Ferroelectric materials exhibit a wide spectrum of functional properties,including switchable polarization,piezoelectricity,high non-linear optical activity,pyroelectricity, and non-linear dielectric behaviors.These properties are indispensable for application in electronic devices such as sensors,microactuators,infrared detectors,microwave phase filters and,ultimately,non-volatile memories.Application of ferroelectric bulk form materials have been limited by leakage problems,likely due to low resistivity,defects, and non-stoichiometry issues.Rencently,people expect to change the shape and size of ferroelectric materials to address this problem,and more and more people show a great deal of interest in the synthesis and properties of one-dimensional ferroelectric nanostructures.At the same time,one-dimensional nanostructures are the most potential materials which can be realized in nano-electric devices,nano-photonics devices and nano-mechanics devices,and have also the especial properties of physics and chemistry compared to their bulk materials.Crystal structure and state of polarization is an importand problem not only to its bulk form,but to nanostructured ferroelectric materials.Therefore,the synthesis of one-dimensional ferroelectric nanostructures is the key problem to know how its crystal structure and state of polarization are influenced by the shape and size of ferroelectric materials.Certainly,the synthesis of one-dimensional ferroelectric nanostructures with a controllable size and shape is critical not only in new device applications such as high-density magnetically recorded ferroelectric memory but also from a fundamental point of view.There are many ways to fabricate nanotubes,for example,thermal evaporation, liquid phase method,the anodic aluminum oxide（AAO）membrane method.In all methods,AAO membrane method requires simple devices and lower cost,and AAO membrane with pore diameters of 10～200 nm remains stable at high temperature and in organic solvents,and the pores are uniform in size and well aligned perpendicular to the membrane surface.These advantages make AAO templates ideal for the synthesis of oxide nanotubes and nanowires.In this dissertation,BiFeO3（BFO）and Pb(Zr0.52Ti0.48)O3（PZT）particles and nanotubes have been successfully synthesized.The obtained samples were characterized by X-ray diffraction（XRD）、X-ray photoelectron Spectroscopy（XPS）、Energy dispersive X-ray spectroscopy（EDX）、UV-Visible Absorbance Spectrum、Scanning electron Microscopy（SEM）and transmission electron microscopy（TEM）.The major work in this dissertation includes the following two parts:1.Fabrication,Structural Characterization of BFO particles and nanotubesBFO particles were synthesized by sol-gel method.The XRD showed the particles are of a rhombohedrally distorted perovskite structure,the crystal parameters are ar=5.6107（?）and ar=59.478°.At the same time,the structure instability was investigated by SEM,TEM;Multiferroic BFO nanotube arrays were synthesized by means of the sol-gel method utilizing the anodic aluminum oxide（AAO）membrane technique.The microstructure and components of the BFO nanotubes were investigated by means of XRD,SEM,TEM and XPS,and our as-prepared BFO nanotubes exhibited a polycrystalline perovskite structure,and this study further proves that we have obtained pure phase BFO nanotubes.Simultaneously,the new Y-junction BFO nanotubes were fabriccated successfully and investigated.2.Fabrication,Structural Characterization of PZT particles and nanotubesPZT particles were synthesized by sol-gel method.The XRD showed the particles are of a perovskite structure,the crystal parameters are ar=4.070（?）and ar=89.650°.At the same time,the structure instability was investigated by SEM,TEM and UV-Visible Absorbance Spectrum;PZT nanotubes were synthesized by means of the sol-gel method utilizing the AAO membrane technique.The microstructure and components of the PZT nanotubes were investigated by means of SEM,TEM and XPS,and our as-prepared PZT nanotubes exhibited a polycrystalline perovskite structure.
Post about "nanotubes"
Synthesis and Characterization of One-dimensional Si Nanomaterials and Their Applications as Negative Electrodes in Lithium Ion Batteries
One-dimensional silicon-based nanoscale materials have attracted great interest in the last few years owing to the excellent compatibility with the present silicon technology, and the superior and unique properties of quantum confinement effect and small size effects. Silicon nanowires （SiNWs） and silicon nanotubes （SiNTs） with various morphologies were successfully fabricated by using chemical vapor deposition method. The morphologies, structures and compositions of these nanomaterials were investigated in detail. Furthermore, the optical properties of SiNWs and SiNTs were analyzed though Raman, PL （Photoluminescence） and CL （Cathodoluminescence） spectrum. The application of SiNWs as anode materials in lithium ion batteries was also studied.The main results are summarized as follows:1. Different one-dimensional silicon nanomaterials, i.e., SiNWs and SiNTs, were synthesized by chemical vapor deposition of SiH4 at 480℃through controlling the flow rate of SiH4 at 10 sccm and 5 sccm. By increasing the growth temperature from 400℃to 600℃, the transition from gold-encapsulated, bamboo-like SiNTs of smaller diameters （400℃） to bamboo-like SiNTs （480℃）, and eventually to completely hollow SiNTs of larger diameters （600℃） was observed. For the samples grown at 400℃, the nanostructures have diameters of around 50～70 nm. As the growth temperature increases, the diameters of the products increase to 70～100 nm at 480℃and 80～150nm at 600℃. All the three samples are amorphous, while the morphology are different from each other.①The products obtained at 480℃are bamboo-like SiNTs, which are composed of a series of periodic dome-shaped hollow compartments. In addition, we found that the encapsulated catalytic particles are located at the tips of the SiNTs, and the nanotubes have a wave-shaped outer surface.②Compared to the bamboo-like SiNTs with dome-shaped interior grown at 480℃, the products grown at 400℃reveal that gold nanoparticles are encapsulated along the bamboo-like SiNTs, which we called gold-encapsulated SiNTs with dome-shaped interior.③The hollow interiors along the tubular structures synthesized at 600℃tend to connect with each other, and the products are inclined to form completely hollow SiNTs. No crystal lattice stripes were observed in the HRTEM （High resolution Transmission Electron Microscopy） images, suggesting that all the three samples are amorphous, which were further confirmed by selected area electron diffraction.2. A modified vapor-liquid-solid （VLS） mechanism was proposed to explain the formation of different morphologies of SiNTs. When the liquid droplet becomes supersaturated, silicon growth begins at some nucleation site. At this time, the radius of curvature of one side on the droplet becomes smaller than the other side, which leads to the formation of the additional pressure on the gold surfaces. Thus the liquid droplets are squeezed away by these anisotropic pressures, leaving a dome-shaped （similar to geometry of Au particles） void. If the surface diffusion at 480℃is quick enough to completely wrap the liquid droplet before the additional force to reach a critical point, a solid part will be formed between two dome-shape voids and lead to the obtain of bamboo-like SiNTs. Otherwise, defects will be formed between the two adjacent hollow parts and the formation of silicon nanotubes with completely hollow interior is preferred. At lower temperature （e.g., 400℃）, the liquid droplet will be elongated, instead of being squeezed away suddenly. Driven by the decrease of the surface free energy, the two parts of the elongated particle will separate suddenly, subject to the formation of two individual gold nanoparticles and compartment with dome-shaped void.3. Photoluminescence spectroscopy （PL） and cathodoluminescence spectroscopy and imaging （CL） was used to investigate the optical properties of SiNWs and SiNTs. Two major broad bands were found around 455 and 500 nm for SiNTs, and 455 and 530 nm for SiNWs, respectively; however, the PL intensity of SiNTs was much higher than that of SiNWs. As temperature decreased, both the PL intensity of SiNWs and SiNTs increased gradually. When the temperature was lower than 200 K, these materials appeared two blue emission bands which were attributed to the excess Si atoms in Si nanostructures. The CL spectrum of bamboo-like SiNTs, which is the same as that of SiNWs, has two major bands 470 and 630 nm.4. The SiNTs were observed at about 420 and 520 cm-1 by Raman scattering measurements which were attributed to amorphous SiNTs and excess Si atom in the nanostructures, respectively. Raman spectroscopy of crystalline SiNWs showed a downshift and asymmetric broadening of the Raman first order TO （First-order transverse optical phonon mode, 1TO） phonon peak when compared with the bulk mode, and a shoulder peak at 494 cm-1 was also observed. As the decrease of the laser power, the shoulder peak became clear, while did not shift with the changes of the laser power. The 1TO phonon peak shifted from 508 cm-1 to lower wave number as the decreasing laser power.5. SiNWs electrodes were fabricated by two methods. Method I is to spread as-synthesized SiNWs slurry on current collector; Method II is to directly synthesize SiNWs on a substrate of stainless steel. The electrodes prepared by Method I have shown capacity fading and short battery lifetime, while the other one has a stable capacity over many cycles. The SiNWs prepared by Method II also displayed high capacities at higher currents. In addition, the cyclability of the SiNWs at the faster rates was also excellent. X-ray diffraction （XRD） patterns of SiNWs electrodes （Method II） at open circus potential and various cut-off potentials during the initial discharging process reveal the disappearance of the initial crystalline Si and the start of the formation of amorphous LixSi. The structural features of SiNWs during the initial Li insertion process were studied by SEM （Scanning electron microscopy） and TEM （Tranmission electron microscopy） to understand the high capacity and good cyclability of our SiNWs electrodes. SiNWs before electrochemical reaction were crystalline. However, after charging with Li, the SiNWs had roughly textured sidewalls, and the average diameter increased. Despite the large volume change, the SiNWs remained intact and did not break into smaller particles which are closely related to the 1D structure. Facile strain relaxation in the SiNWs allows them to increase in diameter and length without breaking. Furthermore, the space between each SiNWs allows for better accommodation of the large volume changes without the initiation of fracture that can occur in bulk or micron-sized materials.
One-dimensional or normal one-dimensional structure inorganic nanomaterials have potential application in electronics、photonics、mechanics areas and so on. The nanofibers have been attracted by many researchers and have become the hot study of nano-technology due to their superior optical, acoustic, electrical, magnetic, thermal and mechanical properties. The illuminant rare-earth oxide materials have been widely used in high-tech fields. The study of preparation, properties, and application of the rare-earth oxide nanofibers have become an important subject. In recent years, the electrospining combined with sol-gel is a relatively convenient and useful way to fabrication inorganic nanofibers. Against the back ground of preparation and application of one-dimensional nanomaterials, the article reports on the latest progress in research of one-dimensional naonomaterials and our research achievements with the emphasis of preparing one-dimensional nanomaterials. The contents are as follows:1. The TiO2-ZrO2 complex nanotubes were prepared by sol-gel coating of electrospining polymer fibers. PBS nanofibers were used as substrate, PBS-TiO2-ZrO2 coaxial nanofibers were fabricated using sol-gel coating technique to fill PBS nanofibers that were prepared by electrospining. The TiO2-ZrO2 complex nanotubes were obtained via calcining PBS-TiO2-ZrO2 coaxial nanofibers. SEM、TEM and TG techniques were performed to the nanotubes.2. The inorganic BaO-TiO2 nanofibers have been fabricated by sol-gel combined with electrospining method. PVP was used as substrate, ethanol was used as solvent, while barium acetate and Tetra-n-butyl titanate were used as precursor. The PVP/Ba（CH3COO）2/TiO2 composite nanofibers were fabricated by electrospining. The inorganic BaO-TiO2 nanofibers were obtained via calcining PVP/Ba（CH3COO）2/TiO2 composite nanofibers. TG, SEM, IR, and XRD techniques were performed to the organic and inorganic nanofibers.3. The inorganic Mn doped ZnO nanofibers have been fabricated by sol-gel combined with electrospining method. PVP was used as substrate, ethanol was used as solvent while Mn（CH3COO）2 and Zn（CH3COO）2 was used as precursor. The PVP/Mn（CH3COO）2/Zn（CH3COO）2 composite nanofibers were fabricated by electrospining. The inorganic Mn doped ZnO nanofibers were obtained via calcining PVP/Mn（CH3COO）2/Zn（CH3COO）2 composite nanofibers. TG, SEM, IR, XRD and Fluorescence spectrometer techniques were performed to the organic and inorganic fibers. The XRD indicated that the production structure was ZnMn2O4 crystalline.4. The inorganic La2O3 nanofibers have been fabricated by sol-gel combined with electrospining method. PVP was used as substrate, ethanol was used as solvent while LaAC3 was used as precursor. The PVP/LaAC3 composite nanofibers were fabricated by electrospining. The inorganic La2O3 nanofibers were obtained via calcining PVP/LaAC3 composite nanofibers. TG, SEM, IR, XRD and Fluorescence spectrometer techniques were performed to the organic and inorganic fibers.
Preparation and It’s Mechanism of TiO2 Nanotubes via Anodization in Halide Ions Containing Electrolyte
The unique physical chemistry properties of TiO2 nanotube films derived from high surface-to-volume ratios and specific architectures, making them of great applicable potential in the fields of photocatalysis, gas sensing, photoelectrolysis, and photovoltaics. Therefore, the fabrication of TiO2 nanotube films and the exploration of their potential in practical application have been attracting more and more attention. As a simple electrochemical method, anodization has been widely used in preparation of valve metal (Ti, Zr, Nb, W, Ta and Hf) and aluminum oxide nanotubes or nanoporous films. In the present work, TiO2 nanotubes or nanoporous film was fabricated via anodization of pure Ti in halide ions containing electrolyte. In order to optimize anodization process, morphology and crystalline of TiO2 nanotubes as well as anodization mechanism was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD).TiO2 nanotubes film was fabricated via anodization of pure Ti in fluoride ions containing electrolyte. Morphology of TiO2 nanotubes prepared via Ti anodization in the organic electrolyte showed that the wall thickness of tube reduced with the increase of distance from the bottom. The reason was considered to be chemical dissolution of nanotubes in the solution. At the same time, nanowires covered the nanotubes were thought to be formed by rupture of the upper part of nanotubes in smallest thickness under surface stress.The formation mechanism of TiO2 nanotubes in chloride containing electrolyte was explored through the study of the preparation parameters’effect on pit corrosion of titanium surface and the formation of nanotubes. Formation of appropriate amount of Cl2 led to the formation of nanotubes. Pit corrosion and formation of nanotubes in different areas of titanium surface formed in different time. the chlorine ions in aqueous solution anodizing. At the same time, we recognized that the surface stress, resulted by oxidation of Ti, led to the change of morphology and direction of nanotubes. Due to the formation of nanotubes in different time, nanotubes in different orientation appeared on the surface. On the basis of research in anodization in halogen ions containing electrolyte, both two-step anodization method and ethanol bath were used to fabricate freestanding nanotubes. The mechanism of two-step anodization was discussed. Nanoporous TiO2 was prepared via anodization of Ti substrate from ethanol bath method under the same conditions. The freestanding nanotubes membrane was used to study the crystalline of TiO2 nanotubes through XRD and TEM. The result shows that the third generation TiO2 nanotubes is a mixture of amorphous and anatase TiO2 .
In recent years,nanomaterials,as new type material structures,have attracted considerable attention because of their unique properties and potential applications.At the present time,the studies of SnO2 are almost confined in bulk material at large, however,their nanostructures will have more applications.The reason is that the size of nanostructures reduced to nanometer scale will cause a dramatic increase of surface area to volume ratio,and the quantum sizeconfinement effect is also expected to play an important role in the development of nanotechnology.Therefore,nanostructures of SnO2,such as SnO2 nanoclusters,maybe have more advanced properties perhaps.Computational simulation,which is the third extremely powerful tool to study physical world following experiments and theories,plays a very important role in science and technology,it provides a bridge between theory and experiment.There are two kinds of computational methods to study nanoscale materials.One is ab initio or first-principle calculation;the other is empirical or semi-empirical method.In this thesis,we report the results of density functional theory calculations on the atomic structures of small tin oxide nanoclusters（SnO2）n by using an efficient code,DMol3.The two-dimensional honeycomb structures as the unit cell are to be used to predict the structures of SnO2 monolayers（MLs）.The geometric and electronic structures of SnO2 nanotubes（SnO2 NTs）,which is obtained by rolling the MLs of SnO2,are also investigated.Finally,we investigated the geometric and electronic structures of doped（6,6） and（9,0） SnO2 NTs with Pt substituting Sn atom on the sidewall of SnO2 NTs and their gas sensitivity.This thesis covers the following aspects:Ⅰ.The Theoretical Fundamentals Used in Our Research WorkIn this chapter,the theoretical fundamentals of the first principle calculation without any empirical parameters are described briefly.This method is an effective tool for material design and the studies of the material properties. Ⅱ.The Theoretical Study of SnO2 Clusters and NTsThe structures of different isomers are investigated by density functional theory （DFT）,and the most stable configurations are obtained by comparing their binding energies.For n=1,the configuration of SnO2 is linear;for n=2-4,the most stable configurations are rhombic chains with several rhombus,which are perpendicular to each others;and for n=5-8,it is different from the（SNO2）4,the rhombic chain no longer has the lowest binding energy,the most stable configuration is one-dimensional honeycomb structures;but when n increasing to 9,the two-dimensional honeycomb structures become the most sable configurations.The most stable structure of layered SnO2 consists of a triple layer of O-Sn-O with lattice parameters a=5.69（?） and b=3.25（?）.The calculated binding energies are 14.03 and 14.48 eV/SnO2 for MLs and for bulk SnO2 respectively.The difference of them is only 0.45eV,which implies that SnO2 MLs can be easily synthesized.The SnO2 NTs can be classified into “armchair”（n,n）,”zigzag”（n,0） and chiral （n,m） NTs,similar to CNTs,depending on the rolling direction.We have studied the variation of strain energy involved in different SnO2 NTs as a function of tube diameter,and found that SnO2 NTs can be more easily synthesized than SnS2 NT by comparing the strain energies of SnS2 NTs.Furthermore,we studied the band gaps, and the evolution of the band gaps of these tubes as a function of tube diameter, noting that the value of the HOMO-LUMO gap increases as the tube diameter increases within the same chirality,even though the gaps of the armchair NTs seem to be smaller than those of zigzag NTs for a given diameter.Ⅲ.The Theoretical Study of Pt-doped SnO2 Nanotubes and the Gas SensitivityIn the chapter 3,we have investigated the optimized configurations and electronic structures of functionalized（6,6） and（9,0） SnO2 NTs with Pt substituting Sn atom on the sidewall of SnO2 NTs.It is clear that the structure distortion due to Sn substituted with Pt atom occurs in the region around the doping site on the tube,and the bang gap is smaller than that of pristine nanotube,and the activity of Pt-doped SnO2 NTs is increased.When gas molecules,such as CO,are introduced to the pristine or doped SnO2 NTs,they are physically adsorbed on the surface of these nanotubes,resulting that their electronic structures are modified.It is interesting to be used in detection of toxic gases.
Nanotechnology makes the means and capability of recognizing and rebuilding of the physical world extend to the level of atom and molecule.The nanomaterial is the basis of the application of nanotechnology.It is a hotspot in the present research of the materials science.According to the different phase of materials,preparation methods are to be divided into three classes:solid phase reaction,liquid phase reaction and gas phase reaction.This paper mainly introduces the way of preparation and characterization of the low dimension of nanomaterials.The structure, morphology and character of the nanomaterials were employed by the X-ray diffraction（XRD）（D/Max-2400X）,transmission election microscopy（TEM, JEM-2100EX）,high resolution transmission electronmicroscopy（HRTEM, JEM-2010）,field emission scanning electron microscope（FE-SEM,Hitachi S-4800）, photoluminescence apparatus（PL,Shimadzu RF-5301） and so on.The important results are as follows:（Ⅰ） Formation of Si nanowires1、Si nanowires were synthesized by cathode arc plasma.2、TEM and SEM images indicate that the as-prepared Si nanowires have uniform diameters of between 10-20nm.3、The growth mechanism of the Si nanowires have been discussed and illustrated.4、The photoluminescence of the as-prepared Si nanowires have been investigated.（Ⅱ） Formation of the SbSn nanotubes1.SnSb nanotubes are successfully prepared by heat treatment of pure SnSb nano-sized particles which were obtained by DC arc discharge.2.TEM and SEM images indicate that the as-prepared SnSb nanotubes have rough surfaces and a uniform diameter of about 200 nm.3.A possible growth mechanism of the SnSb nanotubes was proposed.（Ⅲ） Sb2S3 nano-flakes prepared via hydro-thermal method 1.Sb2S3 nano-flakes are successfully prepared by hydro-thermal treatment of pure Sb2O3 nano-sized particles which were obtained by DC arc discharge.2.TEM and SEM results show that the product prepared in neutral solution （ph=7） is Sb2S3 nano-flakes with a uniform thickness of about 20nm.3.The band gap of the as-prepared Sb2S3 nano-flakes is about 1.72eV according to its absorption spectra of UV and visible.
TiO2 is an important kind of inorganic materials,have very good application prospects in many fields.However,TiO2 has a large band gap（3.2eV）,which results in low sunlight absorption efficiency.Up to now,this is still one of critical problems confining the widespread applications of TiO2 as either photocatalyst or photovoltaic material.Many methods have been employed for improving the visible light response of TiO2 such as substitution by metal or nonmetal element,dye sensitization,modifications with some inorganic semiconductors.In this study,a series of nanocrystalline TiO2/MnTiO3 composite samples were prepared by a hydrothermal method and investigated by XRD,UV-vis DRS,Raman spectrum and SPS,respectively.As we predicted,the photo absorption property of TiO2 was obvious improved after the modification with MnTiO3.There are visible changes in XRD,Raman spectra and SPS results after loading with MnTiO3,which was interpreted by the surface defect changes due to MnTiO3 loading.TiO2/MnTiO3 composite nanotubes were successfully synthesized by hydrothermal method.The spectroscopic properties of the samples were,respectively,characterized. After the loading of MnTiO3,the surface states of the samples is changed,which conduces the variation of lattice parameter in TiO2.Moreover,with the increase of MnTiO3 quantity,the visible-light absorption performance of the composite nanotube samples were gradually improved.Obvious changes can be observed in the Raman spectra after the modification of MnTiO3.All these results can offer new foundation for the further research about the photocatatytic property of TiO2/MnTiO3 composite nanotubes.
TiO2,with a wide direct band gap 3.0eV（rutile） and 3.2eV（anatase）, is an important n-type semiconducting material. High-aspect-ratio TiO2 nanotubes and nanowires who possess favorable photocatalyse and sensing properties, are attracting broad attention. In this thesis,we thesis,we prepare TiO2 nanotubes films and investigate their optical absorption and humidity sensing properties; synthesize TiO2 and Na2Ti3O7 nanowires and study their humidity sensing properties. A series of important results are obtained.In this paper, high-ordered P-doped TiO2 nanotube arrays films with the tube diameters of 20-100nm have been prepared by electrochemical anodize method in the mixture electrolyte of HF and H3PO4. Through the measurements of TiO2 nanotubes films by scanning electron microscopy（SEM） and X-ray diffraction, it was found that the TiO2 nanotubes we prepared is uniformed and ordering tubes arrays. The tubes vertically growth on the Ti plate, and parallel each other. FESEM micrographs show that the tube diameters are increased with the increasing voltages. The diameters of tubes formed in 1% H3PO4 and 0.5% HF, at 10V, 15V, 20V and 25V for 2h, are about 20nm, 70nm, 100nm and110nm. When the voltages increase to 27.5V and 30V, the nanotubes morphologies are destroyed. The TiO2 nanotubes formed in 1% H3PO4 and 0.5% HF at 20V voltage for 2h are uniform and arranged orderly, so it is the perfect condition for the synthesization of TiO2 nanotubes. The unannealed nanotubes is amorphous, the sample annealed at 300℃is anatase and the rutile appears in the sample annealed at 600℃.With the increasing the amount of H3PO4 from 1% to7%, the primary peak of anatase shifts from 25.43°to 25.3°.The studies on optical absorptions of the TiO2 nanotubes indicate many conclusions. The optical absorption edge of the sample formed in 1% H3PO4 and 0.5% HF shows t red-shift comparing with that of the sample formed in 0.5% HF. This phenomenon indicates that the use of H3PO4 could change of band gap of TiO2 and further induce the red-shift of the optical absorption edge. With the increasing voltage, the optical absorption edge also show obvious red-shift. The possible reason is the applied voltage could influence the dopant in the TiO2, and induce the optical absorption edge shifting to longer wavelength. The absorption in ultraviolet area is obviously enhanced with more H3PO4 being used.The studies on the humidity sensing properties of the sensor made of TiO2 nanotube arrays show the conclusion as follow: The novel sensor based on TiO2 nanotube arrays is effective. The sensors based on the samples annealed at 400℃, 500℃and 600℃show different response to the change of relative humidity. The sample annealed at 600℃show the highest sensitivity with the two roders change in resistance at 11-95 % RH.TiO2 and Na2Ti3O7 nanowires were synthesized by a simple hydrothermal method. Through the measurements of FESEM and TEM, it is found that the nanowires are of typical lengths ranging from several micrometers to several tens of micrometers. The average diameter of the nanowires is found to be about 100 nm, some nanowires form bundles of～500 nm in diameter and some of the nanowires lay close to each other to form bundles. The XRD patterns show the direct production of hydrothermal reaction is Na2Ti3O7 nanowires, after treating by dilute HCl, the H+ replace the Na+ to form the H2Ti3O7 nanowires. The H2Ti3O7 nanowires which is annealed at high temperature would change to TiO2 nanowires.We fabricated the humidity sensors based on TiO2 and Na2Ti3O7 nanowires.and investigated the humidity sensing properties of these sensors. It is found that both the two sensor show high sensitivity to the change of relative humidity from 11 to 95% at low frequencese. The response time of TiO2 and Na2Ti3O7 nanowires sensors is 9s and 5s, the recovery time is 13s and 6s. It indicates that the Na2Ti3O7 nanowires shows more rapid response to the humidity change than TiO2 nanowires. There are not obvious change on sensitivity, response and recovery time of Na2Ti3O7 nanowires sensors, which indicate its humidity sensing properties is better than TiO2 nanowires sensor. It can be noted that the sensing element exhibits a narrow hysteresis loop during cyclic humidity operation. The maximum humidity hysteresis is around 3% RH under about 80% RH, <5%, is up to the mustard of the normal humidity sensor. In the test of humidity response of the sensor at different temperatures, the curves of resistance vs. humidity show parallel shift. The average temperature coefficient between 15 and 35 oC is about 0.2 % RH / oC in the humidity range of 11–95 % RH. But there is no obvious change on the sensitivity, response and recovery time.
Anodic aluminum oxide (AAO) have ordered arrays of uniform nanochannels, making it a important material in the preparation of one-dimensional nano-materials. In this work, we prepared polymer nanotubes using AAO as template, the surface functionalizaiton of AAO membrane by ATRP was also studies.Porous alumina oxide membrane (AAO) as a template to prepare a variety of one-dimensional array of polymer nanotubes. The PEI and PAN nanotubes array has been prepared by this method, and the different wall thickness of nanotubes was prepared by changing the polymer concentration. The polymer nanotubes were further carbonized to carbon nanotubes.A facile method for surface-initiated atom transfer radical polymerization (ATRP) on the anodic aluminum oxide (AAO) membranes has been developed. The AAO membrane was firstly functionalized by poly(dopamine), the bromoalkyl initiator was then immobilized on the poly(dopamine) functionalized AAO membrane surface in a two-step solid-phase reaction, followed by ATRP of acrylic acid (AAc) and Methyl methacrylate (MMA) in a aqueous solution. The polymer-grafted AAO membranes were characterized by X-ray photoelectron spectroscopy (XPS), fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The XPS and FTIR results indicated that PAAc was successfully grafted on the AAO membrane surface. The results indicate that the thickness of the grafted polymer inside the isocylindrical pores of AAO membranes could be well controlled by changing the reaction time and monomer concentration.
Thermoelectric（TE） materials are functional materials,which can directly convert electricity into heat energy or reversely.They are promising materials in engergy area and have been applied in power generators and cooling/heating devices.Bi2Te3 and its alloys are the best TE materials available near room temperature currently.Bi2Te3 and Bi2Se3 both have wide applications in TE area and Bi2Se3 can be used in optical area additionally.In the present work,hydrothermal method is applied to synthesize Bi2Te3 and Bi2Se3 nanopowders.X-ray diffraction（XRD）,high-resolution transmission electron microscopy （HRTEM） and field emission scanning electron microscopy（FESEM） are used to investigated phases and morphologies of products respectively.Chemical and crystalline mechanisms during the synthesis were investigated.Some important results of the work are listed below.Bi2Se3 and Bi2Te3 nanopowders have been successfully synthesized using an easy chemical method.Nanoparticles of Bi2Se3 and Bi2Te3 as small as several tens nanometers were obtained at 105℃.Intact hexagonal Bi2Se3 crystals are observed in the product reacting at 190℃more than 16 hours with several hundreds nanometers in diameter.32 hours are necessary to react completely,for avoiding impurities.The grain sizes of Bi2Se3 increased with the increasing of temperature obviously.Intact hexagonal Bi2Se3 nanoplates were successfully synthesized,using ethylene glycol （EG） as solution.EG is solution,reductant and dispersant in this process.Bi2Se3 nuclei form gradually since the reduction of EG is weak,crystals can grow slowly with enough building-blocks,thus there are few defects.Influence of some important additions were studied.Experimental result shows that the reactive order,morphologies of products are directly affected by the amount of NaOH.Also, the amount of NaBH4 should not more than two times to the amount of reactants.Too much NaBH4 leads to impurities such as BiTe or Bi4Se3.Ordering Bi2Se3 nano-arrays were fabricated by controlling the amount of NaOH.These arrays are composed of nanoplates about 30 nm thick while the whole arrays are 20μm in size.XRD and TEM were used to analyze the crystalline mechanism of these nano-arrays. The results showed that NaOH was the key of the nano-arrays.These nano-arrays are formed on the by-product Bi2SeO2,which are considered as natural templates.The（0 1 5） surface of Bi2Se3 and（1 0 1） surface of Bi2SeO2 match each other and Bi2Se3 crystals grow along their a or b-axis.