Fabrication of symmetric hierarchical hollow PbS microcrystals via a facile solvothermal process

Symmetric hierarchical hollow PbS structures consisting of nanowalls were successfully fabricated by a facile solvothermal process in ethylenediamine at 120 degrees C for 12 h, employing lead acetate trihydrate and dithizone as precursors; the thickness of the nanowalls is about 80 nm. No surfactants or other templates were used in the process. The synthesized product was characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), ultraviolet-visible spectrometer (UV-vis), near-infrared absorption spectroscopy (near-IR), and fluorescence spectrophotometer. The effect of the reaction conditions on the size and morphologies of PbS structures was investigated. The results show that the temperatures, solvent, and sulfur sources are crucial factors on the morphologies and sizes of the symmetric hierarchical hollow PbS microcrystals. A possible growth mechanism of hierarchical hollow PbS structures is presented. UV-vis absorption spectrum holds a weak peak at 253 nm; the near-infrared absorption spectrum of PbS microcrystals has the two absorption peaks centered at 9613 cm(-1) (1040 nm) and 6771 cm(-1) (1477 nm), showing a blue shift compared with the bulk PbS (approximately 3020 nm). And the fluorescence spectrum of PbS microcrystals consists of an emission peak with a maximum at 305 nm. These PbS microcrystals may have potential applications in the fundamental study of nanostructures as well as fabricating nanodevices.     

Flutelike porous hematite nanorods and branched nanostructures: synthesis, characterisation and application for gas-sensing

Flute-like porous alpha-Fe2O3 nanorods and branched nanostructures such as pentapods and hexapods were prepared through dehydration and recrystallisation of hydrothermally synthesised beta-FeOOH precursor. Transmission electron microscopy (TEM), high-resolution TEM and selected area electron diffraction analyses reveal that the nanorods, which grow along the [110] direction, have nearly hollow cavities and porous walls with a pore size of 20-50 nm. The hexapods have six symmetric arms with a diameter of 60-80 nm and length of 400-900 nm. The growth direction of the arms in the hexapod-like nanostructure is also along the [110] direction, and there is a dihedral angle of 69.5 degrees between adjacent arms. These unique iron oxide nanostructures offer the first opportunity to investigate their magnetic and gas sensing properties. The nanostructures exhibited unusual magnetic behaviour, with two different Morin temperatures under field-cooled and zero-field-cooled conditions, owing to their shape anisotropy and magnetocrystalline anisotropy. Furthermore, the alpha-Fe2O3 nanostructures show much better sensing performance towards ethanol than that of the previously reported polycrystalline nanotubes. In addition, the alpha-Fe2O3 nanostructure based sensor can selectively detect formaldehyde and acetic acid among other toxic, corrosive and irritant vapours at a low working temperature with rapid response, high sensitivity and good stability.     

功能化PbS量子点的水相合成及结构表征

在水溶液中以Pb(NO3)2和Na2S为原料,巯基乙酸为稳定剂,合成了水溶性PbS量子点.用透射电子显微镜、扫描电子显微镜、粒度分析仪和红外光谱对PbS量子点进行了表征,结果表明所合成的PbS量子点的平均粒径为25 nm左右,分散性好,且巯基乙酸成功修饰于PbS纳米粒子表面,使其具有进一步与生物分子偶联的作用.     

Sonochemical synthesis of hollow PbS nanospheres

PbS hollow nanospheres with diameters of 80-250 nm have been synthesized by a surfactant-assisted sonochemical route. The nanostructures were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), (high-resolution) transmission electron microscopy [(HR)TEM], and scanning electron microscopy (SEM) images. Structural characterization indicates that shells of the hollow spheres are composed of PbS nanoparticles with diameters of about 12 nm. The formation of the hollow nanostructure was explained by a vesicle-template mechanism, in which sonication and surfactant play important roles. Furthermore, uniform silica layers were successfully coated onto the hollow spheres via a modified St?ber method to enhance their performance for promising applications.     

Sonochemical synthesis of mass single-crystal PbS nanobelts

Based on sonochemical technique, large-scale PbS nanobelts are successfully synthesized in the mixed solution of PbCl₂ and Na₂S₂O₃. These nanobelts are characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), selected area electronic diffraction, energy dispersive X-ray spectroscopy, and high-resolution TEM. The as-synthesized PbS nanobelts have width of about 80 nm, length up to several millimeters, and width-to-thickness ratio of about 5. In addition, the growth mechanism of PbS nanobelts is suggested.     

Synthesis and evolution of PbS nanocrystals through a surfactant-assisted solvothermal route

We present a surfactant-assisted solvothermal approach for the controllable synthesis of a PbS nanocrystal at low temperature (85 degrees C). Nanotubes (400 nm in length with an outer diameter of 30 nm), bundle-like long nanorods (about 5-15 mum long and an average diameter of 100 nm), nanowires (5-20 mum in length and with a diameter of 20-50 nm), short nanorods (100-300 nm in length and an axial ratio of 5-10), nanoparticles (25 nm in width with an aspect ratio of 2), and nanocubes (a short axis length of 10 nm and a long axis length of 15 nm) were successfully prepared and characterized by transmission electron microscopy, scanning electron microscopy, and powder X-ray diffraction pattern. A series of experimental results indicated that several experimental factors, such as AOT concentration, ratio of [water]/[surfactant], reaction time, and ratio of the reagents, play key roles in the final morphologies of PbS. Possible formation mechanisms of PbS nanorods and nanotubes were proposed.     

Synthesis of lead chalcogenide nanocrystals by sequential ion implantation in silica

Lead chalcogenide (PbS, PbSe, and PbTe) nanocrystals were synthesized by sequential implantation of Pb and one of the chalcogen species into pure silica. The implantation energy and fluence were chosen so that the implantation profiles practically overlap at a depth approximately 150 nm with a maximum concentration of about 0.3 atom %. Annealing for 1-8 h at 850-900 degrees C triggers nanocrystal growth, which is monitored by high-resolution (HRTEM) and conventional transmission electron microscopy (TEM), secondary-ion mass spectrometry (SIMS), and Rutherford backscattering spectrometry (RBS). Striking differences are found in the depth distributions and microstructures of the resulting nanocrystals. We show that the differing chemical interactions of Pb and chalcogens (between each other and with silica) play a crucial role in chalcogenide nucleation and growth. Using available information on chalcogen redox states in silicate glass, we propose a nonclassical nucleation and growth mechanism consistent with our experimental results. The complex chemistry involved at the microscopic level is shown to impair control over the nanocrystal size distribution. Finally, PbS nanocrystal-doped silica is shown to emit intense photoluminescence (PL) in the 1.5-2 microm wavelength range, an effect that we relate to the above nucleation and growth scheme.     

多树枝结构和立方结构PbS的水热合成及形成机理

在无模板条件下,用Pb(NO₃)₂做铅源,(CH₄N₂S)做硫源,用水热法在160 ℃反应24 h制备了结晶度好的多树枝结构PbS。利用XRD、SEM、EDX、TEM对产物进行了表征,结果表明所得产物为面心立方多树枝状结构,单个树枝的长度为1.0～3.0 μm。此外,在碱性条件下丙三醇/水体系中制备了具有不同凹面的立方结构PbS,边长为2.0～5.0 μm。对2种不同形态PbS的影响因素进行了讨论,并提出了形成机理。同时对其荧光及紫外性质进行了研究,结果表明立方结构的PbS在309和373.5 nm处出现了2个荧光峰,在211和232 nm处出现了2个紫外吸收峰。     

硫化铅纳米材料合成的新方法

以硫代碳酸盐为原料 ,用室温液相反应合成出前驱物硫代碳酸铅 ,在高压釜中 10 0℃加热 2h即得纳米PbS .用X射线粉末衍射 ,透射电镜对产物的组成、大小、形貌进行表征 .结果表明 ,产物纳米PbS为立方晶系结构 ,平均粒径为 2 0nm     

球状、立方状及空心立方状PbS纳米晶的控制合成及其形成机理

以醋酸铅为铅源,硫代乙酰胺为硫源,在表面活性剂十二烷基硫酸钠(SDS)和十六烷基三甲基溴化铵(CTAB)共同作用下,通过简单地调节水热反应的反应温度控制合成出球状、立方状和空心立方状PbS纳米晶。利用XRD、TEM对合成产物的结构和形貌进行了表征,发现合成的球状、立方状和空心立方状PbS纳米晶尺寸均一,直径为100 nm左右。对球状、立方状和空心立方状PbS纳米晶的形成机理进行了初探,结果表明反应温度较低时,水热反应初始阶段形成的PbS小颗粒呈球形,在表面活性剂SDS的烷基链模板和CTAB微胶束软模板共同作用下生成球状PbS纳米晶;反应温度较高时,水热反应初始阶段形成的PbS小颗粒由于自身的立方相岩盐晶体结构的影响有呈立方状趋势,在SDS和CTAB共同作用下产物堆积成空心立方体状或立方状。     

The solventless syntheses of unique PbS nanowires of X-shaped cross sections and the cooperative effects of ethylenediamine and a second salt

Unique PbS nanowires with x-shaped cross sections, with diameters in the range of 300-800 nm with an average of 598 nm (sigma = +/-21.7% ), and lengths of up to several tens of micrometers, have been made by a solventless method. Such nanowires show high adsorptivities of the PbS nanooctahedra, which can be washed off by ultrasound. The suitable precursor is obtained from a Pb(NO3)2/octanoate/ethylenediamine/dodecanethiol molar ratio of 1:2:1:1.6, and the PbS nanowires are produced by the thermolysis of such precursors at 280 degrees C for 1 hour. The X-ray diffraction, scanning electron microscopy, and transmission electron microscopy characterizations of the products and the keys of the morphological control have been reported. For the formation of such products, two cooperative effects are found to be crucial, the roles of ethylenediamine and a second salt, lead octanonate.     

液相合成方形PbS纳米晶的光学特性

采用一种简单、温和的液相合成方法制备了PbS纳米晶，利用透射电镜和高分辨透射电镜对PbS纳米晶的形貌与晶型结构进行了表征．研究了PbS纳米晶的光学吸收和光致发光特性，并比较分析了包覆剂聚乙烯吡咯烷酮(PVP)和回流时间对产物光学特性的影响．结果表明：PVP分子链中的O原子与纳米晶表面吸附的游离态Pb原子形成Pb-O配位键，使产物的激子吸收大为减弱，同时引起了表面浅束缚态能量的升高，最终导致了荧光淬灭现象．     

六边形及圆形SmF3微米盘的水热合成与表征

以Sm(NO3)3·6H2O和不同的氟化物(NaBF4,NH4F)在120℃的低温水热条件下反应得到了六边形及圆形的SmF3微米盘.通过X射线衍射(XRD)、场发射扫描电子显微镜(FE-SEM)和透射电子显微镜(TEM)对产物的晶相和形貌进行了表征.XRD结果显示所得的产物是结晶良好的六方晶系.SEM和TEM测试表明得到大量均匀的厚度约为200 nm的盘状结构.研究发现氟化物种类以及反应时间对形成不同形貌的盘有重要影响.讨论了可能的形成机理.进一步研究了SmF3:Tb3+和SmF3:Eu3+掺杂后的产物的荧光性质.     

High performance thermoelectrics from earth-abundant materials: enhanced figure of merit in PbS by second phase nanostructures

Lead sulfide, a compound consisting of elements with high natural abundance, can be converted into an excellent thermoelectric material. We report extensive doping studies, which show that the power factor maximum for pure n-type PbS can be raised substantially to ~12 μW cm(-1) K(-2) at >723 K using 1.0 mol % PbCl(2) as the electron donor dopant. We also report that the lattice thermal conductivity of PbS can be greatly reduced by adding selected metal sulfide phases. The thermal conductivity at 723 K can be reduced by ~50%, 52%, 30%, and 42% through introduction of up to 5.0 mol % Bi(2)S(3), Sb(2)S(3), SrS, and CaS, respectively. These phases form as nanoscale precipitates in the PbS matrix, as confirmed by transmission electron microscopy (TEM), and the experimental results show that they cause huge phonon scattering. As a consequence of this nanostructuring, ZT values as high as 0.8 and 0.78 at 723 K can be obtained for nominal bulk PbS material. When processed with spark plasma sintering, PbS samples with 1.0 mol % Bi(2)S(3) dispersion phase and doped with 1.0 mol % PbCl(2) show even lower levels of lattice thermal conductivity and further enhanced ZT values of 1.1 at 923 K. The promising thermoelectric properties promote PbS as a robust alternative to PbTe and other thermoelectric materials.     

MnOOH纳米棒的反胶束法制备及表征

采用水溶液/CTAB/正丁醇/庚烷四组分组成的反相胶束体系,制备了MnOOH纳米棒,并用透射电镜(TEM)、高分辨透射电镜(HRTEM)和X射线粉末衍射(XRD)进行了表征.结果显示所得MnOOH为单斜晶系,直径约为10 nm、长度约为200 nm.实验表明,不同的反应时间所得纳米棒的长度不同,但直径可以保持不变.     

Synthesis and characterization of PbS nanorods in W/O microemulsion system

PbS nanorods have been successfully synthesized in water-in-oil (W/O) microemulsion containing non-ionic surfactant OP, n-pentanol, cyclohexane, and aqueous solution. The effects of the molar ratio of water to surfactant (ω₀), the concentration of reactants and the ageing time on the morphologies of PbS nanoparticles were investigated. The microstructures, morphologies and properties of the synthesized products were characterized by means of X-ray diffraction, transmission electron microscopy, and ultraviolet-visible (UV-VIS) absorption spectroscopy, respectively. The results showed that the synthesized rod-like products are composed of cubic phase PbS. These nanorods have an average diameter of about 100 nm, and an average length of about 500 nm. In the UV-VIS absorption spectrum, the absorption edge of PbS nanorods exhibit a blue shift compared with that of bulk PbS, indicating the quantum confinement effect of PbS nano-particles     

TiO2 surface modification and characterization with nanosized PbS in dye-sensitized solar cells

The nanoporous TiO2 films utilized in dye-sensitized solar cells (DSSCs) possess a large surface-to-volume ratio, which facilitates the adsorption of sensitizing dye and the recombination due to the high density of surface traps. In this paper, nanosized PbS was fabricated on the TiO2 films. The components of the modified TiO2 film were studied by X-ray diffraction (XRD) and electron probe microanalysis (EPMA), while the structure of the film was characterized with BET physisorption and high-resolution scanning electron microscopy (HRSEM). The results showed that the PbS particles were 2-3 nm and discrete on the surface of TiO2. Diffusion photovoltage (PV) spectroscopy was employed to study the charge separation and diffusion processes inside modified and unmodified TiO2 films. The diffusion PV signals revealed that the traps on the surface of TiO2 were extremely reduced due to the presence of PbS. The results of transient photovoltage and back I-V characteristics showed that the back reaction, that is, the recombination due to the reaction between an electron on TiO2 and the hole-transporting media, was retarded significantly.     

N2流量对GaN的形貌及光学和电学性能的影响

采用化学气相沉积法(CVD)在Si(100)衬底上以Ni为催化剂,金属Ga和NH3为原料合成了GaN微纳米结构,并研究了N2流量对产物GaN的形貌及光学和电学性能的影响。利用场发射扫描电子显微镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)、Xray能谱仪(EDS)、光致发光谱(PL)和霍尔效应测试仪(HMS-3000)等测试手段对样品的形貌、结构、成分、光学和电学性能进行了分析。结果表明,随着N2流量的增加,产物GaN的形貌发生了由微米棒到蠕虫状线再到光滑纳米线的转变;生成的GaN均为六方纤锌矿结构;样品均表现出383 nm的近带边紫外发射峰和470 nm左右的蓝光发射峰;所有样品均为p型;并对产物GaN的形貌转变机理进行了分析。     

微波辅助合成石墨烯/氧化镍复合材料及其表征

本文通过微波辅助的方法,快速而有效地在热膨胀石墨烯(RG)的缺陷上原位合成氧化镍纳米颗粒,形成石墨烯/氧化镍复合材料(RG/NiO)。利用X-射线衍射(XRD),拉曼光谱(Raman),傅里叶变换红外(FTIR),扫描电镜(SEM),透射电镜(TEM),热重-差热(TGA-DSC)对所制备样品的结构、形貌和NiO在复合材料中的含量进行表征。结果表明,热膨胀石墨烯层数约7~8层,层间距约为0.35 nm,缺陷多,在水热和微波处理后抗氧化性明显变差。复合材料中氧化镍颗粒平均粒径为25 nm,均匀而密集地分散在石墨烯平面上,同时在复合材料中的含量为19.8%。     

微波辅助合成石墨烯/氧化镍复合材料及其表征

本文通过微波辅助的方法,快速而有效地在热膨胀石墨烯(RG)的缺陷上原位合成氧化镍纳米颗粒,形成石墨烯/氧化镍复合材料(RG/NiO)。利用X-射线衍射(XRD),拉曼光谱(Raman),傅里叶变换红外(FTIR),扫描电镜(SEM),透射电镜(TEM),热重-差热(TGA-DSC)对所制备样品的结构、形貌和NiO含量在复合材料中的含量进行表征。结果表明,热膨胀石墨烯层数约7~8层,层间距约为0.35nm,缺陷多,在水热和微波处理后抗氧化性明显变差。复合材料中氧化镍颗粒平均粒径为25nm,均匀而密集地分散在石墨烯平面上,同时在复合材料中的含量为19.8%。