Mesocrystalline TiO<Subscript>2</Subscript>/sepiolite composites for the effective degradation of methyl orange and methylene blue

Mesocrystalline TiO₂/sepiolite (TiS) composites with the function of adsorption and degradation of liquid organic pollutants were successfully fabricated via a facile and low-cost solvothermal reaction. The prepared TiS composites were characterized by FESEM, HRTEM, XRD, XPS, N₂ adsorption-desorption, UV–vis DRS, and EPR. Results revealed the homogeneous dispersion of highly reactive TiO₂ mesocrystals on the sepiolite nanofibers. Thereinto each single–crystal–like TiO₂ mesocrystal comprised many [001]-oriented anatase nanoparticles about 10–20 nm in diameter. The photocatalytic activity was further evaluated by the degradation of anionic dye (methyl orange) and cationic dye (methylene blue) under the UV-vis light (350≤λ≤780 nm) irradiation. By selecting appropriate experimental conditions, we can easily manipulate the photocatalytic performance of TiS composites. The optimal TiS catalyst (the sepiolite content of 28.5 wt.%, and the reaction time of 24 h) could efficiently degrade methyl orange to 90.7% after 70 min, or methylene blue to 97.8% after 50 min, under UV-vis light irradiation. These results can be attributed to their synergistic effect of high crystallinity, large specific surface area, abundant hydroxyl radicals, and effective photogenerated charge separation.     

Fabrication and properties of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> composites

Composites in the form of precipitated powders, hybrid xerogels, and SiO₂ core/TiO₂ shell particles have been produced via hydrolysis of precursors (alkoxides and inorganic derivatives of titanium and silicon) and have been characterized by differential thermal analysis, X-ray diffraction, adsorption measurements, and macroelectrophoresis. The results demonstrate that heat treatment of the composites leads to crystallization of the titanium-containing component and, accordingly, reduces their specific surface area. Hydrothermal treatment enables the fabrication of materials in which TiO₂ nanocrystals are evenly distributed over an amorphous SiO₂ matrix.     

Functionalization of electrospun magnetically separable TiO<Subscript>2</Subscript>-coated SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanofibers: strongly effective photocatalyst and magnetic separation

Magnetically separable TiO₂-coated SrFe₁₂O₁₉ electrospun nanofibers were obtained successfully by means of sol–gel, electrospinning, and coating technology, followed by heat treatment at 550–650 °C for 3 h. The average diameter of the electrospun fibers was 500–600 nm. The fibers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). The optimized calcining temperature was determined by XRD and the analysis of decolorizing efficiency of methylene blue (MB) under UV–vis irradiation. The photocatalytic activity of the TiO₂-coated SrFe₁₂O₁₉ fibers was investigated using ultraviolet–visible absorbance by following the photooxidative decomposition of a model pollutant dye solution, MB in a photochemical reactor. In contrast to pure TiO₂ fibers, the TiO₂-coated SrFe₁₂O₁₉ fibers have higher absorption in 250–750 nm wavelength regions. The presence of SrFe₁₂O₁₉ not only broadened the response region of visible-light, but also enhanced the absorbance for UV light. The decolorizing efficiency of MB under UV–vis irradiation was up to 98.19%, which was a little higher than that of Degussa P25 (97.68%). Furthermore, these fibers could be recollected easily with a magnet in a photocatalytic process and had effectively avoided secondary pollution of treated water.     

Synthesis of silver and sulphur codoped TiO<Subscript>2</Subscript> nanoparticles for photocatalytic degradation of methylene blue

In the present work, silver and sulphur codoped TiO₂ (Ag–S/TiO₂) photocatalysts were effectively prepared by sol–gel technique. The prepared samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray analysis (EDX), Fourier transform infrared (FTIR) spectroscopy, diffuse reflectance UV–Vis spectroscopy (UV-DRS) and photoluminescence (PL). The XRD patterns consisted of anatase crystalline phases and the particle size and shape of the prepared samples were observed by SEM and HR-TEM. The presence of doping ions was confirmed by EDX analysis, the decreased band-gap energy of Ag–S codoped TiO₂ nanoparticles was investigated by UV-DRS. The decreased in the intensity of Ag–S codoped TiO₂ was absorbed due to the lower separation of electron–hole pairs were confirmed by PL spectrum. The Ag–S codoped TiO₂ showed higher photocatalytic activity than pure and single-doped TiO₂ in the photodegradation of methylene blue (MB) aqueous solution under visible light irradiation. The given work was a good model to associate the considering of the synergistic effect of metal and non-metal codoped TiO₂ in the photocatalysis and photo electrochemistry.     

Facile synthesis of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanoparticles and its photocatalyst application

The strontium hexaferrite (SrFe₁₂O₁₉) nanoparticles have been successfully synthesized by co-precipitation route. The effect of various parameters such as calcination temperature and chelating agents were screened to achieve optimum condition. Different chelating agents such as amino acids (proline, alanine, aspartic acid) and surfactants (SDBS, PVP, and EDTA) were used. Compared with the amino acids, the surfactants increase the particle size and the best result was observed for alanine. The SrFe₁₂O₁₉ nanoparticles showed enhanced photocatalytic activity in the degradation of methyl orange under visible light irradiation (λ?>?400 nm). The degradation rates of the methyl orange were measured to be as high as 95% in 220 min. The nanoparticles were also characterized by several techniques including FT-IR, XRD, SEM, and VSM. The VSM measurement showed a saturation magnetization value (Ms) of 32 emu/g. The SEM images proposed that the particles are almost spherical with an average particle size of 90 nm.     

Visible photocatalytic degradation of methylene blue on magnetic semiconducting La<Subscript>0.2</Subscript>Sr<Subscript>0.7</Subscript>Fe<Subscript>12</Subscript>O<Subscript>19</Subscript>

Methylene blue (MB) is a representative of a class of dyestuffs resistant to biodegradation. This paper presents a novel photocatalytic degradation of MB by La_0.2Sr_0.7Fe₁₂O₁₉ compound, which is a traditional permanent magnet and displays a large magnetic hysteresis (M–H) loop. The remnant magnetic moment and coercive field are determined to be 52 emu/g and 5876 Oe, respectively. UV–Visible optical spectroscopy reveals that La_0.2Sr_0.7Fe₁₂O₁₉ is simultaneously a semiconductor, whose direct and indirect band gap energies are determined to be 1.47 and 0.88 eV, respectively. The near infrared band gap makes it a good candidate to harvest sunlight for photocatalytic reaction or solar cell devices. This magnetic compound demonstrates excellent photocatalytic activity on degradation of MB under visible illumination. The colour of MB dispersion solution changes from deep blue to pale white and the absorbance decreases rapidly from 1.8 down to zero when the illumination duration extends to 6 h. Five absorption bands did not make any blue shifts along with the reaction time, suggesting a one-stepwise degradation process of MB, which makes La_0.2Sr_0.7Fe₁₂O₁₉ a unique magnetic catalyst and differs from TiO₂ and other conventional catalysts.     

Photocatalytic degradation of methylene blue by Au-deposited TiO<Subscript>2</Subscript> film under UV irradiation

A TiO₂ photocatalytic film was prepared by the sol–gel and dip-coating methods. Au-loaded TiO₂ photocatalytic films were produced by the photodeposition method. The photocatalytic activity of the films under UV irradiation was evaluated by measuring the degradation of absorbance for a methylene blue (MB) aqueous solution. Au particles deposited on the TiO₂ film improved the photocatalytic activity under the O₂ bubbling condition. On the other hand, under N₂ or Ar bubbling, the doubly reduced form of MB, leuco-methylene blue (LMB), was formed at the beginning of UV irradiation, and then both MB and LMB were decomposed gradually by the photocatalytic reaction. In this process, Au particles on the TiO₂ film behave as electron traps.     

Preparation and microwave absorption properties of nanosized Ni/SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> magnetic powder

A new type of Ni-coated strontium ferrite powder was prepared with electroless plating enhanced by ultrasonic wave at room temperature. The morphology, crystal structure and microwave absorption properties of the Ni-coated powder were investigated with field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), EDS and vector network analyzer. The results show that the powder possesses excellent microwave absorption properties. The maximum microwave loss of the composite powder reaches −41.3 dB. The bandwidth with the loss above −10 dB reaches 8 GHz.     

Synthesis of magnetic Cu/CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocomposite as a highly efficient Fenton-like catalyst for methylene blue degradation

A magnetic Cu/CuFe₂O₄ nanocomposite was synthesized by a facile one-pot solvothermal method and characterized as an excellent Fenton-like catalyst for methylene blue (MB) degradation. The content of zero-valent copper (Cu⁰) in Cu/CuFe₂O₄ composite could be simply controlled by changing the dosage of sodium acetate in the synthetic process, and the Fenton-like catalytic performance of Cu/CuFe₂O₄ composite enhanced with increasing the Cu⁰ content. In the presence of H₂O₂ (15 mM), the as-synthesized 3-Cu/CuFe₂O₄ nanocomposite could remove 99% of MB (50 mg/L) after only 4 min at pH 2.50, greatly higher than that of pure CuFe₂O₄ and Cu⁰ under the same condition. The enhancement activity of Cu/CuFe₂O₄ nanocomposite was due to the synergistic effect between Cu⁰ and CuFe₂O₄. The radical capture experiments and coumarin fluorescent probe technique confirmed that MB was degraded mainly by the attack of OH^· radicals in Cu/CuFe₂O₄–H₂O₂ system.     

Microwave absorption properties of substituted BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/TiO<Subscript>2</Subscript> nanocomposite multilayer film

The nanocomposite multilayer film (NCMF) of substituted BaFe₁₂O₁₉ and TiO₂ was prepared using sol-gel method. BaFe_10.5Al_1.5O₁₉, BaFe_10.1Al_1.9O₁₉ and BaFe_11.4Cr_0.6O₁₉ with different absorption frequencies were selected to fabricate the multilayer film with TiO₂. The morphology, crystalline structure and microwave absorption property of the NCMF were investigated with an atomic force microscopy, X-ray diffraction and vector network analyses. The results show that the NCMF is uniform without microcracks and it is an ideal microwave attenuation material with a broad frequency range. Its maximum loss efficiency is about −40 dB. The frequency range with the loss above −10 dB is more than 7 GHz. The multilayer film assembles the achievements of each layer film. Moreover, the compounding of ferrites with TiO₂ is helpful to absorb more microwave energy. TiO₂ particles block the growth of ferrite grains and make most of their size within nanometers. TiO₂ also improves the dielectric loss efficiency of the NCMF.     

SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> fibers from titanium-modified polycarbosilane

We developed a process for preparing SiO₂/TiO₂ fibers by means of precursor transformation method. After mixing PCS and titanium alkoxide, continuous SiO₂/TiO₂ fibers were fabricated by the thermal decomposition of titanium-modified PCS (PTC) precursor. The tensile strength and diameter of SiO₂/TiO₂ fibers are 2.0 GPa, 13 μm, respectively. Based on X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM) measurements, the microstructure of the SiO₂/TiO₂ fibers is described as anatase–TiO₂ nanocrystallites with the mean size of ~10 nm embedded in an amorphous silica continuous phase.     

Effects of samarium dopant on photocatalytic activity of TiO<Subscript>2</Subscript> nanocrystallite for methylene blue degradation

Sm³⁺-doped TiO₂ nanocrystalline was synthesized by a sol–gel auto-combustion method and characterized by X-ray diffraction, Brunauer-Emmett-Teller method (BET), UV–vis diffuse reflectance spectroscopy (DRS), and also photoluminescence (PL) emission spectroscopy. The photocatalytic activity of Sm³⁺–TiO₂ catalyst was evaluated by measuring degradation rates of methylene blue (MB) under either UV or visible light. The results showed that doping with the samarium ions significantly enhanced the photocatalytic activity for MB degradation under UV or visible light irradiation. This was ascribed to the fact that a small amount of samarium dopant simultaneously increased MB adsorption capacity and separation efficiency of electron-hole pairs. The results of DRS showed that Sm³⁺-doped TiO₂ had significant absorption between 400 nm and 500 nm, which increased with the increase of samarium ion content. The adsorption experimental demonstrated that Sm³⁺–TiO₂ had a higher MB adsorption capacity than undoped TiO₂ and adsorption capacity of MB increased with the increase of samarium ion content. It is found that the stronger the PL intensity, the higher the photocatalytic activity. This could be explained by the points that PL spectra mainly resulted from surface oxygen vacancies and defects during the process of PL, while surface oxygen vacancies and defects could be favorable in capturing the photoinduced electrons during the process of photocatalytic reactions, so that the recombination of photoinduced electrons and holes could be effectively inhibited.     

Shape-controlled synthesis of Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals and their catalysis of the degradation of methylene blue

Various sizes and shapes of Mn₃O₄ nanocrystals have been prepared in a one-pot synthesis in extremely dilute solution by soft template self-assembly. To better control size and shape, the effects of varying the growth time, reaction temperature, surfactant, and manganese source were examined. The average size of octahedral Mn₃O₄ crystallites was found to be related to the reaction time, while higher reaction temperature (150 °C) and the use of a cetyltrimethylammonium bromide/poly(vinylpyrrolidone) (CTAB/PVP) mixture allowed construction of a better-defined octahedral morphologies. When PVP or poly(ethylene oxide)-poly(propylene oxide) (P123) was used as template, large-scale agglomeration resulting in loss of the octahedral morphology occurred and crystallites with a quasi-spherical shape were obtained. The nano-octahedral crystallites were shown to be an efficient catalyst for the oxidation of methylene blue.      

Preparation of TiO<Subscript>2</Subscript>/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/CF composites for enhanced microwave absorbing performance

To meet the demand of electromagnetic absorption, cheap and easily available microwave absorbents are urgently required. As an important functional material, carbon fibers (CFs) have been widely reported, however, too high conductivity easily leads to the impedance mismatch, which is not favorable to the microwave absorbing performance (MAP). To address this challenge, in this study, novel TiO₂/Fe₃O₄/CF composites with tunable magnetic were synthesized by hydrothermal method and characterized by SEM, XRD, XPS and VSM. As absorbents, the minimum reflection loss (R_L) value is ??41.52 dB at a thickness of 2.1 mm, and the corresponding bandwidth with effective attenuation (R_L?<???10 dB) is up to 5.65 GHz (4.54–10.19 GHz). More importantly, the plausible mechanisms for the enhanced MAP are explored.     

Preparation and characterization of various morphologies of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nano-structures: investigation of magnetization and coercivity

Hard magnetic SrFe₁₂O₁₉ (SrFe) nanostructures were synthesized by a facile chemical precipitation procedure. The influence of temperature, concentration and different capping agents on the particle size and morphology of the magnetic nanoparticles was investigated. The synthesized ferrites were characterized by X-ray diffraction pattern, scanning electron microscope, and Fourier transform infrared spectroscopy. Ferromagnetic property of the hexaferrite nanostructures was determined by vibrating sample magnetometer. The results show hard magnetic ferrite with a high coercivity about 2800–4000 Oe and saturation magnetization around 11–14 emu/g were synthesized.     

The effect of nano sized SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> additions on the magnetic properties of chromium-doped strontium-hexaferrite ceramics

Strontium hexaferrite (SrFe₁₂O₁₉) which crystallizes in the hexagonal system and has a uniaxial magnetoplumbite structure, displays distinctive magnetic characteristics, good chemical stability, good tribological properties and a weak temperature dependent coercivity at about room temperature. In the present work the synthesis conditions for the solid-state preparation of the chromium-doped hexaferrite SrCr_0.3Fe_11.7O₁₉ were optimised and the effect on the magnetic properties of this compound of additions of nanosized SrFe₁₂O₁₉ was studied. The nanosized SrFe₁₂O₁₉ additive, synthesized by the citrate–nitrate reaction, was substituted in varying amounts for a commercial calcium silicate borate sintering additive mixture. A combination of 0.75 wt% of nano-sized SrFe₁₂O₁₉ with 0.75 wt% of the commercial additive increases the intrinsic coercivity, remanence magnetization and rectangularity ratio and results in superior magnetic properties than obtained with 1.5 wt% of nanosized SrFe₁₂O₁₉ or the commercial sintering additive alone.     

SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> ferrites and hard magnetic PVA nanocomposite: investigation of magnetization,coecivity and remanence

In this work, various morphologies of SrFe₁₂O₁₉ (SrFe) nanostructures were synthesized via a simple sol–gel method. The effect of concentration, temperature and various surfactants on the morphology and particle size of the magnetic seeds was investigated. The prepared magnetic products were characterized by X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy techniques. Alternating gradient force magnetometry reveals that the samples exhibit hard magnetic property with the coercivity up to 5300 Oe. Strontium ferrite was added to poly vinyl alcohol to prepare the magnetic polymeric matrix thin film nanocomposites. The saturation magnetization and coercivity decreased due to agglomeration of magnetic nanoparticles in polymer matrix.     

Photoreduction synthesis of silver on Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanocomposites and their catalytic activity for the degradation of methyl orange

This paper demonstrates the preparation of pure TiO₂, 40% of Bi₂O₃ in TiO₂ and Ag loaded Bi₂O₃/TiO₂ nanocomposites by the hydrothermal method followed by the photoreduction process. The crystal structure, morphology and composition of the samples were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy respectively. The dispersion of Ag nanoparticles on the surface of Bi₂O₃/TiO₂ nanocomposites are found to bring the conduction band near to the valence band, resulting in the narrow band gap compared to pure TiO₂ and Bi₂O₃/TiO₂ nanocomposites. The XRD analysis demonstrated that silver nanoparticles were dispersed finely on the surface of Bi₂O₃/TiO₂ nanocomposites. All the characterization results revealed that the Ag/Bi₂O₃/TiO₂ nanocomposites were smaller crystallite size, stronger absorbance in the visible region and greater surface area than pure TiO₂ and Bi₂O₃/TiO₂ nanocomposites. The photoluminescence intensity decreases with an increase in the UV-illumination time of Ag loaded Bi₂O₃/TiO₂ revealing a decrease in the recombination rate of electron–hole pairs. In order to test them as a photocatalyst, methyl orange was used as a standard. The photocatalytic degradation of methyl orange shows that the ABT5 sample exhibits the maximum degradation efficiency of 99% within 180 min of irradiation.     

Ultra-long SiO<Subscript>2</Subscript> and SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> tubes embedded with Pt nanoparticles using magnus green salt as templating structures

For the first time, magnus green salt (MGS, [Pt(NH₃)₄][PtCl₄]) fibers precipitated by solvent modification have been employed as a structure-directing modifier to synthesize single silica and silica/titania microtubes via a sol–gel process. In the case of titania tubes, tetraethylorthosilicate must be used as a capping agent to hinder the aggregation of primary MGS fibers and to serve as a protective layer against thermal stress during the metal salt fiber reduction. This implies that SiO₂/TiO₂ tubes result. The synthesized tubular materials were imaged by scanning and transmission electron microscopy, while their composition was determined by energy dispersive X-ray analysis and thermogravimetric analysis. Crystallinity and thermal stability of the tube walls were studied using X-ray diffraction analysis. The obtained oxide tubes possess high aspect ratios (80–200) because they are up to 60 μm in length, but only 300–700 nm in thickness. The key aspects of the synthesis approach are that the templating MGS fibers control the internal diameter of the oxide tubes, while the synthesis conditions control their wall thickness. The suggested method is a simple approach which produces, at low temperatures, very long oxide tubes with a very high amount of Pt (48–51 wt%) directly incorporated inside the tubes. To the best of our knowledge, filling of SiO₂ or SiO₂/TiO₂ nanotubes with such a dense population of Pt metal nanoparticles has not been demonstrated so far; our own experiments with [Pt(NH₃)₄](HCO₃)₂ as templating salt formed only tubes containing about 40 wt% Pt and were only about 20 μm long. The now formed more Pt-rich tubes are expected to have vivid applications in (photo)catalysis and in fabricating novel devices, such as nano- or sub-microcables.