Ultrasonic pretreatment for hydrothermal synthesis of SAPO-34 nanocrystals

Synthesis of SAPO-34 nanocrystals which has been recently considered as a challenging task was successfully performed by sonochemical method using TEAOH as structure directing agent (SDA). The products were characterized by XRD, SEM, EDX, BET and TGA. The average crystal size of the final product prepared sonochemically is 50 nm that is much smaller than that of synthesized under hydrothermal condition and the morphology of the crystals changes from uniform spherical nanoparticles to spherical aggregates of cube type SAPO-34 crystals respectively. In the case of sample synthesized sonochemically with aid of hydrothermal condition, the surface area is significantly upper than that of obtained by the conventional static hydrothermal technology with almost the same crystallinity. SAPO-34 framework synthesized by just ultrasonic treatment is unstable and a significant part of SAPO-34 nanocrystals is transformed to the dense phase of AlPO₄ structure, i.e., Cristobalite. Contrary to hydrothermal method that at least 24 h of the synthesis time is required to obtain fully crystalline SAPO-34, sonochemical-assisted hydrothermal synthesis of samples leads to form fully crystalline SAPO-34 crystals taking only 1.5 h. In a sonochemical process, a huge density of energy for crystallization is provided by the collapse of bubbles which formed by ultrasonic waves. The fact that small SONO-SAPO-34 crystals could be prepared by the sonochemical method suggests a high nucleation density in the early stages of synthesis and slow crystal growth after nucleation.     

Synthesis of NaP zeolite at room temperature and short crystallization time by sonochemical method

NaP zeolite nano crystals were synthesized by sonochemical method at room temperature with crystallization time of 3 h. For comparison, to insure the effect of sonochemical method, the hydrothermal method at conventional synthesis condition, with same initial sol composition was studied. NaP zeolites are directly formed by ultrasonic treatment without the application of autogenous pressure and also hydrothermal treatment. The effect of ultrasonic energy and irradiation time showed that with increasing sonication energy, the crystallinity of the powders decreased but phase purity remain unchanged. The synthesized powders were characterized by XRD, IR, DTA TGA, FESEM, and TEM analysis. FESEM images revealed that 50 nm zeolite crystals were formed at room temperature by using sonochemical method. However, agglomerated particles having cactus/cabbage like structure was obtained by sonochemical method followed by hydrothermal treatment. In sonochemical process, formation of cavitation and the collapsing of bubbles produced huge energy which is sufficient for crystallization of zeolite compared to that supplied by hydrothermal process for conventional synthesis. With increasing irradiation energy and time, the crystallinity of the synthesized zeolite samples increased slightly.     

Comparison between ZnO nanowires grown by chemical vapor deposition and hydrothermal synthesis

Vertically aligned zinc oxide nanowires (NWs) were synthesized by two different techniques: chemical vapor deposition (CVD) and hydrothermal synthesis. To compare the effects of different growth conditions, both F-doped SnO₂ (FTO) coated-glass and silicon wafers were used as substrates. Before NWs growth, all the substrates were covered with a ZnO seed layer film obtained with the same procedure, which acts as nucleation site for the subsequent growth of the nanowires both during CVD and hydrothermal synthesis. We studied the influence of the two synthesis techniques and the growth duration on the final morphology, orientation, and density of the ZnO NWs using electron microscopy and X-ray diffraction, while the NWs optical quality was addressed by UV–Vis spectroscopy. By discussing advantages and disadvantages of both synthesis methods, we finally show that the application purpose often drives the choice of the NWs growth process and the substrate to be used.     

Hydrothermal synthesis and photocatalytic properties of WO3 nanorods by using capping agent SnCl4·5H2O

Hexagonal tungsten trioxide (h-WO₃) nano-rods of different sizes are prepared via hydrothermal synthesis using a capping agent of SnCl₄·5H₂O. The size of the synthesized WO₃ nanoparticles can be controlled by changing concentration of the capping agent SnCl₄·5H₂O alone. We also investigate microstructures and optical properties of the WO₃ nanorods and propose a synthesis mechanism for the nanorods. The photocatalytic activities of the h-WO₃ nanorods are evaluated by degradation of Rhodamine-B (RhB), revealing that these nanorods exhibit excellent photocatalytic properties. The capping agent SnCl₄·5H₂O is found to be critical to governing sizes and properties of the h-WO₃ nanorods. Our results demonstrate that functional nano-crystallites with tunable size and morphology can be synthesized via a facile hydrothermal synthesis process by adjusting the concentration of capping agent alone. Such a facile hydrothermal synthesis process should be applicable to other types of nanomaterials and relevant to a wide range of applications.     

Conversion of silica by-product into zeolites by thermo-sonochemical treatment

The fine powdered silica by-product of processing of aluminum fluoride (fertilizer plant, Lithuania) was used for zeolite synthesis as silica and aluminum source. The effect of sonication time and the time of hydrothermal synthesis on crystallinity of the synthesized zeolite were studied. This allowed the transformation of the by-product to the mixture of Na–P zeolite and Na–X zeolite. It was determined that ultrasonic-assisted hydrothermal action effected the “diamond” shape formation of Na–P zeolite with clear crystal edges. Na–P zeolite had the morphology of pseudo-spherical forms constituted by small plates when hydrothermal treatment (without sonication) was use for the preparation of zeolites. Moreover, it was determined that ultrasonic-assisted hydrothermal method effected a reduction in the crystal size compared with the zeolites which were synthesized only by using hydrothermal synthesis. The total amount of zeolites as high as 88–93% was achieved after 24 h of hydrothermal treatment followed or unfollowed by sonication. By using longer duration (20 min) of ultrasound pretreatment it is possible to reduce the duration of hydrothermal synthesis: from 24 h to 12 h of hydrothermal treatment. In this case, similar results of total amount of zeolites were detected. In the present work, low-cost raw materials, such as silica by-product have been investigated for the production of zeolites.     

Terahertz time domain spectroscopy of hydrothermally synthesized boehmite and ammonium dawsonite nanostructures

The frequency dependent optical and dielectric properties of boehmite (AlOOH) and ammonium aluminum carbonate hydroxide (AACH) nanostructures, prepared at different temperatures via hydrothermal synthesis, were studied by using terahertz time domain spectroscopy (THz-TDS). The complex refractive indices, absorption coefficients and complex dielectric constants were determined and compared for different synthesis temperatures. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were also performed to confirm the formation of boehmite and AACH. Scanning electron microscopy (SEM) was performed to study the morphology of nanostructures. The study reveals the formation of AACH at higher temperatures and decrease in refractive index with increasing synthesis temperature. The higher absorption coefficient and lower refractive index and dielectric constant were observed for AACH than for boehmite.     

Study of nanocomposite thick-film butanol vapor sensors

Gas sensing characteristics of multi-walled carbon nanotubes coated with tin dioxide nanoparticles nanocomposite thick-film structures (MWCNTs/SnO₂) prepared using hydrothermal synthesis, sol–gel technique and their combined process were investigated. Gas response test measurements of all studied nanocomposite structures carried out in air/target gas mixture showed that the most and at one time selective response to butanol vapor exposure in comparison to other mainly toxic and harmful gases such as acetone, toluene, formaldehyde, dimethylformamide, and others is observed for samples obtained by hydrothermal synthesis with 1:4 and 1:200 weight ratios of the nanocomposite components, respectively. These sensors are characterized by relatively short response and recovery times about 12 and 100 s, respectively, as well as low operating temperatures in the range of 150–200°C.     

The beneficial use of ultrasound in synthesis of nanostructured Ce-doped SAPO-34 used in methanol conversion to light olefins

Methanol to olefins process is an interesting route for synthesis of light olefins over nanostructured catalysts. The present research deals with catalyst development by sonochemical method for methanol to olefins reaction with the aim of reaching the most efficient catalyst. The CeSAPO-34 catalyst was prepared via ultrasound assisted hydrothermal method and characterized by XRD, FESEM, PSD, EDX, BET and FTIR techniques. The characteristics and performance of this sample were compared to the catalyst prepared by conventional hydrothermal method. XRD patterns reflected the higher crystallinity of the catalyst synthesized by ultrasound application. In comparison, particles with smaller sizes obtained by applying ultrasonic irradiation. The catalyst obtained using ultrasound had the longer lifetime and sustained desired light olefins at higher values.     

The electron beam irradiation damage on nanomaterials synthesized by hydrothermal and thermal evaporation methods--an example of ZnS nanostructures

Using transmission electron microscopy-related techniques, we have compared the degradation behaviors of several different types of ZnS nanostructures, including the ZnS nanosheets synthesized by hydrothermal method (with different oxygen impurity concentration) and ZnS nanobelts grown using thermal evaporation. We have identified that displacement damage, sputtering, and oxidation mechanisms exist during the electron irradiation process. While oxidation of the nanostructure is always observed, displacement damage appears to be the dominant mechanism contributing to the final structural collapse of ZnS nanosheets (synthesized via hydrothermal methods), but sputtering mechanism becomes critical in changing the surface roughness of the ZnS nanobelts (grown by thermal evaporation). The specific damage mechanisms of these nanomaterials disclose that different synthesis process results in different structure quality (particularly impurity related interior defects) of the ZnS nanostructures, which determines their specific degradation behaviors under the electron beam irradiation.     

Study on preparation and properties of molybdenum alloys reinforced by nano-sized ZrO<Subscript>2</Subscript> particles

The nano-sized ZrO₂-reinforced Mo alloy was prepared by a hydrothermal method and a subsequent powder metallurgy process. During the hydrothermal process, the nano-sized ZrO₂ particles were added into the Mo powder via the hydrothermal synthesis. The grain size of Mo powder decreases obviously with the addition of ZrO₂ particles, and the fine-grain sintered structure is obtained correspondingly due to hereditation. In addition to a few of nano-sized ZrO₂ particles in grain boundaries or sub-boundaries, most are dispersed in grains. The tensile strength and yield strength have been increased by 32.33 and 53.76 %.     

An ultrasonic characterization of ferrofluid

Nanoparticles of Cr₂O₃ are prepared through hydrothermal synthesis process using CrO₃/PVA in aqueous solution using sucrose as a reducing agent. The calcination temperature is taken 300 and 350 °C. XRD and SEM of the powdered Cr₂O₃ particles are done for the characterization. The average particle size is found 30–80 nm. It is found that average particle size increases with calcination temperature. The UV–visible absorption spectra are taken for the study of photo-physical properties of ferrofluids. Ultrasonic velocity and absorption measurements are performed in Cr₂O₃ ferrofluid using variable path interferometer and pulse-echo techniques, respectively. The achieved results are discussed in correlation with the magnetic and other physical properties of Cr₂O₃.     

水热法制备MgWO4 及其发光性质

以硝酸镁、钨酸钠为原料,氢氧化钠和硝酸作为pH调节剂,在180~230 ℃水热条件制备纯相的MgWO₄。探讨了水热反应温度对MgWO₄纯相形成以及煅烧温度对其晶型、发光性质的影响。分别用粉末X射线衍射、荧光光谱、扫描电子显微镜和综合热分析等手段对样品进行表征。结果表明,水热法可以直接制得不含结晶水MgWO₄晶体,属于四方晶系,形貌呈片状,厚度约为几个纳米。样品热重分析和高温煅烧的结果表明,水热法所得MgWO₄晶体在850 ℃附近出现晶型转化,由四方晶系转变为单斜晶系,并导致发光性质的明显变化。SEM显示煅烧前的样品形貌为片状,不同温度煅烧后由片状逐渐向棒状转变。     

基于LNG冷能的海水冷冻淡化机理研究

为利用液化天然气(LNG)的冷能实现海水冷冻淡化,研究了海水在超低温环境下的冷冻淡化机理,试验测试了海水在不同冷冻条件下的制冰淡化性能参数,分析了各因素对海水冷冻淡化过程的作用机理及性能影响,比较得出了该工艺系统的最优运行参数。该研究结果为基于LNG冷能的海水冷冻淡化系统工艺设计提供了重要的参考依据。     

Carbon-coated hollow CoO microporous nanospheres synthesized by CoF<Subscript>2</Subscript> as the intermediates as anode materials for lithium-ion batteries

Uniformly carbon-coated hollow CoO microporous nanospheres have been successfully synthesized by the facile hydrothermal method using CoF₂ as the intermediates and glucose as the carbon source. The whole synthesis process can avoid using the toxic surfactant additives and tedious post-processing. The glucose-derived carbon not only suppresses the aggregation of CoO nanoparticles, but also plays an important role on the stabilization of hollow CoO microporous nanosphere structure. The specific structure can largely improve the electronic conductivity and accommodate the volume change of CoO electrode in the electrochemical processes. When used as anode materials of lithium ion batteries, the hollow CoO/C microporous composites exhibit exceptionally high-rate performances, high-specific capacity, and improved cycle performances. This study may provide a new approach for the synthesis of carbon-coated hollow microporous architecture electrode for high-performance batteries.     

西南印度洋超慢速扩张脊海底热液硫化物中金银矿物的富集特征及富集机制研究

通过电感耦合等离子体光谱仪(ICP-AES)以及扫描电镜等手段对超慢速扩张的西南印度洋中脊热液区的3个硫化物样品的金银含量及其赋存状态进行了研究。通过ICP-AES测定金银含量,结果发现3个样品均有Au和Ag富集的现象。通过能谱-扫描电镜联用(SEM/EDS),在三个样品中发现了大量的金银矿物。其中S27-4中,主要以不规则粒状的银金矿和自然金的形式赋存于硫化物中或者晶粒之间,而S35-22中,则发现了大量的银矿物和部分银金矿。能谱分析表明银矿物中常伴随有一定量的卤族元素,推测以卤化银的形式存在,银金矿除了以粒间金赋存还可以呈乳滴状被吸附在黄铁矿表面或者晶棱上,推测与黄铁矿表面缺陷有关。S35-17样品中银金矿是唯一被发现的矿物相,以包体金、吸附金和间隙金形式赋存。由于不同样品中,银金矿的摩尔比有所不同,指示形成环境有所不同。研究结果表明,S27-4的成矿流体中,Ag主要以AgCl-₂络合物迁移,Au经历了以AuCl-₂络合物到AuHS0络合物为主的转变,指示了其温度从中高温到中低温的变化过程,说明了传导冷却在这个变化过程中有重要作用。S35-22中金银矿物的形成也具有类似的富集机制,但S35-22中卤化银的形成显示了早期高温高氯度的流体环境。而黑烟囱样品S35-17中银金矿的形成则与热液流体与海水的混合作用有密切关系。     

Preparation of CeO2 by a simple microwave–hydrothermal method

Cerium carbonate hydroxide (orthorhombic Ce(OH)CO₃) hexagonal-shaped microplates were synthesized by a simple and fast microwave–hydrothermal method at 150 °C for 30 min. Cerium nitrate, urea and cetyltrimethylammonium bromide were used as precursors. Ceria (cubic CeO₂) rhombus-shape was obtained by a thermal decomposition oxidation process at 500 °C for 1 h using as- synthesized Ce(OH)CO₃. The products were characterized by X-ray powder diffraction, field-emission scanning electron microscopy, thermogravimetric analysis and Fourier transformed infrared spectroscopy. The use of microwave–hydrothermal method allowed to obtain cerium compounds at low temperature and shorter time compared to other synthesis methods.     

Reductive hydrothermal synthesis of La(OH)<Subscript>3</Subscript>:Tb<Superscript>3+</Superscript> nanorods as a new green emitting phosphor

A reductive hydrothermal process with use of hydrazine hydrate as a protecting agent is proposed to synthesize La(OH)₃:Tb³⁺ (Tb mol% = 0, 1, 5, 10, and 20) nanorods. The oxidation of Tb³⁺−Tb⁴⁺ was effectively prevented in the presence of hydrazine hydrate; hence the La(OH)₃:Tb³⁺ nanorods exhibited much stronger green photoluminescence than the product prepared by the normal hydrothermal process. X-ray diffraction and transmission electron microscopy were employed to characterize the products, the results of which revealed that all the products were one-dimensional rod-like nanostructures of hexagonal structure (∼20 nm in diameter). The reductive hydrothermal process is desirable for the synthesis of other efficient Tb³⁺ doped nanophosphers.     

水热条件下钛酸钡晶粒生长基元模型研究

以水热法制备钛酸钡微粉（晶粒）实验为基础，通过建立钛酸钡晶粒生长基元的数学模型和基元稳定能计算，对水热条件下钛酸钡晶粒成核和生长过程作了研究 关键词：     

Growth mechanism studies of ZnO nanowire arrays via hydrothermal method

Well-controlled ZnO nanowire arrays have been synthesized using the hydrothermal method, a low temperature and low cost synthesis method. The process consists of two steps: the ZnO buffer layer deposition on the substrate by spin-coating and the growth of the ZnO nanowire array on the seed layer. We demonstrated that the microstructure and the morphology of the ZnO nanowire arrays can be significantly influenced by the main parameters of the hydrothermal method, such as pH value of the aqueous solution, growth time, and solution temperature during the ZnO nanowire growth. Scanning electron microscopy observations showed that the well oriented and homogeneous ZnO nanowire arrays can be obtained with the optimized synthesis parameters. Both x-ray diffraction spectra and high-resolution transmission electron microscopy (HRTEM) observations revealed a preferred orientation of ZnO nanowires toward the c-axis of the hexagonal Wurtzite structure, and HRTEM images also showed an excellent monocrystallinity of the as-grown ZnO nanowires. For a deposition temperature of 90 °C, two growth stages have been identified during the growth process with the rates of 10 and 3 nm/min, respectively, at the beginning and the end of the nanowire growth. The ZnO nanowires obtained with the optimized growth parameters owning a high aspect ratio about 20. We noticed that the starting temperature of seed layer can seriously influence the nanowire growth morphology; two possible growth mechanisms have been proposed for the seed layer dipped in the solution at room temperature and at a high temperature, respectively.     

Theoretical design and experimental study of hydrothermal synthesis of KNbO3

In the framework of the Lencka-Riman thermodynamic model, we give a theoretical design for the hydrothermal synthesis of pure KNbO₃ powder in a K-Nb-O tri-component system, where the stability yield diagrams and the optimum conditions (i.e., synthesis temperature, precursor concentrations, solution pH) are provided. Additionally, a hydrothermal experiment is carried out to synthesize KNbO₃ powder by reacting niobium pentoxide with potassium hydroxide at a temperature above 523 K and highly alkaline conditions. It is found that the experiment is in great agreement with the theoretical design. This research shows that the newly developed Lencka-Riman model is a powerful theoretical tool for designing hydrothermal synthesis of new materials.