Effects of nucleating agents on crystallization and microstructure of fluorophlogopite mica-containing glass–ceramics

The alteration of crystallization behavior, microstructure, and thermal properties of fluorophlogopite mica-containing glass–ceramics by nucleating agent is systematically studied. TiO₂, TiO₂ + ZrO₂, and ZrO₂ have been doped as the nucleating agents in the SiO₂–MgO–Al₂O₃–B₂O₃–K₂O–MgF₂ (BMAPS) glass system and prepared by the melt-quench technique. The glass without nucleating agent is also prepared to ascertain the influence of nucleating agent. Addition of nucleating agents effectively increases the softening as well as glass transition temperatures. From the DSC study, it is found that the fluorophlogopite mica crystallization exotherm exhibited in the temperature range 800–850 °C and the activation energy varies in the range 167–182 kJ/mol. The opaque mica glass–ceramics are derived from these BMAPS glasses by a controlled heat treatment process and heat treatment at 1050 °C is found to be optimum. The mica crystals were identified as fluorophlogopite for all the four BMAPS glasses by X-ray powder diffraction (XRD) and subsequently confirmed by FTIR spectroscopy. Excellent matching with fluorophlogopite crystal was obtained in Zirconia-containing glass–ceramic as perceived from the XRD and FTIR studies. The microstructure of interlocked card-like mica flake crystals is found to form as seen from scanning electron microscopy, and such microstructure is obtained when ZrO₂ has been used as nucleating agent. Glass–ceramic without nucleating agent possesses Vickers hardness value 4.58 Gpa and it is increased with addition of the nucleating agent (5.67–6.56 GPa), ZrO₂-containing glass–ceramic possess lower hardness (5.67 GPa) and better machinability. Therefore, ZrO₂ is the most efficient nucleating agent to generate fluorophlogopite mica in these glass–ceramics useable for SOFC applications.     

Oxalic acid assisted hydrothermal synthesis and optical absorption property of WO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanocomposites

The WO₃/TiO₂ nanocomposites were successfully prepared via a facile oxalic acid assisted hydrothermal process. The oxalic acid played a vital role on the preparation of WO₃/TiO₂ nanocomposites. Notably, it has been observed that the nanocomposites exhibited the wider absorption edge, and the higher photocatalytic activity, compared with pure TiO₂. In addition, the photocatalytic mechanism was proposed, and it elaborated that WO₃/TiO₂ nanocomposite promoted the separation of the photoproduction carriers, and improved photocatalytic activity. The WO₃/TiO₂ nanocomposite may have a potential application as a UV–visible photocatalyst.     

Fabrication of TiO<Subscript>2</Subscript>/ZnO composite nanofibers with enhanced photocatalytic activity

TiO₂/ZnO composite nanofibers have been successfully prepared by electrospinning technique. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, Raman spectrum, X-ray photoelectron spectroscopy and UV–Vis diffuse reflectance spectroscopy, were used to characterize the as-synthesized nanofibers. The photocatalytic studies revealed that the TiO₂/ZnO nanofibers exhibited enhanced photocatalytic efficiency of photodegradation. Additionally, the recycling experiment of TiO₂/ZnO nanofibers had been done, demonstrating that TiO₂/ZnO nanofibers have high efficiency and stability.     

Preparation of porous sheet composite impregnated with TiO<Subscript>2</Subscript> photocatalyst by a papermaking technique

Titanium dioxide (TiO₂) powder-containing sheet composites, called TiO₂ sheet, were prepared by a papermaking technique, and their photocatalytic efficiency was investigated. The TiO₂ powders were homogeneously scattered over the fiber-mix networks tailored within the catalyst sheet. Under UV irradiation, the TiO₂ paper could decompose p-hydroxyacetophenone (p-HAP), although the degradation efficiency by the TiO₂ sheet was lower than that by the TiO₂ powder. Scanning electron microscopy revealed that coverage of the TiO₂ particles inside the sheet by alumina binder which was used to improve the sheet strength caused the deterioration of the photocatalytic performance. Internal addition of alumina binder made the TiO₂ sheet porous and such a TiO₂ sheet exhibited high photocatalytic performance equivalent to that of TiO₂ powder. The porous structure of TiO₂ sheet might contribute to effective transport of p-HAP to the surface of TiO₂ particles inside the sheet, resulting in high degradation performance. In addition, TiO₂ sheet prepared using TiO₂ sol showed higher photocatalytic efficiency than TiO₂ powder and it was indicated that the porous sheet structure might provide suitable conditions for TiO₂ catalysis for photodecomposition.     

Characterization of Zr-doped TiO<Subscript>2</Subscript> prepared by homogenous co-precipitation without high-temperature treatment

Zr-doped TiO₂ (anatase) was prepared by the homogenous co-precipitation method of the aqueous solutions containing TiOSO₄ and ZrCl₄ using urea as the precipitation agent. Nanocrystallites of Zr-doped TiO₂, 6–9 nm in size, intergrown with amorphous phase form 1–2 μm porous spherical clusters. Crystallite size of anatase decreases with increasing Zr content, and the catalyst becomes totally amorphous at 10 mol.% Zr. All samples exhibit high specific surface area, which increases with the addition of zirconium (from 391.3 to 689.1 m² g⁻¹).     

Preparation and photoelectrochemical characterization of WO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanotube array electrode

WO₃/TiO₂ nanotube array electrode was fabricated by incorporating WO₃ with TiO₂ nanotube array via a wet impregnation method using ammonium tungstate as the precursor. TiO₂ and WO₃/TiO₂ nanotube arrays were characterized by field emission scanning electron microscopy, X-ray diffraction, and energy dispersive X-ray analysis. In order to characterize the photoelectrochemical properties of WO₃/TiO₂ electrode, electrochemical impedance spectroscopy, and steady-state photocurrent (i _ss) measurement at a controlled potential were performed in the supporting electrolyte containing different concentrations of glucose. The photoelectrochemical characterization results reveal that WO₃/TiO₂ nanotube array electrode possesses a much higher separation efficiency of the photogenerated electron–hole pairs and could generate more photoholes on the electrode surface compared with the pure TiO₂ nanotube array electrode. The i _ss for glucose oxidation at WO₃/TiO₂ nanotube array electrode is much higher than that at the pure TiO₂ nanotube array electrode.     

TiO<Subscript>2</Subscript> nanocrystals grown on graphene as advanced photocatalytic hybrid materials

A graphene/TiO₂ nanocrystals hybrid has been successfully prepared by directly growing TiO₂ nanocrystals on graphene oxide (GO) sheets. The direct growth of the nanocrystals on GO sheets was achieved by a two-step method, in which TiO₂ was first coated on GO sheets by hydrolysis and crystallized into anatase nanocrystals by hydrothermal treatment in the second step. Slow hydrolysis induced by the use of EtOH/H₂O mixed solvent and addition of H₂SO₄ facilitates the selective growth of TiO₂ on GO and suppresses growth of free TiO₂ in solution. The method offers easy access to the GO/TiO₂ nanocrystals hybrid with a uniform coating and strong interactions between TiO₂ and the underlying GO sheets. The strong coupling gives advanced hybrid materials with various applications including photocatalysis. The prepared graphene/TiO₂ nanocrystals hybrid has superior photocatalytic activity to other TiO₂ materials in the degradation of rhodamine B, showing an impressive three-fold photocatalytic enhancement over P25. It is expected that the hybrid material could also be promising for various other applications including lithium ion batteries, where strong electrical coupling to TiO₂ nanoparticles is essential.     

On the synthesis,characterization and photocatalytic applications of nanostructured TiO<Subscript>2</Subscript>

Nanocrystalline semiconducting materials are attracting much attention due to their potential applications in solar energy conversion, nonlinear optics, and heterogeneous photocatalysis. In the present investigation, we have synthesized nanostructured TiO₂ photocatalysts, which have been used in the photocatalytic degradation of phenol (one of the most common water pollutants). These catalysts have been prepared through sol-gel technique using titanium tetra-isopropoxide as a raw material for synthesis. Characterization techniques such as XRD, SEM and TEM have been employed for structural/microstructural investigations. XRD results show that the as synthesized TiO₂ nanopowder exhibit anatase phase, TiO₂. The average sizes of the TiO₂ nanopowders are ∼ 5–10 nm. The optical properties of the samples were investigated through UV-visible and fluorescence techniques. It has been observed that absorption edge corresponds to ∼ 410 nm (bandgap, ∼ 3.02 eV). The emission peak in the fluorescence spectrum at ∼ 418 nm corresponds to the bandgap energy of ∼ 2.97 eV. Concentration of phenol (initial concentration, ∼ 100 ppm) with illumination time was monitored by measuring the absorbance of pure and illuminated phenol through UV-visible spectrophotometer. Salient feature of this study relates to the fact that the present sol-gel synthesized TiO₂ nanopowders have been found to be better photocatalysts for phenol degradation than the presently employed commercial TiO₂ (P-25, Degussa) photocatalyst. Thus, whereas phenol concentration, with the presently synthesized TiO₂ nanopowders, the concentration of phenol decreases up to ∼ 32% but for commercial TiO₂ nanopowder (P-25, Degussa), it decreased only up to ∼ 25%. The improved surface area is considered as an important factor for the aforesaid decrease in phenol concentration.     

Fabrication of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> double layer thin films with self-cleaning and photocatalytic properties

Transparent antireflective SiO₂/TiO₂ double layer thin films were prepared using a sol–gel method and deposited on glass substrate by spin coating technique. Thin films were characterized using XRD, FE-SEM, AFM, UV–Vis spectroscopy and water contact angle measurements. XRD analysis reveals that the existence of pure anatase phase TiO₂ crystallites in the thin films. FE-SEM analysis confirms the homogeneous dispersion of TiO₂ on SiO₂ layer. Water contact angle on the thin films was measured by a contact angle analyzer under UV light irradiation. The photocatalytic performance of the TiO₂ and SiO₂/TiO₂ thin films was studied by the degradation of methylene blue under UV irradiation. The effect of an intermediate SiO₂ layer on the photocatalytic performance of TiO₂ thin films was examined. SiO₂/TiO₂ double layer thin films showed enhanced photocatalytic activity towards methylene blue dye.     

Preparation of sub-micron size anatase TiO<Subscript>2</Subscript> particles for use as light-scattering centers in dye-sensitized solar cell

The sub-micron size anatase TiO₂ particles with size about 0.2-0.3 μm were synthesized with basic peptizing agent and hydrothermal method and added into TiO₂ film as light scattering center. The addition of the sub-micron size anatase TiO₂ particles enhanced light scattering and dye adsorption abilities of the TiO₂ film. When the weight proportion of the sub-micron size/nano-size TiO₂ particles in the TiO₂ film attained to 1.25/10, the highest energy conversion efficiency about 7.41% was obtained, which was 23% enhancement comparing with the TiO₂ film containing pure nano-size TiO₂ particles. It presented an efficient way for improving the photovoltaic performance of dye-sensitized solar cell.     

Photocatalytic oxidation of dibenzothiophene using TiO<Subscript>2</Subscript>/bamboo charcoal

Photocatalytic oxidation of dibenzothiophene (DBT) using TiO₂-loaded bamboo charcoals (BC) prepared by wet impregnation was studied. Results obtained here can be used as the reference for evaluating reactions in hydrocarbons, which aims at the development of an oxidative desulfurization process for fuel oils. Technological conditions (the amount of photocatalysts, hydrogen peroxide, and TiO₂ loading) were also investigated in detail. The results show that TiO₂/BC improves the dispersed degree of TiO₂ catalyst, which shows a better photocatalytic performance than pure TiO₂. We also found a special characterization of TiO₂/BC, it can locate just at the oil–water phase boundary. The oxidation proceeds in the oil phase and most of the oxidation products transfer to water phase, resulting in the successive removal of DBT from the n-octane phase without additional extraction by solvent. In addition, kinetics parameters of the photocatalytic oxidation of DBT were measured and calculated. The result shows the kinetics of photocatalytic oxidation of DBT is first order.     

Ag<Subscript>2</Subscript>S/Bi<Subscript>2</Subscript>S<Subscript>3</Subscript> co-sensitized TiO<Subscript>2</Subscript> nanorod arrays prepared on conductive glass as a photoanode for solar cells

TiO₂ nanorod arrays (TiO₂ NRAs) were synthesized through a hydrothermal method. Ag₂S and Bi₂S₃ were then grown on the surface of TiO₂ NRAs with successive ionic layer adsorption and reaction method. The pristine rutile TiO₂ NRAs, Ag₂S/TiO₂, Bi₂S₃/TiO₂, and Bi₂S₃/Ag₂S/TiO₂ electrodes were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, ultraviolet–visible absorption spectroscopy, and electrochemical analysis. According to photoelectrochemical (PEC) measurement, an enhanced short circuit current density was obtained for the co-sensitized TiO₂ NRAs under simulated sunlight illumination, which was 10.7 times higher than that of the TiO₂ NRAs. Appropriate potential positions of conduction band and valence band of Bi₂S₃ that match well those of rutile TiO₂ NARs and Ag₂S lead to the improved PEC performance. In addition, the PEC property of the co-sensitized TiO₂ NRAs under visible light irradiation was also investigated and showed a dramatically enhanced photocurrent response.     

Preparation of rutile (TiO<Subscript>2</Subscript>) nanostructured materials at low temperature from TiCl<Subscript>4</Subscript> aqueous solution

The synthesis of rutile (TiO₂) nanostructured materials at low temperature from TiCl₄ aqueous solution was described. TiO₂ coatings on polystyrene (PS) particles were prepared by layer-by-layer assembly technique. The samples were characterized by DTA-TG, SEM, XPS, TEM and XRD techniques. The experimental results showed that pure rutile-TiO₂ coatings with nanocrystal structure were synthesized at 100 °C. On the surface of PS particles, sphere-type TiO₂ coatings exhibited uniform shape and a narrow size distribution. The amount of TO₂ (wt%) and shell thickness of particles increased with the adding of coating layers. Hollow TiO₂ spheres were obtained by calcination at 450 °C. TiO₂/PS with 2 coating layers showed higher degradation rate. The photocatalytic activity of hollow TiO₂ spheres was higher than that of TiO₂/PS.     

Sonocatalytic damage of composite TiO<Subscript>2</Subscript>/ZnO powder to bovine serum albumin under ultrasonic irradiation

The composite TiO₂/ZnO was prepared by mixing nano-sized TiO₂ and ZnO powders directly, in the molar proportion of 4:6, followed by heat-treatment at 500°C for 40 min. The products were charactered by powder X-ray diffraction and transmission electron microscopy. The test of sonocatalytic activities of the composite TiO₂/ZnO powders was carried out through the damage of bovine serum albumin (BSA). Otherwise, the effects of several factors on the damage of BSA molecules were evaluated by means of UV-vis and fluorescence spectra. It was found that the damage degree was aggravated with the increase of ultrasonic irradiation time and composite TiO₂/ZnO addition amount. These research results were of great significance for driving sonocatalytic method to treat tumor in clinic application.     

Synthesis and characterization of TiO<Subscript>2</Subscript>-incorporated silica foams

Titania-incorporated silica (TiO₂–SiO₂) porous materials have great applications in diverse areas. In this work, TiO₂–SiO₂ porous materials with tunable Si/Ti molar ratio (R) have been successfully prepared through a one-pot method under a near-neutral condition. With decreasing Si/Ti R, a phase transition from a macroporous foam-like structure to mesostructure is observed. The resultant TiO₂–SiO₂ porous materials possess large surface areas and high pore volumes. In addition, the titania species are homogenously dispersed in silica matrix when Si/Ti R ≥ 10. Our contribution provides a convenient method to synthesize TiO₂/SiO₂ porous materials with very large pore size, high pore volume, and relatively high titania content well dispersed in the silica wall framework.     

Sintering characteristic and microwave dielectric properties of ultra-low loss Li<Subscript>2</Subscript>Mg<Subscript>3</Subscript>TiO<Subscript>6</Subscript> ceramic prepared by reaction-sintering process

Microwave dielectric properties and microstructures of ultra-low loss Li₂Mg₃TiO₆ ceramic prepared by reaction-sintering method (RS) and conventional solid-state reaction method (CS) have been investigated. The XRD patterns and SEM images revealed that the single phase of Li₂Mg₃TiO₆ and uniform morphology are obtained by both RS and CS methods at the optimal sintering temperatures. In order to further investigate the effects of different sintering methods on the microwave dielectric properties of Li₂Mg₃TiO₆ ceramics, the oxide polarizabilities and packing fraction were calculated based on the Rietveld refinement. The calculation results revealed that the RS method was more beneficial to the microwave dielectric properties of Li₂Mg₃TiO₆ ceramics in comparison with CS method. Excellent microwave dielectric properties for Li₂Mg₃TiO₆ ceramics with enhanced Q?×?f value of 157,036 GHz could be obtained using RS method sintered at 1250 °C for 6 h.     

Electrophoretic deposition of Sn-doped TiO<Subscript>2</Subscript> nanoparticles and its optical and photocatalytic properties

In this research, Sn-doped TiO₂ (Sn–TiO₂) nanoparticles were synthesized by a simple sol–gel method. The structure and composition of the as-prepared sample were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible absorption spectroscopy. Electrophoretic deposition (EPD) technique was used to deposit thin films of Sn–TiO₂ on 316L stainless steel (316L SS) substrate. In order to achieve a fine and high-quality layer on the electrode surface, N-phenyl-p-phenylenediamine (NPPDA) was used as a new dispersant and charging agent in ethanolic suspensions. Based on zeta potential and conductivity measurements of the suspensions, an optimum concentration of the NPPDA dispersant was found to be 3.0 g l^?1. The in-situ EPD kinetics was also studied. The prepared Sn–TiO₂ film was used for the photodegradation of methylene blue (MB) under UV, visible and sun lights. The results revealed that the Sn–TiO₂ film could be able to degrade the MB under sunlight. The calculated degradations were 44, 65, and 73% after 2, 4 and 5 h, respectively. The relation between \(\ln \left( {\frac{{{{\text{A}}_0}}}{{\text{A}}}} \right)\) and time was linear, so it was proved that the photocatalytic degradation of MB can be characterized by pseudo-first order reaction kinetics.     

Mechanisms of antibacterial activity and stability of silver nanoparticles grown on magnetron sputtered TiO<Subscript>2</Subscript> coatings

Nanomaterials with high stability and efficient antibacterial activity are of considerable interest. The preparation of silver nanoparticles (AgNPs) on titania coatings and their effective antibacterial activity against Staphylococcus aureus ATCC 6538 were reported. Titanium dioxide (TiO₂) coatings with AgNPs were prepared on Si wafers using the reactive magnetron sputtering method. The surface topography of AgNPs/TiO₂ coatings imaged using scanning electron microscopy revealed that the size and surface density of AgNPs grown by the photoreduction of silver ions were dependent on the concentration of AgNO₃ in the primary solution and the time of TiO₂ exposure to UV illumination. Evaluation of the antimicrobial properties and surface analysis before and after the biological test of AgNPs/TiO₂ coatings indicates their high antimicrobial stability and durability. Furthermore, the interdependence between the concentration of released silver and bacterial growth inhibition was demonstrated. In addition, direct contact killing and released silver-mediated killing have been proposed as a bactericidal mechanism of action of tested coatings with AgNPs.     

Photocatalytic activity of polypyrrole/TiO<Subscript>2</Subscript> nanocomposites under visible and UV light

A series of polypyrrole (PPy)/titanium dioxide (TiO₂) nanocomposites were prepared in different polymerization conditions by ‘in situ’ chemical oxidative polymerization. The nanocomposites were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy spectra (XPS), and UV–Vis diffuse reflectance spectra. The photocatalytic degradation of methyl orange (MO) was chosen as a model reaction to evaluate the photocatalytic activities of TiO₂/PPy catalysts. The results show that a strong interaction exists at the interface between TiO₂ and PPy, the deposition of PPy on TiO₂ nanoparticles can alleviate their agglomeration, PPy/TiO₂ nanocomposites show stronger absorbance than neat TiO₂ under the whole range of visible light. The obtained PPy/TiO₂ nanocomposites exhibit significantly higher photocatalytic activity than the neat TiO₂ on the degradation of MO aqueous solution under visible and UV light illumination. The reasons for improving the photocatalytic activity were also discussed.     

Conductivity of Sm<Subscript>2</Subscript>TiO<Subscript>5</Subscript> and Sm<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>

The oxygen-ion conductivity of porous materials, the coarse-grained pyrochlore-like Sm₂Ti₂O₇ and fine-grained Sm₂TiO₅ compounds, produced by mechanical activation of initial oxides is studied at 400–1000 °C. The Sm₂TiO₅ samples contain ～15 wt % of the nanosized pyrochlore-like Sm₂TiO₅ phase in addition to the rhombic phase. As determined by impedance spectroscopy, the ionic conductivities of Sm₂TiO₅ and Sm₂Ti₂O₇ at 1000°C are 1.3 × 10^?3 and 1.8 × 10^?4 S cm^?1, and the activation energies of the bulk and grainboundary conductivities of the materials are 1.04 and 1.24 eV for Sm₂TiO₅ and 1.69 and 1.80 eV for Sm₂Ti₂O₇.