Crosslinking of alkylpolysiloxane filsm on various types of glass surfaces including fused silica using γ-radiation of a60cobalt-source. Comparison to crosslinking by thermal peroxid treatment

Summary Crosslinking of alkylpolysiloxane stationary phases, especially in thick film capillary columns, is useful for the homogenous coating of fused silica and pretreated alkaliglass surfaces. The films of the stationary liquid are immobilized against solvent rinsing using CH₂Cl₂, pentane, and acetone, and maintain homogenity even at high temperature. Various doses of -radiation from a⁶⁰Co. source were used for the crosslinking instead of the thermal peroxid treatment recently described by other authors. The effect of the -radiation crosslinking-procedure was investigated in comparison to the peroxid method in regard of: decrease of stationary phase content by solvent rinsing, separation efficiency, tailing behaviour, and bleeding of the columns obtained. Similar results as with the cumylperoxid-treatment were achieved using the -radiation-method. By -radiation no polar functional groups or moleculs are introduced into the stationary phase, however, as with the peroxid method. Less than 20% of the various stationary liquids are usually removed from the columns by solvent rising after crosslinking using both methods depending on the doses of radiation and the cumylperoxid concentration applied respectively.Dedicated to Dr. L. S. Ettre on the occasion of his 60th birthday.     

The thermochemical reactivity of silicate minerals in hydrogen and methane

The thermochemical reduction of transition metal silicates, i.e. garnierite (Ni,Mg)₆[(OH)₈(Si₂O₇)], chrysocolla (Cu,Al)₂H₂Si₂O₅(OH₄)·nH₂O, dioptase CuSiO₃·H₂O, willemite Zn₂SiO₄, and hemimorphite Zn₄Si₂O₇(OH)₂·H₂O has been studied. By means of combined thermogravimetric/mass spectrometric measurements, X-ray diffraction and analytical scanning electron microscopy it is shown that in a 5% H₂/95% N₂ or in a methane atmosphere the transition metals are selectively reduced at temperatures qualitatively corresponding to their electrochemical potential. Mixtures of elemental transition metals and quartz, SiO₂, are obtained as solid products. Depending on the nature of the parent mineral, different mixtures of volatile products are obtained. Principal volatile product, however, is water vapour. The reduction in methane leads to the formation of syngas.The authors acknowledge the financial support of the Schweizerisches Bundesamt für Energiewirtschaft as well as the Fonds der Chemischen Industrie.     

Fused silica capillary column GC/MS for the analysis of priority pollutants

Operational characteristics have been determined for fused silica capillary column (FSCC) GC/MS as applied to “extractable” priority polutants. Chromatographic data show excellent relative retention time (RRT) intralaboratory precision and interlaboratory accuracy when multiple internal standards are empolyed. Potential chromatographic problems, such as column overload and “double peaking”, are addressed. Response factor relative standard deviations (RSD) at 50 ng for most of the extractable priority pollutants over the long term indicated precise determination (i.e. RSD generally ≤ 10%). Linearity was demonstrated over two orders of magnitude for FSCC GC/MS analysis of compounds with relatively low and high RF (response factor) values. Potential quantitative problems, such as saturation, are discussed. For certain aromatic priority pollutants interlaboratory RF agreement was observed. This was noted as perhaps the most important property of FSCC GC/MS analysis when the multiple internal standard approach is utilized. Determinations of extractable priority pollutants are directly compared for paced column GC/MS and FSCC GC/MS analysis of separate and composited extracts. For six extracts analyzed in triplicate, the latter configuration was shown to produce more consistent results. In view of the superior analysis logistics of composite extract FSCC GC/MS analysis, this approach was established as the preferred method for the analysis of priority pollutants classified as extractable.     

纳米二氧化硅的表面改性研究

以γ-缩水甘油醚丙基三甲氧基硅烷(GPTMS)对酸催化水解正硅酸乙酯(TEOS)聚合得到的纳米二氧化硅胶粒表面进行接枝改性,用激光粒径仪测定二氧化硅颗粒的粒径,并用透射电子显微镜(TEM)观察了改性前后二氧化硅胶粒的分散状况,采用傅立叶红外(FTIR)光谱法对改性前后的二氧化硅粉体进行了分析,通过热失重分析(TGA)法对GPTMS接枝改性二氧化硅胶粒表面的接枝度进行分析计算,同时对颗粒溶胶的ζ电位进行了测试,结果表明:改性后二氧化硅胶粒分散性大大提高,硅烷偶联剂浓度对接枝度有显著影响,当GPTMS的浓度为1mL/S iO2(g)时,接枝度达到最大,且颗粒表面的物理化学性能发生显著变化。     

Preparation and pervaporation performance of high-quality silicalite-1 membranes

High-performance silicalite-1 membranes were successfully synthesized on novel porous silica tubes by two-step in-situ hydrothermal synthesis.The flux and separation factor towards ethanol/water mix- ture at 60℃were 0.56 kg/(m2·h)and 84,respectively.The as-synthesized silicalite-1 membranes were characterized by scanning electron microscopy(SEM).The influence of different synthesis conditions on the separation performance of the silicalite-1 membranes was investigated.It was found that the average flux of silicalite-1 membranes was improved by about 26?ter filling the silica tubes with mixed solution containing glycerol and water.After calcinating at 400℃for 5 h repeatedly,membrane synthesized on silica tube still showed high pervaporation performance towards ethanol/water mixture even at a calcination rate of 4℃/min,which suggested that silica support was more suitable for pre- paring high-performance silicalite-1 membranes.     

高温合成NaY沸石

提出了应用NaY沸石导向剂提供全部硅源合成NaY沸石的新方法, 研究了高温条件下合成NaY沸石的规律和特点, 发现在高温条件下合成NaY沸石不仅晶化速度快, 而且可以在不加有机物的条件下合成较高硅铝比[n(SiO2)/n(Al2O3)=6]的NaY沸石.     

Electrochromatography in packed tubes using 1.5 to 50 μm silica gels and ODS bonded silica gels

Summary Electrochromatography (that is HPLC where the eluent is driven along the column by electro-osmosis using fields of up to 100 kV m⁻¹) promises plate efficiencies for HPLC which are comparable to those attained in capillary gas chromatography, but this requires that narrow-bore columns can be successfully packed with submicron particles. This paper demonstrates that we have now moved a considerable distance towards this goal. We show (1) that, following theory, there is no evidence of any reduction in electroosmotic velocity in columns packed with particles down to 1.5 μm diameter, (2) that reduced plate heights as low as unity are attainable for unretained solutes using both slurrypacked and drawn-packed columns 30 to 200 μm bore and up to 1 m long when packed with conventional 3 and 5 μm silica gels or with 1.5 μm impermeable silica spheres, (3) that columns driven electrically show higher plate efficiencies than identical columns driven by pressure, and (4) that 100,000 plate HPLC separations can be achieved in relatively short times of 30 minutes using in situ derivatised drawn packed capillaries containing 3 and 5 μm ODS-silica gels.     

MoPO／SiO2催化剂上丙烷选择氧化制丙烯醛

 研究了MoPO／SiO2催化剂对丙烷选择氧化制丙烯醛的催化性能．MoO／SiO2催化剂主要表现出对丙烷氧化脱氢的催化性能，在该催化剂中添加磷后，丙烷转化率和选择氧化产物丙烯醛的选择性明显提高．催化剂的X射线衍射、拉曼光谱、程序升温还原、吡啶吸附红外光谱和程序升温脱附等表征结果表明，MoO／SiO2催化剂主要含有MoO3晶相，添加磷后，形成了表面多钼酸物种，磷以PO4四面体结构存在于表面，可能形成部分Mo—O—P键，从而抑制了MoO3在MoPO／SiO2上的形成，起到分隔活性中心的作用．在MoO／SiO2催化剂中添加磷后，催化剂的B酸和L酸酸性均增强，有利于丙烷在MoPO／SiO2催化剂表面活性的提高．由此可见，催化剂表面结构和酸性的变化可能是导致MoPO／SiO2催化性能提高的原因．     

Action of a Fluorescent Chemosensor for Cu2+ Encapsulated in Silica Xerogel

The fluorescent chemosensor of the type Ant-NH-O-O-NH-Ant for Cu²⁺ ions has been designed by means of a supramolecular approach, as follows: two anthracene (Ant) fragments as fluorophore subunits have been linked by a noncyclic NH-O-O-NH quadridentate ligand as a receptor. The interaction of Cu²⁺ - receptor is signalled through the enhancement of the anthracene fluorescence when the receptor, i.e., the dioxodiamine chain subunit of the sensor is able to stop a photoinduced electron-transfer mechanism. The experiments with the chemosensor encapsulated in silica xerogel by the sol-gel processing are described.     

Peculiarities of the silica surface center structure in rigid dehydroxidation conditions

A model of molecular claster and nonempirical calculation schemes MP2/6‐31G*, MP4/6‐31G*, and MP2/DZVP2 were applied to study electronic and energy characteristics of the surface centers of different SiO₂ modifications in rigid dehydroxidation conditions. It was established that depending on an angle α = Si′O′Si″ (where O′ is an oxygen atom of the nearest to the surface layer), O* atom corresponding with two surface Si atoms, could (i) form a chemical bond with one of the Si′ or Si″‐centers (an asymmetric configuration, α > 118° ÷ 120°); or (ii) be common for these centers (a symmetric configuration, α < 118° ÷ 120°). It was also established that when α > 132° ÷ 133°, the basic state was triple and at α < 132° ÷ 133°, it was single. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007