Effect of S- and Sn-doping to the optical properties of ZnO nanobelts

In this study, the optical properties of S- and Sn-doped ZnO nanobelts, grown by thermal evaporation, were investigated. The sulfur and tin contents in the nanobelts were about 12% and 8% (atomic), respectively. The average widths of the S- and Sn-doped ZnO nanobelts were 73 and 121 nm, respectively. Room temperature photoluminescence (PL) spectroscopy exhibits significantly different optical properties for the two types of nanobelts. The PL result of the S-doped ZnO nanobelts shows the broad visible emission with no detectable ultraviolet (UV) peak, while the PL result of the Sn-doped sample shows two emission bands, one related to UV emission with a strong peak at 376 nm that is blue-shifted by 4 nm in comparison to pure ZnO nanobelts, and another related to green emission with a weak peak. A weak peak in the UV region at 383 nm appeared after annealing the S-doped ZnO nanobelts at 600 °C. Additionally, the annealed S-doped nanobelts show a stronger peak in the visible emission region in comparison to that observed prior to annealing. The Sn-doped ZnO nanobelts are also affected by annealing, as the UV emission peak is blue-shifted to 372 nm after annealing.     

3D hopping conduction in SnO2 nanobelts

The temperature dependence of the electrical transport of an individual tin oxide nanobelt was measured in darkness from 400 to 5 K. We found four intrinsic electrical transport mechanisms through the nanobelt. It starts with thermally activated conduction between 400 K and 314 K, followed by nearest‐neighbor hopping conduction between 268 K and 115 K and variable range hopping conduction below 58 K, with a crossover from the 3D Mott to the 3D Efros–Shklovskii regime at 16 K. We claim that this sequence reveals the three‐dimensional nature of the electrical transport in the SnO₂ nanobelts, even though they are expected to behave as one‐dimensional systems. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

单晶MgO纳米带的生长特性和发光性能

本文采用直流电弧等离子体喷射化学气相沉积法(DC Arc Plasma Jet CVD),在氢气和氩气的高温等离子体作用下直接分解硝酸镁,在Mo衬底上制备了单晶MgO纳米带,并采用SEM、TEM及XRD等测试手段进行了形貌与结构表征,研究了生长时间对MgO纳米带形貌的影响。结果表明,生长时间为0.5 min时,生长出顶部带有Mo纳米颗粒的"蝌蚪状"MgO纳米带,而整个纳米结构被较多的非晶MgO覆盖;当生长时间增加到2 min时,顶部的Mo纳米颗粒几乎脱落,同时长出若干个纳米带,形成"树枝状";生长时间进一步增加到5 min时,形成完整的"带状",其宽度约30~50 nm;而生长时间达到12 min时,纳米带又转变为"棒状"。机理分析表明,Mo催化VLS生长模式和VS生长模式共同作用下生长了MgO纳米带。另外,通过FTIR谱结合PL谱分析了缺陷及其引起的光致发光性能。由于MgO纳米带存在低配位氧离子(OLC2-)空位等结构缺陷,具有紫蓝发光特性,而随着生长时间的增加,结构缺陷变少,随之紫蓝发射峰强度变弱。本文首次采用该方法制备了单晶MgO纳米带,该方法工艺简单,生长速率快,是非常经济、有效和环境友好的方法。     

Construction of Hydrocarbon Nanobelts

Linearly fused hydrocarbon nanobelts are a unique type of double‐stranded macrocycles that would serve as not only the powerful hosts in supramolecular science but also the templates to grow zig‐zag carbon nanotubes with defined diameters. Fully conjugated hydrocarbon nanobelts such as belt[n]arenes would also possess unique physical and chemical properties. Despite the importance, both fully conjugated and (partially) saturated hydrocarbon nanobelts remain largely unexplored because of the lack of cyclization methods. Reported here is the construction of nanometer sized H₁₂‐belt[12]arenes based on the strategy to close up all fjords of resorcin[6]arene by means of six‐fold intramolecular alkylation reactions of resorcin[6]arene derivatives. All resulting H₁₂‐belt[12]arenes produce a very similar nanobelt core structure with six benzene rings and six boat 1,4‐cyclohexadiene rings being alternately linear‐fused to give a nearly equilateral hexagonal cylinder. The average long diagonal is around 1 nm and the height of the cylinder is about 0.3 nm. The acquired H₁₂‐belt[12]arenes would be the potential precursors to various hydrocarbon nanobelts including fully conjugated belt[12]arenes.     

Fabrication and photocatalytic activity of LaFeO3 ribbon-like nanofibers

LaFeO₃ ribbon-like nanofibers were synthesized via a sol–gel-assisted electrospinning method. The differences in morphology and photocatalytic property of LaFeO₃ nanofibers prepared through different needles were investigated. At the same time, the morphology and photocatalytic activity of porous LaFeO₃ nanobelts formed at different calcination temperatures were also investigated. Scanning electron microscopy results revealed that the obtained ribbon-like LaFeO₃ nanofibers made using a coaxial needle contained a large number of pores. Moreover, with the increase of calcination temperature, the morphology of the fibers also changed. X-ray diffraction analysis showed a series of fibers all in orthorhombic LaFeO₃ phase but no other impurities. In addition, the photocatalytic activity of LaFeO₃ nanofibers was studied for the degradation of methylene blue under visible light. The results demonstrated that ribbon-like nanofibers exhibited excellent photocatalytic activity compared with the others and the LaFeO₃ nanobelts calcined at 500°C had the best photocatalytic activity. Based on the experimental results, possible forming mechanisms involving in LaFeO₃ nanofibers through different needles are also discussed.     

Solution route to inorganic nanobelt‐conducting organic polymer core‐shell nanocomposites

A facile and versatile solution‐based approach was developed to prepare semiconductor metal oxide nanobelt‐conducting organic polymer core‐shell nanocomposites. Well‐defined nanobelts of several types of oxide nanobelts were combined with conducting polymer [polypyrrole (PPy) and polyaniline (PANi)] via in situ polymerization in aqueous solution to obtain a new type of inorganic–organic composite nanostructure. Samples were characterized by using X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, electron energy loss spectra, high‐resolution transmission electron microscopy, and ultraviolet–visible techniques. Electron energy loss spectra revealed the existence of C?C and C? N bonds in coating layers to prove the encapsulation of PPy or PANi. The red‐shift of absorption band at high‐energy was observed for PPy‐encapsulated composites via ultraviolet–visible spectroscopy, and significant absorption band shifts were also encountered to PANi‐encapsulated composites, which suggest possibilities of band‐gap tuning of such metal oxide‐conducting polymer composites to be applied especially in solar cell devices. However, the sacrifice of nanobelts‐core led to hollow structures of PPy and PANi, which expands the synthetic strategies to prepare conducting polymer nanotubes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2892–2900, 2005     

Synthesis of morphologically controlled tin sulfide nanostructures

Different tin sulfide nanostructures, such as nanobelts, nanorightangles, nanorods, and nanosheets, have been synthesized via an efficient solvothermal process. The thickness and width of SnS nanobelts are less than 30 nm and in the range of 50–300 nm, respectively. A nanorightangle is composed of two nanobelts. The influence of synthetic parameters, such as reaction temperature and sulfur sources, on the morphologies of tin sulfide has been investigated.     

Preparation and visible light photocatalytic activity of mesoporous N, S-codoped TiO2(B) nanobelts

The mesoporous N, S-codoped TiO₂(B) nanobelts are synthesized via hydrothermal synthesis and post-treatment, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂ adsorption-desorption measurements (BET), X-ray photoelectron spectra (XPS), and UV-vis diffuse reflectance spectra (DRS). The results show that the prepared samples are mesoporous structured and exhibit stronger absorption in the visible light region with red shift in the absorption edge. The photocatalytic activity of N, S-codoped mesoporous TiO₂(B) nanobelts is evaluated by the photocatalytic photodegradation of potassium ethyl xanthate (KEX) under visible light irradiation. It is found that the photocatalytic activity of the prepared samples increases with increasing the molar ratio of thiourea to Ti (R). At R = 3, the photocatalytic activity of the N, S-codoped TiO₂(B) sample TBLTS-3 reaches a maximum value. With further increasing R, the photocatalytic activity of the sample decreases. The high photocatalytic activity of N, S-codoped TiO₂(B) nanobelts can be attributed to the balance between strong absorption in visible light region and low recombination rate of electron/hole pairs.     

Hydrothermal Synthesis of Na0.28V2O5 Nanobelts and their Electrochemical Behavior in Lithium Batteries

A simple low temperature hydrothermal method was found to yield Na_0.28V₂O₅ nanobelts after two days at 130 °C in acidic medium (H₂SO₄) without using any surfactant. The obtained products were characterized by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), and Raman spectroscopy. Their morphology was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Additionally, their electrochemical behavior in a lithium battery was investigated. The XRD pattern shows that the product is composed of monoclinic Na_0.28V₂O₅ nanobelts. From the FTIR spectrum, the band centered at 961 cm^–1 is assigned to V=O stretching vibration, which is sensitive to intercalation and suggests that Na⁺ ions are inserted between the vanadium oxide layers. SEM/TEM analyses reveal that the products consist of a large quantity of nanobelts which have a thickness of 60–150 nm and a length of several tens of micrometers. The electrochemical results show that the nanobelts exhibit an initial discharge specific capacity of 390 mAh · g^–1, and its stabilized capacity still remained around 200 mAh · g^–1 after the 18th cycle.