Silver Nanoparticles Filling in TiO2 Hollow Nanofibers by Coaxial Electrospinning

This study investigated the coaxial electrospinning process of silver filling in TiO₂ ultrafine hollow fibers using polyvinyl pyrrolidone (PVP) sol/titanium n-butyloxide (Ti(OC₄H₉)₄) and PVP sol/silver nanoparticles as pore-directing agents. The bicomponent fibers were heat treated at 200 °C and calcined at 600 °C. Silver particles having diameters of 5 to 40 nm were deposited on the inner surface of the long hollow TiO₂ nanofibers (outer diameter of 150.300 nm) with mesoporous walls (thickness of 10.20 nm). The morphological structure of the filled ultrafine hollow fibers has been studied by means of infrared (IR) spectrum, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The diameters and wall thicknesses of the hollow fibers could be tuned by adjusting the electrospinning parameters. Compared with other nanostructured TiO₂ materials, such as mesoporous Ag-TiO₂ blending fibers, TiO₂ hollow nanofibers, TiO₂ nanofibers, and TiO₂ powders, the silver filled TiO₂ hollow fibers exhibited a higher photocatalytic activity toward the degradation of methylene blue.     

Controllable Fabrication of TiO2 1D‐Nano/Micro Structures: Solid,Hollow, and Tube‐in‐Tube Fibers by Electrospinning and the Photocatalytic Performance

The solid, hollow, and tube‐in‐tube porous nanofiber structures of TiO₂ are synthesized successfully by a simple non‐coaxial electrospinning method without using a complicated coaxial jet head, combined with adjusting the concentration of the TiO₂ precursor and the pinhole diameter of the jet head and by final calcination. The formation mechanisms of different structured TiO₂ fibers are discussed in detail. This method is facile and effective, and easy to scale up. Furthermore, it is a versatile method for constructing tube‐in‐tube fibers of other metal oxides such as ZrO₂, SiO₂, SnO₂, and In₂O₃. The photocatalytic activity of tubular TiO₂ nanofibers for the degradation of 2‐chlorophenol and 2,4‐dichlorophenol under UV or visible‐light irradiation is better than the one of commercial available TiO₂ powder, rutile, and anatase TiO₂ fibers.     

Structural characterization and photocatalytic activity of hollow binary ZrO2/TiO2 oxide fibers

The formation of hollow binary ZrO₂/TiO₂ oxide fibers using mixed precursor solutions was achieved by activated carbon fibers templating technique combined with solvothermal process. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N₂ adsorption, X-ray photoelectron spectroscopy (XPS), UV-vis, and infrared (IR) spectroscopy. The binary oxide system shows the anatase-type TiO₂ and tetragonal phase of ZrO₂, and the introduction of ZrO₂ notably inhibits the growth of TiO₂ nanocrystallites. Although calcined at 575 °C, all hollow ZrO₂/TiO₂ fibers exhibit higher surface areas (>113 m²/g) than pure TiO₂ hollow fibers. The Pyridine adsorption on ZrO₂/TiO₂ sample indicates the presence of stronger surface acid sites. Such properties bring about that the binary oxide system possesses higher efficiency and durable activity stability for photodegradation of gaseous ethylene and trichloromethane than P25 TiO₂. In addition, the macroscopic felt form for the resulting materials is more beneficial for practical applications than traditional catalysts forms.     

LiCoO2 Hollow Nanofibers by Co‐Electrospinning Sol‐Gel Precursor

LiCoO₂ xerogel hollow nanofibers were first prepared by co‐electrospinning the sol precursor, and the polycrystalline LiCoO₂ hollow nanofibers were obtained after calcination of the xerogel fibers. The obtained hollow nanofibers made up of 20～30 nm nanocrystals were about 100 nm to several micrometers in outer diameter. The hollow nanofibers were detected by means of SEM, TEM, TG, DSC, FTIR, and XRD techniques.     

Photocatalytic Crystalline and Amorphous TiO2 Nanotubes Prepared by Electrospinning and Atomic Layer Deposition

In this work core/shell composite polymer/TiO₂ nanofibers and from those TiO₂ nanotubes were prepared. First, poly(vinyl alcohol) (PVA) and poly(vinylpyrrolidone) (PVP) fibers were synthetized by electrospinning. They were covered with a 100 nm thick amorphous TiO₂ layer by atomic layer deposition at 50 °C. Later the polymer core was removed by two different methods: dissolution and annealing. In the case of dissolution in water, the as-prepared TiO₂ nanotubes remained amorphous, while when annealing was used to remove the polymers, the TiO₂ crystallized in anatase form. Due to this, the properties of amorphous and crystalline TiO₂ nanotubes with exactly the same structure and morphology could be compared. The samples were investigated by SEM-EDX, ATR-IR, UV-Vis, XRD and TG/DTA-MS. Finally, the photocatalytic properties of the TiO₂ nanotubes were studied by decomposing methyl-orange dye under UV light. According to the results, crystalline anatase TiO₂ nanotubes reached the photocatalytic performance of P25, while amorphous TiO₂ nanotubes had observable photocatalytic activity.     

On heat transfer and flow characteristics of jets impinging onto a concave surface with varying jet arrangements

A new electrospinning process was developed for preparing TiO₂ nanofibers using a water-soluble Ti-precursor, [bis(kappa1O-hydroxo)(bis(kappa2O,O′-lactato)titanium(IV)] commonly known as titanium(IV) bis (ammonium lactato) dihydroxide (TiBALDH). The importance of the study is justified by the fact that Ti-precursors used for electrospinning, sol–gel, hydrothermal and other fiber synthesis processes are mostly non-water soluble. Accordingly, anatase TiO₂ nanofibers of diameter between 20 and 140 nm were synthesized by electrospinning and annealing. Polyvinylpyrrolidone (PVP) and different concentrations of TiBALDH were dissolved in a mixture of water, ethyl alcohol and acetic acid to optimize the electrospinning conditions. The thermal decomposition and fragmentation of PVP, TiBALDH and the fibers with 50% mass fraction of TiBALDH were studied by TGA-MS measurements. The fibers were then annealed at 1 °C min^?1 until 600 °C. The TiO₂ fibers were characterized using SEM–EDX, FTIR and XRD

     

Porous α-Fe2O3 hollow microspheres and their application for acetone sensor

Porous α-Fe₂O₃ hollow microspheres were synthesized through a simple and efficient carbon sphere template method. The samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and N₂ adsorption-desorption. Structural characterization indicated that as-prepared α-Fe₂O₃ hollow microspheres had porous structure with around 200 nm in diameter and thin shell about 10 nm thick. The average pore size and Brunauer-Emmett-Teller specific surface area of α-Fe₂O₃ hollow microspheres were 6.5 nm and 111.6 m²/g, respectively. The gas sensing behavior investigation showed that as-synthesized α-Fe₂O₃ hollow microspheres exhibited very good gas sensing property to acetone vapor.     

Multichannel hollow TiO2 nanofibers fabricated by single-nozzle electrospinning and their application for fast lithium storage

Multichannel hollow TiO₂ nanofibers were synthesized via a facile single-nozzle electrospinning method based on phase-separation mechanism. Compared to normal TiO₂ nanofibers, hollow TiO₂ with higher surface area gave rises to a higher surface contribution and ensured a short diffusion path for ion transport. Thus hollow TiO₂ demonstrated superior cyclic ability and excellent rate capability.     

Enhanced ethanol sensing properties of WO3 modified TiO2 nanorods

Pristine and WO₃ decorated TiO₂ nanorods (NRs) were synthesised to investigate n-n-type heterojunction gas sensing properties. TiO₂ NRs were fabricated via hydrothermal method on fluorine-doped tin oxide coated glass (FTO) substrates. Then, tungsten was sputtered on the TiO₂ NRs and thermally oxidised to obtain WO₃ nanoparticles. The heterostructure was characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy. Fabricated sensor devices were exposed to VOCs such as toluene, xylene, acetone and ethanol, and humidity at different operation temperatures. Experimental results demonstrated that the heterostructure has better sensor response toward ethanol at 200 °C. Enhanced sensing properties are attributed to the heterojunction formation by decorating TiO₂ NRs with WO₃.     

Synthesis and characterization of hollow LiNiO<Subscript>2</Subscript> fibers via sol-electrospinning method

Hollow LiNiO₂ fibers have been prepared with a capillary spinneret electrospinning technique combined with the sol–gel method, and the possible mechanism for the fabrication of the hollow fibers was discussed. The xerogel fibers and those calcined at different temperatures were characterized by thermogravimetric (TG) analysis, X-ray diffractometry (XRD), Fourier transform infrared (FT-IR) spectrum, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and etc. The Polyvinyl Pyrrolidone (PVP) has an important role in the formation of hollow LiNiO₂ fibers.     

Shell-in-Shell TiO2 hollow microspheres and optimized application in light-trapping perovskite solar cells

The shell-in-shell structured TiO₂ hollow microspheres with enhanced light scattering ability were synthesized via a facile one step hydrothermal process. The diameter of the microsphere is about 1.5 μm, the core of the unique shell-in-shell structure is composed of TiO₂ nanoparticles with a diameter of about 15 nm, while the shell is constructed with ∼50 nm TiO₂ nanocubes. The hollow space between the outer shell and the inner shell is about 230 nm. The formation mechanism of the unique shell-in-shell structure is interpreted. The design and the optimized application of shell-in-shell structured TiO₂ hollow microspheres in the light-trapping perovskite solar cells are also investigated. Owing to the light scattering properties of the shell-in-shell structure of the hollow microsphere, the optimized photoelectrode exhibits an enhanced photoelectric conversion efficiency of 4.29% using perovskite CH₃NH₃PbI₃ as the sensitizer. The shell-in-shell hollow TiO₂ microsphere shows a 21.2% increase in conversion efficiency when compared with P₂₅ nanoparticels photoanode. The conversion efficiency enhancement is mainly attributed to the increase of short-current density induced by the light scattering effect.     

High ethanol sensitivity of Palladium/TiO2 nanobelt surface heterostructures dominated by enlarged surface area and nano-Schottky junctions

TiO₂ nanobelts were prepared by the hydrothermal growth method. The surface of the nanobelts was coarsened by selective acid corrosion and functionalized with Pd catalyst particles. Three nanobelt samples (TiO₂ nanobelts, surface-coarsened TiO₂ nanobelts and Pd nanoparticle/TiO₂ nanobelt surface heterostructures) were configured as gas sensors and their sensing ability was measured. Both the surface-coarsened nanobelts and the Pd nanoparticle-decorated TiO₂ nanobelts exhibited dramatically improved sensitivity to ethanol vapor. Pd nanoparticle-decorated TiO₂ nanobelts with surface heterostructures exhibited the best sensitivity, selectivity, working temperature, response/recovery time, and reproducibility. The excellent ethanol sensing performance is attributed to the large surface area and enhancement by Schottky barrier-type junctions between the Pd nanoparticles and TiO₂ nanobelts.     

The rheology of Torlon solutions and its role in the formation of ultra-thin defect-free Torlon hollow fiber membranes for gas separation

Fundamental understanding of the material science and rheological engineering to fabricate Torlon^® 4000T-MV and 4000TF hollow fiber membranes with an ultra-thin and defect-free dense-selective layer for gas separation has been revealed. We have firstly investigated the rheology of Torlon^® 4000T-MV and 4000TF dope solutions, and then determined the effect of temperature-correlated shear and elongational viscosities on the formation of Torlon^® fibers for gas separation. Interestingly, Torlon^® 4000T-MV and 4000TF possess different rheological characteristics: the elongational viscosity of Torlon^® 4000T-MV/NMP solution shows strain thinning, while Torlon^® 4000TF/NMP solution shows strain hardening. The balanced viscoelastic properties of dope solutions, which are strongly dependent on the spinning temperature, have been found to be crucial for the formation of a defect-free dense layer. The optimum rheological properties to fabricate Torlon^® 4000T-MV/NMP hollow fibers appear at about 48–50 °C, and the resultant fibers have an O₂/N₂ selectivity of 8.37 and an apparent dense layer thickness of 781 Å. By comparison, the best Torlon^® 4000TF fibers were spun at 24 °C with an O₂/N₂ selectivity of 8.96 and a dense layer of 1116 Å. The CO₂/CH₄ selectivity of the above two Torlon^® variants is 47 and 53.5, respectively.     

Preparation and properties of barium-ferrite-containing glass ceramic fibers via an electrospinning/sol–gel process

Barium-ferrite-containing glass ceramic fibers were successfully prepared by the combination of a sol–gel process and electrospinning technique using basic iron formate, barium acetate and boric acid as the starting materials. After leaching of barium borate matrix, pure phase BaFe₁₂O₁₉ fibers were obtained. The relationship of aged time and viscosity of the precursor solution was studied and the results showed that the viscosity corresponding to the spinnable state was 1–4 Pa s. The morphology, structure and magnetic properties of the obtained fibers were characterized with scanning electron microscopy, transmission electron microscopy, fourier transform infrared spectroscopy, thermo gravimetric analysis–differential scanning calorimetry, vibrating sample magnetometer. The X-ray diffraction results indicate that only the M-type Ba-ferrite and Ba-borate exist. The fibers had rough surface and hollow structure with the diameter no more than 1 μm. The fibers were composed of 40 nm BaFe₁₂O₁₉ nanoparticles embedded in the borate matrix. The coercivity and saturation magnetization of the synthesized fibers were 4,106.9 Oe and 17.8 emu/g, respectively.     

Mg/Na-doped rutile TiO2 nanofiber mats for high-speed and anti-fogged humidity sensors

Mg²⁺ and Na⁺ doped rutile TiO₂ nanofibers have been prepared through in situ electrospinning technique and calcination with poly(vinyl pyrrolidone) (PVP) nanofibers as sacrificed template. The as-prepared composite nanofibers are spin-coated onto a ceramic substrate with three pairs of carbon interdigital electrodes to measure its humidity sensing behaviors. The product exhibits high-speed response (2 s) and recovery (1 s) for detecting moisture. Additionally, under UV irradiation, a water contact angle (θ) of nearly 0° has been observed based on the product, providing our humidity sensor with the anti-fogged properties.     

Detection of liquid petroleum gas using mixed nanosized tungsten oxide-based thick-film semiconductor sensor

The thick-film semiconductor sensor for liquid petroleum gas (LPG) detection was fabricated using a mixed WO₃-based sensor. We present the characterization of both their structural properties by means of XRD measurements and the electrical characteristics by using gas-sensing properties. The sensing characteristics such as sensitivity, working range, cross-sensitivity and response time were studied by using nanosized WO₃-based mixed with different metal oxides (SnO₂, TiO₂ and In₂O₃) and doped with noble metals (Au, Pd and Pt). The WO₃-based mixed with 5 wt.% In₂O₃ and 0.5 wt.% Pd showed the higher sensing characteristic at low concentration of LPG sensor at an operating temperature 225 °C.     

Bi2Ti2O7/TiO2复合纤维：原位水热合成及光催化性能

采用静电纺丝技术制备的TiO2纤维作为模板和反应物,通过原位水热合成了具有异质结构的Bi2Ti2O7/TiO2复合纤维。利用X射线衍射(XRD)、扫描电镜(SEM)、能量散射光谱(EDS)、高分辨透射电镜(HRTEM)和紫外可见吸收光谱(UV-Vis)等分析测试手段对样品的结构和形貌进行表征。以罗丹明B为模拟有机污染物进行光催化降解实验。结果表明:花状Bi2Ti2O7纳米结构均匀地生长在TiO2纤维上,制备了Bi2Ti2O7与TiO2相复合的光催化材料,其光谱响应范围拓宽至可见光区,与纯TiO2纤维相比可见光催化活性显著提高,且易于分离、回收和循环使用。初步探讨了Bi2Ti2O7/TiO2异质结的生长机制和光催化活性提高机理。     

Preparation of PA6/nano titanium dioxide (TiO2) composites and their spinnability

In this work, surface modification technique with coupling agents and anchoring polymerization was adopted to tailor the surface properties of nanoscaled titanium dioxide (TiO₂). Ethyl glycol sols with TiO₂ were prepared in order to simulate the dispersibility of differently modified TiO₂ in a molten polyamide 6 (PA6) matrix. The modified TiO₂ were melt compounded with PA6 and composites and fibers were prepared. The average filler diameter of 47 nm (in composites) and 44 nm (in fibers) indicated homogeneous dispersion of TiO₂ in the matrix, whereas unmodified TiO₂ showed agglomerated structures in the PA6 matrix. The mechanical properties of the composite fibers were improved as compared to pure PA6 fibers and composite fibers with unmodified TiO₂.     

Preparation and photocatalytic activity of B,Ce Co-doped TiO2 hollow fibers photocatalyst

A series of B, Ce co-doped TiO₂ (B, Ce-TiO₂) photocatalytic materials with a hollow fiber structure were successfully prepared by template method using boric acid, ammonium ceric nitrate and tetrabutyltitanate as precursors and cotton fibers as template, followed by calcination at 500°C in an N₂ atmosphere for 2 h. Scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption-desorption measurements, and UV-visible spectroscopy (UV-Vis) were employed to characterize the morphology, crystal structure, surface structure, and optical absorption properties of the samples. The photocatalytic performance of the samples was studied by photodegradation phenol in water under UV light irradiation. The results showed that the TiO₂ fiber materials have hollow structures, and the fiber structure materials showed better photocatalytic properties for the degradation of phenol than pure TiO₂ under UV light. In the experiment condition, the photocatalytic activity of B, Ce co-doped TiO₂ fibers was optimal of all the prepared samples. In addition, the possibility of cyclic usage of B, Ce co-doped TiO₂ fiber photocatalyst was also confirmed, the photocatalytic activity of TiO₂ fibers remained above 90% of that of the fresh sample after being used four times. The material was easily removed by centrifugal separation from the medium. It can therefore be potentially applied for the treatment of water contaminated by organic pollutants.     

Preparation of Mn2O3 and Mn3O4 nanofibers via an electrospinning technique

Thin PVA/manganese acetate composite fibers were prepared by using sol-gel processing and electrospinning technique. After calcinations of the above precursor fibers, Mn₂O₃ and Mn₃O₄ nanofibers with a diameter of 50-200 nm could be successfully obtained. The fibers were characterized by TG-DTA, Scanning electron microscopy, FT-IR, WAXD, respectively. The results showed that the crystalline phase and morphology of nanofibers were largely influenced by the calcination temperature.