硅胶负载型硫酸锆表面相结构的理论研究

采用量子化学ASED-MO(含原子对排斥的EHMO法)为基础的结构自动优化EHTOPT法研究了硅胶负载型硫酸锆表面相的结构特征。在对硅胶表面结构单元和四水硫酸锆单体空间模型结构参数进行优化的基础上,依据四水硫酸锆与硅胶载体表面的成键状态、电荷布居及能量变化,从理论上分析了四水硫酸锆与载体表面之间静电和脱水的相互作用的合理模型及硅胶负载型硫酸锆的结构稳定性,阐明了硫酸锆在载体表面的分散趋向于单分散的特征。     

Preparation and characterization of poly(methyltetradecylsiloxane) stationary phases immobilized by gamma radiation onto zirconized silica

The preparation of stationary phases with enhanced chemical stability in alkaline eluents has been the principal objective of many chromatographers. New and improved silica substrates and advanced chemical modification methods are among the possibilities being investigated to reach this objective. The present work has evaluated these two possibilities for new stationary phases. First, the silica surface was modified by reaction with zirconium tetrabutoxide to produce zirconized silica particles having about 21% (w/w) of zirconium. Then poly(methyltetradecylsiloxane) (PMTDS) was immobilized onto this surface using different doses (50-120 kGy) of gamma radiation. These new phases were characterized using elemental analysis and infrared and solid-state (29)Si-nuclear magnetic resonance (NMR) spectroscopies. These new stationary phases presented column efficiencies of about 68,000 plates m(-1), symmetric peaks for apolar compounds and retention factors that depend on the irradiation dose and show improved stability in high pH mobile phases. The separation of several pharmaceuticals at pH 11 is presented.     

Selective separation behavior of silica gel for zirconium in simulated high level radioactive liquid waste

Zirconium in simulated high level radioactive liquid waste (HLLW) was selectively adsorbed and separated by self-made high adsorption activity silica gel. The selective adsorption mechanism was analyzed according to the structure character of self-made silica gel and performance of zirconium in acid simulated HLLW. The results show that the adsorption selectivity of self-made silica gel for zirconium is strong, because zirconium has higher positive charge and zirconium ion hydrolyzes easily. Distribution coefficient of self-made silica gels for zirconium is 53.5 ml/g. There are 6.5 (OH)/nm² on the surface on self-made silica gels which provide more adsorption activity places, thus self-made silica gels have higher adsorption capacity for zirconium (31.4 mg/g). The elution rate of the adsorption of zirconium on self-made silica gel by 0.2 mol/l H₂C₂O₄ is more than 99%. The solubility of the self-made silica gel in nitric acid is low, the chemical stability of self-made silica gel is very strong.     

IR-spectroscopic study of lewis acid centers on polyzirconiummethylsiloxanes

Acid centers on the surface of polyzirconiummethylsiloxanes (PZMS) containing 5 and 10% ZrO₂ were studied by diffuse-reflectance IR-spectroscopy. Deuterated acetonitrile adsorbed at room temperature at a 96 torr saturated vapor pressure was used as a probe-molecule for acid centers. It was shown that zirconium ions were not built into the matrix but were situated predominantly on the surface of the siliconoxygen framework of silica gels. The introduction of zirconium ions into the polymethylsiloxane matrix at the stage of sol formation caused the appearance of Lewis acid centers (coordinatively unsaturated zirconium ions) on the surface of PZMS along with centers of the physical adsorption of CD₃CN.     

Zirconia based monoliths used in hydrophilic-interaction chromatography for original selectivity of xanthines

Monolithic capillary columns based on zirconia were prepared directly from zirconium alkoxide. They were also prepared coating a classical silica based monolithic column with zirconium butoxide. Using the gradual evolution of the theophylline/caffeine separation factor, it was found that successive zirconia coatings produced the progressive fading of surface silanols replaced by Zr–OH groups. The behavior of a silica monolith coated four times with zirconium butoxide was very similar to that of a pure zirconia monolith. The dramatic change in xanthine separation factor observed with zirconia stationary phases and the theophylline and caffeine probe solutes was used to develop a complete separation of xanthines on zirconia stationary phase in less than 6 min. The three dimethylxanthine isomers, theophylline, theobromine and paraxanthine, are very difficult to separate in RPLC with classical C₁₈ stationary phases. The three isomers were easily separated in HILIC mode on a zirconia based stationary phase.     

Pervaporation Separation and Catalysis Activity of Novel Zirconium Silicalite-1 Zeolite Membrane

Novel zirconium silicalite‐1 zeolite membrane was hydrothermally prepared on the mullite porous support at 150–185°C for 40–72 h by an "in situ" method using tetraethyl orthosilicate (TEOS), zirconium butoxide (ZBOT) and tetrapropylammonium hydroxide (TPAOH) as silica source, zirconium source and organic structure directing agent, respectively. X‐ray diffraction (XRD) patterns, fourier transformed infrared (FT‐IR) spectra, and inductively coupled plasma‐atomic emission spectrometry (ICP) of the accompanying zeolite powder confirmed that the zirconium was isomorphously incorporated into the zeolite framework. The surface chemical compositions of the obtained membrane were measured with an energy‐dispersive X‐ray spectral analyzer (EDS), and the membrane morphologies were observed by a scanning electron microscope (SEM). The results showed that the zeolite crystals growing on the support were zirconium silicalite‐1 zeolites, and the dense membrane layer was composed of the well inter‐growing zeolite crystals. The zirconium silicalite‐1 zeolite membrane, which was derived from the synthesis solution having a molar ratio of 1.00SiO₂:0.01ZrO₂:0.17TPAOH:120H₂O, showed high ethanol permselectivity with a flux of 1.01 kg/(m²·h) accompanied with a separation factor of 73 for ethanol/water (5/95, w/w) system under a pervaporation condition at 60°C. Moreover, this membrane displayed pervaporation‐aided catalysis activity for iso‐propanol oxidation with hydrogen peroxide as oxidant, and the corresponding iso‐propanol conversion was 35%.     

锆基色谱填料的制备方法和物理化学性质

氧化锆基质色谱填料适合于碱性物质,特别是生物大分子的分离,因而具有良好的应用前景。它的制备方法对其物理化学性质有很大的影响,从而影响填料的色谱性能。该文对氧化锆微球的制备方法及其物理化学性质进行了综述。分析表明,目前氧化锆基质色谱填料的制备方法存在着难以克服的缺点,要制备理想的锆基色谱填料需要新的思路。     

大比表面负载氧化铁的氧化硅层柱磷酸锆制备和 催化性能研究

提出了一种以氧化硅层柱磷酸锆(SiO~2-ZrP)的前驱体,氨丙基硅酸酯嵌入磷酸锆(APS-ZrP)为载体制备负载氧化铁的氧化硅层术磷酸锆的新方法。与传统方法相比,新方法制得的样品具有较大的比表面和孔容。X射线粉末衍射(XRD)和程序升温还原(TPR)的结果表明采用新方法有利于氧化铁在载体表面的高度分散,分散阈值为0.25gFe~2O~3/g(SiO~2-ZrP),远超过直接以SiO~2-ZrP为载体浸渍草酸铁铵的传统方法得到样品。同时,用新方法制得的氧化铁催化剂表现了较高的乙苯脱氢活性,是一类值得研究的催化材料。     

Application of zirconium-modified silica gel as a stationary phase in the ion-exclusion chromatography of carboxylic acids I. Separation of benzenecarboxylic acids with tartaric acid as eluent and with UV-photometric detection

The application of zirconium-modified silica gels (Zr–Silicas) as stationary phases for ion-exclusion chromatography with UV-photometric detection (IEC–PD) for mono-, di-, tri- and tetrabenzenecarboxylic acids (pyromellitic, trimellitic, hemimellitic, o-phthalic, salicylic and benzoic acids) and phenol was carried out using tartaric acid as the eluent. Zr–Silicas were prepared by the reaction of the silanol group on the surface of silica gel with zirconium tetrabutoxide [Zr(OCH₂CH₂CH₂CH₃)₄] in ethanol solution. The effect of the amount of zirconium adsorbed on silica gel on chromatographic behavior of these benzenecarboxylic acids and phenol was investigated. As a result, Zr–Silica adsorbed on 20 mg zirconium g⁻¹ silica gel was the most suitable stationary phase in the IEC–PD for the simultaneous separation of these benzenecarboxylic acids and phenol. Excellent simultaneous separation and highly sensitive UV detection at 254 nm for these benzenecarboxylic acids and phenol were achieved in 20 min by the IEC–PD using the Zr–Silica column (250×4.6 mm I.D.) and a 10 mM tartaric acid at pH 2.5 as eluent.     

新型大孔有机膦酸锆的合成及其表征

论文以草甘膦锆(ZrGP)为原料、乙二醇和乙醇混合物为共撑物,介绍了一种新型孔材料的合成方法。利用乙醇将草甘膦锆层板撑开后,乙二醇两端的羟基与草甘膦锆内不同层板上的羧基发生脱水成酯反应,进而生成窗口型孔材料。扫描电镜和XRD分析表明,合成得到的材料内部孔径大约为55 nm左右,是典型的大孔。由于所形成的孔壁由无机骨架和有机链共同组成,该孔材料具有较大的比表面积,达到260 m2.g-1。此外,该孔材料孔内存在大量的可配位基团,因而该材料在吸附、催化等领域会有广阔的应用前景。     

DETERMINATION OF THE DEGREE OF BONDED PHASE ON THE SURFACE OF SILICA GEL BY XPS

Attention is being increasingly paid to the new material prepared by bonding organic molecules on the surface of silica gel in the preparation of catalyst or packing material for liquid chrotnatographic column.There has not been a quantitative method for determination or characterizing the degree of bonded phase on surface of silica gel yet.This paper provides a new semi-quantitative method.     

Surface confined ionic liquid as a stationary phase for HPLC

Trimethoxysilane "ionosilane" derivatives of room temperature ionic liquids based on alkylimidazolium bromides were synthesized for attachment to silica support material. The derivatives 1-methyl-3-(trimethoxysilylpropyl)imidazolium bromide and 1-butyl-3-(trimethoxysilylpropyl)imidazolium bromide were used to modify the surface of 3 microm diameter silica particles to act as the stationary phase for HPLC. The modified particles were characterized by thermogravimetric analysis (TGA) and (13)C and (29)Si NMR spectroscopies. The surface modification procedure rendered particles with a surface coverage of 0.84 micromol m(-2) for the alkylimidazolium bromide. The ionic liquid moiety was predominantly attached to the silica surface through two siloxane bonds of the ionosilane derivative (63%). Columns packed with the modified silica material were tested under HPLC conditions. Preliminary evaluation of the stationary phase for HPLC was performed using aromatic carboxylic acids as model compounds. The separation mechanism appears to involve multiple interactions including ion exchange, hydrophobic interaction, and other electrostatic interactions.     

New stationary phases for high-performance liquid chromatography based on poly(methyltetradecylsiloxane) thermally immobilized onto zirconized silica

The modification of silica with zirconium oxide followed by sorption and thermal immobilization of poly(methyltetradecylsiloxane) (PMTDS) is used to prepare a reversed stationary phase for high-performance liquid chromatography. The thermal immobilization of PMTDS on zirconized silica was optimized using a central composite design. The new stationary phase was characterized by spectroscopic and chromatographic methods. Stationary phases with good reproducibility and good chromatographic performance for various compounds were obtained. PMTDS thermally immobilized on zirconized silica presented quite significant chemical stability at pH 10 and 50 degrees C.     

Stability of high-performance liquid chromatography columns packed with poly(methyloctylsiloxane) sorbed and radiation-immobilized onto porous silica and zirconized silica

Reversed-phase packing materials were prepared from HPLC silica and from zirconized HPLC silica support particles having sorbed poly(methyloctylsiloxane) (PMOS) as the stationary phase. Portions of zirconized material were subjected to 80 kGy of ionizing radiation. Columns prepared from these packing materials were subjected to 5000 column volumes each of neutral and alkaline (pH 10) mobile phases, with periodic tests to evaluate chromatographic performance. It was shown that the PMOS stationary phase sorbed onto zirconized silica requires an immobilization treatment (such as gamma irradiation) for long term stability while prior surface zirconization of the silica support surface greatly improves the chromatographic stability of the stationary phase when using alkaline mobile phases.     

Inverse gas chromatography in the examination of modified fillers

Dispersive and specific surface properties of silica modified with silanes, titanium and zirconium coupling agents were characterised by means of inverse gas chromatography. This method was also successfully applied in the examination of raw and modified silicates.     

Ethylene polymerization over supported MAO/(nBuCp)2ZrCl2 catalysts: Influence of support properties

The catalytic system methylaluminoxane (MAO) and bis(n-butylcyclopentadienyl)zirconium dichloride ((nBuCp)₂ZrCl₂) was immobilized on commercial silica, silica-alumina and aluminophosphate calcined at different temperatures. The properties of the supports were determined by using N₂ adsorption-desorption isotherms at 77 K, FT-IR spectroscopy and SEM. After aluminium and zirconium impregnation, the catalysts were analyzed by ICP-AES, FT-IR and UV-vis spectroscopy. Ethylene polymerizations were carried out in a Schlenk tube at 70 °C and 1.2 bar of ethylene pressure. The polyethylene obtained was characterized by GPC, DSC and SEM.Catalysts supported on silica-alumina exhibited higher polymerization activity than those supported on silica and aluminophosphate. Besides, the activity of MAO/(nBuCp)₂ZrCl₂ catalytic system supported on silica-alumina and aluminophosphate decreased strongly with support calcination temperature, while remained almost constant when silica was employed as support. All these experimental features suggest a role of the support acid properties and hydroxyl group population in the generation of active polymerization species.     

大孔SO42-/ZrO2-SiO2复合固体酸制备及催化性能

利用浸渍水解法在大孔SiO2载体上组装固体酸制备出大孔径SO42-/ZrO2-SiO2复合固体酸催化剂。用扫描电镜、红外光谱仪和粉末X射线衍射仪等对其进行表征,结果表明:大孔SiO2载体的毛细管效应促使ZrO2以纳米薄层方式均匀地沉积在SiO2薄层表面,并抑制了ZrO2晶体的生长和晶相的转变,载体的大孔全连通的结构赋予该复合材料高的通透性(孔径在1~2μm)、两面活性点和大的比表面积(约156 m2.g-1)。Hammett指示剂法测得经550℃焙烧后产物的酸强度H0值小于-13.75,属于固体超强酸。以乙酸正丁酯的合成为探针反应考察硫酸浸渍液浓度、焙烧温度等制备条件对其催化活性的影响,结果表明,该SO42-/ZrO2-SiO2固体酸具有较好的催化活性,当焙烧温度为550℃和硫酸浸渍液浓度为1.5 mol.L-1时,超强酸对酯化反应的催化酯化率达到97%。     

Evaluation of silica from different vendors as the solid support of anion‐exchange chiral stationary phases by means of preferential sorption and liquid chromatography

Chromatographic performance of a chiral stationary phase is significantly influenced by the employed solid support. Properties of the most commonly used support, silica particles, such as size and size distribution, and pore size are of utmost importance for both superficially porous particles and fully porous particles. In this work, we have focused on evaluation of fully porous particles from three different vendors as solid supports for a brush‐type chiral stationary phase based on 9‐O‐tert‐butylcarbamoyl quinidine. We have prepared corresponding stationary phases under identical experimental conditions and determined the parameters of the modified silica by physisorption measurements and scanning electron microscopy. Enantiorecognition properties of the chiral stationary phases have been studied using preferential sorption experiments. The same material was slurry‐packed into chromatographic columns and the chromatographic properties have been evaluated in liquid chromatography. We show that preferential sorption can provide valuable information about the influence of the pore size and total pore volume on the interaction of analytes of different size with the chirally‐modified silica surface. The data can be used to understand differences observed in chromatographic evaluation of the chiral stationary phases. The combination of preferential sorption and liquid chromatography separation can provide detailed information on new chiral stationary phases.     

Evaluation of the acid properties of porous zirconium-doped and undoped silica materials

A series of porous silica and Zr-doped silica molecular sieves, belonging to the MCM-41 and MSU families, were prepared and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N₂ adsorption at 77 K. Their acid properties have been evaluated by NH₃-TPD, adsorption of pyridine and deuterated acetonitrile coupled to FT-IR spectroscopy and the catalytic tests of isopropanol decomposition and isomerization of 1-butene. The acidity of purely siliceous solids were, in all cases, very low, while the incorporation of Zr(IV) into the siliceous framework produced an enhancement of the acidity. The adsorption of basic probe molecules and the catalytic behaviour revealed that Zr-doped MSU-type silica was more acidic than the analogous Zr-MCM-41 solid, with a similar Zr content. This high acidity observed in the case of Zr-doped silica samples is due to the presence of surface zirconium atoms with a low coordination, mainly creating Lewis acid sites.     

Effect of Zirconia Precursor on the Properties of ZrO2-SiO2 Sol-Gel Oxides

Sol-gel zirconia-silica oxides were synthesized with two zirconium precursors, zirconium n-butoxide and zirconium acetylacetonate, and two different hydrolysis catalysts, HCl and H₂SO₄. The samples prepared with HCl were additionally sulfated with a 1 M solution of H₂SO₄. Characterization was performed with FTIR and ²⁹Si-MAS-NMR spectroscopy, as well as with nitrogen adsorption. Because zirconium and silicon alkoxides have different hydrolysis rates, it was necessary to perform a pre-hydrolysis of the silicon alkoxide before mixing. The atom distribution in the ZrO₂-SiO₂ system depended on the zirconium precursor, which also determined the zirconium incorporation in the silica lattice, which was greater for zirconium acetylacetonate. The zirconium precursor also was responsible for the silanol concentration, which increases when samples were sulfated. Sulfating stabilizes the specific surface area. On sulfate samples calcined at 800°C BET areas larger than 500 m²/g were obtained.