A study on defect controlled morphology of Organic/Inorganic composite nanofibers with different heat flow rates

One dimensional nanofibers of organic and inorganic materials have been used in filters, optoelectronic devices, sensors etc. It is difficult to obtain ultra fine fibers of inorganic materials having lengths in the order of millimeter as they tend to break during formation due to thermal and other mechanical stresses. In this study, we have investigated the mechanism to prevent the defect formation and the breaking ZnO nanofibers by using optimized heat flow rates. ZnO nanofibers were obtained by heat treating the PVA composites fibers formed by electrospinning. The morphology and structural characteristic of prepared samples were investigated by Scanning electron microscopy and X-ray diffraction. It was found that the morphology of the composite and annealed nanofibers could be influenced by the concentration of the polymer content and heat flow rate during thermal treatment respectively. A lower concentration favors the formation of defects along the fiber and the number of defects reduces when the concentration is increased. The reasons for the formation of defects and their reduction, and the observed structural changes of ZnO nanofibers during heat treatment are also discussed.     

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.     

Stability of ZnO nanofibers in processing liquid agents

The aim of the research was to determine the impact of developers, removers and solvents on the stability of ZnO nanofibers. Surface imaging of nanofiber morphology was studied using Scanning Electron Microscope. From the obtained results a set of factors which have the least influence on the etching of ZnO nanofibers during device processing was selected. The dependence of the grains size on the fibers robustness in the liquid solutions was investigated. It was found that the nanofibers calcinated at higher temperatures were more stable. This was due to the grain size of the fiber as the fibers calcinated at higher temperatures revealed larger grain size. The studies have shown that smaller grains were dissolved much faster, leaving the porous core of the ZnO nanofiber.     

ZnO films grown on cotton fibers surface at low temperature by a simple two-step process

Zinc oxide (ZnO) films have been synthesized and deposited onto cotton fiber surface using a simple two-step process. At first step, the cotton fiber surface was coated with a conductive layer of zinc-cellulose complex by rinsing the fibers in zinc chloride solution. After that, the growth of ZnO films was carried out in zinc acetate aqueous solution at room temperature, with alkaline aqueous solution drops continuously added under magnetic stirring. The morphology of the as-prepared ZnO-coated cotton fibers was characterized by scanning electron microscopy. Infrared and photoluminescence spectra were used to confirm the existence of ZnO. In addition, the formation mechanism of ZnO-coated cotton fibers is discussed in detail.     

Electrospun nanofibers of p-type NiO/n-type ZnO heterojunctions with enhanced photocatalytic activity

One-dimensional electrospun nanofibers of p-type NiO/n-type ZnO heterojunctions with different molar ratios of Ni to Zn were successfully synthesized using a facile electrospinning technique. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance (DR) spectroscopy, resonant Raman spectroscopy, photoluminescence (PL) spectroscopy, and surface photovoltage spectroscopy (SPS) were used to characterize the as-synthesized nanofibers. The results indicated that the p-n heterojunctions formed between the cubic structure NiO and hexangular structure ZnO in the NiO/ZnO nanofibers. Furthermore, the photocatalytic activity of the as-electrospun NiO/ZnO nanofibers for the degradation of rhodamine B (RB) was much higher than that of electrospun NiO and ZnO nanofibers, which could be ascribed to the formation of p-n heterojunctions in the NiO/ZnO nanofibers. In particular, the p-type NiO/n-type ZnO heterojunction nanofibers with the original Ni/Zn molar ratio of 1 exhibited the best catalytic activity, which might be attributed to their high separation efficiency of photogenerated electrons and holes. Notably, the electrospun nanofibers of p-type NiO/n-type ZnO heterojunctions could be easily recycled without a decrease of the photocatalytic activity due to their one-dimensional nanostructural property.     

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.     

Growth of ZnO nanorod forests and characterization of ZnO-coated nylon fibers

ZnO nanorod forests were grown wrapping nylon fibers using a two-step process. In the first step, the formation of ZnO seeds at nylon fiber surfaces was induced by the dip coating of ZnO nanosols; in the second step, the growth of the ZnO seeds into nanorod forests was carried out via a wet chemical route in a bath containing an equimolar solution of zinc nitrate hexahydrate and hexamethylenetetramine. The as-obtained ZnO-coated nylon fibers were characterized by scanning electron microscopy, Energy dispersive X-ray spectrum imaging, and X-ray diffraction, respectively. Thermal gravimetric analysis of the pristine and the ZnO-coated nylon fibers was also conducted.     

ZnO纳米线阵列湿度传感器研究

采用水热法在Au/Ni叉指电极上原位生长出整齐的ZnO纳米线阵列。纳米线的平均直径和长度分别为50 nm和5μm,且沿[0001]方向高度择优生长。测试了基于纳米线阵列的湿敏器件对不同湿度电容和电阻响应,并分析了它的工作机制。实验结果表明,这些器件具有相对较大的灵敏度和较短的响应和恢复时间,从而说明ZnO纳米线阵列在湿敏领域有很好的应用前景。     

Nano-octopus: a new form of branching carbon nanofiber

A new multibranched octopus-type structure of carbon nanofibers is synthesized from a natural precursor, camphor, by a thermal chemical vapor deposition technique. An alloy of Cu:Ni catalyst is prepared by electrochemically coating nickel on a copper sheet, with nickel sulfate as an electrolyte, and heating that nickel-coated copper sheet to a higher temperature. Deposition of carbon on these substrates leads to the formation of a branched nanostructure in the temperature range of 923 K to 1023 K. The fiber diameter increases from 30 nm to 250 nm with increasing pyrolysis temperature. Detailed morphology and the internal structure of these fibers are studied by scanning and transmission electron microscopy.     

Optical and magnetic properties of Cu-doped ZnO nanoparticles

Cu-doped ZnO nanoparticles were synthesized by a simple chemical method at low temperature with Cu:Zn atomic ratio from 0 to 5 %. The synthesis process was based on the hydrolysis of zinc acetate dehydrate and copper acetate tetrahydrate heated under reflux to 65 °C using methanol as a solvent. X-ray diffraction (XRD) analysis reveals that the Cu-doped ZnO crystallize in a wurtzite structure with a change of crystal size from 12 nm for undoped ZnO to 5 nm for Cu-doped ZnO. These nano size crystallites of Cu doped ZnO self-organized into microspheres. The XRD patterns, Scanning electron microscopy and transmission electron microscopy micrographs of doping of Cu in ZnO confirmed the formation of microspheres and indicated that the Cu²⁺ is successfully substituted into the ZnO host structure of the Zn²⁺ site. Cu doping shifts the absorption onset to blue from 373 to 350 nm, indicating an increase in the band gap from 3.33 to 3.55 eV. A relative increase in the intensity of the deep trap emission of Cu-doped ZnO is observed when increasing the concentration of Cu. Magnetic measurements indicate that Cu-doped ZnO samples are ferromagnetic at room temperature except pure ZnO.     

Preparation of single conjugated polymer nanofibers with high opto-electric response

Single pristine poly(p-phenylene vinylene) (PPV) nanofibers were prepared by electrospinning. The fibers were characterized by fluorescence microscopy, scanning electron microscopy, and polarized fluorescence spectra. The results indicated that the fibers were stretched and oriented toward to rollup direction during the electrospinning process and PPV polymer molecules were oriented with their conjugated backbones along the PPV fiber direction. The parallel array of countable PPV nanofibers was assembled into a photoconductor device. The device shows much higher sensitivity to photo detection than device with PPV film, indicating efficient carrier transport in the well-oriented polymer fibers. This facile, easily operated method for the fabrication of well-oriented fibers indicates its potential application in optoelectronic devices.     

Statistical optimization of the electrospinning process for chitosan/polylactide nanofabrication using response surface methodology

In this study, chitosan/polylactide (CP) blend solutions in trifluoroacetic acid as a co-solvent with different blend ratio were electrospun. Effects of different CP ratio and process parameters on the diameter of electrospun nanofibers were experimentally investigated. The fiber morphology and the distribution of fiber diameter were investigated by scanning electron microscopy. Response surface methodology (RSM) was used to define and evaluate a quantitative relationship between electrospinning parameters, average fiber diameters and its distribution for each chitosan–polylactide ratio. Applied voltage and polymer solution extrusion rate are the process variables which control the fiber diameter at similar spinning distances (15 cm). Fiber diameter was correlated to these variables by using a second-order polynomial function. The fibers were of diameter ranging from 94 to 389 nm. The predicted fiber diameters were in good agreement with the experimental results. Contour plots were obtained to identify the processing variables suitable for producing nanofibers. It was concluded that ratio of polylactide and chitosan in the blend polymer played an important role to the diameter of fibers and standard deviation of fiber diameter. The processing factors were found statistically significant in the production of nanofibers.     

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.     

Synthesis of ultrafine lanthanum ferrite (LaFeO3) fibers via electrospinning

Ultrafine one-dimensional LaFeO₃ nanofibers were synthesized by electrospinning utilizing sol-gel precursors. The surface morphology, microstructure and crystal structure were investigated by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The nanofibers with smaller diameter were continuous and uniformly distributed. Typical fiber diameter was between 180 nm and 220 nm and the average diameter was 200 nm. The fibers consisted of many single-crystal LaFeO₃ grains and the grain size was about 20-50 nm. The relationship between the diameter of as-synthesized fibers and the PVP concentration of the precursor was investigated. The experimental results indicated that the PVP concentration had a great impact on the fiber size and 5.89 wt.% PVP concentration in sol-gel precursors was advantageous to the formation of more uniform electrospun composite fibers with smaller diameter.     

Nanofibrous TiO2-core/conjugated polymer-sheath composites: synthesis, structural properties and photocatalytic activity

Nanofibrous TiO2-core/conjugated polymer-sheath composite nanocables were synthesized by in-situ chemical oxidative polymerization of aniline with oxidant in the presence of TiO, nanofibers prepared through an electrospinning process. During the polymerization process, aniline molecules were adsorbed on the surface of TiO2. Upon the addition of oxidant, the polymerization of aniline takes place on the surface of the TiO2 nanofibers and polyaniline (PANI) is gradually deposited on their surface. The resulting TiO2-PANI nanocomposites have a coaxial nanocable structure. The morphological and structural properties of the composite nanocables were analyzed by using high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) and UV-visible spectroscopy (UV-vis), respectively. The HRTEM images proved that PANI (20 nm thickness) covered the surface of the TiO2 nanofibers. Also, the photocatalytic activity for the degradation of organic dyes on fibrous photocatalysts under UV-light was studied. The photocatalytic experiments showed that dye could be degraded more efficiently on the TiO2-PANI composite nanocables than on pure TiO2, due to the charge transfer from PANI to TiO2. The method for the synthesis of these unique structured composite nanocables is simple, rapid and reproducible. This facile method may be developed to produce multifunctional nanocomposites of various polymers with metal oxide fibers on a large scale for various technological applications such as sensors, solar cells, and catalysts.     

Direct imaging of copper catalyst migration inside helical carbon nanofibers

By using a double-aberration-corrected (scanning) transmission electron microscope (STEM/TEM) at an acceleration voltage of only 80 kV, we demonstrate that, due to the low solubility of copper (Cu) in carbon and its affinity with oxygen (O), single-crystal Cu catalysts dissociate into small cuprous oxide (Cu2O) nanoparticles after the growth of carbon nanofibers, and Cu2O nanoparticles ultimately localize on the fiber surfaces. This new finding is a step toward a better understanding of the interactions between Cu catalysts and carbon nanomaterials and could suggest a simple and effective method for eliminating Cu impurities from the fibers.     

AZO中空纳米纤维的制备及光催化性能

为了制备高效环保的光催化剂,首先通过静电纺丝制备了PVA(聚乙烯醇)纳米纤维膜,再通过水热合成法在PVA纳米纤维外包覆一层锌铝氢氧化物制得AZO(掺杂铝元素的氧化锌)前驱体@PVA,将AZO前驱体@PVA在空气气氛下高温煅烧成功制备出AZO中空纳米纤维。采用扫描电子显微镜、X射线衍射仪、X射线光电子谱仪、热重分析仪、紫外分光光度计等对样品的形态、结构、性能进行测试表征,结果显示AZO中空纳米纤维具有良好的光催化降解染料性能。     

Synthesis and Characterization of Cu Nanoparticles Embedded in PAN/β-Cyclodextrin (β-CD) Composite Nanofiber Films

In the study, PAN/β-cyclodextrin (β-CD) one dimensional composite nanofibers were synthesized with sol-gel method and electrospinning, and then, we dipped the composite nanofibers into NaBH₄ aqueous solution acted as reducing agent to fabricate PAN/β-CD/Cu composite nanofibers. We got the PAN/β-CD/Cu composite nanofibers with different concentration of β-CD, and Cu nanoparticles formed on its surface. The final products were characterized using scanning electronic microscope (SEM), fourier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM). The results of characterization showed that the Cu nanoparticles with small size were well-distributed on the composite nanofibers.     

Epitaxial growth of ZnO nanorods on electrospun ZnO nanofibers by hydrothermal method

In this paper, we report a new ZnO nanofibers-nanorods structure which was successfully prepared by the electrospun ZnO nanofibers as seed to guide hydrothermal epitaxial growth of the ZnO nanorods. The structure was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL). The XRD results indicate that ZnO nanofibers obtained at 600° have high crystallinity with a typical hexagonal wurtzite structure. Furthermore compared with the strongest diffraction of ZnO nanofibers in (101) plane, the diffraction from (002) plane of ZnO nanofibers-nanorods becomes the strongest. The SEM shows that the diameters of epitaxial-grown ZnO nanorods on ZnO nanofibers were approximately 100–200?nm. The PL spectrum shows that the ZnO nanofibers-nanorods have a broad green-yellow emission around 537?nm, in contrast to that of ZnO nanofibers, the peak had obvious redshift about 24?nm and the luminous intensity weakened.     

芳纶纤维表面改性及其对芳纶/橡胶复合材料黏合性能的影响

以原位乳液聚合方法合成水性聚氨酯预聚体（WPUP）包覆纳米ZnO粒子（ZnO@WPUP）,将KOH预处理后的芳纶纤维浸渍在改性ZnO乳液中进行二次处理,进一步与天然橡胶硫化,得到ZnO@WPUP改性芳纶/橡胶复合材料,并通过FTIR、SEM和H抽出实验等测试分析ZnO@WPUP对芳纶/橡胶复合材料黏合性能的影响。结果表明：WPUP能有效提高ZnO分散性,随着WPUP含量增加,ZnO@WPUP在芳纶纤维表面分散更加均匀,纤维表面粗糙度增大,改善了芳纶纤维表面橡胶的黏附量,从而大幅度提高芳纶/橡胶复合材料的黏结强度。