Hydrothermal synthesis of different SnO2 nanosheets with CO gas sensing properties

In this work, 2D SnO₂ nanosheets were synthesized via a polyvinylpyrrolidone (PVP)-assisted hydrothermal method. X-ray diffraction and scanning electron microscopy were used to examine the chemical composition and nanostructures. It was found that the concentration of PVP played a critical role in governing the assembly process of nanostructures. Further, their gas-sensing performances were investigated comprehensively. The nanosheet-III structures were found to show the most superior gas-sensing properties due to their largest specific surface and fashionable assembly.     

Hydrothermal synthesis of different TiO2 nanostructures: structure, growth and gas sensor properties

A type of titanium precursor, H-exchanged titanate nanobelts, was used to prepare nanosized anatase titanium dioxide (TiO₂) with various morphologies by hydrothermal method. Nanorods, nanobelts, nano-polyhedrons and nanoparticles were successfully synthesized. We found that CTAB and EDTA-4Na⁺ play critical roles in synthesizing the nanorods and nano-polyhedrons. All the samples exhibit rapid response and recovery time to ethanol, but Nanorods, nanobelts and nano-polyhedrons show lager response than nanoparticles.     

Hydrothermal synthesis of different 3D SnO2 nanostructures and their gas-sensing properties

Different morphologies of 3D SnO₂ nanostructures, including sphere-like, net-like, and flower-like, have been successfully synthesised via a facile hydrothermal method. The products were characterized by X-ray diffraction and scanning electron microscopy. The possible growth mechanism of different SnO₂ nanostructures was discussed in detail. We found that the citric acid and PEG play significant roles in synthesizing the flower-like and net-like nanostructures. Furthermore, the gas-sensing properties of the samples were investigated towards the reducing ethanol gas. The results indicate that the flower-like and net-like SnO₂ show larger gas sensing properties than sphere-like SnO₂.     

Hydrothermal synthesis of bismuth sodium titanate particles with different morphologies

Nanostructured Na_0.5Bi_0.5TiO₃ particles have been synthesized by a hydrothermal synthesis method using a layered titanate H_1.07Ti_1.73O₄·nH₂O as a Ti precursor. The obtained Na_0.5Bi_0.5TiO₃ particles showed different morphologies including plate-like, wire-like, and cubic-like structures in different hydrothermal conditions. The effect of the NaOH concentration on the growth and morphology evolution of hydrothermally derived Na_0.5Bi_0.5TiO₃ powders were investigated. It was found that alkaline concentration had a great effect on the phase and morphology of the resultant powders. The dissolution–recrystallization and in situ topotactic transformation mechanisms were suggested in different alkaline concentrations according to the evolution process.     

水热合成氧化铁纳米结构及机理分析

利用硝酸铁与油酸钠反应所得的化合物在高温水热条件下分解制备多种氧化铁纳米结构.研究了水热反应温度、反应时间和热处理工艺对于产物结构的影响,并且探讨了产生各种纳米结构的机理.在高温较短反应时间下,可以制得直径为15nm,长度为3μm的纳米线结构,延长反应时间至25h,得到边长为15nm的氧化铁四方颗粒.将含有羟基氧化铁相的氧化铁纳米线在不同温度下进行热处理,得到了直径为15nm,长度为1μm的氧化铁纳米线和直径为1～3μm的氧化铁微米球.     

Hydrothermal synthesis of titanate nanowire arrays

A simple templateless synthesis strategy for titanate nanowire arrays was developed by employing hydrothermal reactions. Hydrothermal treatment of metallic titanium powder with H₂O₂ in a 10 M NaOH solution produced a new sodium titanate compound, Na₂Ti₆O₁₃·xH₂O (x ∼ 4.2), as arrays of nanowires of lengths up to 1 mm. The nanowires were characterized by using XRD, SEM, TGA, and TEM. The nanowires have exceptionally large aspect ratios of 5000 or higher, and they can form arrays over a large area of 2 × 3 cm². Investigations on the reaction products in varied conditions indicate that the array formation requires simultaneously controlled formation and crystal growth rates of the Na₂Ti₆O₁₃·xH₂O phase.     

Hydrothermal synthesis of lead doped barium titanate

Lead doped barium titanate was synthesized hydrothermally at 363 K for 140 h. A molar formula of Ba_(1–x)Pb _x TiO₃ was used, where x ranged between 0.025 and 0.75. The crystal structure, phase purity, and particle morphology was investigated by x-ray diffraction, Raman spectroscopy and electron microscopy. Under the synthesis conditions used, lead (Pb²⁺) was shown to incorporate into the perovskite structure when the dopant was kept below 20%. Above 20% Pb, other phases appeared and at 75% Pb no reaction to the perovskite structure took place. Unexpectedly, barium titanate containing from 2.5% Pb to 10% Pb appeared to be of orthorhombic symmetry. This was concluded by total pattern fitting of x-ray diffraction profiles and from splitting of the 222 reflection. The factors controlling the tendency for these materials to adopt orthorhombic symmetry as opposed to the more commonly observed tetragonal or cubic symmetries are briefly discussed.     

Hydrothermal synthesis of fibrous lead titanate powders

A fibrous lead titanate (PbTiO₃) powder with light-yellow colour has been prepared by hydrothermal synthesis. The influences of Pb/Ti ratio (0.3 to 1.0) in the mixture and reaction time on the formation of fibrous PbTiO₃ under hydrothermal conditions have been investigated. The preferable conditions for preparing fibrous perovskite-type PbTiO₃ from fibrous potassium titanate are that the Pb/Ti ratio is 1.0, reaction temperature 150 °C and time 72 h. The particles of fibrous powder of perovskite type are usually less than 2 m in diameter and more than 50 m in length. The fibrous morphology is essentially unchanged up to about 650 °C, but it disappeared after heating to 1000 °C.     

Synthesis and growth mechanism of CuO nanostructures and their gas sensing properties

CuO nano-particles, nano-rods, nano-sheets and nano-flowers were synthesized by the hydrothermal routes with copper salts under different additions. The obtained samples were characterized by X-ray diffraction and scanning electron microscopy. We investigated the effects of precursors on the formation of CuO with different morphologies and proposed their possible formation mechanisms. In addition, the obtained CuO nano-flowers are found to show better sensing performances than the other three low-dimensional CuO nanostructures. Our results also demonstrate that gas sensing properties of nanocrystals can be significantly improved by tailoring shape and morphology of the nanocrystals. The CuO nano-flowers may hold substantial promise in low-dimensional gas-sensing applications.     

Hydrothermal synthesis of spindle-like ZnS hollow nanostructures

Spindle-like hollow nanostructures of zinc sulfide (ZnS) have been successfully synthesized by hydrothermal process using a simple surfactant emulsion template. The morphologies of ZnS nanostructures were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and field-emission scanning electron microscopy (FE-SEM). It is found that most of the products including twin ellipsoids with connected hollow cores are reminiscent of spindle-like structures. The lengths, widths and the thickness of the shell are in the range of 1-2 μm, 300-450 nm and 20-40 nm, respectively. Selected area electron diffraction (SAED) and X-ray powder diffraction (XRD) patterns show that the shell is composed of sphalerite ZnS polycrystals.     

CuS纳米空心管结构的水热合成

以氯化铜和硫代乙酰胺为原料,在碱性条件下,利用低温简单水热法合成了硫化铜纳米空心管结构。通过XRD、TEM、FT-IR等检测方法对产品进行了结构和形貌分析。结果表明,所得硫化铜产品为六方相铜蓝矿结构,纳米空心管结构,纳米管的直径为150～200nm,长度为1.5～2.5μm;在1110cm-1处出现Cu-S键的红外特征吸收峰;同时对可能的生长机理做了阐述。     

Room temperature solid-state synthesis and ethanol sensing properties of sea-urchin-like ZnO nanostructures

ZnO gas-sensing materials were prepared by one-step solid-state reaction at room temperature. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) were used to characterize the hierarchal ZnO nanocrystals. The results indicate that ZnO clusters are assembled with nanosheets when no surface-active agent is present. When surface-active agent PEG-10000 was added, sea-urchin-like ZnO are assembled from ZnO nodules. The rods have an average diameter of 33 nm and length of about 100 nm. The primary gas-sensing results show that sea-urchin-like ZnO have good gas sensitivity to ethanol vapor.     

Size-controlled synthesis and gas sensing application of tungsten oxide nanostructures produced by arc discharge

Several different synthetic methods have been developed to fabricate tungsten oxide (WO(3)) nanostructures, but most of them require exotic reagents or are unsuitable for mass production. In this paper, we present a systematic investigation demonstrating that arc discharge is a fast and inexpensive synthesis method which can be used to produce high quality tungsten oxide nanostructures for NO(2) gas sensing measurements. The as-synthesized WO(3) nanostructures are characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), finger-print Raman spectroscopy and proton induced x-ray emission (PIXE). The analysis shows that spheroidal-shaped monoclinic WO(3) crystal nanostructures were produced with an average diameter of 30?nm (range 10-100?nm) at an arc discharge current of 110?A and 300?Torr oxygen partial pressure. It is found that the morphology is controlled by the arc discharge parameters of current and oxygen partial pressure, e.g.?a high arc discharge current combined with a low oxygen partial pressure results in small WO(3) nanostructures with improved conductivity. Sensors produced from the WO(3) nanostructures show a strong response to NO(2) gas at 325?°C. The ability to tune the morphology of the WO(3) nanostructures makes this method ideal for the fabrication of gas sensing materials.     

纳米花/棒SnO2的水热法制备及其气敏性

以SnCl4和NaOH为原料,200℃水热条件下在预引入SnO2晶种的FTO导电玻璃上一步制备纳米花/棒多级结构SnO2.利用SEM,XRD,N2吸附-脱附和气敏测试仪等测试产物的形貌、晶相组成和气敏性能.结果显示:产物为四方晶相,多级结构中垂直于基底的纳米棒阵列形成"纳米地毯",其上生长球形纳米花,纳米棒和花瓣均由绒状纤维聚集而成;其比表面积为109.8 m2/g,是普通沉淀法SnO2粉体的13倍;其具有较高的气敏性,对1000×10-6浓度丙酮的灵敏度达36.1,是普通沉淀法SnO2粉体的7.9倍.     

Copper phthalocyanine quasi-1D nanostructures: growth morphologies and gas sensing properties

The growth conditions of meso- and nanoscopic copper phthalocyanine quasi-1D structures, single crystalline whiskers and "nanowebs" were investigated on various technologically important substrates and were compared to existing literature. The synthesized morphologies were used to fabricate organic conductometric gas-sensing devices, and their sensitivity and selectivity toward NOx were investigated. The obtained results demonstrate excellent sensitivity and selectivity of these quasi-1D chemiresistors. Both the response time of the quasi-1D CuPc sensors and their overall gas sensing performance can be further enhanced by reducing the surface-to-bulk ratio of these nano- and meso-structures.     

Hydrothermal synthesis and characterization of bismuth titanate regular tetrahedron crystallites

Bi₁₂TiO₂₀ (BTO) single crystals were synthesized by a hydrothermal process in KOH solution at 180 °C for 4 h from Ti(OC₄H₉)₄ and Bi(NO₃)₃·5H₂O compounds. The effects of processing parameters on the growth and morphology of BTO single crystals were investigated. The KOH concentration, reaction time and temperature had a great effect on the phase composition and morphology of the resultant crystals. BTO phase could not be obtained with KOH concentrations lower than 3 M or higher than 5 M. XRD, SEM and TEM were used to characterize the samples. BTO single crystals were regular tetrahedron in morphology and 10 μm or so in size.     

Facile synthesis and gas sensing properties of nanotriangular tin oxide

In the present study we report a simple and convenient chemical route using pentaerythritol as a structure-directing agent for the synthesis of crystalline nanotriangular SnO₂. We propose the scheme for the formation of nanotriangular structures wherein the preliminary spherical nanocrystallites are formed due to the low surface energy associated with them. These spherical nanocrystallites grow into the various linear intermediate shapes like Y, bi and tripods, which finally lead to the triangles, pyramids and bipyramids. Such variation in the structure occurs due to the structure directing pentaerythritol. These polycrystalline SnO₂ nanomaterials with structural peculiarities were tested for the gas sensing characteristics. Their response towards ethanol vapor, H₂ and LPG were investigated. It was found to exhibit high response towards ethanol vapors at the operating temperature of 250 °C.