超临界CO2流体干燥合成ZrO2气凝胶及其表征

以无机盐为原料,采用沉淀法结合超临界CO2流体干燥技术成功地制备了ZrO2气凝胶.借助TG/DSC、XRD、TEM、DLS以及N2物理吸附等手段对其性能进行表征.结果显示,超临界CO2流体干燥可以有效地防止干燥过程中胶体粒子之间的硬团聚作用,在基本保持湿凝胶网络结构的情况下实现液相的脱除,从而使合成的ZrO2具有高比表面积和大孔体积等特点.此外,样品的TEM和DLS分析显示,纳米ZrO2颗粒首先形成具有空间网络结构的簇团,尺寸为数百个纳米的簇团堆积形成ZrO2气凝胶;气凝胶的空间网络结构特征在中等温度的热处理过程中不会遭到完全破坏.     

Nickel-catalyzed deposition of Cu film on PET fabric with supercritical fluid

Polyester fabric was catalyzed with Nickel(II) acetylacetonate (Ni(acac)₂) in supercritical carbon dioxide (scCO₂) prior to electroless copper plating . The nickel activated polyester fibers were then characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. Deposited weight, surface morphology, crystal structure, surface resistance, electromagnetic interference shielding effectiveness and thermal loss of the copper plated polyester fabrics catalyzed with nickel in scCO₂ were investigated. The results indicate that the amount of copper deposited onto polyester fabric catalyzed with Ni(acac)₂ in scCO₂ is much more than that without scCO₂. Deposition rate of copper particles onto polyester fabric increases with increased temperatures of scCO₂. The copper particles are uniformly coated on the polyester fibers. The surface resistance of the copper plated fabric is 50 mΩ/sq when the temperature of scCO₂ is increased to 90?°C. The electromagnetic interference shielding effectiveness of the copper plated polyester fabric is 60–80 dB at frequencies ranging from 2 to 18 GHz. These results suggest that catalysis in scCO₂ for electroless copper plating provides polyester fabric with excellent electrical conductivity, surface resistance and electromagnetic interference shielding effectiveness.     

超临界流体沉积法制备纳米Cu/SBA-15复合材料

采用超临界流体沉积法,以无机盐Cu(NO₃)₂为前驱物,超临界CO₂为溶剂,乙醇为共溶剂,在压力20 MPa左右、温度 50℃ 条件下将Cu(NO₃)₂沉积到SBA-15介孔分子筛的孔道中。反应完成后,用氢气对前驱物进行还原,得到纳米线和纳米颗粒Cu/SBA-15复合材料。用透射电镜(TEM)和X射线衍射(XRD)对Cu/SBA-15复合材料进行表征,发现在SBA-15孔道内部填充了Cu 纳米线和分散的Cu 纳米颗粒。Cu 纳米线平均直径为6nm,长度为几纳米到几微米,并且沿着孔道生长,能够随着孔道发生弯曲;Cu纳米粒子的平均尺寸为3.2nm,高度分散。同时,实验中还发现,通过控制反应条件,能够控制复合材料中纳米结构的形貌(纳米线或者纳米颗粒) 。实验结果表明,超临界流体沉积法是制备担载型复合材料的有效方法。选择合适的共溶剂可以用超临界CO₂溶解无机盐,并可以通过控制反应条件,控制所制备的复合材料中纳米结构的形貌。     

Design at the nanometre scale of multifunctional materials using supercritical fluid chemical deposition

Recent developments in multifunctional devices show the interest in combining different materials to obtain specific properties. Through supercritical fluid chemical deposition (SFCD), silica spheres, used as a model support, were coated with copper nanoparticles (5-17?nm) with a tuneable amount of coverage (40-80%). The coating process is based on the reduction of metal precursors with hydrogen in a supercritical CO(2)/isopropanol mixture in a temperature range between 100 and 150?°C at 24?MPa. Several parameters were studied such as temperature, residence time or mass ratio of precursor/silica spheres, allowing control of the size of the copper nanoparticles and of the amount of coverage from metal nanoparticles scattered onto the surface to a metal nanoparticle thin film.     

Introduction of helium into metals by magnetron sputtering deposition method

High concentration helium, up to 16 at.%, was introduced into Ti films through magnetron sputtering method in a He/Ar complex atmosphere. The introduced helium distributes homogeneously in the films and mainly forms small helium bubbles. Helium thermodesorption experiments were carried out, from which it was found that the thermodesorption properties of the introduced ⁴He are similar to those of radiogenic ³He in titanium tritides. Titanium alloy films containing helium were also prepared through this way and a comparison of thermodesorption properties was made between them and Ti–He films.     

Morphology and energy transfer in PbS quantum dot arrays formed with supercritical fluid deposition

Lead sulfide (PbS) quantum dots (QDs) were synthesized in our lab with controllable and tunable sizes. Supercritical fluid CO₂ (sc-CO₂) provides a useful tool to deposit PbS QDs on substrate surfaces with lateral uniformity. Either in the PbS/toluene solution or in the sc-CO₂ fabricated film, the absorbance maxima of the PbS QDs do not show an obvious dependence on the PbS QD concentrations. Fluorescence spectra of PbS QDs obtained from the films prepared by the sc-CO₂ method indicate energy transfer between PbS QDs with different sizes, the small QDs serving as energy donors and large ones as acceptors. Samples formed with sc-CO₂ method measured by photoluminescence (PL) show a red-shift and an enhanced emission intensity with respect to samples formed with solution deposition method (SDM), specifically at cryogenic temperatures.     

Supercritical fluid deposition of vanadium oxide on multi-walled carbon nanotube buckypaper for supercapacitor electrode application

Composite electrodes were fabricated for supercapacitor applications by depositing vanadium oxide onto multi-walled carbon nanotube (MWCNT) buckypaper using supercritical fluid deposition (SFD). The deposited thin vanadium oxide layer showed amorphous structure with excellent uniformity. In aqueous KCl electrolyte, the vanadium oxide exhibited a constant pseudo-capacitance of ～ 1024 F g(-1), which was independent of the oxide material loading (up to 6.92 wt%) and voltage scan rate (up to 100 mV s(-1)). The highest specific electrode capacitance achieved was ～ 85 F g(-1), which was almost four times that of the pristine buckypaper electrode.     

Porosity of resorcinol-formaldehyde organic and carbon aerogels exchanged and dried with supercritical organic solvents

Organic and carbon aerogels have been prepared from resorcinol-formaldehyde resin diluted with various amounts of water. Water was exchanged by acetone or ethanol, and the gels were subsequently dried with supercritical acetone or with supercritical ethanol. We showed that the nature of the solvent with which water was exchanged only had a minor impact on the porosity of the resultant aerogels. In contrast, the same solvents used as drying fluids in the supercritical state led to significant differences, but only in the case of diluted gels. When the initial dilution was low, similar results were indeed obtained with both solvents. Ethanol was shown to lead to higher shrinkages and higher bulk densities than acetone. A higher chemical degradation of the resin during the drying process was also observed when ethanol was used.     

Effect of supercritical drying parameters on the electrochemical properties of vanadium oxide-based aerogels

This paper examines the effect of supercritical drying parameters (including the nature of the solvent) on the electrochemical properties of vanadium oxide-based aerogels. It is shown that, among vanadium oxide-based aerogels prepared using different solvents (supercritical CO₂, n-hexane, and n-octane), the material obtained in n-hexane is superior in discharge capacity characteristics: its capacity is 350 to 250 mAh/g in the first seven cycles. The aerogel obtained in supercritical CO₂ has a far lower capacity: 80–105 mAh/g.     

Sample deposition device for off-line combination of supercritical fluid chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A new sample deposition device for off-line SFC-MALDI combination of supercritical fluid chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was assembled. This device was successfully applied to the detailed characterization of synthetic silicone oils. SFC was used to separate samples of silicone oils on micropacked capillary columns and to determine their molecular mass distribution. The separated fractions for the identification studies were obtained from SFC runs at defined time intervals. Using the constructed deposition device, these fractions were sprayed directly from the restrictor on the target probe covered with a proper matrix. MALDI-TOF MS was used for the identification of individual oligomers in the separated fractions and also in the unfractionated sample. The determined molecular mass distributions based on supercritical fluid chromatography with flame ionization detector, MALDI-TOF MS, and combined SFC-MALDI measurements were compared and the results were in a good agreement. The sample deposition device is based on a common plotter unit, complemented by a microcontroller PIC16C84. The unit is connected by an RS-232 interface to a PC with the main control software running under MS Windows. The new sample deposition device made the off-line combination SFC-MALDI simpler, faster, and more sensitive.     

绿色超临界流体的应用研究

超临界流体具有与气体相似的密度、粘度、扩散系数等特性 ,应用领域日益广泛 ,主要有 :萃取、催化反应、结晶、吸附、材料制备、环境保护、食品工业、医药工业、染色工业、色谱分析、生物工程等。论述了超临界流体在这些领域的最新研究成果 ,重点介绍超临界流体在环境保护、染色工业、吸附过程、陶瓷脱脂、材料制备过程中的应用     

Thermodynamic behavior of supercritical fluid mixtures

The recent surge of interest in supercritical extraction has brought the unusual properties of supercritical mixtures into the focus of attention. We discuss some of the properties of binary mixtures in a range around the gas-liquid critical line from the point of view of supercritical solubility. The general thermodynamic relationships that govern the enhancement of supercritical solubility are readily derived by a mathematical method introduced by Ehrenfest. The enhancement is governed by a strong divergence centered at a critical end point. We give the classical and nonclassical power-law behavior of the solubility along the experimental paths of constant temperature or pressure. The factor multiplying the strong divergence contains the partial molar volume or enthalpy of the solute in the supercritical phase. These partials are quite anomalous, especially if the mole fraction of the solute is small. They diverge at the solvent's critical point. We cite experimental evidence of these divergences, especially the results of recent experiments in dilute near-critical salt solutions. The anomalies found in these salt solutions are common to all dilute near-critical mixtures with a nonvolatile second component. We show that on experimentally convenient paths the solubility in a binary liquid mixture near its consolute points is not strongly enhanced. Finally, we sketch a nonclassical model based on the decorated lattice gas that can be used to describe supercritical solubility enhancement at low solubility, with the pure solvent used as a reference.Invited paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Supercritical fluid extraction—Supercritical fluid chroomatography for analysts of a prostglandin: HPMC dispersion

An on-line SFE-SFC system was used to extract and chromatograph a synthetic prostaglandin from hydroxypropyl methylcellulose (HPMC), which is a widely used material in controlled-release drug formulations. The only sample preparation for the on-line SFE-SFC analysis of the dispersion was weighing the sample into the extraction vessel insert. The extraction efficiency for a four-minute extraction was approximately 65%.     

Atomic layer deposition of transition metals

Atomic layer deposition (ALD) is a process for depositing highly uniform and conformal thin films by alternating exposures of a surface to vapours of two chemical reactants. ALD processes have been successfully demonstrated for many metal compounds, but for only very few pure metals. Here we demonstrate processes for the ALD of transition metals including copper, cobalt, iron and nickel. Homoleptic N,N'-dialkylacetamidinato metal compounds and molecular hydrogen gas were used as the reactants. Their surface reactions were found to be complementary and self-limiting, thus providing highly uniform thicknesses and conformal coating of long, narrow holes. We propose that these ALD layers grow by a hydrogenation mechanism that should also operate during the ALD of many other metals. The use of water vapour in place of hydrogen gas gives highly uniform, conformal films of metal oxides, including lanthanum oxide. These processes should permit the improved production of many devices for which the ALD process has previously not been applicable.