Hybridized ZnO nanostructures on carbon-fiber through combustion synthesis induced by joule heating

Zinc Oxide nanostructures have been hybridized on carbon fiber bundles though joule-heating carbon fiber coated with metallic zinc powder. Upon sufficient heat transfer from the carbon fiber in ambient atmospheric conditions, the metallic Zinc coating will undergo combustion. The combustion reaction will yield a variety of ZnO nanoparticles on the carbon fiber bundles. This simple cost-effective technique provides a fast, non-catalytic, and economic approach for the hybridization of ZnO nanowires on advanced textiles. The integration of ZnO nanostructures on the carbon fiber bundles can open up new avenues for multifunctional composites or smart materials. The ZnO nanostructures on the carbon fiber bundle have been characterized through SEM, XRD, and TEM. The new method and minimum heating rates to cause ignition of Zn powders are discussed.     

Rapid synthesis of thin SAPO-34 membranes using microwave heating

SAPO-34 membranes were prepared by microwave (MW) heating method using a colloidal solution containing tetraethylammonium hydroxide as a template. SAPO-34 in the form of seed and membranes were investigated for their properties such as morphology, pore characteristic, crystallinity and thickness, using characterization method of scanning electron microscope (SEM), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), FT-IR and nitrogen adsorption-desorption. SAPO-34 membrane was also prepared using conventional hydrothermal heating and studied for its comparison with those formed by MW heating. SAPO-34 membrane containing homogenous SAPO-34 crystals with average size of ~0.7 μm was formed during MW heating. Compare to the conventional hydrothermal heating, MW heating facilitates formation of SAPO-34 crystals with narrower size distribution due to the highly uniform volumetric heating provided by microwave heating. MW heating was able to produce thinner SAPO-34 membrane (1–2 μm) where as hydrothermal heating formed thicker SAPO-34 membrane (~3.6–5.5 μm). The synthesis time for membrane formation was significantly shortened from 24 h for conventional hydrothermal heating to 2 h for microwave heating at 200 °C.     

Rapid carbothermic synthesis of silicon carbide nano powders by using microwave heating

This paper reports an improved procedure for synthesis of silicon carbide nanopowders from silica by carbothermic reduction under fast microwave-induced heating. The powders have been prepared by direct solid-state reaction in a 2.45 GHz microwave field in nitrogen atmosphere after 40 h milling. For the first time, the formation of silicon carbide (β-SiC) as a major phase can be achieved at 1200 °C in 5 min of microwave exposure, resulting in nano sized particles ranging from 10 to 40 nm under optimized synthesis condition. The Rietveld quantitative phase-composition analysis confirmed that the major SiC polytype is cubic SiC (β-SiC) with 98.5(4) weight fraction and the remained is minor hexagonal SiC polytypic (α-SiC) phases. Therefore this method is the most efficient one for SiC powder synthesis in terms of energy and time saving as well as preparation of SiC nano powders.     

Seeds-induced synthesis of SiC by microwave heating

α-SiC particles were used as heating seeds to prepare SiC from coal minerals with microwave heating method. Coating technique was carried out to prepare composite raw powders in three different methods. Heating temperatures were at 1000?°C, 1050?°C, 1100?°C, 1150?°C, 1200?°C for 10min, respectively. XRD, SEM techniques were carried out to characterize samples. It was found that different distribution between C and α-SiC particles from different mixing method leads to different microwave heating behavior and growth mechanisms. V-V reaction leads to in situ nucleation and grain growth on the surface of α-SiC seeds which contact with C particles. Well-grown β-SiC particulates appear. Hybrid V-V reaction V-L reaction lead to local microwave plasma and diffusion-precipitation with a very thin layer of SiO₂ between raw C particles and α-SiC seeds. Local fine β-SiC whiskers and particulates on the surface of α-SiC seeds co-exist. Primary V-V reaction leads to nucleation and grain growth along reacted C-SiO₂ interface with very thick layer of SiO₂ between raw C and α-SiC seeds. Substantial β-SiC whiskers appear. Transformation from β-SiC to α-SiC on the surface of as-formed whiskers will be enhanced by microwave plasma at high temperature.     

Facile synthesis of different morphologies of Te-doped ZnO nanostructures

Te-doped ZnO nanostructures were synthesized by an annealing (vapor–solid) process under ambient conditions, and characterized in terms of their morphological, structural, compositional and optical properties. The structural and morphological characterizations revealed that the synthesized nanostructures were well-defined multipods, needles and spherical particles, and possessed well-crystalline ZnO wurtzite hexagonal phase. Also, in the X-ray diffraction studies, the presence of a shift in the peak positions towards a lower angle, and a decrease in the intensity, with an increase in the Te concentration, as compared to the undoped ZnO, were observed. The chemical composition confirmed the presence of Te, in the case of multipod and needle morphologies. The effect of doping on the crystalline quality and optical properties was also investigated, by using photoluminescence (PL) and Raman spectrometers. The Raman results demonstrated that the doped ZnO nanostructures had a lower crystalline quality than the undoped ZnO. Moreover, the PL results showed a decrease in the band gap for the doped ZnO nanostructures, in comparison to the undoped ZnO. A possible growth mechanism was also proposed.     

Development of microwave susceptors based on SiC composites and their application for a one-step synthesis of ZnO nanostructures

We report on the synthesis of silicon carbide (SiC)-based composites containing different proportions of aluminum and/or vanadium III oxides. These composites have been successfully tested as susceptors into a commercial microwave oven operating at 2.45?GHz frequency. After 120?s only of microwave irradiation, the generated temperature has reached a plateau of 1750?°C, which was obtained for SiC composite containing 10?wt% of Al₂O₃ and/or V₂O₃. Furthermore, the structural properties of these composites were investigated by means of X-ray diffraction and scanning electron microscopy before and after exposure to microwaves irradiation. These SiC-based susceptors were then used as a source of heat to synthesize a nanostructured ZnO material through two different processes, namely the zinc metal evaporation/condensation occurring under air, and through a rapid thermal decomposition of zinc acetates and nitrates precursors. The structural analysis supported the possibility to grow nanostructures of controlled morphologies via the control of the microwave power and the type of precursor employed. We believe that this proposed one-step microwave assisted method provides a simple and efficient alternative to synthesize various oxide nanostructures in a very short reaction-time.     

Solvothermal synthesis of microsphere ZnO nanostructures in DEA media

Microsphere ZnO nanostructures (ZnO-MNs) were synthesized via solvothermal method in diethanolamine (DEA) media. DEA was utilized to terminate the growth of ZnO nanoparticles which forms the ZnO-MNs. The ZnO-MNs were characterized by a number of techniques, including X-ray diffraction analysis (XRD) and field emission scanning electron microscopy (SEM). The ZnO-MNs prepared by solvothermal process at the temperature of 150 °C for 6, 12, 18, and 24 h exhibited a hexagonal (wurtzite) structure with sizes ranging from 2 to 4 μm. The growth mechanism and morphology of the ZnO-MNs were also investigated, and it was found that the ZnO-MNs were formed by ZnO nanoparticles with average particle size of 25 ± 5 nm. To show role of DEA in the formation of Zn-MNs, effect of MEA (monoethanolamine) and TEA (triethanolamine) on morphology of the final product are also investigated. The results showed that DEA is a good polymerization agent that can be used as a stabilizer in the solvothermal technique for preparing fine ZnO powder.     

均匀沉淀结合微波制备纳米氧化锌

以醋酸锌和浓氨水为原料,采用均匀沉淀结合微波制备纳米氧化锌。通过XRD,SEM对样品进行表征。以亚甲基蓝(MB)的光催化脱色降解为模型反应,考察分散剂及其用量、超声条件及微波热解时间对降解实验的影响。研究表明,以0.5%聚乙二醇20000为分散剂,超声处理10 min,微波热解15 min得到六方纤锌矿结构,直径20～50 nm、长度约为1μm的纳米棒状氧化锌粉体,该纳米材料在紫外光下具有高催化活性,照射2.5 h,可以使MB溶液的脱色率达99%以上。     

Rapid synthesis and photocatalytic activity of ZnO nanowires obtained through microwave-assisted thermal decomposition

This work reports a new method for large scale production of ZnO nanowires (ZnO-NWs) by microwave assisted thermal decomposition (MATD). This method is simple, economical and reproducible; in addition, the production of material exceeds 95% without using preferential growth precursors. The reaction occurs in only 3 min with minimal energy expenditure. ZnO-NWs produced at 1200 W had diameters ranging between 20 and 70 nm and lengths that varied between 1 and 15 µm, were totally crystalline and showed preferential growth in the [001] direction. Using XRD and HRTEM, it was determined that ZnO presented a hexagonal, wurtzite structure. The relationship between graphite and ZnO, the power of the reaction system and the reactor humidity each played an important role in this method and need to be properly controlled to optimize the production of nanowires. The reactor used allowed for the separation of the reaction products; for that reason, the ZnO-NWs produced had a high degree of purity, as determined by XRD. The photocatalytic activity of ZnO-NWs in methyl orange (MO) decreased as the pH increased; this behavior is common in ZnO because basic pH increased the interaction between the MO and ZnO. The synthesis process, growth mechanisms and photocatalytic activity of ZnO-NWs are discussed in this work.     

Rapid and low temperature synthesis of high purity Ti2SC powder by microwave hybrid heating

Ti₂SC powders were successfully synthesised at relatively low temperature by a microwave hybrid heating method. The mixtures of Ti, C and S or TiS₂ with different molar ratios were heated to investigate the formation of Ti₂SC phase. It was confirmed that Ti₂SC with high purity was achieved using TiS₂ as sulphur source. The results indicated that the synthesis temperature of Ti₂SC was ～500°C lower, and holding time was only one-twentieth compared with those reported by other methods. The high purity Ti₂SC powders from Ti/TiS₂/C with the molar ratio of 2.85:1.15:2 obtained at 1100°C for 3?min were uniform, and the average particle size was 1–2?μm.     

微波辐射快速合成阿斯匹林

阿斯匹林是众所周知的解热镇痛、抗风湿类 药.近年来它的新用途不断被发现,作为治疗和预 防心脑血管疾病的药物已被广泛应用于临床.阿 斯匹林通常用水杨酸和乙酸酐反应来合成,传统 的方法是用酸催化[1],用固体氢氧化钠催化的方 法也有报道[2].微波辐射促进有机反应是80年代 后期兴起的一项有机合成新技术[3],它可以极大 地促进有机反应,使反应速度较传统的实验技术 大大提高.本文介绍了以固体碳酸钠为催化剂,在 家用微波炉中.由水杨酸和乙酸酐快速合成阿斯 匹林的实验方法.微波输出功率为595 W,辐射时 间60 s,收率可达92.5%.     

微波场选择性加热过程中的影响因素分析

对微波场加热过程中所涉及的液体高径比、测温方式、微波功率等影响因素进行了考察,并通过水在不同温度下的温升速率,使用SPSS软件,通过线性回归分析的方法,对介电常数、密度、粘度、比热4种液体物理常数的影响力大小进行了统计分析。结果表明,微波场作用下,各物理常数对于温升的影响力大小为:介电常数>密度>粘度>比热。最后,通过对甘油、油酸、1,4-丁二醇、四氯化碳、苯甲醇5种有机溶剂在微波场中的温升速率进行分析,确定了各物理常数的影响力大小关系。     

Soapless emulsion polymerization of butyl methacrylate through microwave heating

Soapless emulsion polymerization of n‐butyl methacrylate (BMA) was carried out through microwave heating with potassium persulfate (KPS) as an initiator at 73 ± 2°C. The influence of the monomer amount, the initiator amount, and the addition of ethanol on the monomer conversion, the particle size, and its distribution were studied. The results indicate that microwave polymerization had a much higher rate and produced smaller particles with a slightly broader size distribution compared with normal polymerization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2455–2459, 2001     

Controlled synthesis of carbon nanostructures using aligned ZnO nanorods as templates

By combining in situ X-ray photoemission spectroscopy, ex situ high resolution transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy, we show that chemical vapor deposition (CVD) on vertically aligned ZnO nanorods can synthesize different carbon nanostructures (CNs), whose morphology is driven by the ZnO nanorods and whose dimensions and structures change as a function of the process temperature. The CNs range from amorphous carbon cups, completely covering the nanorods, to high density one-dimensional carbon nano-dendrites (CNDs), which start to appear like short hairs on the ZnO nanorods. The nanorods are partially etched when the process is done at 630–800 °C, while they are completely etched at temperatures higher than 800 °C. In the latter case, CNDs emerge from a porous carbon sponge formed at the substrate interface but they are preferentially aligned along the location of the pristine ZnO nanorods. When used as a chemiresisitor the CND–ZnO structures have a higher sensitivity to ammonia compared to chemiresistors made by bare ZnO nanorods, to other one-dimensional CNs, like carbon nanotubes or other metal/metal-oxides hybrid CNs.     

Rapid synthesis and antiviral activity of (quinazolin-4-ylamino)methyl-phosphonates through microwave irradiation

This study describes the simple synthesis of new (quinazolin-4-ylamino) methylphosphonates via microwave irradiation. Substituted-2-aminobenzonitrile reacted with 1,1-dimethoxy-N,N-dimethylmethanamine at a reflux condition to obtain N'-(substituted-2-cyanophenyl)-N,N-dimethylformamidine (1). The subsequent reaction of this intermediate product with α-aminophosphonate (2) in a solution containing glacial acetic acid in 2-propanol through microwave irradiation resulted in the formation of (quinazolin-4-ylamino)methyl-phosphonate derivatives 3a to 3x, which were unequivocally characterized by the spectral data and elemental analysis. The influence of the reaction conditions on the yield of 3a was investigated to optimize the synthetic conditions. The relative optimal conditions for the synthesis of 3a include a 1:1 molar ratio of N'-(2-cyanophenyl)-N,N-dimethylformamidine to diethyl amino(phenyl)methylphosphonate and a 4:1 volume ratio of isopropanol to HOAc in the solvent mixture, at a reaction temperature of 150 °C, with a microwave power of 100 W and a corresponding pressure of 150 psi for 20 min in the microwave synthesizer. The yield of 3a was approximately 79%, whereas those of 3b to 3x were approximately 77% to 86%. Some of the synthesized compounds displayed weak to good anti-Tobacco mosaic virus (TMV) activity.     

XPS and optical studies of different morphologies of ZnO nanostructures prepared by microwave methods

Zinc oxide (ZnO) nanostructures of various morphologies were prepared using a microwave-assisted aqueous solution method. Herein, a comparative study between three different morphologies of ZnO nanostructures, namely nanoparticles (NPs), nanoflowers (NFs) and nanorods (NRs) has been reviewed and presented. The morphologies of the prepared powders have been studied using field effect scanning electron microscopy (FESEM). X-ray diffraction (XRD) results prove that ZnO nanorods have biggest crystallite size compared with nanoflowers and nanoparticles. The texture coefficient (T_c) of three morphologies has been calculated. The T_c changed with varying morphology. A comparative study of surfaces of NPs, NFs and NRs were investigated using X-ray photoelectron spectroscopy (XPS). The possible growth mechanisms of ZnO NPs, NFs and NRs have been described. The optical properties of the ZnO nanostructures of various morphologies have been investigated and showed that the biggest crystallite size of ZnO nanostructures has lowest band gap energy. The obtained results are in agreement with experimental and theoretical data of other researchers.     

微 波快速合成芳氧乙酸

在无溶剂体系中，使用微波辐射快速合成了３种芳氧乙酸。该方法反应条件温和、反应时间短、收率高，操作简便。反应２．５－３ｍｉｎ收率可达８６．８％－９４．１％。     

微波快速合成1,4-萘醌

用微波辐射氧化1-萘酚合成1,4-萘醌,最佳反应条件是:HAc用量0.4mL,H2O2用量0.6mL,反应时间2min,微波功率280W,产率为50.9%。     

微波加热合成聚磷酸铵的工艺研究

以磷酸二氢铵和尿素为原料,采用微波加热研究聚磷酸铵的最优聚合工艺条件。分别考察不同原料配比、反应温度和反应时间对聚磷酸铵中五氧化二磷含量、氮含量和聚合度的影响。通过实验得出微波加热聚合聚磷酸铵的最优条件为：磷酸二氢铵与尿素物质的量比为1:1.1、反应温度为170 ℃、反应时间为20 min,样品经XRD检测为Ⅰ-型聚磷酸铵,该条件下得到的产品五氧化二磷质量分数为70.33%、氮质量分数为14.34%、聚合度为50.33,符合化工行业标准HG/T 2770—2008一等品指标要求。     

Facile synthesis of ZnO nanostructures and enhancement of their sinterability via short-time cryo-milling

Zinc oxide (ZnO), a wide band-gap semiconductor, has received a great interest due to its potential applications in various fields both as nanostructures and as sintered compacts. In this study, we report on the synthesis of the ZnO nanostructures and facilitation of their sintering for the production of fine-grained dense compacts. The facile synthesis of gram scale ZnO nanostructures was achieved by thermal decomposition of zinc acetate dihydrate (Zn(Ac)₂·2H₂O) or Zn(Ac)₂·2H₂O/graphite mixtures at 300 °C for 12 h. Thermal decomposition of Zn(Ac)₂ resulted in the formation of mostly ZnO nanoparticles with wurtzite structure along with ZnO nanorods, while the addition of graphite significantly promoted the growth of ZnO nanowires. Microstructural and phase properties of the obtained ZnO nanostructures were determined by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) techniques, all of which revealed the successful synthesis of high quality ZnO nanostructures. In addition to synthesis and characterization of the ZnO nanostructures, we report on the enhancement of their sinterability by a subsequent cryogenic milling for a short duration of 5 min. As a result of the applied cryo-milling, fabrication of highly dense (96.2%) sintered compacts with fine grain sizes (572 nm) could be achieved after pressureless sintering at 1000 °C for 2 h.