell thickness on the photocatalytic activity with ZnO/TiO2 core/shell nanorod microspheres

TiO2 shell has been fabricated directly on the surface ZnO nanorod microspheres by thermal decomposition of tetrabutyl titanate in octadecane. The thickness of the coverage with TiO2 was controlled by the amount of tetrabutyl titanate added. The core/shell nanorods have anatase TiO2 shells after annealed at 873 K in air. This method enables us to tailor the thickness of TiO2 shell for desired photooxidation application in phenol degradation. ZnO nanorods showed a relatively low efficiency in the photooxidation reaction of phenol. After coating atanase TiO2, the photocatalytic activity of the ZnO/TiO2 core/shell nanocomposites was significantly enhanced in photocatalytic degradation of phenol. It was also found that the thickness of the TiO2 shell affected the catalytic efficiency of ZnO/TiO2 core/shell nanorod microspheres.

A Versatile Kinetics-Controlled Coating Method To Construct Uniform Porous TiO2 Shells for Multifunctional Core–Shell Structures

The development of a simple and reproducible route to prepare uniform core@TiO(2) structures is urgent for realizing multifunctional responses and harnessing multiple interfaces for new or enhanced functionalities. Here, we report a versatile kinetics-controlled coating method to construct uniform porous TiO(2) shells for multifunctional core-shell structures. By simply controlling the kinetics of hydrolysis and condensation of tetrabutyl titanate (TBOT) in ethanol/ammonia mixtures, uniform porous TiO(2) shell core-shell structures can be prepared with variable diameter, geometry, and composition as a core (e.g., α-Fe(2)O(3) ellipsoids, Fe(3)O(4) spheres, SiO(2) spheres, graphene oxide nanosheets, and carbon nanospheres). This method is very simple and reproducible, yet important, which allows an easy control over the thickness of TiO(2) shells from 0 to ~25, ~45, and ~70 nm. Moreover, the TiO(2) shells possess large mesoporosities and a uniform pore size of ~2.5 nm, and can be easily crystallized into anatase phase without changing the uniform core-shell structures.

Synthesis and Upconversion Luminescence of NaYF4:Yb, Tm/TiO2 Core/Shell Nanoparticles with Controllable Shell Thickness

NaYF4:Yb, Tm/TiO2 core/shell nanoparticles were synthesized by a two-step method. First, the NaYF4:Yb, Tm nanocrystals were prepared using solvothermal technology; then, TiO2 shells were deposited on the nanocrystals by the hydrolysis of titanium ethoxide (TEOT) to form core/shell structures. By controlling the reaction time, we can adjust the thickness of TiO2 shell and thereby the weight percentage of TiO2 in the core/shell nanoparticles. The effect of shell thickness on the upconversion fluorescence of NaYF4:Yb, Tm nanocrystals was investigated in detail.