Controlled fabrication of nanosized TiO2 hollow sphere particles via acid catalytic hydrolysis/hydrothermal treatment

TiO₂ hollow spheres of controlled size were synthesized by combined acid catalytic hydrolysis and hydrothermal treatment, which involves the deposition of an inorganic coating of TiO₂ on the surface of carbon spheres prepared by a hydrothermal method and subsequent removal of the carbon spheres by calcination in air. The obtained TiO₂ hollow spheres were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and powder X-ray diffraction. The results revealed that the size and surface morphology of the TiO₂ hollow spheres can be controlled by adjusting the concentration of the aqueous solution of glucose used to produce the template carbon spheres. Increasing the concentration of the glucose solution increased the average diameter of the TiO₂ hollow spheres from 190 to 300 nm. TiO₂ hollow spheres prepared using a glucose solution with a concentration of 0.7 mol/L are uniform in size with a diameter of 220 nm and shell thickness of 28 nm. The phenol removal rate of the sample prepared by calcination at 600 °C is 1.35 times higher than that of TiO₂ made by the same method without using the carbon template.     

TiO2/SnO2 double-shelled hollow spheres-highly efficient photocatalyst for the degradation of rhodamine B

TiO₂/SnO₂ double-shelled hollow spheres are successfully synthesized by two-step liquid-phase deposition method using carbon sphere templates. The formation process of TiO₂/SnO₂ hollow spheres is discussed. The samples are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and UV–vis absorption spectroscopy. The behavior of photogenerated charges in the TiO₂/SnO₂ heterojunction structures has been investigated through surface photovoltage spectroscopy. The TiO₂/SnO₂ hollow spheres which are realized show significantly enhanced photocatalytic activities, with respect to the cases of SnO₂ and TiO₂ hollow spheres. Furthermore, TiO₂/SnO₂ hollow spheres show good recyclable photocatalytic activities.     

Template-assisted hydrothermal synthesis and photocatalytic activity of novel TiO2 hollow nanostructures

TiO₂ hollow nanostructures were successfully synthesized by a controlled hydrothermal precipitation reaction using Resorcinol–Formaldehyde resin spheres as templates in aqueous solution, and then removal of the RF resins spheres by calcination in air at 450 °C for 4 h. The obtained TiO₂ hollow spheres were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N₂ adsorption–desorption analysis, and UV–visible diffuse reflectance spectroscopy. The photocatalytic activity of the as-prepared samples was evaluated by photocatalytic decolorization of rhodamine B aqueous solution at ambient temperature under UV illumination. The results indicated TiO₂ hollow nanostructures exhibit the excellent photocatalytic activity probably due to the unique hollow micro-architectures.     

Layer-by-layer synthesis of hollow spherical CeO<Subscript>2</Subscript> templated by carbon spheres

CeO₂ hollow spheres were successfully prepared via a layer-by-layer (LBL) method using carbon spheres as sacrificial template and hexamethylenetetramine as precipitating agent. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectrum (XPS) were used for their characterization. The obtained products exhibit hollow spherical structure with a diameter of ca. 250 nm as well as the thin shell about ca. 20 nm composed of various oriented polycrystals, and the Brunauer–Emmett–Teller (BET) surface area was measured to be 126 m² g⁻¹. Calcination temperature is found to be crucial to the integrity of the hollow spheres and has to be below 973 K to achieve well defined hollow spheres. CO conversion was used as a catalytic test reaction revealing that the activity of the hollow spherical products was substantially higher than that of the non-hollow counterpart.     

Synthesis of 3D porous ceramic scaffolds obtained by the sol-gel method with surface morphology modified by hollow spheres for bone tissue engineering applications

In the present work, we modified the surface morphology of 3D porous ceramic scaffolds by incorporating strontium phosphate (SrP) hollow nano-/microspheres with potential application as delivery system for the local release of therapeutic substances. SrP hollow spheres were synthesized by a template-free hydrothermal method. The influence of the reaction temperature, time and concentration of reactants on precipitates' morphology and size were investigated. To obtain a larger number of open hollow spheres, a new methodology was developed consisting of applying a second hydrothermal treatment to spheres by heating them at 120 °C for 24 h. The X-ray diffraction (XRD) analysis indicated that spheres consisted of a main magnesium-substituted strontium phosphate phase ((Sr_0.86Mg_0.14)₃(PO₄)₂). The scanning electron microscopy (SEM) micrographs confirmed that spheres had hollow interiors (～350 nm size) and an average diameter of 850 nm. Spheres had a specific surface area of 30.5 m²/g, a mesoporous shell with an average pore size of 3.8 nm, and a pore volume of 0.14 cm³/g. These characteristics make them promising candidates for drug, cell and protein delivery. For the attachment of spheres to scaffolds’ surface, ceramic structures were immersed in an ethanol solution containing 0.1 g of hollow spheres and kept at 37 °C for 4 h. The scaffolds with incorporated spheres were bioactive after being immersed in simulated body fluid (SBF) for 7 days and spheres were still adhered to their surface after 14 days.     

Preparation of platinum-doped hollow spheres and their electrocatalytic activity in water electrolysis

Pure TiO₂ hollow spheres were prepared by using poly(styrene-methacrylic acid) latex particles as template; thereafter, titania hollow spheres were coated by platinum with an appropriate amount of choloroplatinic acid solution to obtain Pt/TiO₂ catalysts. The morphology and structure of nonstructural Pt/TiO₂ hollow spheres were characterized by BET, XRD, TGA, SEM and TEM analysis. In the samples, a remarkably uniform layer of Pt consisting of particles from 5 to 70 nm in size was formed over TiO₂ hollow spheres. We found the electrocatalytic nature of the samples by cyclic voltammetric experiment in acidic solution. The anodic peak current density of 20 wt% Pt-loaded TiO₂ hollow particles was observed 2.5 times higher than that of 5 wt% Pt/TiO₂ in the same experimental condition. Also, the anodic current density of 20 wt% Pt/TiO₂ hollow spheres calcined at various temperatures followed the order: 400 °C≈500 °C>600 °C. The electrocatalytic activity of the Pt-loaded TiO₂ hollow spheres depends on the amount of atomic platinum present in the sample; a higher concentration of platinum results in a larger current density value in anodic sweep, resulting in more oxygen production during electrolysis. Pt/TiO₂ hollow sphere catalysts have also shown long term electrocatalytic stability in acidic media.     

Hollow microspheres of NiO as anode materials for lithium-ion batteries

NiO hollow spheres are prepared by heating the NiCl₂/resorcinol-formaldehyde (RF) gel in argon at 700 °C for 2 h, and subsequently in oxygen at 700 °C for 2 h. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are employed to characterize the structure and morphology of the as-prepared NiO hollow spheres. These hollow spheres have a diameter of about 2 μm, which are composed of NiO particles of about 200 nm. The electrochemical properties of these NiO hollow spheres are investigated to determine the reversible capacity and cycling performance as anode materials for lithium-ion batteries, and the advantages of their hollow spherical morphology to the electrochemical performance are discussed.     

Dye-sensitized solar cells based on double-layered TiO2 composite films and enhanced photovoltaic performance

Dye-sensitized solar cells (DSSCs) are fabricated based on double-layered composite films of TiO₂ nanoparticles and hollow spheres. The photoelectric conversion performances of DSSCs based on nanoparticles/nanoparticles (PP), hollow spheres/hollow spheres (HH), hollow spheres/nanoparticles (HP), and nanoparticles/hollow spheres (PH) double-layered films are investigated, and their photo-electric conversion efficiencies are 4.33, 4.72, 4.93 and 5.28%, respectively. The enhanced performance of TiO₂ nanoparticles/hollow spheres double-layered composite film solar cells can be attributed to the combined effect of following factors. The light scattering of overlayer hollow spheres enhances harvesting light of the DSSCs and the underlayer TiO₂ nanoparticle layer ensures good electronic contact between film electrode and the F-doped tin oxide (FTO) glass substrate. Furthermore, the high surface areas and pore volume of TiO₂ hollow spheres are respectively beneficial to adsorption of dye molecules and transfer of electrolyte solution.     

Facile fabrication of porous hollow CeO2 microspheres using polystyrene spheres as templates

Porous hollow CeO₂ microspheres were fabricated using negative-charged PS microspheres as templates by a facile method. The hollow CeO₂ microspheres were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and N₂ adsorption?Cdesorption. The results showed that the as-synthesized hollow CeO₂ microspheres are well monodisperse and uniform in size. The porous shells of hollow microspheres are relatively rough and composed of tiny nanoparticles. The external diameter, internal diameter, and shell thickness of hollow CeO₂ microspheres are about 190, 160, and 15?nm, respectively. A possible mechanism for the formation of hollow CeO₂ spheres was also discussed.     

Monodisperse hollow TiO2 spheres for thermal insulation materials: Template-free synthesis,characterization and properties

Hollow TiO₂ spheres were easily fabricated through a template-free solvothermal route only using tetrabutyl titanate (TBT) as raw material and absolute ethanol as solvent. The morphology of hollow TiO₂ spheres was successfully controlled by adjusting the reaction time and reaction temperature. The formation process of hollow TiO₂ spheres includes three steps based on the experimental results: the hydrolysis of TBT to produce Ti(OH)₄ clusters in water formed from an ethanol etherification reaction under high temperature and high pressure, the assembly of Ti(OH)₄ clusters into solid spheres, and the transformation of solid TiO₂ spheres into hollow TiO₂ spheres. Furthermore, the as-prepared hollow TiO₂ spheres exhibited good thermal insulation performance including heat barrier and heat reflection.     

Preparation of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> hollow spheres and their activity in methylene blue photodecomposition

PSA [poly-(styrene-methyl acrylic acid)] latex particle has been taken into account as template material in SiO₂ hollow spheres preparation. TiO₂-doped SiO₂ hollow spheres were obtained by using the appropriate amount of Ti(SO₄)₂ solution on SiO₂ hollow spheres. The photodecomposition of the MB (methylene blue) was evaluated on these TiO₂-doped SiO₂ hollow spheres under UV light irradiation. The catalyst samples were characterized by XRD, UV-DRS, SEM and BET. A TiO₂-doped SiO₂ hollow sphere has shown higher surface area in comparison with pure TiO₂ hollow spheres. The 40 wt% TiO₂-doped SiO₂ hollow sphere has been found as the most active catalyst compared with the others in the process of photodecomposition of MB (methylene blue). The BET surface area of this sample was found to be 377.6 m²g⁻¹. The photodegradation rate of MB using the TiO₂-doped SiO₂ catalyst was much higher than that of pure TiO₂ hollow spheres.     

Hydrothermal synthesis and visible-light photocatalytic activity of α-Fe2O3/TiO2 composite hollow microspheres

Novel α-Fe₂O₃/TiO₂ composite hollow spheres were successfully synthesized by a template-assisted precipitation reaction using urea as a precipitating agent and carbon spheres as templates in a mixed solvent of water and ethanol, and then calcined at 400 °C for 4 h. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption isotherms, and vibrating sample magnetometer. The influence of calcination temperature and the molar ratio of titanium to iron (R) on the photocatalytic activity of the samples was investigated. The results indicated that the composite spheres show magnetic characteristics at room temperature and good photocatalytic activity under visible-light irradiation compare to the single-component α-Fe₂O₃ particles. This method can be further applied to synthesize nanocomposites of magnetic metal oxide and other metal oxide.     

Thermal and Structural Characterization of TiO2 and TiO2/Polymer Micro Hollow Spheres

Micro hollow spheres, synthesized by the coating of tetradecane filled microcapsules with titanium dioxide, are characterized using thermal gravimetry (TG), infrared spectroscopy (IR), Hg‐porosimetry and scanning electron microscopy (SEM). The investigations show a strong dependence of the coating efficiency on the initial pH (precipitation in water or dilute sulfuric acid) as well as the specific capsule surface present in solution. Since the process is dominated by heterogeneous precipitation, the coating efficiency is governed by the counteracting processes of capsule‐TiO₂ and TiO₂‐TiO₂ agglomeration. TG‐IR analysis of the capsules shows the vaporization of tetradecane prior to the decomposition of the polymeric wall to carbon monoxide, carbon dioxide and water. After the extraction or calcination of the core microcapsules, stable inorganic and organic‐inorganic hollow spheres are obtained.     

Preparation of ZnO-TiO2 Composite Fine Particles Using the Ultrasonic Spray Pyrolysis Method and Their Characteristics on Ultraviolet Cutoff

ZnO-TiO₂ composite fine particles were prepared by ultrasonic spray pyrolysis of TiO₂ (anatase) particles suspended in Zn(NO₃)₂ aqueous solution. The morphology and the crystalline phases of fine particles were studied with varying nebulizing solution compositions, reactor temperature, and nitrogen carrier gas flow rate. The aggregate particles produced were spheres of ZnO (wurtzite structure) and TiO₂ (anatase), whose diameters ranged from 0.36 to 0.5μm. These particles were hollow or solid aggregate particles consisting of ultrafine primary particles with diameters ranging from 10 to 100 nm. The crystallinity of prepared particles was improved by increasing the reactor temperature and lowering the flow rate of nitrogen. The largest crystallites were obtained at a solution concentration ratio of C_Zn(NO3)2/C_TiO2 = 10:7. These composite particles showed a combined ultraviolet cutoff characteristic of ultraviolet light shielding in the wide range of wavelength ranging from 200 to 370 nm.     

Synthesis and characterisation of thin-film TiO2 dye-sensitised solar cell

A TiO₂ dye-sensitised solar cell (DSSC) is fabricated and characterised using: X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), electron diffraction X-ray (EDX) analysis, UV–vis spectrometry and a current?voltage (I?V) test. Thicker anatase TiO₂ gives rise to better crystallinity and subsequently leads to better cell efficiency. Mesoporous TiO₂ with a suitable, average pore size results in higher conversion efficiency. Smaller particle sizes lead to higher dye uptake and increase short circuit current density, J_sc. Addition of scattering layer and/or dual TiCl₄ treatment for DSSCs having optimum thickness enhanced their performance. A DSSC having double TiO₂ layers (20 nm+50 nm) with dual TiCl₄ treatment achieved the highest conversion efficiency of 9.78%.     

A facile approach to synthesize SiO2?·?Re2O3 (Re?=?Y,Eu, La,Sm, Tb,Pr) hollow sphere and its application in drug release

Multifunctional SiO₂ · Re₂O₃ (Re = Y, Eu, La, Sm, Tb, Pr) hollow spheres (HSs) have been fabricated using an acidic Re³⁺ ion solution. Under ultraviolet radiation, functional HSs emit different colors of light according to the different rare-earth ions embedded into the shell of SiO₂ hollow spheres. The as-prepared hollow capsules were characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, Brunauer-Emmett-Teller method, scanning electron microscopy, and energy-dispersive spectrometry. Drug loading and release experiments have been carried out using SiO₂ · Eu₂O₃ HSs that acted as drug carriers. The results demonstrate that the multifunctional HSs exhibit a high storage capacity and the ability of retaining drug stability and activity, which indicates that the as-synthesized fluorescent hollow capsules are a potential candidate as drug delivery materials.     

Pulsed laser ablation in liquid synthesis of ZnO/TiO2 nanocomposite catalyst with enhanced photovoltaic and photocatalytic performance

In this work, we employed an impurity-free nanoparticle synthesis technique, known as pulsed laser ablation in liquid (PLAL), to integrate titanium dioxide nanoparticles (TiO₂ NPs) into zinc oxide nanorods (ZnO NRs) with varying relative proportions. The main objective of this integration was to enhance the charge carrier separation of photo-generated electron hole pairs during solar irradiation. For the synthesis process, an Nd:YAG laser at 532 nm wavelength was applied as an ablation source, along with deionized water as a solvent medium in which the precursor materials were dispersed prior to laser irradiation. The nanocomposites were characterized by X-ray diffraction (XRD), UV–vis absorption and in-situ Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM) and field emission scanning electron microscopy (FE-SEM). The synthesized nanocomposites were primarily utilised in two applications: firstly, as a catalyst in the degradation of methyl orange (MO) and secondly, as photo-anode in dye sensitized solar cell (DSSC). Our research has demonstrated that optimal performance was obtained for the nanocomposite containing 10% and 90% (by weight) TiO₂ NPs and ZnO respectively, which we define as the ideal nanocomposite. Relative to pure ZnO, the photo-conversion efficiency of the ideal composite was improved substantially by 63.73%, whilst the photo-degradation rate was enhanced by 3 fold. The oxidation state and the microstructural of the segregated ideal nanocomposite confirms that oxygen vacancy defects were created when perfect surface integration occurs between TiO₂ and ZnO. Nonetheless, we believe that the performance enhancement is predominantly due to the excellent charge carrier separation and fast interfacial electron flow in this nanocomposite.     

Preparation and antibacterial activity of Ag/TiO2-functionalized ceramic tiles

An Ag/TiO₂ coating was deposited onto glazed ceramic tiles by a sol-gel and spraying method at high temperatures. The coating was characterized by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The results showed that silver was present in rutile-TiO₂, and the temperature did not change the phase composition of the samples. The Ag/TiO₂ coating had a higher roughness than the TiO₂ coating. The tape test (D 3359–08) showed that the coatings prepared at 950 °C and 1000 °C had good adhesion to the ceramic tile substrate. The antibacterial activity of the coating was tested by photocatalytic sterilization experiments. The results showed that the Ag/TiO₂ coating had a higher antibacterial activity than the TiO₂ coating, and the sterilization efficiency of Escherichia coli, Staphylococcus aureus, Shigella, and Salmonella exceeded 99.655% under 2 h of visible light irradiation. This research provides a method to create Ag/TiO₂ coatings with good thermal resistance, adhesion, and antibacterial activity. This improves the low photocatalytic activity caused by the anatase-to-rutile transformation of TiO₂ at high temperatures and the poor adhesion at low temperatures.     

Microstructural and Optoelectronic Studies on Polyaniline: TiO2 Nanocomposites

Thin films of polyaniline (PANi) and PANi: titanium oxide (TiO₂) composites have been synthesized by sol–gel spin coating technique. The TiO₂ powder of particle size 50–60 nm was synthesized by the sol–gel technique and the polyaniline was synthesized by the chemical oxidative polymerization of aniline. The composite films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy and the four-probe method. The results were compared with corresponding data on pure polyaniline films. The intensity of diffraction peaks for PANi:TiO₂ composites is lower than that for TiO₂. The characteristic FTIR peaks of pure PANi are observed to shift to a higher wavenumber in PANi:TiO₂ composite, which is attributed to the interaction of TiO₂ particles with PANi molecular chains. The resistivity measurement shows that the molecular chain constitution of polyaniline is the most important carrier in the polyaniline: nano-TiO₂ composite.     

Nanocrystalline carbon–TiO2 hybrid hollow spheres as possible electrodes for solar cells

Nanocrystalline C-doped TiO₂ hybrid hollow spheres were prepared by solvothermal synthesis by controlling calcinations of mixtures of furfural, chitosan or saccharose with titanium isopropoxide. The origin of the carbon influences the texture, the crystalline framework, and the optical and photoelectrochemistry properties of the TiO₂. The results indicate that the carbon–TiO₂ hybrid hollow spheres may be used as TiO₂-based film electrodes for use in solar cells.