Fabrication of TiO2/ZnO composite nanofibers by electrospinning and their photocatalytic property

TiO₂/ZnO composite nanofibers with diameters in the range of 85–200 nm were fabricated via the electrospinning technique using zinc acetate and titanium tetra-isopropoxide as precursors, cellulose acetate as the fiber template, and N,N-dimethylformamide/acetone 1:2 (v/v) mixtures as the co-solvent. After treated with 0.1 mol/L NaOH aqueous solution, TiO₂/zinc acetate/cellulose acetate composite nanofibers were transformed into TiO₂/Zn(OH)₂/cellulose composite nanofibers. TiO₂/ZnO composite nanofibers were obtained by calcinating the hydrolyzed composite fibers at 500 and 700 °C for 5 h. The structure and morphology of composite nanofibers were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. With the blending of ZnO into TiO₂, a new crystallite ZnTiO₃ was formed in addition to the ZnO and TiO₂ crystallites, and the ultraviolet light absorption efficiency was enhanced according to the UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of TiO₂/ZnO composite nanofibers toward the decomposition of Rhodamine B and phenol was investigated. Almost 100% Rhodamine B and 85% phenol were decomposed in the presence of TiO₂/ZnO composite nanofibers under mild conditions. The results demonstrated that the blending of ZnO in the TiO₂/ZnO composite nanofibers increased the photocatalytic efficiency. The optimum ZnO content in the TiO₂/ZnO composite nanofibers was 15.76 wt% to reach the most efficient photocatalytic activity. A schematic diagram of photocatalytic mechanism of TiO₂/ZnO composite nanofibers was also presented.     

Fabrication and texture evolution of hexagonal YMnO3 nanofibers by electrospinning

Hexagonal YMnO₃ nanofibers were successfully fabricated by sol-gel preparation based on electrospinning. The as-spun fibers dried at 125 °C were round and had a rather uniform diameter around 0.7 μm-2 μm over its length. In order to get pure hexagonal YMnO₃ nanofibers, crystalline structures and microstructures of fibers at various temperatures for 6 h were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The reasonable evaluations for the change of morphology with the increasing temperature were proposed. After being heated at 1100 °C for 6 h, the pure hexagonal YMnO₃ nanofibers were obtained with a reduced diameter ranging from 200 nm to 800 nm and the fibers were homogenous in chemical constitution over its length.     

Titania nanofibers prepared by electrospinning

TiO₂ nanofibers with a diameter of 54-78 nm have been successfully prepared by electrospinning method using a solution that contained poly(vinyl pyrrolidone) (PVP) and Ti(IV)-isopropoxide. The effect of viscosity and applied electric field on the morphology of the electrospun titania fibers was investigated. It has been observed that the increase in electric field causes bead formation and discontinuity in nanofiber morphology.     

Synthesis and characterization of Co3O4/RuO2 composite nanofibers fabricated by an electrospinning method

Co₃O₄-RuO₂ composite nanofibers (NFs) were synthesized by an electrospinning method and were calcinated at 400°C for 1 hr in air. Scanning electron microscopy and high-resolution transmission electron microscopy (HRTEM) examinations show that all the synthesized NFs have uniform surface morphology and their diameters are in the range of ~ 30-~70 nm. X-ray diffraction (XRD) results show that crystalline Co₃O₄ phase and RuO₂ phase coexist in the composite NF matrix which is confirmed by X-ray photoemission spectroscopy. In addition, the HRTEM energy-dispersive X-ray spectroscopy mapping results show that the Co₃O₄ and RuO₂ phases are uniformly distributed across the NF matrix.     

Preparation of Fe3O4/PVA nanofibers via combining in-situ composite with electrospinning

A novel approach, combining in-situ composite method with electrospinning, was used to prepare high magnetic Fe₃O₄/poly(vinyl alcohol) (PVA) composite nanofibers. Fe₃O₄ magnetic fluids were synthesized by chemical co-precipitation method in the presence of 6 wt.% PVA aqueous solution. PVA was used as stabilizer and polymeric matrix. The resulting Fe₃O₄/PVA composite nanofibers were characterized with field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffractometer (XRD), respectively. These composite fibers showed a uniform and continuous morphology, with the Fe₃O₄ nanoparticles embedded in the fibers. Magnetization test confirmed that the composite fiber showed a high saturated magnetization (M_s = 2.42 emµ·g^-1) although only 4 wt.% content.     

Complicated surface structure of flower-like bunches of LiV0.1Mn1.9O4 nanofibers

LiV_0.1Mn_1.9O₄ nanofibers were synthesized via a conventional solid-state reaction. The nanofibers tend to form bunches with flower-like shapes. Since this interesting form provides a 3D structure, surface analysis of such flowers is of particular interest and was performed by means of small-angle X-ray scattering (SAXS) via the concept of fractal geometry. The results obtained from experimental measurements suggested a fractal dimension close to 3, which is indicative of a 3D structure. This provides an excellent accessibility of the material for diffusion-based reactions, since diffusion within the material is easy through such ordered nanofibers.     

Degradation of 1,4-dioxane in water using TiO2 based photocatalytic and H2O2/UV processes

1,4-dioxane is a synthetic compound found in industrial effluent and subsequently contaminates water bodies due to its high solubility and high volatility. It is of concern due to its toxic and hazardous nature and has been listed as a class 2B carcinogen. This study involved optimisation of the photocatalytic and H(2)O(2)/UVC processes for 1,4-dioxane removal. Different photocatalysts and loadings were investigated for the degradation of low concentrations of 1,4-dioxane in water including a commercial P25, a synthesised magnetic photocatalyst and an immobilised sol-gel system. A commercial catalyst (Degussa P25) was the most efficient. A lifetime study of the sol-gel reactor showed that the coating was stable over the time period studied. The optimum H(2)O(2) concentration in the H(2)O(2)/UVC process was found to be 30ppm. The addition of H(2)O(2) to the photocatalytic process for 1,4-dioxane removal caused a decrease in rate for the commercial P25 photocatalyst and an increase in rate for the lab-made magnetic photocatalyst.     

Synthesis and photocatalytic oxidation properties of titania hollow spheres

The hollow spheres of anatase TiO₂ with higher photocatalytic activity have been fabricated by spherical CaCO₃ nanoparticles as a template, and titanium sulfate (Ti(SO₄)₂) as a precursor, and the CaCO₃ templates were dissolved subsequently in dilute HNO₃ solution. The TiO₂ hollow spheres samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N₂ adsorption-desorption isotherms. The characterization results indicate that as prepared TiO₂ hollow spheres sample was transformed to anatase phase in calcined at 400 °C, and the anatase TiO₂ hollow spheres have a higher specific surface area and show much better photocatalytic activity than commercial P25 in the photodegradation of Rhodamine B under the UV irradiation.     

Preparation and humidity sensing properties of Ba0.8Sr0.2TiO3 nanofibers via electrospinning

Ba_0.8Sr_0.2TiO₃/Poly (vinylpyrrolidone) (BST/PVP) composite fibers were successfully synthesized via electrospinning. The ceramic nanofibers were obtained after calcining the composite at 800 °C for 2 h. The morphology and structure of the BST fibers were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results reveal that the as-synthesized BST nanofibers show a diameter of 50-150 nm with the length over 0.1 mm, and a well-defined perovskite crystal structure. The electrical properties of the as-synthesized BST nanofibers were investigated through an impedance-type humidity sensor. The nanofibers exhibited excellent humidity sensing properties at room temperature. The possible sensing mechanism was proposed.     

Decoration of carbon nanotubes with nearly monodisperse MFe2O4 (MFe2O4, M = Fe, Co, Ni) nanoparticles

Magnetic monodisperse ferrite MFe₂O₄ (M = Fe, Co, Ni) nanoparticles have been successfully deposited on carbon nanotubes (CNTs) by in situ high-temperature hydrolysis and inorganic polymerization of metal salts and CNTs in polyol solution. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectrometry (EDS) and vibrating sample magnetometer (VSM) investigations were used to characterize the final products. The influencing factors for formation of CoFe₂O₄ nanoparticles along CNTs have also been discussed briefly. The main advantage of this synthetic strategy is that it is beneficial for the fabrication of magnetic CNTs with a compact layer of nanoparticles and could be extended to prepare series of ferrite/CNTs nanocomposites via the substitution of metal cations.     

Preparation and characterization of hollow glass microspheres-cobalt ferrite core-shell particles based on homogeneous coprecipitation

Hollow glass microspheres-CoFe₂O₄ (HGMs-CF) core-shell particles were successfully synthesized directly by using the homogeneous coprecipitation method at 90 °C without calcination. The morphology, composition, microstructure and the magnetic property of the samples were characterized by SEM, XRD, EDX and VSM, respectively. The results showed that the HGMs-CF core-shell particles exhibited smooth, compact and continuous CoFe₂O₄ coating on the surface of the HGMs. The Fe/Co atom ratio of the CoFe₂O₄ coating was 2.2, saturation magnetization (M_s) and coercivity (H_c) of the samples were 46 emu/g and 612 Oe, respectively. It was suggested that this method could be applied to the scale industry production for high purity products.     

Synthesis of highly conductive polyaniline nanofibers

Polyaniline nanofiber product synthesized by using both potassium biiodate, KH(IO₃)₂, and sodium hypochlorite oxidant shows high electrical conductivity of greater than 100 S cm^− 1. The nanofiber product also shows not only a long nano-size fibril structure with average diameter of ~ 50 nm and length of ~ 4 μm but also high crystallinity. It was observed that the nanofibers synthesized using the two oxidants give both high electrical conductivity and high crystallinity compared to polyaniline synthesized using commonly known ammonium peroxydisulfate (APS) oxidant. We also found that dimensional and morphological uniformity of PANI nanofibers were greatly improved when the two oxidants were used. The long length and high crystallinity will probably be the contributing factors to have high conductivity. Order of the oxidant addition for the synthesis has no effect on quality of the product. Characterization study was made via UV/Vis absorption spectra, X-ray diffraction (XRD) and scanning electron microscopy (SEM) as well as conductivity measurement.     

Flat epitaxial ferromagnetic CoFe2O4 films on buffered Si(001)

Ferromagnetic films of spinel CoFe₂O₄ have been grown epitaxially on Si(001) using CeO₂/YSZ double buffer layers. The heterostructures were built in a single process by pulsed laser deposition with real-time control by reflection high-energy electron diffraction. YSZ and CeO₂ grow cube-on-cube on Si(001) and CoFe₂O₄ grows with (111) out-of-plane orientation, presenting four in-plane crystal domains. The interface with the buffer layers is smooth and the CoFe₂O₄ surface is atomically flat, with roughness below 0.3 nm. The films are ferromagnetic with saturation magnetization around 300 emu/cm³. The properties signal that CoFe₂O₄ is a good candidate for monolithic devices based on ferromagnetic insulating spinels.     

The fabrication of PPV/C60 composite nanofibers with highly optoelectric response by optimization solvents and electrospinning technology

We have successfully loaded C60 into a PPV precursor using CS2 and ethanol as mixed solvents and fabricated uniform PPV/C60 composite nanofibers by electrospinning for the first time. C60 was homogeneously distributed in nanofibers. The PL spectra analysis confirmed the formation of a composite and revealed the obvious fluorescent quenching comparing with pure PPV nanofibers. Countable electrospun composite nanofibers on a Au interdigitated electrode showed a fast and highly optoelectric response under 100 mW/cm² light irradiation by a Xe lamp. The results showed that photo induced charge transfer took place at the interface of PPV and C60 and suggested the great potential in the field of micro/nano organic optoelectric devices, especially in micro/nano organic photoswitches.     

Effect of working pressure on the properties of BaTiO3-CoFe2O4 composite films deposited on STO (100) by PLD

The BaTiO₃-CoFe₂O₄ (BTO-CFO) composite films were grown on SrTiO₃ (STO) (100) substrates at 750 °C under various working pressures by pulsed laser deposition. The composite film grew into a supersaturated single phase at the working pressure of 10 mTorr, BTO and CFO (00 l) oriented hetero-epitaxial films on STO (100) at 100 mTorr, and a polycrystalline composite film at 500 mTorr. The slow growth rate at high working pressure led to the phase separation in the composite film. The CFO was compressively strained along out-of-plane due to the lattice mismatch with the BTO matrix phase. The BTO-CFO composite film grown at 100 mTorr showed reversible switching of ferroelectric polarization and magnetic hysteresis with strong magnetic anisotropy.     

Synthesis and electrochemical properties of Co3O4 nanofibers as anode materials for lithium-ion batteries

Co₃O₄ nanofibers as anode materials for lithium-ion batteries were prepared from sol precursors by using electrospinning. The morphology, structure and electrochemical properties of Co₃O₄ nanofibers were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and charge-discharge experiments. The results show that Co₃O₄ nanofibers possessed typical spinel structure with average diameter of 200 nm. The initial capacity of Co₃O₄ nanofibers was 1336 mAhg^− 1 and the capacity reached 604 mAhg^− 1 up to 40 cycles. It was suggested that the high reversible capacity could be ascribed to the high surface area offered by the nanofibers' structure.     

Preparation of mesoporous tantalum oxide and its enhanced photocatalytic activity

Mesoporous Ta₂O₅ was synthesized by a surfactant-assisted sol-gel method under mild condition. Based on XRD pattern, the products, obtained by calcination at 600 and 700 °C, were found to be in the amorphous and the orthorhombic phases, respectively. The morphology and pore structure of the products were characterized by SEM, TEM and nitrogen adsorption-desorption measurements. The photocatalytic activity was evaluated by measuring the degradation of methylene blue under UV irradiation. Mesoporous orthorhombic Ta₂O₅ showed higher photocatalytic activity than that of the mesoporous sample in the amorphous state, although orthorhombic Ta₂O₅ had a lower surface area. The reason of this enhanced photocatalytic property is discussed.     

Preparation of one-dimensional photonic crystals by sol-gel process for magneto-optical materials

One-dimensional photonic crystal (PC) of periodically alternating low (SiO₂) and high (TiO₂) refractive index materials was prepared by sol-gel dip coating method that controls the thickness of each layer with nanometer level. The photonic band gap of high reflectivity was verified at wavelengths between 590 nm and 820 nm, which became significant with increasing the number of bilayer. The UV-vis spectra, SEM image and glow discharge optical emission spectroscopy indicate the periodic structure of SiO₂/TiO₂ multilayer. The magnetic layer of CoFe₂O₄ was also prepared by a sol-gel dip coating method. After the annealing at 700 °C, the single phase of CoFe₂O₄ film with spinel structure, without any preferred crystalline orientation, was obtained. In addition, the one-dimensional magnetophotonic crystal (MPC), in which the magnetic defect layer of CoFe₂O₄ is introduced into the periodic structure, was prepared. The light was localized at the magnetic defect due to the interference of the multilayer film, and the localized transmittance was observed around 530 nm. The Faraday rotation of MPC shows a peak at ∼ 570 nm which is close to the localized peak of transmittance. This may correspond to the enhancement of Faraday rotation due to the localization of light.     

Facile synthesis of single crystalline vanadium pentoxide nanowires and their photocatalytic behavior

High quality single crystalline vanadium pentoxide (V₂O₅) nanowires were grown on sapphire and ITO coated glass substrates using spin coating followed by annealing process. The nanowires formed by this method are found to be approximately 5 μm long with an average diameter of 100 nm. The thickness of the spin coated vanadium precursor film played a vital role to form uniform seed layers which are essential for the growth of high quality V₂O₅ nanowires. The growth mechanism was investigated with respect to temperature and thickness of the precursor film. The synthesized nanowires have been proven to be a potential photocatalyst for the degradation of toluidine blue O dye under ultraviolet irradiation.