Synthesis and optical properties of MgO-doped ZnO microtubes using microwave heating

The Zn_1−xMg_xO (x = 0%, 2% and 5%) microtubes have been successfully synthesized via a microwave heating method. The as synthesized microtubes were carefully investigated. Field emission scanning electron microscope (FE-SEM) showed that all the microtubes exhibit an exact hexagonal hollow structure with smooth surfaces and straight characteristics throughout their whole lengths. UV–Vis measurement indicates that the absorption peak for ZnO microtube was shifted from 378.88 nm (3.27 eV) to 369.91 nm (3.35 eV) for Zn_0.95Mg_0.05O microtube. Room temperature photoluminescence (PL) spectra showed that the intensity of UV emission peak decreased with increase of MgO concentration and the visible emission band showed a blue shift from 538.06812 nm for ZnO microtube to 529.54114 nm for Zn_0.95Mg_0.05O microtube. Energy-dispersive spectrometer (EDS) analysis revealed the presence of Zn and O as the only elementary components with the absence of MgO as a doping material.     

Synthesis of LSX zeolite by microwave heating

Low silica X (LSX) zeolite was synthesised by traditional and microwave heating. In both syntheses the X zeolite showed high crystallinity and purity, low silicon/aluminium molar ratio and a potassium content per unit cell of around 7 wt.%. Microwave heating decreased the time of synthesis respect to the traditional heating under the same conditions. The reduction of the synthesis time was due to uniformity of the heating stage by microwaves. Microwave heating decreased the nucleation and crystallisation time. Basic catalytic properties were checked in the toluene alkylation with methanol. There were no differences in the catalytic activity for toluene alkylation between both LSX zeolites.     

High quality ZnO/CuO nanocomposites synthesized by microwave assisted reaction

Highly crystalline zinc oxide (ZnO) and ZnO/CuO nanocomposite powders have been synthesized by a facile microwave irradiation method. The resulting powders were characterized in terms of structural, optical and morphological properties by X-ray diffraction (XRD), room temperature photoluminescence (PL) spectroscopy and scanning electron microscopy (SEM), respectively. XRD patterns revealed the formation of ZnO/CuO nanocomposites with good crystalline quality. SEM images displayed the formation of hexagonal ZnO and flower shaped agglomeration of ZnO/CuO nano-flakes with uniform production. The strong UV emission peak observed at around 380 nm show enhanced intensity for ZnO/CuO nanocomposite. Compared to ZnO nanoparticles, ZnO/CuO composites exhibit good transparency with sharp absorbance edges. The simplicity of synthesis route coupled with better optical and PL emission properties propose the microwave synthesized ZnO/CuO nanocomposite powders a promising material for optoelectronic devices.     

共沉淀-微波法合成LiFePO4/C正极材料

以有机表面活性剂聚乙二醇(PEG)为碳源,采用共沉淀-微波法合成了锂离子电池正极材料LiFePO4/C,探讨了微波烧结时间对样品结构和性能的影响,并用XRD、TEM、激光粒度分析和恒电流充放电测试对LiFePO4/C样品的结构、形貌和电化学性能进行了表征.结果表明:微波烧结9 min的样品为单一的橄榄石晶体结构和较好的电化学性能,在室温下,以0.1C、0.2C和1C进行充放电,首次放电比容量分别达到154.3mAh/g、139.7mAh/g和123.9mAh/g,循环20次后仍保持在152.3mAh/g、134.3mAh/g和118.5mAh/g.     

Enhanced room-temperature magnetoresistance of hybrid graphene nanosheets produced by a laser-assisted process

Journal of Materials Science - The major challenges in the commercialization of spintronic devices lie in the high-dimensional materials with low spin-current generation efficiency and expensive...     

高能微波辐照合成类石墨烯氮化碳纳米片的结构特征

以碳纤维为微波吸收剂,基于微波辐照法直接处理三聚氰胺,快速高效地合成类石墨烯结构的氮化碳纳米片。借助于场发射扫描电子显微镜、透射电子显微镜、原子力显微镜、X射线衍射和傅里叶变换红外光谱等分析手段,对微波合成产物进行表征。结果表明:与常规热缩聚合成的石墨相氮化碳相比,高能微波技术合成产物具有明显的纳米片特征,即成功地制备得到类石墨烯结构的氮化碳纳米片。同时,与超声剥离或氧化刻蚀得到的类石墨烯氮化碳纳米片相比,高能微波技术合成产物表面光滑平整,且可发现脆性断裂的现象,呈现出一定的刚性。     

Synthesis of linear ZnO structures by a thermal decomposition method and their characterisation

The semiconductor zinc oxide (ZnO) is a promising material for applications in optoelectronics, photochemistry and chemical sensing. Furthermore, ZnO structures can be grown with a large variety of sizes and shapes. Devices with ZnO rods or wires as their core elements can be used in solar cells, gas sensors or biosensors. In this article, an easy approach for the non-aqueous wet chemical synthesis of ZnO structures is presented that employs the solvent trioctylamine (TOA) and the surfactant hexamethylenetetramine (HMTA). Using the thermal decomposition method, rod-shaped structures were grown that are suitable for the fabrication of electrical devices. A detailed study was carried out to investigate the effects of various reaction parameters on the growth process. Both the concentration of the surfactant HMTA and the zinc precursor zincacetylacetonate (Zn(acac)₂) were found to show strong effects on the resulting morphology. In addition to structural characterisation using XRD, SEM and TEM, also optical properties of rod-shaped ZnO structures were measured. Rod-shaped structures were obtained for the following conditions: reaction time 4 h, reaction temperature 70 °C, 1 mmol of Zn(acac)₂, 4 mmol of HMTA and 25 mL of the solvent TOA. Photoluminescence and photoluminescence excitation spectroscopy of samples grown under these conditions provided information on levels of defect states that could be critical for chemical sensing applications. Two narrow peaks around 254 and 264 nm were found that are well above the band gap of ZnO.     

Synthesis,structure, and room-temperature ferromagnetism of Ni-doped ZnO nanoparticles

In this paper, Ni-doped ZnO (Zn_1−x Ni _x O, in which 0 ≤ x ≤ 0.05) diluted magnetic semiconductors nanoparticles are prepared by an ultrasonic assisted sol–gel process. Transmission electron microscopy shows sphere-like nanoparticles with an average size of about 25 nm. From the analysis of X-ray diffraction, the Ni-doped ZnO nanoparticles are identified to be a wurtzite structure, but impurity phases are observed when the Ni content x reaches 0.05. Sample structures are further studied by Raman spectra, from which a broad and strong Raman band in the range of 500–600 cm⁻¹ is observed in Zn_1−x Ni _x O. With the increment of x, wurtzite structures degrade gradually. The magnetic properties are measured using superconducting quantum interference device at room temperature; the Zn_1−x Ni _x O (x ≤ 0.02) nanoparticles show ferromagnetism. However, for the sample of Zn_0.95Ni_0.05O, paramagnetism is observed, which may be ascribed to ferromagnetic–antiferromagnetic competition.     

Synthesis of relatively monodisperse ZnO nanocrystals from a precursor zinc 2,4-pentanedionate

Monodisperse ZnO nanoparticles were successfully prepared through the decomposition of zinc acetylacetonate precursor in oleylamine. The samples were characterized by transmission electron microscope, X-ray diffraction and infrared spectroscopy. The particle size and morphology could be modified through tuning the reaction temperature, reaction period and concentration of zinc acetylacetonate. The grain size of monodisperse ZnO could be obtained at 205 and 300 °C for 1 h with 1:100 molar ratio of acetylacetonate and oleylamine, respectively. The average grain size of ZnO nanoparticles increased and the shape of ZnO particles varied with the reaction period prolonging or reaction temperature increasing. Some ZnO particles had self-aggregated into a belt using a solution of 1:10 molar ratio of zinc acetylacetonate and oleylamine at 250 °C for 1 h. The oleylamine plays an important role in preventing aggregation of ZnO nanoparticles.     

ITO thin films prepared by a microwave heating

ITO thin films were prepared by irradiating 2.45 GHz of microwave with an output power of 700 W using a commercial kitchen microwave oven. A substrate temperature went up and down rapidly between 100 and 650 °C in a minute by a dielectric loss of SnO₂ layer pre-deposited on a glass substrate. We found that the electrical and optical properties of films were affected by the atmosphere in a microwave irradiation, while the sintering was completed within a few minutes. Although the electrical resistivity was not reduced below 5.0 × 10^− 4 Ω·cm in this study, the results lead to the possibility of a practical rapid synthesis of ITO transparent conducting oxide films.     

Synthesis of indium tin oxide powder by solid-phase reaction with microwave heating

Indium tin oxide (ITO) powder was synthesized from indium oxide and tin oxide powders by a solid-phase method using microwave heating and conventional heating methods. Microwave heating could reduce the treatment time necessary for the completion of the solid-phase reaction by 1/30. This decrease was attributed to an increase in the diffusion rate of Sn at the local heat spot in the indium oxide formed by microwave irradiation. However, microwave heating also decreased the amount of ITO produced, since the powder layer of the raw material was heated unevenly and had an uneven temperature distribution.Therefore, a microwave heating method including a mixing process was proposed in order to diminish the uneven progress of the ITO synthesis reaction in the powder layer. This revised method could increase the conversion to ITO, which is higher than that obtained by using the conventional heating method. Hence, the electric conductivity of the powder layer obtained by the proposed method was higher than that of the commercially supplied ITO powder layer.     

Influence of Mg doping on the microstructure and PL emission of wurtzite ZnO synthesized by microwave processing

In this paper, we report the synthesis of nano-structured Zinc Oxide (ZnO) and Magnesium doped Zinc Oxide (ZnO:Mg) using air stable and inexpensive chemicals, by microwave assisted processing. The as-synthesized ZnO and ZnO:Mg nanopowders were annealed at 800 °C for 1 h. The samples were further characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and room temperature photoluminescence (PL) spectra. The crystallite size of ZnO decreased from 24 to 16 nm, and the intensity of most prominent vibration band of ZnO becomes weak when Mg dopant is added. SEM images of Mg doped ZnO showed clearly distinct hexagonal shaped nanoparticles with good crystalline quality and size contrast to ZnO. The PL result indicate that the ZnO exhibit strong and sharp UV emission peak at 380 nm. Our result showed that, by doping magnesium into ZnO, the UV emission peak shift towards the lower wavelength at ~370 nm with increasing intensity, which may be attributed to the size confinement. From this study, the microwave processing method has been proved to be successful for preparing other metal oxide nanopowders with good crystal quality.     

Effect of Sn doping on microstructural and optical properties of ZnO nanoparticles synthesized by microwave irradiation method

Pure and Sn-doped ZnO nanostructures have been synthesized by the microwave irradiation method. The influence of Sn loading on the morphology and microstructure was evaluated by using field emission scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive spectrum analysis techniques, X-ray diffraction, and Fourier transform infrared spectroscopy. A change in the growth pattern, from needle-like particles for pure ZnO to agglomerated spherical crystallites for Sn-doped ZnO, has been observed. TEM observations indicated that the average particle size of the pure ZnO nano needles is in the range of 40–60 nm, whereas on addition of Sn spherical nanoassemblies size lies in the range of 10–21 nm. The pure ZnO and Sn-doped ZnO nanostructures were further characterized for their optical properties by UV–Vis reflectance spectra (DRS) and photoluminescence (PL) spectroscopy.     

Nanostructured metal sulphides synthesized by microwave-assisted heating: a review

Journal of Materials Science: Materials in Electronics - In recent decades, nanostructured metal sulphides (MSs) have gained great interest due to their extensive applications ranging from...     

Synthesis of copper and copper(I) oxide nanoparticles by thermal decomposition of a new precursor

The present investigation reports, the novel synthesis of nanoparticles Cu and Cu₂O using thermal decomposition and its physicochemical characterization. The nanoparticles copper powder have been prepared using [Bis(salicylidiminato)copper(II)], [Cu(sal)₂], as precursor. Cu nanoparticles are initially formed and subsequently oxidized to form Cu₂O. Transmission electron microscopy (TEM) analysis demonstrated nanoparticles Cu₂O with an average diameter of about 10 nm. As-prepared copper nano-particles were characterized by X-ray diffraction measurements (XRD), scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX), and Fourier transform infra-red spectroscopy (FTIR). XRD analysis revealed broad pattern for fcc crystal structure of copper metal and cubic cuprite structure for Cu₂O. Optical absorption measured by UV–visible spectroscopy was used to monitor oxidation course of Cu → Cu₂O and to determine the band-gap energy about 2.4 eV for Cu₂O nanoshells.