A new approach to obtain calcium cobalt oxide by microwave-assisted hydrothermal synthesis

This study describes the effect of microwave-assisted hydrothermal synthesis on the crystalline phase-formation, microstructural characteristics, and thermoelectric performance of Ca₃Co₄O₉. Synthesis parameters, such as time, temperature, KOH concentration, and oxidation states of Co ions, to produce this compound, were studied. X-ray diffraction and X-ray photoelectron spectroscopy showed that the most critical parameters for the phase formation are the oxidation states of Co ions. Ca₃Co₄O₉ can be obtained by microwave-assisted hydrothermal synthesis at 503 K for 30 min and thermal treatment at 1173 K for 120 min. Scanning electron microscopy images showed that the sample exhibits randomly oriented particles with plate-like morphology and range size between 0.4 and 1.2 μm. From measurements of electrical resistivity, thermal conductivity, and Seebeck coefficient, we obtained a figure of merit of ~0.008 at 300 K.     

水热法合成羟基氧化镓与优化探索

羟基氧化镓（GaOOH）是合成氮化镓的重要原料,其微观形态特征对所制备氮化镓的物理性能有着重要影响。以氧化镓、浓盐酸、氨水为原料,用水热法合成出羟基氧化镓,并探讨了浓盐酸用量对羟基氧化镓纯度的影响。对合成产物进行XRD表征,结果表明合成产物为羟基氧化镓,且随着浓盐酸用量的增加,羟基氧化镓产品的纯度提高。     

水热法制备羟基氧化镓纳米晶体

提供一种以氧化镓为原料,140℃下用水热法制得不同长径比的羟基氧化镓纳米棒和纳米粒子的新工艺。研究了溶液的pH、水热时间及水热温度对纳米羟基氧化镓晶体粒子形态及尺寸的影响。采用X射线衍射（XRD）,透射电镜（TEM）等方法对制备的纳米羟基氧化镓形貌进行了表征。结果表明,溶液的pH增大,羟基氧化镓纳米棒的长径比增大,pH=12时,得到单分散性纳米粒子;延长水热时间,酸性条件下样品形貌基本不变,碱性条件下纳米棒长度及长径比变大;水热温度为180℃时,形成由纳米线组成的骨状纳米棒样品。     

Photoluminescent and antimicrobial properties of silver-doped indium hydroxide synthesized by one-step microwave-assisted hydrothermal method

Silver-doped indium hydroxide In_(1-x)(OH)₃:_xAg (with x = 0, 1, 2, 4, and 8 mol%) of Ag nanoparticles were synthesized by the microwave-assisted hydrothermal (MAH) method at 140°C for 30 minutes. These nanoparticles were characterized by X-ray diffraction (XRD), fourier transformed infrared (FT-IR) spectroscopy, and optical diffuse reflectance. Photoluminescence (PL) spectra were acquired with a 350 nm beam of a krypton ion laser as an excitation source. The antibacterial activities of the samples were evaluated against gram negative Escherichia coli bacteria and gram positive Staphylococcus aureus bacteria using the disc diffusion method. The results showed that all diffraction peaks present in XRD patterns could be indexed to the cubic lattice related to the In(OH)₃ phase. Broadband photoluminescence behavior in visible range spectra was observed for all samples with a maximum peak centered in the blue and green regions. The antibacterial activities showed that In_(1-x)(OH)₃: _xAg nanoparticles have a promising bactericide that can be used for deactivating microbes.     

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.     

Green facile fabrication of polyimide by microwave-assisted hydrothermal method and its decomposition dynamics

A microwave-assisted hydrothermal technique was proposed in this work to fabricate polyimide using ethanol as sole solvent, and the decomposition dynamics of the resulting polyimide was also investigated. The preparation process involved that the ammonium carboxylic ester intermediates could be able to cyclize de-alchoholation, thus generating imide ring structures. The obtained polyimide exhibited excellent thermal properties. Specifically, the glass transition temperature of the polyimide was around 267.8 °C, and it begun to decompose gradually from about 550 °C. A novel method was employed to choose the dynamics model according to the linear correlation between g(α) and 1/β. As a result, the three-dimensional diffusion (Jander) model was much more suitable for the thermal decomposition process of the resulting polyimide, and the thermal decomposition mechanism was explained by using the model. The apparent activation energy (E _a) values calculated by Flynn–Wall–Ozawa and Kissinger methods were similar showing the same variation tendency. Furthermore, a series of fitting polynomials for E _a and pre-exponential factor (A) values were achieved to reflect the trend more accurately. The dynamics results revealed that the decomposition process was complex and could be regarded as multistep reactions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48484.     

Surfactant-assisted hydrothermal synthesis of Fluoridated Hydroxyapatite nanorods

Fluoridated Hydroxyapatite (FHA) nanorods were synthesized using Apricot Tree Gum (ATG) as a novel surfactant and then compared with Ethylenediaminetetraacetic acid disodium salt dihydrate (EDTA) and Sodium Dodecyl Sulfate (SDS) as conventional surfactant agents under hydrothermal condition (70 °C and 1 atm). The effects of pH values and various types of surfactants on the formation of the FHA nanorods, crystalline phase, and chemical compositions were investigated using Field Emission Scanning Electron Microscopy (FESEM) equipped by Energy Dispersive X-ray (EDX), X-Ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). The findings indicated application of the presented ATG as surfactant is able to produce the hexagonal nanorods of FHA along their c-axis direction. Moreover, it is illustrated that diameter and length of nanorods which is obtained by ATG surfactant are bigger than EDTA and SDS. In addition, it is demonstrated that pH values can play a major role on formation of hexagonal FHA nanorods. The increase of pH transformed the shape of synthesized FHA from particles to rods. Ultimately, based on the similarity of synthesized FHA nanorods to the shape, structure, and composition of enamel; it is suggested for its potential to be used for dental applications.     

Visible emission from Ce-doped ZnO nanorods grown by hydrothermal method without a post thermal annealing process

Visible light-emitting Ce-doped ZnO nanorods [NRs] without a post thermal annealing process were grown by hydrothermal method on a Si (100) substrate at a low temperature of 90°C. The structural investigations of Ce-doped ZnO NRs showed that the Ce³⁺ ions were successfully incorporated into the ZnO lattice sites without forming unwanted Ce-related compounds or precipitates. The optical investigation by photoluminescence spectra shows that the doped Ce³⁺ ions in the ZnO NRs act as an efficient luminescence center at 540 nm which corresponds to the optical transition of 5d → 4f orbitals in the Ce³⁺ ions. The photoluminescence intensity of the Ce-doped ZnO NRs increased with the increasing content of the Ce-doping agent because the energy transfer of the excited electrons in ZnO to the Ce³⁺ ions would be enhanced by increased Ce³⁺ ions.     

Size and morphology-controlled synthesis of mesoporous hydroxyapatite nanocrystals by microwave-assisted hydrothermal method

We report the rapid microwave-assisted hydrothermal synthesis of mesoporous hydroxyapatite (HAp) nanocrystals with controlled size, morphology, and surface area using various organic modifiers as regulators. The products were analyzed for their crystalline nature, phase purity, morphology, particle size and pore size distribution. Results indicated that ascorbic acid, cetyltrimethyl ammonium bromide (CTAB) and polyvinylpyrrolidone (PVP) play an important role to obtain needle like, rod like and fiber like mesoporous HAp nanocrystals with different specific surface area by controlling growth habit of HAp along c-axis. In addition, the prepared samples were B-type carbonated HAp similar to bone minerals. Therefore, the present approach can be a promising way to obtain precursor for making tissue engineering scaffolds, drug/protein delivery carriers and bone fillers with tunable characteristics.     

Size-controlled synthesis of spinel nickel ferrite nanorods by thermal decomposition of a bimetallic Fe/Ni-MOF

In this work, size-controlled synthesis of nickel ferrite nanoparticles was achieved by the calcination of a bimetallic (Fe/Ni) metal-organic framework (MOF). The bimetallic MOF (Fe₂Ni-MIL-88B) itself was prepared by a two-step route. The first step involved synthesis of the secondary building unit (SBU) by reacting stoichiometric amounts of Ni and Fe precursors with acetic acid. A ligand substitution reaction (terephthalate replaces acetate) in the SBU leads to the formation of the MOF, which was characterized by PXRD, FTIR, SEM and TEM. Afterwards, the MOF was calcined under air atmosphere to obtain nickel ferrite nanorods. PXRD analysis confirmed the spinel structure of the nickel ferrites while electron microscopic analysis (SEM, TEM) revealed their nanorod-like morphology. By increasing the calcination temperature from 600 to 1000 °C, particle size increased from 16 to 32 nm. Oxidation of benzyl alcohol was used as a model test reaction to probe the applicability of spinel nickel ferrite nanorods for catalysis. Interestingly, the largest nanorods exhibited the highest activity (86% conversion), thus demonstrating the potential of spinel ferrites in catalyzing oxidation reactions.     

One-step hydrothermal microwave-assisted synthesis of LaFeO3 nanoparticles

Lanthanum orthoferrite (LaFeO₃) powders were synthesized via a highly efficient one-step hydrothermal microwave-assisted synthesis at relatively low temperatures of 240 °C and pressure of 60 bar. The use of microwave irradiation for heating during the synthesis intensifies the LaFeO₃ crystallization process leading to reduced synthesis duration at least 16 times as compared with conventional heating (3 versus 48 h).     

Ethanol sensing properties of tungsten oxide nanorods prepared by microwave hydrothermal method

Tungsten oxide nanorods have been prepared by a simple microwave hydrothermal (MH) method via Na₂SO₄ as structure-directing agent at 180 °C for 20 min. The structure and morphology of the products are characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The obtained nanorods are about 20–50 nm in diameter and several micrometers in length. The ethanol sensing property of as-prepared tungsten oxide nanorods is studied at ethanol concentration of 10–1000 ppm and working temperature of 370–500 °C. It was found that the sensitivity depended on the working temperatures and also ethanol concentration. The results show that the tungsten oxide nanorods can be used to fabricate high performance ethanol sensors.     

Morphology-controlled synthesis of tungsten oxide hydrates crystallites via a facile,additive-free hydrothermal process

Tungsten oxide hydrates crystallites with a diversity of morphologies were successfully synthesized by employing peroxo-polytungstic acid as the precursor via a facile and additive-free hydrothermal process. The crystal structure, morphology and orientation relationship were investigated by using X-ray diffractometer, scanning electron microscopy and transmission electron microscopy. Results show that with the increase of the hydrothermal reaction time, the product morphology shows an obvious evolution from hexagonal plates to round angular blocks and to hexagonal gears, through irregular nanosheets and to cuboid rods finally. Furthermore, the driving force of this morphology evolution was found to be correspondent with the interesting change of the orientation growth and the phase transition of tungsten oxide hydrates under the hydrothermal process.     

氢氧化锆热分解反应动力学研究

热重研究结果表明,氢氧化锆热分解是一失重率为21.5%的一阶失重过程,失重峰值温度与差示扫描量热法分析吸热峰值温度基本吻合。在非等温条件下,采用单加热速率微分Achar和积分Coats-Redfern方程,结合多加热速率法Kissinger方程,以线性相关性和动力学参数的比较作为判断依据,推断Zr(OH)4热分解过程由化学反应机理控制,计算得到反应活化能E=52.30 kJ/mol,lg A=4.767。     

Rapid and controllable synthesis of nitrogen doped reduced graphene oxide using microwave-assisted hydrothermal reaction for high power-density supercapacitors

Nitrogen doped reduced graphene oxide (N-RGO) is synthesized using microwave-assisted hydrothermal (MAHA) reaction. The proper configurations of nitrogen atoms in graphene sheets considerably increase the intrinsic electrical properties of N-RGO resultantly improving its capacitance and other kinetic properties in supercapacitor. Here, under the controlled MAHA reaction, we adjusted the ratio of nitrogen configurations (pyridinic-N, pyrrolic-N and quaternary-N) for the most optimum supercapacitor performances of N-RGOs in the shortest time ever reported, and clarified that its enhanced electrical conductivity and supercapacitor performances are attributed to its enlarged concentration of quaternary-N. With this MAHA reaction, we present a supercapacitor based on N-RGO, which is capable of displaying the promising electrochemical properties.     

碳分法制备易溶氢氧化铝研究

通过无晶种碳分法制备了易溶氢氧化铝。研究了反应温度、通气速度、二氧化碳体积分数、铝酸钠溶液苛性比（氧化钠与氧化铝物质的量比）等条件对氢氧化铝酸溶率的影响。适宜工艺条件：反应温度为65~75 ℃、通气速度为400 L/h、二氧化碳体积分数为30%~38%、铝酸钠溶液苛性比为1.48。在此条件下制得氢氧化铝酸溶率大于95%。X射线衍射（XRD）和扫描电镜（SEM）表征表明,物相组成是影响氢氧化铝产品酸溶性的主要原因。     

Low-temperature synthesis of CdWO4 nanorods via a hydrothermal method

Cadmium tungstate (CdWO₄) nanorods were successfully synthesized via a hydrothermal process and characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and photoluminescent spectra techniques (PL). A pure monoclinic phase of well-crystallized CdWO₄ nanorods, with lengths of 250–400 nm and widths of 30–60 nm, could be readily synthesized at as low temperature as 70 °C.The CdWO₄ nanorods showed a PL emissions peak at 435 nm.     

Causticization of sodium carbonate with rock-salt type magnesium aluminium oxide formed by the thermal decomposition of hydrotalcite-like layered double hydroxide

The causticization behaviour of Na₂CO₃ with rock-salt type oxide, Mg_2(1-x/(2+x) O (M = Al³⁺ and Fe³⁺, x = 0.2 and 0.33), produced by the thermal decomposition of hydrotalcite-like layered double hydroxide was investigated at 30–60°C. The degree of causticization increased with increasing the molar ratio of [rock-salt type oxide]/[Na₂CO₃] and increasing the temperature but decreased with increasing the initial concentration of Na₂CO₃. The causticization behaviour could be adequately described by the equation of anion exchange equilibria between CO₃^2- and OH^? for layered double hydroxide.     

Multiphase calcium phosphate nanorods produced by microwave-assisted molten salt synthesis: Particle size RSM optimization

This study reports the statistical optimization using surface response methodology and genetic algorithms of an auto-ignited microwave molten salt synthesis of multiphase calcium phosphates, as these molecular mixtures integrate both osteoconductive and osteoinductive properties with a good capacity to control biodegradation. The molten salts containing phosphate and calcium precursors were heated in a time- and power-controlled microwave oven to obtain CaP nanopowders. X-ray diffraction, scanning electron microscopy, and infrared spectroscopy were used to characterize the chemical composition and morphology of the resulting samples. Cytocompatibility was measured using an MTT assay. Bioactivity was studied using simulated body fluids for up to 21 days. Results were analyzed using a response surface methodology coupled to a genetic algorithm that showed that the optimal time, microwave power, and amount of synthesis medium were 4.1 min, maximum power, and 4.5 g, respectively. This enabled the production of particles with average lengths and diameters of 1,300 and 120 nm, respectively. The obtained material obtained showed good cytocompatibility, bioactivity, and controllable dimensions.     

Template-free synthesis of large anisotropic gold nanostructures on reduced graphene oxide

The morphologies/dimensions of Au nanostructures can be tailored by merely controlling the reduction degree of graphene oxide surface. Au nanoparticles, long Au nanowires, and semicircular-shaped Au nanoplates are in situ synthesized on slightly, moderately, and highly reduced graphene oxide films respectively, without the need of any templating agent.