Effect of external fields applied during hot-water treatment on the aspect ratio of nanocrystallites formed on SiO<Subscript>2</Subscript>·TiO<Subscript>2</Subscript> coatings derived from sol–gel techniques

SiO₂·TiO₂ coatings were prepared by a sol–gel route. The effect of the external fields including mechanical vibration and electric charge applied during hot-water treatment on titania precipitation at the surface of the coatings was investigated. The shape of the resulting precipitates tended to elongate by applying vibration in a parallel or perpendicular direction, or by applying an electric charge. The organization of titania nanocrystallites possibly occurs because of the concentration gradient of dissolved titania species generated by the external fields during the hot-water treatment. A maximum aspect ratio of 38.1 was achieved for the precipitate prepared by hot-water treatment performed under parallel vibration for 5 h. The shape of the resulting precipitates was also influenced by the content of TiO₂ in the SiO₂·TiO₂ coating, with a smaller proportion of TiO₂ increasing the aspect ratio of the resulting precipitate.     

Performance of Impedimetric Biosensors Based on Anodically Formed Ti/TiO2 Electrodes

The advantages and limitations of impedimetric sensors based on Ti/TiO₂ architectures are described. Titanium dioxide (titania) was potentiostatically formed onto titanium electrodes of 2 mm diameter, at 10 and 30 V in 1 M H₂SO₄. The thickness of the titania layers was ellipsometrically determined to be 30 and 86 nm respectively and they are highly insulating with charge‐transfer resistances in the MΩ range, as they were measured with electrochemical impedance spectroscopy under specific experimental conditions. Low voltage anodization (<10 V) results to amorphous TiO₂, whereas at higher applied voltages (>25 V), anatase is the predominant form. SEM images are indicative of quite smooth, compact coatings without any severe cracks.     

MnO2 multilayer nanosheet clusters evolved from monolayer nanosheets and their predominant electrochemical properties

MnO₂ multilayer nanosheet clusters were prepared via electrochemical deposition route, which shows simpleness and high efficiency. The growth process of MnO₂ multilayer nanosheet clusters was investigated in this paper. The deposited MnO₂ films were characterized by XRD, SEM, TEM, and XPS. In addition, it was also electrochemically characterized by cyclic voltammetry in 1.0 M Na₂SO₄ electrolyte. The MnO₂ multilayer nanosheet clusters show a big specific capacitance, and it can be achieved about 521.5 F g^?1 at 5 mV s^?1. These materials also have a high electrochemical stability.     

Switchable water absorption of paper via liquid flame spray nanoparticle coating

Surface wetting/anti-wetting and liquid absorption are relevant properties of many porous solids including paper and other cellulose-based materials. Here we demonstrate how surface wetting by water and water absorption of commercially available kraft paper can be altered by thin nanoparticle coatings fabricated by liquid flame spray in facile and continuous one-step process. Surface wettability and absorption properties of paper increased with silica and decreased with titania (TiO₂) nanoparticle coatings. Moreover, the water-repellent (superhydrophobic) TiO₂ nanoparticle coated paper could be switched to superhydrophilic and water absorbing by ultraviolet illumination. The experiments revealed that although surface wetting and liquid absorption of nanoparticle coated paper are strongly related to each other, they are two distinct phenomena which do not necessarily correlate. We propose wetting regimes on the nanoparticle coated paper samples on the basis of the experimental observations.     

Oxidation States of Iron in Doped TiO2-SiO2 Sol-Gel Powders: A 57Fe Mössbauer Study

Ceramic coatings obtained by sol-gel routes are more and more attractive for protective purposes. Improved resistance against wet corrosion of steels can be obtained by doping the covering layer with elements like for instance transition ones. It is of major importance to have a clear-cut knowledge of the oxidation state of the doping element, especially after different heat treatments which usually follow the deposition process. Here we report about the oxidation states of 5 wt.% iron doped TiO₂, SiO₂ and mixed sol powders obtained by the sol-gel method with alkoxide precursors added with FeSO₄, 7 H₂O in organic medium. The evolution of the Fe oxidation state versus various heat treatments is followed by ⁵⁷Fe Mössbauer spectrometry supplemented by XRD data. As-dried samples are amorphous and contain ferric Fe cations, with a local distorted oxygen environment. After heating at 500°C during 3 min, ferrous and ferric oxides are evidenced together solely for silica and mixed silica-titania powders, in marked contrast with titania powders where only ferric species exist. The complete ferric state is restored for all samples after annealing at 900°C for one hour.     

Preparation and characterization of SiO2/TiO2 composite microspheres with microporous SiO2 core/mesoporous TiO2 shell

SiO₂/TiO₂ composite microspheres with microporous SiO₂ core/mesoporous TiO₂ shell structures were prepared by hydrolysis of titanium tetrabutylorthotitanate (TTBT) in the presence of microporous silica microspheres using hydroxypropyl cellulose (HPC) as a surface esterification agent and porous template, and then dried and calcined at different temperatures. The as-prepared products were characterized with differential thermal analysis and thermogravimetric (DTA/TG), scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption. The results showed that composite particles were about 1.8 μm in diameter, and had a spherical morphology and a narrow size distribution. Uniform mesoporous titania coatings on the surfaces of microporous silica microspheres could be obtained by adjusting the HPC concentration to an optimal concentration of about 3.2 mmol L⁻¹. The anatase and rutile phase in the SiO₂/TiO₂ composite microspheres began to form at 700 and 900 °C, respectively. At 700 °C, the specific surface area and pore volume of the SiO₂/TiO₂ composite microspheres were 552 and 0.652 mL g⁻¹, respectively. However, at 900 °C, the specific surface area and pore volume significantly decreased due to the phase transformation from anatase to rutile.     

Graphene Nanosheets as a Platform for the 2D Ordering of Metal Oxide Nanoparticles: Mesoporous 2D Aggregate of Anatase TiO2 Nanoparticles with Improved Electrode Performance

Graphene nanosheets are successfully applied as an effective platform for the 2D ordering of metal oxide nanoparticles. Mesoporous 2D aggregates of anatase TiO₂ nanoparticles are synthesized by the heat treatment of the uniformly hybridized nanocomposite of layered titanate–reduced graphene oxide (RGO) at elevated temperatures. The precursor layered titanate–RGO nanocomposite is prepared by self‐assembly of anionic RGO nanosheets and cationic TiO₂ nanosols. The calcination of the as‐prepared layered titanate–RGO nanocomposite at 500 °C induces a structural and morphological change of layered titanate nanoplates into anatase TiO₂ nanoparticles without significant modification of the RGO nanosheet. Increasing the heating temperature to 600 °C gives rise to elimination of the RGO component, leading to the formation of sheetlike porous aggregates of RGO‐free TiO₂ nanoparticles. The nanocomposites calcined at 500–700 °C display promising functionality as negative electrodes for lithium ion batteries. Among the present calcined derivatives, the 2D sheet‐shaped aggregate of TiO₂ nanoparticles obtained from calcination at 600 °C delivers the greatest specific discharge capacity with good capacity retention for all current density conditions applied. Such superior electrode performance of the nanocomposite calcined at 600 °C is attributable both to the improved stability of the crystal structure and crystal morphology of titania and to the enhancement of Li⁺ ion transport through the enlargement of mesopores. The present findings clearly demonstrate the usefulness of RGO nanosheets as a platform for 2D‐ordered superstructures of metal oxide nanoparticles with improved electrode performance.     

Bioactive Ca10(PO4)6(OH)2−TiO2 composite coating prepared by sol-gel process

The sol-gel prepared titania (TiO₂) has recently been demonstrated with a promising bioactivity [1]. It forms a chemical bond with the living bone in the body, although the bonding is not very strong. The present study is intended to improve the bone-bonding ability of the titania gel. The goal is achieved by impregnating the titania with hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂). The processing route includes the following steps: (1) the titania sol solution was prepared; (2) the solution was mixed with fine hydroxyapatite (HA) powders; (3) the mixture was used to produce a coating on a commercial pure titanium (c.p. Ti) or Ti6A14V plate by a dip coating technique; (4) the coating was fired at 400–600°C. The resulting coating is a composite consisting of hydroxyapatite embedded in the matrix of the titania gel. Such HA-TiO₂ composite coating is capable of inducing the hydroxyapatite precipitation from a simulated body fluid. When implanted in femurs of goat, the composite coating shows a bonding with bone. Its bone-bonding strength is twice as high as that of the pure titania gel coating. The results indicate that impregnating with hydroxyapatite is a promising way to increase the bioactivity of the titania gel.     

Zn–HA–TiO2 nanocomposite coatings electrodeposited on a NiTi shape memory alloy

In this work, zinc–hydroxyapatite (Zn–HA) and zinc–hydroxyapatite–titania (Zn–HA–TiO₂) nanocomposite coatings were electrodeposited onto a NiTi shape memory alloy, using a chloride zinc plating bath. The structure of the composite coatings was characterized by X‐ray diffraction, scanning electron microscopy and high‐resolution transmission electron microscopy. According to the results, the Zn–HA–TiO₂ coating exhibited a plate‐like surface morphology, where the addition of the nanoparticles caused to an increase in roughness. It was also found that due to applying a proper stirring procedure during co‐deposition, a homogenous dispersion of the nanoparticles in the coatings was achieved. Also, the addition of the TiO₂ nanoparticles to the Zn–HA–TiO₂ coating enhanced the microhardness and wear resistance. Copyright © 2014 John Wiley & Sons, Ltd.     

Low temperature preparation of anatase TiO2-coated activated carbon

Anatase titania sols were synthesized at low temperature (i.e. 75 °C) by hydrolysis of titaniumn-butoxide in abundant acidic aqueous solution. The prepared TiO₂ nanoparticles were loaded on activated carbon in a rotatory evaporator under vacuum, and then the composite photocatalyst was employed for the removal of phenol from water. The apparent rate constant and quantum yield of the composite photocatalyst enhanced 5 and 2.5 times, respectively, compared to single phase titania. The activated carbon with strong adsorbent activity provided sites for the adsorption of phenol, and the adsorbed phenol migrated continuously onto the surface of TiO₂ particles which were located mainly at the exterior surface of the activated carbon. Some phenol remained adsorbed on the catalyst when no traces of phenol were detected in the water. This adsorbed phenol could be degraded by illuminated titania while maintaining UV-irradiation. The photocatalyst was used for six cycles with degraded rate of phenol still higher than 80%.     

Characterization of Titania/Silica Gel by Means of Low-Pressure Nitrogen Adsorption

Adsorbents synthesized by grafting of titania onto mesoporous silica gel surfaces at different temperatures were studied by means of nitrogen adsorption–desorption and water desorption. The pore size distribution f(R_p) of titania/silica gel depends on the titania concentration (C_TiO2) and the temperature of titania synthesis. Nonuniformity of TiO₂ phase is maximal at a low C_TiO2 value (3.2 wt.% anatase deposited at 473 K), and two peaks of the fractal dimension distribution f(D) are observed at such a concentration of titania, but at larger C_TiO2 values, only one f(D) peak is seen. More ordered filling of pores and adsorption sites by nitrogen, reflecting in the shape of adsorption energy distributions f(E) at different pressures of adsorbate, is observed for adsorbent with titania (rutile+anatase) grafted on silica gel at a higher temperature (673 K).     

Specific intermolecular interactions in a heterogeneous system benzophenone-titanium dioxide

IR spectroscopy methods (experiment, theoretical simulation) have been applied to study the structural features and intermolecular interactions in a two-component heterogeneous nano-size system benzophenone-titanium dioxide (BPh-TiO₂). IR spectra of the sample were recorded at room temperature within the range 400–4000 cm^?1. The spectra display hydrogen bonding determining the intermolecular interactions between titanium dioxide, BPh molecules, and water in the near-surface layers of nanocrystalline TiO₂ particles. IR spectra of free BPh molecules, water, model H-complexes of BPh with water, and the fragment of hydrated titania surface (BPh…HOH and BPh…Ti≡) have been simulated. Experimental and theoretical spectra were analyzed in the region of stretching vibrations of carbonyl, hydroxyl, and other groups sensitive to a variation of intermolecular interactions. It is found that hydrogen bonding in the near-surface layers of nanocrystalline TiO₂ particles in the two-component heterogeneous nanosystem BPh-TiO₂ gives rise to the formation of complexes BPh-O-Ti(OH)-O-, BPh…HOH, along with complexes of-O-Ti(OH)-O-with water and pure water complexes.     

SYNTHESIS OF POLYSTYRENE/TiO2 CORE-SHELL MATERIAL

 TiO₂-coated polystyrene nanoparticles were prepared in a simple way. First, functional PS particles were synthesized by copolymerizing one kind of polymerizable surfactant with styrene. Then the stable dispersions of polystyrene nanoparticles were used as templates, and polystyrene nanoparticles were coated with titania by in situ hydrolysis of tetra-n-butyl titanate (TBT). No surface treatment and centrifugation/redispersion cycle process were needed during the whole experiment. Isolated PS spheres with uniform coatings of titania were obtained when water concentration was lower than a certain level.     

The preparation and characterization of nanostructured TiO2-ZrO2 mixed oxide electrode for efficient dye-sensitized solar cells

The preparation of nanostructured mixed metal oxide based on a sol-gel method with surfactant-assisted mechanism, and its application for dye-sensitized solar cell (DSSC) are reported. The mixed zirconia (ZrO₂) and titania (TiO₂) mesoporous powder possessed larger surface area than the corresponding titania. For the UV action spectra of unsensitized photochemical cell, the mixed zirconia/titania electrode can absorb UV light below 380 nm, corresponding to band gap (E_g) around 3.27 eV, which is higher than that of pure component of titania (). Both of these improved properties, i.e., BET surface area and band gap, contributed to the improvement on a short-circuit photocurrent up to 11%, an open-circuit voltage up to 4%, and a solar energy conversion efficiency up to 17%, for the DSSC fabricated by mesoporous zirconia/titania mixed system when compared to the cell that was fabricated only by nanostructured TiO₂. The cell fabricated by 5 μm thick mixed TiO₂-ZrO₂ electrode gave the short-circuit photocurrent about 13 mA/cm², open-circuit voltage about 600 mV and the conversion efficiency 5.4%.     

Electronic band structure of titania semiconductor nanosheets revealed by electrochemical and photoelectrochemical studies

Electrochemical and photoelectrochemical studies were conducted on self-assembled multilayer films of titania nanosheets on a conductive ITO substrate. Cyclic voltammogram (CV) curves indicated that the titania nanosheet electrode underwent insertion/extraction of Li(+) ions into/from the nanosheet galleries, associated with reduction/oxidation of Ti(4+)/Ti(3+). These processes accompanied reversible changes in UV-vis absorption of the titania nanosheet electrodes. Applying a negative bias of -1.3 V (vs Ag/Ag(+)) and lower brought about absorption reduction where the wavelength is shorter than 323 nm, and vice versa, indicating a flat-band potential of (approximately) -1.3 V and a band gap energy of 3.84 eV. Photocurrents were generated from the titania nanosheet electrodes under a positive bias. The onset potential for photocurrent generation from the titania nanosheet electrodes was around -1.27 V, and the band gap energy estimated from the photocurrent action spectra was 3.82 eV, in excellent agreement with the values obtained from the spectroelectrochemical data. The lack of difference in the band gap energies for titania nanosheet electrodes with different numbers of layers suggests that a nanosheet is electronically isolated in multilayer assemblies without affecting the electronic state of neighboring nanosheets. Similar measurements on the anatase-type TiO(2) electrode revealed that the lower edge of the conduction band for the titania nanosheet is approximately 0.1 V higher than that for anatase, while the upper edge of the valence band is 0.5 V lower.     

NiO/MnO_2分级纳米片阵列复合材料的制备与超电容性能

通过化学浴沉积和水热法在泡沫镍上制备了NiO/MnO_2分级纳米片阵列复合材料,XRD和SEM测试表明NiO纳米片垂直生长在泡沫镍上,交叉形成网状阵列结构;MnO_2纳米介孔泡沫进一步生长在NiO纳米片两侧,与NiO形成了壳核式的复合结构。循环伏安和恒流充放电测试发现,NiO/MnO_2分级纳米片阵列复合材料的电化学性能相比复合前得到明显改善,在1 A·g~(-1)的电流密度下,比电容提高至1 297 F·g~(-1);2 A·g~(-1)下循环1 000次,比电容保持率高达97%,比电容和循环性能的改善是由于分级纳米片阵列复合结构方便了电解液传质,扩大了活性材料与电解液的接触,促进了赝电容反应,提高了NiO和MnO_2的结构稳定性。     

NiO/MnO2分级纳米片阵列复合材料的制备与超电容性能

通过化学浴沉积和水热法在泡沫镍上制备了NiO/MnO₂分级纳米片阵列复合材料,XRD和SEM测试表明NiO纳米片垂直生长在泡沫镍上,交叉形成网状阵列结构;MnO₂纳米介孔泡沫进一步生长在NiO纳米片两侧,与NiO形成了壳核式的复合结构。循环伏安和恒流充放电测试发现,NiO/MnO₂分级纳米片阵列复合材料的电化学性能相比复合前得到明显改善,在1 A·g^-1的电流密度下,比电容提高至1 297 F·g^-1;2 A·g^-1下循环1 000次,比电容保持率高达97%,比电容和循环性能的改善是由于分级纳米片阵列复合结构方便了电解液传质,扩大了活性材料与电解液的接触,促进了赝电容反应,提高了NiO和MnO₂的结构稳定性。     

A Plasma‐Triggered O−S Bond and P−N Junction Near the Surface of a SnS2 Nanosheet Array to Enable Efficient Solar Water Oxidation

A photoelectrochemical (PEC) cell can split water into hydrogen and oxygen with the assistance of solar illumination. However, its application is still limited by excessive bulk carrier recombination and sluggish surface oxygen evolution reaction (OER) kinetics. Taking SnS₂ as an example, a promising layered optoelectronic semiconductor, Ar plasma treatment strategy was used to introduce a SnS/SnS₂ P?N heterojunction and O?S bond near the surface of a SnS₂ nanosheet array, simultaneously increasing the separation efficiency of photogenerated electron–hole pairs in the bulk and lowering the OER overpotential at the surface. The onset potential of the plasma‐treated SnS₂ nanosheet array shifts negatively to 0.16 V, and the photocurrent density at 1.23 V vs. RHE boosts to 2.15 mA cm^?2, which is 7 times that of pristine SnS₂. This work demonstrates a facile plasma treatment strategy to modulate the energy band structure and surface chemical states for improved PEC performance.     

Vibrational spectroscopic study of the antimonate mineral bindheimite Pb2Sb2O6(O,OH)

Raman spectroscopy complimented with infrared spectroscopy has been used to characterise the antimonate mineral bindheimite Pb₂Sb₂O₆(O,OH). The mineral is characterised by an intense Raman band at 656 cm⁻¹ assigned to SbO stretching vibrations. Other lower intensity bands at 664, 749 and 814 cm⁻¹ are also assigned to stretching vibrations. This observation suggests the non-equivalence of SbO units in the structure. Low intensity Raman bands at 293, 312 and 328 cm⁻¹ are assigned to the OSbO bending vibrations. Infrared bands at 979, 1008, 1037 and 1058 cm⁻¹ may be assigned to δOH deformation modes of SbOH units. Infrared bands at 1603 and 1640 cm⁻¹ are assigned to water bending vibrations, suggesting that water is involved in the bindheimite structure. Broad infrared bands centred upon 3250 cm⁻¹ supports this concept. Thus the true formula of bindheimite is questioned and probably should be written as Pb₂Sb₂O₆(O,OH,H₂O).     

Single crystal Raman study of potassium oxalate monohydrate,K2C2O4. H2O,and potassium oxalate monodeuterate,K2C2O4. D2O

Raman spectra of poly crystalline and single crystal K₂C₂O₄. H₂O and K₂C₂O₄. D₂O have been recorded at room temperature. From an earlier neutron diffraction study it is known that the space group is C⁶₂h. The water molecule occupies a C₂ site and the oxalate ion a C₁ site. The assigned water vibrations show small factor group splitting between g modes (Raman active) and u modes (IR active). The internal oxalate vibrations are found to have wavenumbers in good agreement with those reported from Raman studies of other oxalates.