Porous TiO2 Microspheres Research Articles

Enhancing Electrochemical Performances of TiO2 Porous Microspheres through Hybridizing with FeTiO3 and Nanocarbon

The carbon-coated TiO2 (TiO2@C) and FeTiO3 (TiO2/FeTiO3@C) hybrid porous microspheres with a specific surface area of 35.1 m2g−1 have been successfully synthesized by carbonizing the mixture of pyrrole with lab-made TiO2/Fe2O3 porous microspheres. The as-prepared TiO2/FeTiO3@C porous electrode material possessed a reversible capacity of 441.5 mAh g−1 after 300 cycles at a current density of 100mAg−1 and a coulombic efficiency of 99%. Comparing with TiO2, TiO2@C, and TiO2/Fe2O3 porous microspheres, the TiO2/FeTiO3@C porous composites exhibited superior cycling and rate performances, which are rooted in the synergistic effect that generated by little volume variation of TiO2 matrix, high capacity of FeTiO3 and good electrical conductivity of carbon coating (with a thickness of 2–5nm deposited on the surface and inner wall of pores) during the charge/discharge processes.

Synthesis of polyaniline/HF partially etched-hierarchical porous TiO2 microspheres composite with high electrochemical performance for supercapacitors

A novel electrode material of polyaniline/HF partially etched-hierarchical porous TiO2 microspheres (PANI/F-HPTM) composite has been designed and synthesized by the combination of graft polymerization of PANI on the surface of HPTM and subsequent partially etch HPTM using HF. The preparation process is systematically investigated by Fourier transform infrared spectroscopy (FTIR), energy-dispersive spectroscopy analysis (EDS), and X-ray diffraction (XRD). The surface morphology is examined by field-emission scanning electron microscopy (FESEM). The capacitive behaviors are characterized by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD). The unique structure design and partially etched strategy make the composite exhibits desirable electrochemical performance. The maximum specific capacitance of PANI/F-HPTM is 497.6 F g−1 at a current density of 0.7 A g−1, and the specific capacitance retention rate is 81.1 % as the current density increasing from 0.7 A to 14 A g−1. In addition, almost 100 % of its initial specific capacitance can retain after charge/discharge for 1000 cycles. These results demonstrate that partial etching is a good strategy and HPTM are promising templates to prepare high-performance electrode materials for supercapacitors.

Defect-Induced Yellow Color in Nb-Doped TiO2 and Its Impact on Visible-Light Photocatalysis

Doping TiO2 photocatalysts with foreign ions has been deemed an effective method to enhance visible light absorption and thus increase their photocatalytic performance. Herein, we report that Nb-doped TiO2 porous microspheres prepared by ultrasonic spray pyrolysis of peroxide precursor solution are yellow, and the yellow coloration becomes increasingly conspicuous with increasing Nb dopant concentration. Comprehensive spectral analyses show that both surface peroxo species and bulk Ti3+ are introduced into TiO2 microsphere samples together by charge compensation with Nb5+ dopant and are responsible for the coloration of TiO2. The Nb-doped microspheres show higher photocatalytic rates than undoped TiO2 for the degradation of gaseous acetaldehyde under visible irradiation but slower rates under ultraviolet light. Moreover, the photocatalytic mineralization rates of acetaldehyde to CO2 are lowered with Nb doping under both visible and UV irradiation. Correlation between the results of surface photovoltage sp...

Constructing hierarchical porous titania microspheres from titania nanosheets with exposed (001) facets for dye-sensitized solar cells

In this paper, a facile approach for constructing hierarchical porous TiO2 microspheres from TiO2 nanosheets with exposed (001) facets has been demonstrated, which are synthesized using HF generated in situ by reaction of (NH4)2TiF6 and H3BO3 as a capping and stabilizing agent without introducing any additional HF or HCl under hydrothermal condition. The photoanode constructed with hierarchical porous TiO2 microspheres as top layer exhibits an improved photoelectric conversion efficiency (7.44%), which is about 1.2 times larger as than that of the commercial TiO2 nanoparticles as a benchmark photoanode (6.29%). This result is attributed to the superior light-scattering effect of microspheres, excellent light-reflecting ability of the mirror-like plane (001) facets and effective suppression of the back reaction. Therefore, TiO2 microspheres with exposed (001) facets have the potential applications in the construction of dye-sensitized solar cells.

In vitro apatite formation and drug loading/release of porous TiO2 microspheres prepared by sol-gel processing with different SiO2 nanoparticle contents.

Bioactive titania (TiO2) microparticles can be used as drug-releasing cement fillers for the chemotherapeutic treatment of metastatic bone tumors. Porous anatase-type TiO2 microspheres around 15 μm in diameter were obtained through a sol-gel process involving a water-in-oil emulsion with 30:70 SiO2/H2O weight ratio and subsequent NaOH solution treatment. The water phase consisted of methanol, titanium tetraisopropoxide, diethanolamine, SiO2 nanoparticles, and H2O, while the oil phase consisted of kerosene, Span 80, and Span 60. The resulting microspheres had a high specific surface area of 111.7 m(2)·g(-1). Apatite with a network-like surface structure formed on the surface of the microspheres within 8 days in simulated body fluid. The good apatite-forming ability of the microspheres is attributed to their porous structure and the negative zeta potential of TiO2. The release of rhodamine B, a model for a hydrophilic drug, was rapid for the first 6 h of soaking, but diffusion-controlled thereafter. The burst release in the first 6h is problematic for clinical applications; nonetheless, the present results highlight the potential of porous TiO2 microspheres as drug-releasing cement fillers able to form apatite.

Solar photocatalytic activities of porous Nb-doped TiO2 microspheres by coupling with tungsten oxide

Nb doped TiO2 microspheres modified with WO3 (Nb-TiO2/WO3) was prepared by ultrasonic spray pyrolysis method combined with impregnation method. The microspheres were characterized with SEM, TEM, XRD, BET, photoluminescence and UV–vis absorption spectra. The Nb-doping was observed to extend the spectral absorption of TiO2 into visible spectrum, and the absorption onset was red-shifted for about 88nm compared to pristine TiO2 microspheres. Nb-TiO2/WO3 microspheres do not display a red-shifted absorption edge compared with Nb doped TiO2 microspheres. Under solar irradiation, Nb-TiO2/WO3 microspheres showed higher photocatalytic activity for methylene blue degradation compared with that of pure TiO2 microspheres and Nb doped TiO2 microspheres, which could be ascribed to the extended light absorption range and the suppression of electron-hole pair recombination.

A minky-dot-fabric-shaped composite of porous TiO2microsphere/reduced graphene oxide for lithium ion batteries

We describe a novel strategy for fabrication of a unique minky-dot-fabric-shaped composite of well-organized porous TiO2 microspheres and reduced-graphene-oxide (rGO) sheets used as an anode material in lithium-ion batteries. In this composite, the porous TiO2 microspheres act as hosts for fast and efficient lithium storage while the rGO sheets serve as highly conductive substrates. Such unique structural features assure a large contact area between the electrolyte and the electrode, favorable for the diffusion of electrons and Li+ ions. Moreover, they can accommodate volume changes of the electroactive TiO2 materials readily so as to improve the overall electrical conductivity between the electrodes during electrochemical processes. In electrochemical tests, the TiO2–rGO composites used as anodes in lithium-ion batteries exhibited superior performance with a reversible capacity of 100 mA h g−1 at 10 C for up to 100 cycles, as compared to 58 mA h g−1 at 10 C for up to 100 cycles from pure TiO2, suggesting great potential of this unique composite to function as high-rate lithium-ion battery materials.

Hierarchically porous TiO2microspheres as a high performance anode for lithium-ion batteries

Hierarchically porous rutile TiO2 microspheres composed of nanorods were fabricated by using a facile synthetic route. These materials were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, and scanning and transmission electron microscopy (SEM and TEM). Based on a series of experimental results, a self-assembly process for the formation of the hierarchical microspheres was also proposed. Furthermore, the hierarchically porous rutile TiO2 microspheres were used as the negative electrode material in lithium-ion batteries (LIBs) and demonstrated a large reversible charge–discharge capacity of 160.4 mA h g−1 after 100 cycles at 1 C, which was much greater than commercial rutile TiO2 under the same conditions, indicating that these materials had excellent cycling stability and high rate performance.

Hierarchically porous anatase TiO2microspheres composed of tiny octahedra with enhanced electrochemical properties in lithium-ion batteries

Hierarchical porous anatase TiO2microspheres composed of ultrathin rod-like structures in the radial direction were fabricatedviaa growth model of oriented attachment. They exhibited high rate performance and excellent cycling stability.

Synthesis of a tailored SrTiO3–TiO2microspherical photocatalyst and its photogenerated charge properties

A series of SrTiO3–TiO2 microspheres with different porosities were prepared by a facile hydrothermal reaction method in the presence of Sr(OH)2 and titanium glycolate. The photogenerated charge separation and surface trapping process was studied by surface photovoltage (SPV) spectra and corresponding phase spectra. Compared with one-dimension nanowires, the SrTiO3–TiO2 microspheres show structural advantage in photocatalytic degradation under visible-light. The enhanced photocurrent of Rhodamine B (RhB) sensitized SrTiO3–TiO2 porous microspheres reveals that a photosensitization effect leads to the photodegradation process. According to the experimental results, these SrTiO3–TiO2 porous microspheres have great potential applications in photocatalytic decomposition or optoelectronic devices.

Template-free synthesis of hierarchical porous anatase TiO2 microspheres with carbon coating and their electrochemical properties

Hierarchically porous anatase titanium oxide (TiO2) microspheres were synthesized using a green supercritical methanol route over a very short reaction time of 15min without using templates or surfactants. Primary nano-sized particles with diameters of 20–55nm with organic coverage on the surface were loosely aggregated and formed secondary micron-sized particles 1.0–2.5μm in diameter, creating a porous structure with average pores 9–15nm in diameter. When the as-synthesized microspheres were calcined under a Ar/5% H2 condition, carbonization of the organic groups formed an ultrathin and uniform carbon layer on the nano-sized primary particles with a thickness of 0.5–1nm and reduced some of the Ti4+ to Ti3+. Both the hierarchically porous structure and the conductive layer coating had positive effects by increasing Li ion storage capacity. The prepared TiO2 microspheres exhibited a high reversible discharge capacity of 212.3mAhg−1 at 0.1C, a high-rate performance of 77.9mAhg−1 at 8C, and an excellent capacity retention of >97% at the end of 100 cycles at 1.0C, whereas TiO2 nanoparticles without porous structure and surface modification exhibited lower discharge capacities of 161.8mAhg−1 at 0.1C and 5.2mAhg−1 at 8C, and poorer capacity retention of 26%. The considerable improvement in the electrochemical performance was attributed to the nano-sized TiO2 primary particles, porous structure, and carbon coating and Ti3+ incorporation.

Facile synthesis of porous microspheres composed of TiO2 nanorods with high photocatalytic activity for hydrogen production

A facile, high-yield and reproducible hydrothermal route was developed to synthesize novel well-knit (i.e., solid and compacted) and porous anatase TiO2 microspheres, consisting of morphologically controlled and uniform TiO2 nanorods. Field emission scanning electron microscopy (FE–SEM) and transmission electron microscopy (TEM) revealed that the resulting TiO2 microspheres exhibited a nanoporous structure that was formed by the self-assembled accumulation of uniform nanorods, which is reported here for the first time. The effect of the surfactant type, surfactant amount and other additives such as urea and water on the formation of the microspheres was investigated. X-ray diffraction and N2 adsorption–desorption characterization showed that the synthesized TiO2 microspheres exhibited a high degree of crystallinity with a high surface area (∼103.9m2/g), which was twice larger than that of commercial P25. The synthesized TiO2 microsphere photocatalysts also exhibited superior photocurrent density with a 4.8-fold improvement in photocurrent over the commercial P25. Additionally, these TiO2 microspheres showed good performance in the generation of hydrogen.

Silver-incorporated bicrystalline (anatase/brookite) TiO2 microspheres for CO2 photoreduction with water in the presence of methanol

Ag nanoparticles deposited on porous TiO2 microspheres with controllable Ag valence and TiO2 crystal phase were prepared through a sequential hydrothermal, ultrasonic spray pyrolysis and in situ photoreduction process. The crystal phase of TiO2, i.e., pure anatase (A), an anatase-rich anatase/brookite mixture (AB), or a brookite-rich anatase/brookite mixture (BA), was controlled by varying the hydrothermal reaction environment. The as-prepared Ag/TiO2 was dominated by the Ag(I) species, while Ag(0) was the major Ag species upon in situ photoreduction of the as-prepared Ag(I)/TiO2. The Ag/TiO2 composites were applied as photocatalysts for CO2 reduction with H2O, using methanol as a hole scavenger under UV–vis irradiation. Simultaneous production of hydrogen (H2) and carbon-containing fuels (CO, CH4) was observed. The CH4 and H2 production rates by Ag(0)/TiO2 exhibited a two-fold enhancement compared with Ag(I)/TiO2. The Ag(0)/TiO2 catalysts using TiO2(AB) as the support demonstrated 50% higher activity than using TiO2(A) as the support and more than three times higher activity than using TiO2(BA) and TiO2(P25) as the supports. In addition, the novel in situ photoreduction method of producing Ag(0) nanoparticles was superior to conventional ex situ photo-deposition and wet-impregnation methods, as evidenced by one order of magnitude higher activity of the catalysts prepared by the novel method. The superb activity of the Ag(0)/Ti(AB) catalysts was ascribed to their large surface area, small and well-dispersed Ag(0) nanoparticles, and an enhanced interfacial charge transfer between the anatase and brookite nanocrystals.

Hollow mesoporous frameworks without the annealing process for high-performance lithium–ion batteries: A case for anatase TiO2

Hierarchically porous hollow TiO2 microspheres composed of interconnect nanocrystals have been synthesized by a one-pot hydrothermal method without further thermal annealing. The as-prepared materials are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and electrochemical measurements. FESEM shows that the resultant hierarchical mesoporous TiO2 hollow microspheres (HTMs) comprised mesoporous shells with interconnected anatase nanocrystals. TEM reveals that the interconnected structure of hollow microspheres almost remained unchanged with increasing hydrothermal reaction time. The electrochemical measurements results showed that the initial Li insertion/extraction capacity of the electrodes obtained at 180°C for 15h is 158mAhg−1 and 151mAhg−1 at 5C, respectively. Moreover, in the 100th cycle, the reversible capacity still remains about 131mAhg−1, indicating excellent cycling stability and good high-rate performance. The electrochemical impedance spectroscopy measurements indicated that the surface reaction kinetics of TiO2 nanocrystals were improved significantly, which may be attributed to fast charge transfer in the interconnected TiO2 nanocrystals structure. With the advantages of low cost and ease of processing, these HTMs are not only promising LIBs anode materials but also provide a conceptual route of fabricating oxides electrodes in high-performance LIBs in the future.

Porous TiO2(B)/anatase microspheres with hierarchical nano and microstructures for high-performance lithium-ion batteries

Novel hierarchical porous TiO2(B)/anatase microspheres have been prepared by a facile solvothermal approach and evaluated as anode materials for advanced lithium-ion battery applications. The obtained porous microspheres, with diameters ranging from 2.5 to 5.5μm, are assembled by porous TiO2 nanosheets with the lateral size of a few micrometers and thickness of ~13nm; whilst, the nanosheets are formed by aggregations of nanosized primary TiO2 crystallites (~5–7nm). The hierarchical porous structures are verified by BET test results with a typical type-IV isotherm curve, a high surface area (~186.2m2g−1) and two kinds of pores (~4 and 8.3nm). The hierarchical porous TiO2 microspheres present excellent electrochemical performance with high Li storage capacity and excellent high-rate cycling capability (a specific capacity of 117mAhg−1 at the rate of 4000mAg−1 after 4500 cycles), which might be attributed to the enhanced Li+ diffusion and electronic conductivity induced by the hierarchical microstructures, the TiO2(B)/anatase heterojunction, and the pseudocapacitance of TiO2(B). Such hierarchical porous materials might be promising for applications in advanced power type lithium-ion batteries.

Synthesis and photocatalytic activity of porous anatase TiO2 microspheres composed of {010}-faceted nanobelts

Porous anatase TiO(2) microspheres composed of {010}-faceted nanobelts were synthesized through simple thermal treatment of a titanium glycerolate precursor. The as-prepared TiO(2) nanomaterial was shown to serve as an efficient photocatalyst for H(2) evolution, and its activity was more than twice that of the benchmark P25 TiO(2).

Porous TiO2 microspheres with tunable properties for photocatalytic air purification

The synthesis of highly-crystalline porous TiO2 microspheres is reported using ultrasonic spray pyrolysis (USP) in the presence of colloidal silica as a template. We have exploited the interactions between hot SiO2 template particles surface and TiO2 precursor that occur during reaction inside the droplets, to control the physical and chemical properties of the resulting particles. Varying the SiO2 to titanium precursor molar ratio and the colloidal silica dimension, we obtained porous titania microspheres with tunable morphology, porosity, BET surface area, crystallite size, band-gap, and phase composition. In this regard, we have also observed the preferential formation of anatase vs. rutile with increasing initial surface area of the silica template. The porous TiO2 microspheres were tested in the photocatalytic degradation of nitrogen oxides (NOx) in the gas phase. USP prepared nanostructured titania samples were found to have significantly superior specific activity per surface area compared to a commercial reference sample (P25 by Evonik-Degussa).

Synthesis and visible light photocatalytic properties of polyoxometalate–thionine composite films immobilized on porous TiO2 microspheres

Multilayer films (PW12–TH)n (PW12=PW12O403-, TH=thionine) were immobilized on porous anatase TiO2 microspheres by layer-by-layer (LbL) self-assembly method. The porous structure of TiO2 was confirmed by transmission electron microscopy (TEM). Scanning electron microscopy (SEM) showed that TiO2 template particles had a round shape with an average diameter of 250nm. The composite films were characterized by FTIR spectroscopy, UV diffuse reflectance spectroscopy and XRD spectroscopy. The results confirmed the successful immobilization of (PW12–TH)n composite films onto TiO2 microspheres, and the growth of PW12–TH layer pair was uniform. SEM and TEM were also used to characterize the morphology. When PW12–TH composite films were assembled on the template, the surface became rougher with the increasing number of layer pair. The lattice fringe of TiO2 became weaker when immobilized (PW12–TH)n. The photocatalytic properties of the microspheres toward a rhodamine B (RhB) solution were investigated under visible light irradiation. The combination of TiO2 and PW12 showed an excellent photocatalytic performance. Both TH sensitization and PW12 adsorption played important roles during the process of photocatalysis. Moreover, the catalytic property and reusability of as-prepared catalyst were relevant to the number of PW12–TH bilayer. The kinetics of the photodecomposition to rhodamine B followed the first-order reaction.

Hollow anatase TiO2 porous microspheres with V-shaped channels and exposed (101) facets: Anisotropic etching and photovoltaic properties

Owing to the excellent physical and chemical properties for potential application in multiple fields, design and synthesis of semiconductor titanium dioxide with tailor-made crystal facets and V-shaped porous sturcuctures have attracted great research interest. In this work, we prepared hollow anatase TiO2 microspheres (HTS) with exposed (101) facets and V-shaped channels via a novel anisotropic etching method. The obtained HTS microspheres are constructed by two layers, the inner layer is TiO2 nanoparticles, while the outer layer is composed of single-crystal TiO2 nanosheets with highly exposed (101) facets and V-shaped channels. The cooperative effect of hydrogen peroxide with ammonium fluoride and an anisotropic corrosion process are proposed to understand the formation mechanism. Hydrogen peroxide decomposed to form O2 bubbles, which acted as templates for the formation of TiO2 microspheres with cavities. Fluorine ions were able to promote the formation of anatase (001) facets at the beginning of the reaction and then etch the (001) facets with the reaction progress, leaving highly exposed (101) facets and V-shaped channels along the [001] direction. Due to the unique structure of anatase TiO2 (101) single crystal nanosheets and the strong light scattering effects from the V-shaped channels, the dye-sensitized solar cells (DSSCs) based on our HTS sample have a high open voltage of 0.9 V. The optimized DSSC based on our HTS sample showed an overall light-electron conversion efficiency of 7.05% with a lower dye absorption.

Layered mesoporous nanostructures for enhanced light harvesting in dye-sensitized solar cells

Incident-photon-to-current-conversion efficiency of TiO2 photoanodes is increased significantly in the visible and near infrared range of the electromagnetic spectrum by assembling films that are structured on both micrometer and nanometer length scales. Photoanodes assembled from alternating layers of TiO2 nanoparticles and mesoporous TiO2 microspheres increase the overall power conversion efficiencies of dye-sensitized solar cells by as much as 26%. This increase is due to enhanced light scattering by porous TiO2 microspheres and is achieved without sacrificing the specific surface area.