Effects of pH on morphosynthesis and photocatalytic activity of calcium titanium oxides via a facile aqueous strategy

By controlling pH values, calcium titanium oxides with various morphologies had been synthesized via a simple hydrothermal route. No surfactants or templates were involved in the shaping process. The results found that pH values had a crucial effect on the crystal phase and shape evolution of the samples. With increasing pH values, the obtained sample changed from one-dimension (1D) CaTi₂O₅ rod or shuttle-like shape to two-dimension (2D) CaTi₂O₄(OH)₂ nanosheets, and then to three-dimension (3D) CaTiO₃ aggregated prisms, butterfly-like dendrites and cross cubic shapes. The formation mechanism was proposed for the evolution of phase and morphology. 3D CaTiO₃ butterfly-like sample showed good photocatalytic activity due to unique morphology, enhanced light harvesting and large surface area.     

Crystal structure and EPR study of Mn-doped β-tricalcium phosphate

Mn-doped β-tricalcium phosphate was prepared by solid state reaction at 1100 °C. The crystal structure of Ca_2.85Mn_0.15(PO₄)₂, was determined by single crystal X-ray diffraction and found to be rhombohedral, R3c. Unit cell parameters are: a = 10.3419(3); c = 37.025(3) Å (hexagonal setting), Z = 21. Structure refinement data show that from the five Ca positions the Ca(4) site is only half filled and that the Mn²⁺ ions occupy the hexacoordinated Ca(5) site solely. EPR spectroscopy reveals that manganese in solid solutions Ca_3−xMn_x(PO₄)₂ (x = 0.1; 0.28; 0.6) is divalent and supports the structure refinement results that Mn occupies the Ca(5) site with a geometry very near to a regular octahedron.     

Synthesis of Sn-doped ZnO nanorods and their photocatalytic properties

Sn-doped ZnO nanorods were fabricated by a hydrothermal route, and characterized by X-ray diffraction, field emission scanning electron microscope, UV-vis spectroscopy, Raman spectra, solid-state nuclear magnetic resonance (NMR) spectra, and room temperature photoluminescence spectroscopy. Solid-state NMR result confirms that Sn⁴⁺ was successfully incorporated into the crystal lattice of ZnO. Room temperature photoluminescence showed that all the as-synthesized products exhibited a weak UV emission (380 nm) and a strong visible emission (540 nm), but the intensities of the latter emission increased with increase in Sn concentration. The improvement of visible emission at 540 nm in the Sn-doped ZnO samples was suggested to be a result of the lattice defects increased by doping of Sn in zinc oxide. In addition, the photocatalytic studies indicated that Sn-doped ZnO nanorods are a kind of promising photocatalyst in remediation of water polluted by some chemically stable azo dyes.     

Theoretical studies on the defect structure for Mn in KTaO3

The defect structure for Mn²⁺ in KTaO₃ is theoretically studied by using perturbation formulas of the spin Hamiltonian (SH) parameters for 3d⁵ ions in tetragonal symmetry based on the strong-field scheme. By analyzing the electron paramagnetic resonance (EPR) data of the studied system, we suggest that the impurity Mn²⁺ ion occupy the dodecahedral K⁺ site, rather than the octahedral Ta⁵⁺ site. Based on the studies, it is found that the Mn²⁺ impurity undergoes an off-center displacement away from the ideal K⁺ site by about 0.60 Å along the C₄ axis. The above displacement is qualitatively consistent with the recent result based on the generalized gradient approximation (GGA) and that obtained from EPR and dielectric spectroscopy studies.     

Growth and photocatalytic properties of one-dimensional ZnO nanostructures prepared by thermal evaporation

Aligned ZnO nanorods and nanotubes were grown on the silicon substrates by thermal evaporation of high pure zinc powders without any other metal catalyst. The morphology evolution of ZnO nanostructures with prolonged growth time suggested that the growth of the ZnO nanorods and nanotubes follows the vapor–liquid–solid mechanism. ZnO nanoneedle and nanoparticle films were also synthesized by the same way, and their photocatalytic performances were tested for the degradation of organic dye methylene blue. The ZnO nanoneedle films exhibited very high photocatalytic activities. The decomposition kinetics of the organic pollutant was discussed. Moreover, it is found that the ZnO nanoneedle films showed very stable photocatalytic activity.     

Effect of pH on the magnetic and dielectric properties of SiO2/NiZn ferrite nanocomposites

A nitrate-citrate-silica gel was prepared from metallic nitrates, citric acid, and tetraethoxysilane (TEOS) by sol-gel process with different pH value, and it was further used to synthesize Ni_0.5Zn_0.5Fe₂O₄/20 wt.% SiO₂ nanocomposites by auto-combustion. The effect of pH on the magnetic and dielectric properties of SiO₂/NiZn ferrite was studied by electron paramagnetic resonance (EPR), superconducting quantum interference device (SQUID), and impedance analyzer measurements. The pH in the starting solution affects the polymerization of TEOS, the dipole-dipole interactions existing among the NiZn ferrite, and then determines the particle size. Further, varying the pH has a direct effect on the EPR parameters (ΔH_PP and T₂), SQUID parameters (M_s, M_r, and H_c), and dielectric properties (dielectric constant and loss) of the as-synthesized powder.     

Photoluminescence of GaN microcrystallites prepared by a new solvothermal process

GaN microcrystallites have been prepared by a solvothermal process. The influence of the synthesis temperature on the crystallinity of the resulting GaN has been studied on three samples, prepared at 400, 600 and 800°C in the same pressure conditions (150 MPa) and duration (6 h). The resulting powders were characterized by several techniques: X-ray diffraction to evaluate the reaction rate, scanning electron microscopy (SEM) to determine the morphology and size of the microcrystallites and photoluminescence to evaluate the quality of the powders.     

Characterizations and properties of Eu-doped ZnWO4 prepared via a facile self-propagating combustion method

ZnWO₄ and Eu³⁺-doped ZnWO₄ were prepared for the first time via a facile self-propagating combustion method. The structure, morphology and luminescence of the as-prepared ZnWO₄ and Eu³⁺-doped ZnWO₄ were characterized. The photoluminescent property of Eu³⁺-doped ZnWO₄ complexes indicated an energy transfer from WO₄²⁻ groups to Eu³⁺ and suggested an effective doping of Eu³⁺ into the lattice of ZnWO₄. The photocatalytic activity of ZnWO₄ and Eu³⁺-doped ZnWO₄ was investigated by the photodegradation of rhodamine B (RhB). Eu³⁺-doped ZnWO₄ showed enhanced photocatalytic activity in the photodegradation of RhB.     

Nitrogen-doped TiO2 nanotubes with enhanced photocatalytic activity synthesized by a facile wet chemistry method

Nitrogen-doped TiO₂ nanotubes with enhanced photocatalytic activity were synthesized using titanate nanotubes as raw material by a facile wet chemistry method. The resulting nanotubes were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and UV-vis absorption spectroscopy, etc. The photocatalytic activity of nitrogen-doped TiO₂ nanotubes was evaluated by the decomposition of methylene blue under artificial solar light. And it was found that nitrogen-doped TiO₂ nanotubes exhibited much higher photocatalytic activity than undoped titanate nanotubes.     

The microwave effect on the properties of silica-coated TiO2 fine particles prepared using sol-gel method

The silica coating of TiO₂ fine particle was conducted using microwave assisted sol-gel method and conventional sol-gel method to suppress its photo-catalytic activity. The amount and uniformity of silica coating on TiO₂ surface were characterized by X-ray photoelectron spectroscopy (XPS), X-ray fluorescence spectroscopy (XRF), infrared spectroscopy (IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and zeta potential measurements. XPS and XRF results showed that the presence of catalyst and reaction time were important factors to reach high silica amounts. SEM, TEM, and zeta potential results indicated that dense film coating of SiO₂ layer formed on TiO₂ surface in conventional sol-gel method, whereas the nucleation coating was observed on sample prepared by microwave assisted sol-gel method. When photo-catalytic activities and ultraviolet (UV) shielding abilities of these samples were evaluated, the sample prepared by microwave processing showed higher inhibition of photo-catalytic activity and better UV shielding ability than the sample prepared by conventional method. These results suggested that the coating method significantly affected the photo-catalytic activity and UV shielding ability of coated TiO₂.     

Sintering and dielectric properties of BaTiO3 prepared by a composite-hydroxide-mediated approach

High purity tetragonal BaTiO₃ powders consisted of uniform particles of ca. 150 nm in diameter were synthesized by a composite-hydroxide-mediated approach at 240 °C using a novel hydrothermal reaction apparatus with a rolling system. The product showed sinterability superior to the commercial powder, i.e., it could be sintered to full theoretical density at 1200 and 1100 °C without an additive and with 0.3 wt% of Li₂CO₃-0.04 wt% of V₂O₅ mixed sintering aid, respectively. The sintered body of the product also showed piezoelectric properties superior to the commercial one.     

Spectral properties of Tm:NaGd(MoO4)2 crystal

The Tm³⁺:NaGd(MoO₄)₂ crystal with dimensions of Φ 15 × 38 mm² was grown by Czochralski method. Polarized absorption and fluorescence spectra at room temperature were investigated. The absorption bands attributed to ³H₆ → ³H₄ transition have large absorption cross-sections, which are 3.99 × 10⁻²⁰ and 2.36 × 10⁻²⁰ cm² for σ- and π-polarization, respectively. The emission bands corresponding to the ³H₄ → ³H₆ transition are strong and broad with emission cross-sections of 1.33 × 10⁻²⁰ and 1.20 × 10⁻²⁰ cm² for σ- and π-polarization, respectively. The correlative full widths at half maximum are 35 nm for σ-polarization and 36 nm for π-polarization. The fluorescence lifetime for the ³H₄ → ³F₄ transition is 146 μs and the luminescent quantum efficiency is 76.8%.     

Facile 1,4-dioxane-assisted solvothermal synthesis,optical and electrochemical properties of CeO2 microspheres

CeO₂ microspheres, with an average diameter of 1 μm, have been successfully prepared through a facile 1,4-dioxane-assisted solvothermal synthesis, where 1,4-dioxane is acted as a capping agent for the first time. By varying the solvent ratio, the formation mechanism for the CeO₂ microspheres has been proposed on an isotropic growth through the capping function of 1,4-dioxane. The strong UV–vis spectra result indicates that the CeO₂ microspheres are suitable as an UV blocking and shielding material. The cyclic voltammetric measurements of hemoglobin immobilized on CeO₂-Nafion modified glassy carbon electrode reveal a typical characteristic of surface-controlled thin-layer electrochemical behavior of the CeO₂ microspheres.     

Fabrication of microspherical LiMnPO4 cathode material by a facile one-step solvothermal process

The microspherical LiMnPO₄ cathode material was successfully prepared for the first time by a simple one-step solvothermal process in the presence of critic acid. The reaction conditions (reactant concentration, reaction temperature) were used further to fabricate the size, surface coarseness and morphology of the microspherical LiMnPO₄. The as-prepared microspherical LiMnPO₄ at variant conditions exhibited remarkably different discharge capacity and rate capacity, indicating the potential of the suggested method in tuning the morphology and the structure of LiMnPO₄ to improve its electrochemical performance.     

Microwave synthesis of Al-doped SiC powders and study of their dielectric properties

To improve the dielectric properties of β-SiC powders, microwave synthesis was applied to produce SiC powders doped with different amounts of Al from fine powders of Si, C and Al under Ar atmosphere. The dielectric properties of the as-synthesized Al-doped SiC powders were investigated, and the mechanism of dielectric loss by doping has been discussed. The presence of Al influenced the formation of secondary phases (α-SiC and Al₄SiC₄) and the microstructure of the resultant powders. The produced powders form Al-SiC solid-solutions, which seemingly favor defect polarization loss effect in the high frequency region. This is consistent with the measurements of dielectric properties, which showed that doping of SiC with Al causes increase of permittivity, both real and imaginary parts, and loss tangent, within 8.2-12.4 GHz. The results show that SiC doped with 30% Al has the highest real part ?′ and imaginary part ?″ of permittivity and also loss tangent.     

Crystallite, optical and photocatalytic properties of visible-light-driven ZnIn2S4 photocatalysts synthesized via a surfactant-assisted hydrothermal method

A series of ZnIn₂S₄ photocatalysts were synthesized via a surfactant-assisted hydrothermal method. The products were characterized with X-ray diffraction (XRD), UV-vis-near-IR diffuse reflectance spectra (UV-vis), photoluminescence spectra (PL) and field emission scanning electron microscope (FESEM). The results indicated that the CTAB-assisted ZnIn₂S₄ product had a wider band gap than the other three ZnIn₂S₄ products (CPBr-assisted, SDS-assisted and no-surfactant-assisted ZnIn₂S₄). The surfactant (especially CTAB) addition would greatly affect the crystal structure (i.e. d(0 0 6) along the c-axis) of ZnIn₂S₄. The photocatalytic activities of the as-prepared samples were evaluated by photocatalytic hydrogen production from water under visible light irradiation. The CTAB-assisted ZnIn₂S₄ product, with quantum yield (420 nm) determined to be 11.9%, had a much higher photocatalytic activity than the other three ZnIn₂S₄ products in our photocatalytic system. The energy conversion efficiency in the whole visible light region was determined to be 3.1% for the CTAB-assisted ZnIn₂S₄ photocatalyst.     

Low temperature pH dependent synthesis of flower-like ZnO nanostructures with enhanced photocatalytic activity

In the present study we have synthesized flower-like ZnO nanostructures comprising of nanobelts of 20 nm width by template and surfactant free low-temperature (4 °C) aqueous solution route. The ZnO nanostructures exhibit flower-like morphology, having crystalline hexagonal wurtzite structure with (0 0 1) orientation. The flowers with size between 600 and 700 nm consist of ZnO units having crystallite size of ∼40 nm. Chemical and structural characterization reveals a significant role of precursor:ligand molar ratio, pH, and temperature in the formation of single-step flower-like ZnO at low temperature. Plausible growth mechanism for the formation of flower-like structure has been discussed in detail. Photoluminescence studies confirm formation of ZnO with the defects in crystal structure. The flower-like ZnO nanostructures exhibit enhanced photochemical degradation of methylene blue (MB) with the increased concentration of ligand, indicating attribution of structural features in the photocatalytic properties.     

Microwave-assisted fast vapor-phase transport synthesis of MnAPO-5 molecular sieves

MnAPO-5 was prepared by a microwave-assisted vapor-phase transport method at 180 °C in short times. The products were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectra, UV-vis spectroscopic measurement, NH₃-temperature-programmed desorption and esterification reaction. It was found that dry gels prepared with aluminum isopropoxide, phosphoric acid and manganese acetate could be transferred to MnAPO-5 in the vapors of triethylamine and water by the microwave-assisted vapor-phase transport method at 180 °C for less than 30 min. The crystallization time was greatly reduced by the microwave heating compared with the conventional heating. The resulting MnAPO-5 exhibited much smaller particle sizes, higher surface areas and slightly higher catalytic activity in the esterification of acetic acid and butyl alcohol than those prepared by the conventional vapor-phase transport method and hydrothermal synthesis.     

A facile method for rapid preparation of individual titania nanotube powders by a two-step process

Present study reports a facile method for preparing individual TiO₂ nanotube (NT) powders by a two-step process, which includes that TiO₂ NT bundles are rapidly synthesized by an electro-chemical process in perchlorate-containing electrolyte and then they are disaggregated into individual TiO₂ NT powders under an assistance of ultrasonic oscillation treatment. Morphological and microstructural properties of the individual TiO₂ NT powders are characterized by field emission scanning electron microscopy and transmission electron microscopy. Results indicate that the individual TiO₂ NT powders, which have an outer diameter of about 20 nm and an inner diameter of 10 nm, can be easily obtained from the disaggregation of the TiO₂ NT-bundles by combining the electrochemical process with the physical processing. Furthermore, the individual TiO₂ NT powders exhibit higher photocatalytic activity than the TiO₂ NT-bundle powders.     

Applications of Cu2O octahedral particles on ITO glass in photocatalytic degradation of dye pollutants under a halogen tungsten lamp

Cu₂O octahedral microcrystals were prepared on the ITO glass by galvanostatic electrodeposition in CuSO₄ solution with poly(vinylpryrrolidone) as the surfactant. By controlling the electrodeposition time, the microcrystals could be randomly distributed on the ITO glass and separated from each other, resulting in as many as possible {1 1 1} crystalline planes were exposed. Such microcrystals immobilized on ITO glass were employed in photodegradation of dye pollutants in the presence of H₂O₂ under a 150 W halogen tungsten lamp. The photodegradation of methylene blue was taken as an example to evaluate the photocatalytic activities of the octahedral Cu₂O microcrystals. Effects of electrodeposition time and H₂O₂ amount on the degradation efficiency was discussed, giving the optimum conditions and the corresponding degradation mechanism. The catalyst showed high ability in degradation of methylene blue, methyl orange, rhodamine B, eosin B and their mixtures under identical conditions.