Fabrication, structural characterization and formation mechanism of multiferroic BiFeO3 nanotubes

Multiferroic BiFeO3 (BFO) nanotubes have been successfully fabricated by the modified sol-gel method within the nanochannels of porous anodic aluminum oxide (AAO) templates. The morphology, structure and composition of the nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), selected-area electron diffraction (SAED), high resolution TEM, (HRTEM) and energy-dispersive X-ray spectroscopy (EDX). Postannealed (650 degrees C for 1 h), BFO nanotubes were polycrystalline and X-ray diffraction study revealed that they are of the rhomohedrally distorted perovskite crystal structure. The results of SEM and TEM revealed that BFO nanotubes possessed a uniform length (up to 60 microm) and diameter (about 200 nm), which were controlled by the thickness and the pore diameter of the applied AAO template, respectively and the thickness of the wall of the BFO nanotube was about 15 nm. Y-junctions in the BFO nanotubes were observed. EDX analysis demonstrated that stoichiometric BiFeO3 was formed. HRTEM analysis confirmed that the obtained BFO nanotubes made up of nanoparticles (3-6 nm). The possible formation mechanism of BFO nanotubes was discussed.     

阳极氧化铝模板上扩散聚合法制备聚苯胺纳米管(线)阵列

以多孔阳极氧化铝（AAO）为模板，利用扩散聚合法让苯胺单体溶液和氧化剂溶液在一维纳米孔道中相互扩散，在孔内形成聚苯胺（PANI）纳米管和纳米线阵列。利用SEM、TEM、IR和XRD等检测技术对阵列进行表征。结果表明，聚合反应优先发生在孔壁上，并沿孔壁逐层生长，直至形成实心的纳米线阵列。在孔径为60nm的AAO模板内，扩散聚合40min可形成聚苯胺纳米管阵列，2h后形成聚苯胺纳米线阵列；聚苯胺纳米管（线）中同时包含结晶相和无定型相结构。用二探针法测量PANI／AAO复合阵列电阻，计算出单根聚苯胺纳米线的电导率为21．4S／cm。此外，对扩散聚合过程中聚苯胺纳米管（线）阵列的形成原因进行了初步分析和探讨。     

Controlled synthesis of highly ordered LaFeO3 nanowires using a citrate-based sol–gel route

Highly ordered LaFeO₃ nanowires of complex oxide were controlled synthesized with a porous anodic aluminum oxide (AAO) template by a citrate-based sol–gel route. The results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the LaFeO₃ nanowires formed a uniform length and diameter, which were determined by the thickness and the pore diameter of the AAO template, respectively. The results of X-ray diffraction (XRD) and the selected area electron diffraction (SAED) indicated that the LaFeO₃ nanowires had a perovskite-type crystal structure. Furthermore, X-ray photoelectron spectroscopy (XPS) demonstrated that stoichiometric LaFeO₃ was formed.     

A template-based electrochemical method for the synthesis of high dense nickel nanotube arrays

High dense Ni nanotube arrays have been successfully fabricated using electrochemical method with the assistance of anodic aluminum oxide (AAO) template from NiSO4 aqueous solution without any additive. Field emission scanning electron microscope (FE-SEM) results indicate that the pores of AAO template are high uniform and all the pores are filled with Ni nanotubes. Transmission electron microscope (TEM) results demonstrate that the diameter of Ni nanotubes is about 65 nm. The electron diffraction (ED) pattern results show that the Ni nanotubes are polycrystalline. X-ray diffraction (XRD) pattern shows that the electrodeposited nickel is hexagonal crystal structure.     

Silver nanowires prepared by modified AAO template method

Thin film containing highly ordered silver nanowires array was prepared by using anodic aluminum oxide (AAO) template method. The morphology of the silver nanowires was confirmed by scanning electron micrograph (SEM). The result of the SEM showed that the silver nanowires were substantive, parallel, and ordered in the AAO template. Diameter distribution of the silver nanowires indicated that the average diameter was about 35 nm. The composition and structure of the Ag nanowires were investigated by Energy dispersive X-ray (EDX) spectroscopy and X-ray diffraction (XRD) pattern, respectively.     

Template assisted synthesis of SnO<Subscript>2</Subscript> nanorods by immerse and filtration technique,vacuum and drop setting

Honeycomb-shaped and ordered arrays of nanopore AAO template with a uniform pores size was produced utilizing a two-step an anodization process. Highly ordered SnO₂ nanorods arrays have been selectively fabricated via a convenient (immerse and filtration) technique and (vacuum and drop) setting using anodic aluminum oxide (AAO) as a hard template. The morphology of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (FESEM), and Energy-dispersive X-ray spectroscopy (EDX) techniques. The optical characterizations were examined by UV-VIS and Photoluminescence (PL). Scanning microscopy images indicate that the SnO₂ nanorods are relatively uniform with the outer diameter matching well with the pore diameter. XRD and EDX indicated that these polycrystalline SnO₂ nanostructures with well-defined composition were obtained.     

Ni纳米管的电化学模板法制备及表征

本文采用一种简单而有效的电化学方法在硫酸铵体系中利用氧化铝模板(AAO)成功制备出规则有序的Ni的管状纳米阵列.使用这种方法可获得外径约为70nm,内径约为50nm的Ni纳米管.对所得的Ni纳米管进行了扫描电镜(SEM)、透射电镜(TEM)、选区电子衍射图(SAED)和X射线衍射(XRD)分析,结果表明:该方法制备的Ni纳米管高度有序,大小均一,其形貌受控于氧化铝模板的结构,外径与模板的孔径相等.     

Template synthesis of highly ordered hydroxyapatite nanowire arrays

Highly ordered hydroxyapatite (HA) nanowire arrays were synthesized using porous anodic aluminum oxide (AAO) template from sol-gel solution containing P₂O₅ and Ca(NO₃)₂. Theresults of transmission electron microscopy (TEM) and scanning electron microscopy(SEM) revealed that the obtained HA nanowires had a uniform length and diameter andformed highly ordered arrays, which were determined by the pore diameter and thethickness of the applied AAO template. The results of X-ray diffraction (XRD) and X-rayphotoelectron spectroscopy (XPS) demonstrated that the major component was HA. Theselected-area electron diffraction (SAED) results indicated that HA was a polycrystallinestructure. This novel method of preparing highly ordered HA nanowires with a large areamight be important for many applications in biomaterials.     

Polyaniline/CuCl nanocomposites prepared by UV rays irradiation

In present paper, polynailine (PANI)/CuCl nanocomposites were prepared by UV rays irradiation method. In this method, photons in the UV rays and Cu²⁺ ions replaced conventional oxidant such as ammonium persulfate (APS) to promote polymerization of aniline monomer. The PANI/CuCl nanocomposites were characterized by infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscope (HRTEM), and electron diffraction (ED). The results indicated that aniline could polymerize to PANI by UV rays irradiation. Meanwhile, the results of HRTEM and ED confirmed that the CuCl dispersed into PANI was single crystal with cubic crystal structure. A potential formation mechanism of PANI/CuCl nanocomposites was investigated and suggested.     

Synthesis and characterization of polyaniline nanorods/Ce(OH)3-Pr2O3/montmorillonite composites through reverse micelle template

Polyaniline (PANI) nanorods/Ce(OH)₃-Pr₂O₃/montmorillonite (MMT) nanocomposites were synthesized via in situ polymerization of aniline monomer through reverse micelle template (RMT) in the presence of montmorillonite and Ce(OH)₃, Pr₂O₃. In the experiment, sulphosalicylic acid was used as dopant, aniline was designated as oil phase and the aqueous solution comprising Ce³⁺ and Pr³⁺ as water phase. The nanocomposites were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) analysis, Fourier transform infrared (FT-IR) spectroscopy and thermogravimetry-differential thermal analysis (TG-DTA). The results showed that PANI nanorods were synthesized in the interlayer spaces of MMT with uniform spherical rare earth nanoparticles. The thermal stability of the nanocomposites prepared was enhanced drastically compared with pure polyaniline.     

A novel solution-phase route for the synthesis of crystalline silver nanowires

A unique solution-phase route was devised to synthesize crystal Ag nanowires with high aspect-ratio (8-10 nm in diameter and length up to 10 μm) by the reduction of AgNO₃ with Vitamin C in SDS/ethanol solution. The resultant nanoproducts were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD) and electron diffraction (ED). A soft template mechanism was put forward to interpret the formation of metal Ag nanowires.     

An electrokinetic route to rapid synthesis of nickel hydroxide and nickel oxide nanotubes

An electrokinetic route was developed for the synthesis of Ni(OH)2 nanotubes in the nanochannel of anodic alumina oxide (AAO) template. The nanotubes in the template were then converted to NiO nanotubes by calcination in air at 300 degrees. Uniform ordered nanotubes were obtained after selecting proper experimental conditions, such as the ionic concentration, the reaction time and the kind of nickel salts. X-ray diffraction (XRD) analysis indicated that the as-prepared Ni(OH)2 nanotubes were crystalline. Thermogravimetric analysis (TGA) was employed to determine the correlation between temperature and weight lose of the nanotubes. The transmission electron microscope (TEM) and scanning electron microscope (SEM) were used to characterize the morphology and structure of the nanotubes.     

Synthesis of mesoporous silica materials (MCM-41) from iron ore tailings

Highly ordered mesoporous materials were successfully synthesized by using the iron ore tailings as the silica source and n-hexadecyltrimethyl ammonium bromide as the template. The samples were detail characterized by powder X-ray diffraction, scanning electron microscope, high-resolution transmission electron microscopy and N₂ physisorption. The as-synthesized materials had high surface area of 527 m² g⁻¹ and the mean pore diameter of 2.65 nm with a well-ordered two-dimensional hexagonal structure. It is feasible to prepare mesoporous MCM-41 materials using the iron ore tailings as precursor.     

A novel nanostructure of cadmium oxide synthesized by mechanochemical method

Cauliflower-like cadmium oxide (CdO) nanostructure was synthesized by mechanochemical reaction followed calcination procedure. Cadmium acetate dihydrate and acetamide were used as reagents and the resulting precursor was calcinated at 450 °C for 2 h in air. The structures of the precursor and resultant product of the heating treatment were characterized using Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and elemental analysis, X-ray powder diffraction (XRD), energy-dispersive X-ray spectroscopy analysis (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction pattern (ED). SEM and TEM images revealed the cauliflower-like morphology of the sample. This structure includes the bundles of rods and tubes in nanoscale, which combine with each other and form the resulting morphology with the average diameter, 68 nm of the components. ED pattern indicated the single crystal nature of the formed bundles.     

Preparation of gold/polyaniline/multiwall carbon nanotube nanocomposites and application in ammonia gas detection

Composites of multiwall carbon nanotubes (MWNTs), polyaniline (PANI), and gold nanoparticles were prepared by one pot synthesis. Based on the interaction between aniline monomers and MWNTs, aniline molecules were adsorbed and polymerized on the surface of MWNTs. The nanocomposites were characterized by transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoemission spectroscopy (XPS). The sensors based on Au/PANI/MWNT nanocomposites were tested for on-line monitoring of ammonia gas. The results show that the as-prepared sensors have superior sensitivity, and good repeatability upon repeated exposure to ammonia gas.     

Synthesis of high-ordered LiNi0.5Co0.5O2 nanowire arrays by AAO template and its structural properties

High-ordered LiNi_0.5Co_0.5O₂ nanowire arrays were prepared using porous anodic aluminum oxide (AAO) template from sol-gel solution containing Li(OAc), Ni(OAc)₂ and Co(OAc)₂. Electron microscope results showed that uniform length and diameter of LiNi_0.5Co_0.5O₂ nanowires were obtained, and the length and diameter of LiNi_0.5Co_0.5O₂ nanowires are dependent on the pore diameter and the thickness of the applied AAO template. X-ray diffraction and electron diffraction pattern investigations demonstrate that LiNi_0.5Co_0.5O₂ nanowires are a layered structure of LiNi_0.5Co_0.5O₂ crystal. X-ray photoelectron spectroscopy analysis indicates that the most closely resemble stoichiometric layered LiNi_0.5Co_0.5O₂ material has been obtained.     

Novel fabrication of silica nanotubes using multi-walled carbon nanotubes as template

Silica nanotubes were synthesized using multi-walled carbon nanotubes (MWCNTs) as template. The as-obtained samples were characterized by infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM) and photoluminescent (PL) spectroscopy. The results indicate that the thickness of the outer walls is about 10 nm and the inner diameter is completely dependent on the size of MWCNTs. The as-fabricated silica nanotubes emit a strong violet light under excitation of 250 nm.     

Synthesis,structural and magnetic characterization of highly ordered single crystalline BiFeO3 nanotubes

In this work, we report on the fabrication of highly ordered single crystalline BiFeO₃ (BFO) nanotubes by a sol–gel technique using two-step anodic aluminum oxide (AAO) as template. We prepared BFO nanotubes with dimensions of 65 nm in diameter and 3 μm in length, as confirmed by scanning electron microscopy (SEM) measurements. The obtained single crystalline nanotubes present the expected pure phase (BiFeO₃) as confirmed by energy-dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). In addition to the antiferromagnetic behavior, the magnetization curves of the BFO nanotubes also present a ferromagnetic response, which holds from 2 to 300 K. This desirable behavior is associated to the break of the antiferromagnetic helical spin ordering of the BFO nanotubes. Besides the magnetocrystalline anisotropy, the large length-to-diameter ratio induced an uniaxial shape anisotropy, attested by the applied magnetic field angle measurements.     

Synthesis of single-crystalline silver sulfide nanowires by diffusion in porous anodic aluminium oxide template

Highly ordered single-crystalline silver sulfide (Ag₂S) nanowires have been successfully achieved directly using silver nitrate and thioacetamide (TAA) as the reactants, by diffusion in the channels of anodic aluminium oxide (AAO) membrane. The products have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). The results of the research show that the as-prepared Ag₂S nanowires are monodisperse with sizes of about 50 nm in diameter, closely corresponding to the pore size of the AAO membrane. Furthermore, its photoluminescence properties and the growth mechanism are also discussed.     

Study of structural and magnetic properties of (Co–Cu)Fe2O4/PANI composites

The nanocomposites of the polyaniline and Co_1−xCu_xFe₂O₄ (PANI/CoCuFe) were prepared by in-situ oxidative polymerization of aniline. Prepared nanocomposites samples were characterized by using various experimental techniques like X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM), vibrating sample magnetometer (VSM), Mössbauer spectroscopy and ultraviolet–visible spectrophotometry (UV–VIS). The elemental analysis as obtained from the energy dispersive X-ray spectroscopy (EDAX) measurement is in close agreement with the expected composition from the stoichiometry of the reactant solutions. XRD result confirms that all the samples have the single phase cubic spinel structure. Unit cell parameter ‘a’ is found to decrease with the increase in copper ion substitution. The crystallite size was investigated by using the Debye–Scherer formula and it was found in the range of ∼28–37 nm. FE-SEM confirmed the homogeneous and well defined surface morphology of the synthesized samples. FT-IR study showed the main absorption bands corresponding to the spinel structure those arose due to the tetrahedral and octahedral stretching vibrations. Cation distribution was estimated using XRD data. Hysteresis measurements revealed that the saturation magnetization decreased with increase in Cu²⁺ substitution. Magnetic environment of ⁵⁷Fe in Cu-doped cobalt ferrite was investigated by using Mössbauer spectroscopy. Mössbauer study evidenced the ferrimagnetic behavior of the synthesized samples.