SiO2-PEG凝胶体系的热物理化学特征

用程序升温热重法分析了SiO2及SiO2-PEG干凝胶的热物理化学行为,结果表明：采用不同的环境气氛对SiO2-PEG干凝胶进行热处理,聚乙二醇（PEG）表现出不同的热稳定性,并由此影响干凝胶的织构性质;通过对氮气气氛中得到的DTG曲线进行处理,得到不同温度段的表现活化能,说明SiO2干凝胶脱羟反应表现出动力学控制,而SiO2-PEG干凝胶随着温度的升高则表现出动力学控制逐步向表面羟基的扩散控制转变．     

基于单独MBA凝胶纤维的RAFT聚合制备聚合物微米管

研究凝胶形成温度对N,N'-亚甲基双丙烯酰胺(MBA)凝胶纤维尺寸的影响, 发现凝胶纤维平均直径随着凝胶形成温度的降低而降低, 在-25 ℃下可得到平均直径为1.1 μm的小尺寸凝胶纤维. 在不加共聚单体条件下, 以1.1 μm小尺寸MBA纤维为模板和反应单体, 通过可逆加成断裂链转移(RAFT)自由基聚合, 以较高收率得到形貌规整并有一定自支撑能力的聚合物微米管. 研究各种反应条件对聚合反应的影响, 结果表明RAFT试剂用量、引发剂用量及反应温度都会影响产物形貌及收率. 采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)和红外光谱仪表征了聚合物微米管的微观形貌和组成, 热失重分析表明产物具有很高的耐热性能.     

Positive deviation from debye‘s theory in small—angle x—ray scattering

The small-angle x-ray scattering (SAXS) resulting from a non-ideal two-phase system having sharply defined phase boundaries but with micro-fluctuations of electron density within any phase shows a positive deviation from Debye's theory. We have found a simple method suitable for fitting the slit-smeared SAXS data and correcting the positive deviation. The validity of this procedure is tested on porous ZrO_2 xerogel prepared using the sol-gel process.     

钌(Ⅱ)配合物有机改性干凝胶的氧传感性能

采用溶胶-凝胶法以正硅酸乙酯(TEOS)和正辛基三乙氧基硅烷(Octyl-triEOS)为共先驱体制备了掺杂二氯化二联吡啶(二吡啶并[3,2-a 2,3-c]吩嗪)合钌(Ru-Dppz)的干凝胶.考察了Ru-Dppz在乙醇溶液和干凝胶内的荧光行为,发现在干凝胶中配合物的发射光谱较乙醇溶液中有明显蓝移.与固态本体配合物相比,干凝胶内Ru-Dppz的荧光寿命有明显增加.以Ru-Dppz为荧光指示剂的有机改性氧传感材料具有灵敏度高、响应时间短及稳定性好等优点.该复合材料中有机改性剂的加入提高了氧的通透性,降低了发光分子间的浓度自猝灭进而改善了材料传感的灵敏度.     

气体吸附法测定二氧化硅干凝胶的分形维数

提出了一种方便、科学有效的利用气体吸附法测定二氧化硅干凝胶等多孔材料分形维数（表面分形维数和孔分布分形维数）的方法，不需要进行一系列的吸附/脱附实验，只需要利用单一气体的一次吸附/脱附实验得出的样品孔分布、比表面数据，与不同的标尺进行关联，即可同时获得表面分形维数和孔分布分形维数.通过误差分析和校正，保证了结果的可靠性.用上述方法测定了二氧化硅干凝胶的分形维数，以FHH法和SAXS法对所得结果进行了比较和验证，并对吸附/脱附过程所得结果的差异进行了初步分析. 关键词： 分形维数 气体吸附 二氧化硅 干凝胶     

凝胶制备对气相合成MCM-22沸石的影响

以硅酸钠为硅源、硫酸铝为铝源制备硅铝干凝胶，六亚甲基亚胺（HMI）为模板剂，采用气相法合成MCM-22沸石。对硅铝干凝胶进行了29 Si MAS NMR、27 Al MAS NMR、红外以及透射电镜表征，讨论了pH值对硅铝干凝胶及合成MCM 22沸石的影响。结果表明，pH值的改变影响硅铝聚集态、干凝胶的结构及其粒径等物理性质，合成时硅铝干凝胶解聚、气固间传质及固相溶解速度不一致，影响产物MCM-22的结晶度。当制备干凝胶的pH值为8.7～10.7时，得到结晶度高的MCM-22沸石；当pH值增大到11.1时，产物出现杂晶丝光沸石；pH为11.6时只能得到丝光沸石。     

Structural and transport properties of Li-intercalated vanadium pentoxide nanocrystalline films

The X-ray diffraction (XRD), transmission electron microscopy, density, electrical and thermoelectric power (TEP) properties of nanocrystalline Li _x V₂O₅ ? nH₂O xerogel films (0 ≤ x ≤ 22 mol.%) were investigated. The films were produced by the sol–gel technique (colloidal route), which was used to enable high-purity, uniform preparation. The relative intensity of the (002) XRD line increased with increasing Li content. The particle size was found to be about 6.0 nm. Electrical conductivity and thermoelectric power were measured parallel to the substrate surface in the temperature range 300–480 K for the as-prepared films. The electrical conductivity showed that all the samples were semiconductors and that conductivity increased with increasing Li content. The conductivity of the present system was primarily determined by hopping carrier mobility, which was found to vary from 6.81 × 10^?6 to 0.33 × 10^?6 cm² V^?1 s^?1 at 380 K. The carrier density was evaluated to be 8.73 × 10¹⁹–1.118 × 10²¹ cm^?3. The conduction was confirmed to obey non-adiabatic small polaron hopping. The thermoelectric power, or Seebeck effect, increased with increasing Li content. The results obtained indicate an n-type semiconducting behavior within the temperature range investigated.     

Silica xerogel-hydrogen peroxide composites: their morphology, stability, and antimicrobial activity

Hydrogen peroxide was incorporated into silica xerogel matrix over the concentration range from 3.8 to 68.0 wt% via the sol–gel route. The obtained composites were characterized by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The release rates of H₂O₂ from the composites into the aqueous phase were examined. In most cases, a 90% release was attained after ca. 10 min, and it was only slightly dependent on H₂O₂ concentration and particle size. The antimicrobial activity of the composite containing 3.59% H₂O₂ was evaluated against Escherichia coli and Micrococcus luteus. A comparative assay was carried out for aqueous solution of H₂O₂ of the same concentration. The results demonstrated a potent microbicidal efficacy of the composite. Furthermore, diffusion range of the hydrogen peroxide from the solid composite into an agar medium matched that of the H₂O₂ in aqueous solution. The stability tests with the xerogels containing 3.8, 26.4, and 68.0% of H₂O₂ showed that after 63 days respective losses of the H₂O₂ at 3 °C were 8.8, 9.7, and 6.2%. Both the DSC results and the stability tests have shown that the molecular water present in the pores stabilizes the composite, probably through improving the binding of the H₂O₂ molecules onto the silica surface.     

Meldola's Blue Immobilized on a SiO2/SnO2/Phosphate Xerogel,a New Sensor for Determination of Ascorbic Acid in Medicine and Commercial Fruit Juice

A modified carbon paste electrode with SiO₂/SnO₂/Phosphate/Meldola's blue, SSPMelB, was used to study the electrocatalytic oxidation of ascorbic acid by cyclic voltammetry and chronoamperometry. The adsorbed dye mediates ascorbic acid oxidation at an anodic potential of 0.04 V vs. saturated calomel electrode (SCE) at pH 7.0, in 0.5 mol L^?1 solution. The linear range of the sensor is between 4.0×10^?7 and 2.0×10^?3 mol L^?1, with a limit of detection of 4.0×10^?7 mol L^?1. This novel electrode shows good analytical performance for determination of ascorbic acid in medicine and commercial fruit juice.     

Effect of nickel catalyst on physicochemical properties of carbon xerogels as electrode materials for supercapacitor

Carbon xerogels and Ni-doped carbon xerogels prepared by the sol-gel polymerization were examined to reveal the effect of metallic nickel incorporated in carbon matrix on the physicochemical properties of carbon xerogels and their electrochemical performance for supercapacitor electrode in aqueous 6 M KOH solution. As shown by XRD and XPS measurements, the decomposition of nickel precursor in carbon matrix led to the creation of well-crystalline particles of metallic nickel which gave rise to the changes in the morphology, chemical and porous structure of carbon xerogels. Due to the modification of porous structure the surface area increased from 595 m²/g via 632 m²/g up to 660 m²/g for carbon xerogel, 7 wt% and 10 wt% Ni-doped composites, respectively. The enhancement of the surface area occurred along with diminishing the BJH average pore diameter. The value for nickel free xerogel amounted to 11.35 nm, whereas the value of 5.71 nm was measured for 10 wt% Ni xerogel. The changes in the porous and chemical structure created during the formation of carbon-nickel composites as well as the pseudo-capacitive effects arising from the redox reaction of nickel particles present in carbon matrix brought about a significant improvement of electrode capacitance. Electrochemical measurements showed that in comparison with capacitances measured for nickel free electrode (82.1 F/g calculated using the cyclic voltammetry and 88.8 F/g calculated using the galvanostatic charge/discharge method), the respective capacitances for 10 wt% Ni-doped carbon xerogel increased up to 103.0 F/g and 103.4 F/g. These values correspond to 25 and 16% improvement, respectively.