Mesoporous TiO2 Hollow Spheres Research Articles

Water-based epoxy coatings with pH-sensitive TiO2 containers for active corrosion protection of carbon steel

ABSTRACT Smart containers can be produced with polyelectrolyte multilayers that can release inhibitors in response to environmental changes at the coating defects. In this study, mesoporous TiO2 hollow spheres were adopted as carriers for the encapsulation of corrosion inhibitor. The inhibitor-loaded TiO2 containers were modified by polyelectrolyte shells using layer-by-layer self-assembly technology. The release behaviour of the encapsulated inhibitor was investigated using UV–visible spectroscopy. Corrosion protection performance of the epoxy coating with polyelectrolyte-modified TiO2 containers was studied using electrochemical impedance spectroscopy and scanning Kelvin probe (SKP) techniques. Epoxy coating with the polyelectrolyte-modified TiO2 containers provided better barrier properties than that of the blank coating. Waterborne epoxy coating impregnated with the polyelectrolyte-modified TiO2 containers presented a significant self-healing effect after immersion in 0.5 M NaCl solution from the SKP results.

Size controllable synthesis and photocatalytic performance of mesoporous TiO2 hollow spheres

Hollow mesoporous TiO2 spheres (THs) were prepared via template-directed deposition of TiO2 nanoparticles on the surface of carbon spheres. The carbon spheres were used as hard templates. Their diameters were controlled by pH adjustment prior to a hydrothermal process. Physical properties, such as crystallinity, optical characteristics, microstructure and surface morphology of the samples were characterized. The results showed that the diameter of the carbon template could be well controlled in the range of 397–729 nm by adjusting the initial pH value of the dextrose solution from 3 to 10. Hollow TiO2 spheres with average diameters ranging from 171 to 668 nm and shell thicknesses ranging from 28 to 47 nm formed by heat treatment at 450 °C. The photocatalytic performance of hollow TiO2 spheres and TiO2 nanoparticles was examined under UVA irradiation using a methyl orange aqueous solution as an artificial dye. The study revealed that the THs synthesized using a dextrose solution at pH 7 had a higher photocatalytic activity compared to other samples since it had the lowest shell thickness and the proper optical band gap of 3.12 eV with the longest lifetime of electron-hole pair separation.

Non-aqueous preparation of anatase TiO2 hollow microspheres for efficient dye-sensitized solar cells

TiO2 hollow spheres are fabricated by a facile and template-free approach, which is efficient, cost-saving and favorable for large scale production. The as-prepared TiO2 hollow spheres with diameters ranging from 1 to 1.5 μm and a shell thickness of 150 nm are formed by the self-assembly of nanoparticles with a size of about 12 nm. The mesoporous TiO2 hollow spheres possess a high specific surface area up to 166.2 m2 g−1. TiO2 hollow spheres show superior light trapping characteristics and significantly improve the light scattering ability. The formation of hollow structure is interpreted by the Ostwald ripening mechanism. By employing a double-layered photoanode made of the as-prepared TiO2 hollow spheres as the overlayer and P25 as the bottom layer, the dye-sensitized solar cell achieved a power conversion efficiency of 7.90%, which is ascribed to the enhanced dye loading and light scattering ability of TiO2 hollow spheres.

Carbon Quantum Dots Deposed on TiO2 Hollow Spheres for Lithium-Ion Battery Anodes

Lithium-ion batteries (LIBs) have been studied for decades and play an important part in many of our daily activities. However, the demand for higher energy capacity and power density continues to increase, particularly in applications such as electric vehicles (EVs). To satisfy the demands of applications operating at high currents and high power, the development of electrode materials with high power density is required. Owing to its abundance, long cycle life, and low cost, titanium dioxide (TiO2) has been intensively investigated as an anode material. Moreover, TiO2–based anodes exhibit two advantageous properties: 1) a relatively high lithium insertion/extraction voltage (higher than 1.5 V vs. Li+/Li); and, 2) the prevention of lithium plating on the anode. Both characteristics improve the safety of the batteries compared to the use of a lithium metal anode. However, because of the low conductivity of TiO2, it shows poor performance as an anode material for lithium ion batteries. To overcome this limitation, graphene substrates can be used to boost the electrochemical performance of TiO2 since they can enhance the electronic conductivity in the electrode. Unfortunately, the drastic volume expansion and disintegration of graphene surface during charge/discharge is a main obstacle to this approach. Therefore, the particle size and dispersion of graphene substrates are key factors for improving anode conductivity and reliability. Herein, we report a strategy to improve the electrochemical performance of TiO2 and prevent the volume expansion suffered by graphene substrates by combining TiO2 hollow spheres with carbon quantum dots (CQDs) that possess high conductivity and good dispersion. Mesoporous TiO2 hollow spheres are prepared by a sol-gel method using SiO2 spheres as sacrificial templates. The TiO2 hollow spheres provide not only the porosity, but also the large surface area needed to enhance the attachment of CQDs. The CQDs are attached on the surface of TiO2 hollow spheres by a hydrothermal treatment (CQDs@TiO2). These hybrid nanoparticles exhibit higher conductivity and less volume expansion due to their porous . The size of the CQDs@TiO2 was determined to be about 200 nm by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The crystallinity of CQDs@TiO­2 were confirmed by X-ray diffraction (XRD), showing anatase crystal structure. The surface area and pore size distributionwere characterized CR2032-type coin cells are assembled by using the CQDs@TiO2 active materials and LiFePO4 (as the cathode material). Electrochemical properties are characterized by cycling under different C-rates and charging/discharging profiles.

TiO2 hollow spheres as a novel antibiotic carrier for the direct delivery of gentamicin

The TiO2 hollow spheres were synthesized using a green, cheap, and easy process, in which carbonaceous spheres were chosen as the removable template. The prepared materials were characterized by X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDX), Atomic force microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) analysis. According to the results, the obtained mesoporous TiO2 hollow spheres demonstrated an external diameters less than 200 nm with shell thickness around 40 nm. The antibacterial activities of the TiO2 hollow spheres were evaluated against gram-positive (Bacillus subtilis and Staphylococcus aureus) and gram-negative (Escherichia coli and Pseudomonas aeruginosa). No antibacterial activity was found for TiO2 hollow spheres in the used concentrations. TiO2 hollow spheres were loaded with gentamycin as a selected antibiotic to magnify their benefits in biomedical applications. TiO2 hollow spheres exhibited good antibiotic carrier activity for the direct delivery of gentamicin, which was attributed to interaction between gentamicin and surface due to their larger specific surface area, more abundant porous structure, and their spherical morphology. The application of TiO2 hollow spheres as gentamicin carrier undoubtedly opens an avenue to use hollow sphere materials in other drug delivery applications.

Urchinlike Shells of TiO2 Hollow Spheres for Improving the Fire Safety of Epoxy Resin

Titanium dioxide (TiO2) is widely studied because of its excellent properties, which make TiO2 materials suitable for various applications. Here we introduce TiO2 particles with different hierarchical structures which can improve the fire safety of epoxy resin (EP). Both amorphous hydrous TiO2 solid spheres and urchinlike mesoporous TiO2 hollow spheres (UMTHS) can enhance the thermal stability of EP composites. Moreover, cone test results demonstrate that EP/UMTHS with a 2 wt % loading has the lowest heat release rate, total heat release, smoke production rate, and total smoke production values among all the samples. The following plausible mechanism is proposed: urchinlike shells of UMTHS come into contact with each other during the stirring process and partly form a larger shell structure through a fusion process. The physical barrier formed by the fused shell can both shield the composites from external radiation and postpone the transfer of heat and flammable pyrolysis gases.

Synthesis and Characterization of N-Doped Porous TiO2 Hollow Spheres and Their Photocatalytic and Optical Properties

Three kinds of N-doped mesoporous TiO2 hollow spheres with different N-doping contents, surface area, and pore size distributions were prepared based on a sol–gel synthesis and combined with a calcination process. Melamine formaldehyde (MF) microspheres have been used as sacrificial template and cetyltrimethyl ammonium bromide (CTAB) or polyvinylpyrrolidone (PVP) was selected as pore-directing agent. Core–shell intermediate spheres of titania-coated MF with diameters of 1.2–1.6 μm were fabricated by varying the volume concentration of TiO2 precursor from 1 to 3 vol %. By calcining the core–shell composite spheres at 500 °C for 3 h in air, an in situ N-doping process occurred upon the decomposition of the MF template and CTAB or PVP pore-directing surfactant. N-doped mesoporous TiO2 hollow spheres with sizes in the range of 0.4–1.2 μm and shell thickness from 40 to 110 nm were obtained. The composition and N-doping content, thermal stability, morphology, surface area and pore size distribution, wall thickness, photocatalytic activities, and optical properties of the mesoporous TiO2 hollow spheres derived from different conditions were investigated and compared based on Fourier-transformation infrared (FTIR), SEM, TEM, thermogravimetric analysis (TGA), nitrogen adsorption–desorption, and UV–vis spectrophotoscopy techniques. The influences of particle size, N-doping, porous, and hollow characteristics of the TiO2 hollow spheres on their photocatalytic activities and optical properties have been studied and discussed based on the composition analysis, structure characterization, and optical property investigation of these hollow spherical TiO2 matrices.

Designed fabrication of fluorine-doped carbon coated mesoporous TiO2 hollow spheres for improved lithium storage

In this manuscript, we demonstrated a facile route for the controllable design of “Fluorine (F)-doped carbon” (C/F)-treated TiO2 hollow spheres with mesoporous shells (MHTO-C/F). The fabrication of this distinct mesoporous hollow structures and the C/F coating could effectively improve the electrolyte permeability and architectural stability, as well as electrical conductivity and lithium ion mobility. As anticipated, MHTO-C/F has several remarkable electrochemical properties, such as a high specific reversible capacity of 252mAhg−1, outstanding cycling stability of more than 210mAhg−1 after 100 cycles at 0.5C, and good rate performance of around 123mAhg−1 at 5C (1C=168mAg−1). These properties are highly beneficial for lithium storage.

Preparation and characterization of N-doped visible-light-responsive mesoporous TiO2 hollow spheres

Visible-light-responsive N-doped TiO2 mesoporous hollow spheres were prepared by acid-catalyzed hydrolysis, using carbon spheres obtained by glucose hydrothermal carbonization as a hard template. The spheres were characterized using scanning electron microscopy, transmission electron microscopy, N2 adsorption–desorption isotherms, X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. The effects of the N content and calcination temperature on the morphology and photocatalytic activity of TiO2 were investigated. A visible-light response was obtained with TiO2 hollow spheres of diameter 700–850nm, shell thickness 100nm, and a bimodal mesoporosity concentrated at 4–6 and 12–14nm. Phenol degradation of 79.6% was achieved using a catalyst consisting of TiO2 hollow spheres prepared with a Ti:N mass ratio of 1:0.5, and calcined at 600°C.

Large‐scale Synthesis of Urchin‐like Mesoporous TiO2 Hollow Spheres by Targeted Etching and Their Photoelectrochemical Properties

A versatile targeted etching strategy is developed for the large‐scale synthesis of urchin‐like mesoporous TiO2 hollow spheres (UMTHS) with tunable particle size. Its key feature is the use of a low‐temperature hydrothermal reaction of surface‐fluorinated, amorphous, hydrous TiO2 solid spheres (AHTSS) under the protection of a polyvinylpyrrolidone (PVP) coating. With the confinement of PVP and water penetration, the highly porous AHTSS are selectively etched and hollowed by fluoride without destroying their spherical morphology. Meanwhile TiO2 hydrates are gradually crystallized and their growth is preferentially along anatase (101) planes, reconstructing an urchin‐like shell consisting of numerous radially arranged single‐crystal anatase nanothorns. Complex hollow structures, such as core–shell and yolk–shell structures, can also be easily synthesized via additional protection of the interior by pre‐filling AHTSS with polyethylene glycol (PEG). The hollowing transformation is elucidated by the synergetic effect of etching, PVP coating, low hydrothermal reaction temperature, and the unique microstructure of AHTSS. The synthesized UMTHS with a large surface area of up to 128.6 m2 g‐1 show excellent light‐harvesting properties and present superior performances in photocatalytic removal of gaseous nitric oxide (NO) and photoelectrochemical solar energy conversion as photoanodes for dye‐sensitized mesoscopic solar cells.

Preparation of TiO2 hollow spheres for DSSC photoanodes

High crystallinity mesoporous TiO2 hollow spheres (MHS-TiO2) were prepared using the mesoporous carbon hollow sphere template. The MHS-TiO2 contains mainly nanostructured anatase. The mesopore of the MHS-TiO2 has a pore opening in the range of 400–600nm. The refined extended X-ray absorption fine structure spectra indicate that the MHS-TiO2 possesses less the 1st-shell Ti–O coordination numbers than the nano-TiO2. More surface active species (A2 ((Ti=O)O4)) on the MHS-TiO2 are also observed by the component fitted X-ray absorption near edge structure spectroscopy. The MHS-TiO2 photoanode has a better DSSC conversion efficiency than the nano-TiO2 one by at least 40%. Note that the N3 dye molecules are accessible to the mesopores of the MHS-TiO2, and the loading time for N3 can be reduced by at least 70% if compared with those of the nano-TiO2.

Au nanoparticles embedded into the inner wall of TiO2 hollow spheres as a nanoreactor with superb thermal stability

A new nanoreactor-type composite catalyst with Au NPs embedded into the inner wall of the mesoporous TiO2 hollow spheres resulted in an enhanced synergistic effect and superb thermal stability of highly dispersed Au NPs.

Mesoporous titania hollow spheres applied as scattering layers in quantum dots sensitized solar cells

Quantum dots sensitized nanocrystalline TiO2 solar cells (QDSSCs) have attracted great attention for its promising prospects. In order to enhance the effective light absorption path length in the photoanode, a scattering layer is often applied on the back of the transparent absorption layer. Compared with conventional scattering layer films composed of 20 nm and 300 nm TiO2 nanocrystalline, submicrometer-size mesoporous TiO2 hollow spheres are of great interest due to its lower fabrication temperature and hierarchical pore structures. Here we present a novel solvothermal method to prepare mesoporous anatase TiO2 hollow spheres via a hydrophilic template/non-polar solvent interface reaction with carbon sphere as templates, which is easy to control the grain and pore size as well as the shell thickness of the hollow spheres. The TiO2 hollow spheres in average size of 320–330 nm have been applied as the scattering layer materials in CdSe QDSSCs grown by successive ionic layer adsorption and reaction, and a power conversion efficiency of ca. 3.2% has been obtained. The efficiency is higher by 28% than that of the QDSSCs with the scattering layers composed of 20 nm and 300 nm TiO2 particles due to its much higher optical reflectance and longer electron lifetime resulted from its fast diffusion of the electrolyte and lower CdSe loading in the scattering layer. It is indicated that high QDs loading in the scattering layers can cause the downwards displacement of the TiO2 conduction band and lead to lower electron lifetime for the QDSSCs with alkali polysulfide as electrolyte, which was different from the conventional dye-sensitized solar cells.

One-pot template-free preparation of mesoporous TiO2 hollow spheres and their photocatalytic activity

Mesoporous TiO2 hollow spheres were prepared in a solvothermal process, which did not involve any templates and surfactants. Meanwhile, the photocatalytic activity of TiO2 hollow spheres was studied using methyl orange as a probe. The results indicate that the anatase TiO2 hollow spheres with mesoporous walls and high specific surface area (141m2g−1) can be obtained using this simple method. The mean diameter and wall thickness of spheres are about 700nm and 90nm, respectively. Moreover, the as-prepared TiO2 hollow spheres display high photocatalytic activity with 98% of degradation ratio of methyl orange after 30min irradiation.

Facile Synthesis of Mesoporous TiO2 Spheres with Hollow Interiors

The Mesoporous TiO2 hollow spheres are synthesized by a solvothermal reaction without any surfactant and template. The reaction conditions such as reaction temperature, type of precursor, solvent used and their influence on the synthesis of TiO2 hollow spheres are investigated. The synthesized TiO2 hollow spheres are characterized by X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), focused ion beam (FIB) SEM, Barrett-Emmett-Teller (BET) surface areas, and UV-visible diffused reflectance spectroscopy. The synthesized TiO2 spheres have obtained different diameters ranging from 700 nm to 1.79 μm at different reaction temperatures. The shell is composed of numerous single crystalline nanoparticles. The morphology and interiors of the spheres strongly depend upon the experimental parameters such as reaction temperature and a kind of solvent. Especially, interiors of TiO2 hollow spheres such as mesoporous, double shell and single wall structures at various reaction temperatures are discussed with the aid of TEM and FIB SEM measurements.