Diffuse reflectance infrared Fourier transform spectral study of the interaction of 3-aminopropyltriethoxysilane on silica gel. Behavior of amino groups on the surface

 Three silica gel sample systems, modified with 3-amino-propyltriethoxysilane (APTS), were prepared by sequentially sampling the reaction mixture at various time intervals, and the diffuse reflectance infrared Fourier transform (DRIFT) spectra of these samples were measured in the regions 2700–3500 and 1300–2000 cm^-1. The IR bands observed at 1597 and 1629–1633 cm^-1 were assigned to the deformation modes of NH₂ and NH⁺ ₃ groups, respectively. The intensities of these two bands are dependent on both the APTS concentration used in the preparation and the reaction time. The results are summarized as fol-lows. For the sample systems in which smaller APTS concentration were used, most of the NH₂ groups of the aminopropyl segments are converted into the NH⁺ ₃ groups on the surface, showing that the SiO^-…H⁺NH₂-type structure is predominantly stabilized on the surface of the silica gel. As the APTS concentration in the reaction mixture increases, the population of NH₂ groups in the silane layer coated onto the surface increases. Interpretation of the CH stretch region further suggests that cyclic structures may be formed on the surface as a consequence of the formation of NH⁺ ₃ groups. Received: 18 November 1996 Accepted: 14 February 1997     

Surface structure of silica gel reacted with 3-mercaptopropyltriethoxysilane and 3-aminopropyltriethoxysilane: formation of the S–S bridge structure and its characterization by Raman scattering and diffuse reflectance Fourier transform spectroscopic studies

 Silica gel samples, modified with 3-mercaptopropyltriethoxysilane, and their S–S-bridged samples have been prepared. In order to characterize the microstructure of the surface of these silica gel samples, Raman scattering and diffuse reflectance Fourier transform IR spectra of these samples have been examined by comparison with Raman spectra of various n-alkyl disulfides and their related silane polymers. The S–S and C–S stretch modes characteristic of the CH₂SSCH₂ segment, in addition to the SH and C–S stretch modes of the CH₂SH segment, have been assigned for these silica gel samples. It has been found that, even on the surface of the silica gel, a specific conformer is stabilized about the CH₂SSCH₂ segment. Received: 1 May 2001 Accepted: 16 June 2001     

Prepation of poly(N-isopropylacrylamide)-grafted silica gel and its temperature-dependent interaction with proteins

Poly(N-isopropylacrylamide) oligomer was immobilized onto a silica gel surface. The gel adsorbed a hydrophobic protein γ-globulin (IgG) at 37°C, however, did not adsorb IgG at 24°C. The adsorbed IgG at 37°C was adsorbed by lowering the temperatue, No adsorption of a hydrophilic protein bovin serum albumin (BSA) onto this matrix was observed at 37°C nor 24°C.     

Kinetics analysis of colloidal crystallization of silica spheres modified with polymers on their surfaces in acetonitrile

 The nucleation and growth rates in the colloidal crystallization of silica spheres (136 nm in diameter) modified with polymers on their surface were measured by time-resolved reflection spectroscopy. The polymers were poly(maleic anhydride-co-styrene) [P(MA-ST)] and poly(methyl methacrylate) (PMMA). The induction period for nucleation decreased sharply when the sphere concentration increased. The crystal growth process consisted of a fast growing step leading to metastable crystals (rate v ₁) and a slow growth rate accompanied by the formation of stable crystals. The crystal size of the P(MA-ST)/SiO₂ particles decreased from 0.4 to 0.06 mm, whereas v ₁ increased from 13 to 37 μm/s, when the particle concentration increased. The slow step was also observed for almost all the samples but was not analyzed since the rate was too small. For PMMA/SiO₂ dispersions, the crystal size (0.17–0.3 mm) and v ₁ (43–166 μm/s) did not show any relation to the particle concentration but showed a linear relationship with the molecular weight of PMMA. These results suggest the important role of the excluded-volume effects of the polymer layers around the silica surface. The contribution of the repulsion due to the electrical double layers is still effective in the colloidal crystallization in acetonitrile. Received: 6 June 2001 Accepted: 20 September 2001     

NMR analysis of interaction between styrene-divinylbenzene gel beads and small molecules

The interaction of small molecules such as cyclohexane, tetrahydrofuran, and acetonitrile with styrene-divinylbenzene copolymer gel beads were investigated by ¹³C-NMR spectroscopy. When the gel content was 0.1–0.3 g/mL, the ¹³C-NMR spectrum of the solvent displayed two peaks. A sharp peak at lower magnetic field was assigned to the free solvent, and a broad one to the solvent affected by the gel. This signal splitting is attributed to the upfield shift caused by aromatic rings of styrene units in the polymer chain. The nitrile carbon of acetonitrile showed the largest upfield shift. The mobility of small molecules in gel beads was also investigated using the nuclear magnetic relaxation method. In the case of good solvents for gel beads, the mobility was affected by the cross-linking density, whereas poor solvents exhibited little dependence of the cross-linking density. © 1995 John Wiley & Sons, Inc.     

Extraction of copper ions using silica gel with chemically modified surface

The applicability of silica gels for the application in solid-phase extraction was tested. Silica was modified with ketoimine groups. Surface characteristics of the modified silica were determined by elemental analysis, NMR spectra of solid phases (²⁹Si CP MAS NMR), analysis of pore size distribution of the silica support, and nitrogen adsorption-desorption. Newly proposed sorbents with ketoimine groups were applied in the preconcentration of trace amounts of the Cu (II) ions from lake water, post-industrial water, and demineralized water unburdened back to the lake. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

A deprotection procedure using SO3H silica gel to remove non-silyl protecting groups

Protecting groups are indispensable in organic synthesis and there is a great need for a variety of deprotection methods. Here, we investigated the scope of the application of a deprotection procedure using SO₃H silica gel, which we have previously reported as a desilylation procedure. Under these conditions, -OMOM, -OSEM, -OTHP, and -OAc groups and dimethyl acetal were cleaved. Pivaloyloxy, benzyloxy and methoxy carbonyl groups remained intact and selective deprotection of TBS groups in the presence of other protecting groups was accomplished. We succeeded in cleaving an acetyl group on a secondary alcohol in a highly polar nortropine derivative. Our findings here provide another deprotection option and would be helpful in the synthesis of multifunctional compounds.     

Characterization of Surface Modified Silica Nanoparticles by 29Si Solid State NMR Spectroscopy

 Various aerosils surface modified with silane reagents were prepared and investigated by ²⁹Si solid state NMR spectroscopy. The mode of bonding onto the silanol surface (mono- or divalent) can be specified by comparison with chemical shifts from solution. A detailed analysis also leads to the detection of products formed via hydrosilylation reactions. A rough quantification of the surface loading can be obtained by a signal deconvolution process of the silanol resonances on the Aerosil surface.     

Synthesis and characterization of surface-aminated polypyrrole–silica nanocomposites

 Two synthetic routes to surface-aminated polypyrrole–silica nanocomposite particles have been investigated. Route 1 involved the initial synthesis of homopolypyrrole – silica particles as described previously, followed by surface amination using 3-aminopropyltriethoxy-silane. In Route 2 aminated polypyrrole–silica particles were synthesized directly by copolymerising an N-substituted aminopyrrole comonomer with pyrrole in the presence of an ultrafine silica sol. Both types of aminated particles were characterized in terms of their particle size and morphology, long-term colloid stability and degree of amination using transmission electron microscopy, disc centrifuge photosedimentometry and zeta potential measurements, respectively. Received: 19 May 1998 Accepted: 15 June 1998     

Tributylstannylated silicic acid as precursor of organofunctionalized silica gel

Tributylstannylated silicic acid (TBSA), which was regarded as a protected polymeric silanol against self-condensation to give silica gel, was newly prepared from the reaction of water glass (WG) and bis(tributyltin) oxide (TBO). The ratios of Si/Sn contained in TBSA were determined by gravimetric analysis to be in the range of 2–3. The gelation of TBSA in usual organic solvents such as hexane, benzene, and dichloromethane was not observed over 3 weeks. In addition, TBSA was shown to be a convenient precursor for the preparations of silica gel modified with organofunctional groups. From the reaction of TBSA with trimethoxysilanes and aromatic alcohols, the silica gels havingorganofunctional groups were obtained with the elimination of a tributyltin group. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 655–663, 1998     

Vibrational spectra of a ferrocenyl phosphine derivative chemisorbed on 3-aminopropylsilyl modified silica gel

Samples of silica gel dried at different temperatures, silica gel modified with 3-aminopropylsilyl (APS) and silica gel modified with APS and further with a ferrocenyl phosphine derivative were investigated by DRIFT, transmission FTIR and MicroRaman spectroscopy. The reaction between 3-aminopropyltrimethoxysilane (APTMS) and silica gel was mainly identified by the diminishing or vanishing intensity of the stretching band of the free OH groups in the silica gel. Further chemical reaction of the APS groups with a ferrocenyl phosphine derivative (suitable as ligand in homogeneous catalysis) was identified in the IR spectra by the appearance of the CN stretching band of the formed Schiff base, and diminishing intensity of the δ(NH₂) modes. According to the IR spectra the reaction of the ferrocenyl phosphine derivative with the APS-modified silica gel is almost quantitative. From the recorded IR and Raman spectra, conclusions concerning the substitution of APTMS methoxy groups during the chemisorption on silica gel were derived. Through deconvolution of the complex Raman band in the siloxy stretching region of the APS-modified silica gel, the newly formed siloxy bond was identified.     

Thermal analysis of PMMA/gel silica glass composites

Thermal analysis of poly-methylmethacrylate (PMMA) impregnated porous gel silica glasses confirms that the PMMA chains form hydrogen bonds with the pore surface silanol groups. The adopted conditions for the insitu polymerisation result in about 4% of residual monomers trapped in the polymer, most of them in the amorphous structure. The polymer and monomer mixture takes up the whole of the free pore volume. Most of the residual monomer polymerises during the DSC scans above the glass transition temperature providing an excellent probe for the weak glass transition. Polymerisation in the gel silica glass medium affects the glass transition temperature, the length of polymer chains, and the degree of polymerisation.     

柱层析硅胶固载K2CO3催化合成生物柴油的研究

研究了柱层析硅胶-K₂CO₃固体碱催化剂的制备条件,并对其进行XRD、FT-IR和SEM表征分析。结果表明,部分K₂CO₃吸收空气中的CO₂生成KHCO₃,K₂CO₃与 KHCO₃分散到硅胶表面,增强了催化效果。并考查了催化剂用量、醇油摩尔比、反应时间对生物柴油制备的影响。研究表明,催化剂的制备温度为120℃,催化剂用量为原料油质量的5%,醇油摩尔比为12∶1,反应温度70℃,反应时间2h,生物柴油收率可达95.2%。     

硅胶的表面硅烷化处理及其吸附性能研究

为研究改性硅胶对挥发性有机废气的吸附性能,分别采用十六烷基三甲氧基硅烷、辛基三乙氧基硅烷、苯基三甲氧基硅烷、一甲基三乙氧基硅烷对硅胶进行气相改性处理,试验研究了不同改性剂、改性时间对硅胶饱和吸附率的影响,考察了改性硅胶对甲苯、水二组分体系的吸附选择性.结果表明,硅胶对甲苯的吸附主要为物理吸附,长链的硅烷改性剂在60℃、...     

Kinetics of colloidal alloy crystallization of binary mixtures of monodispersed polystyrene and/or colloidal silica spheres having different sizes and densities in microgravity using aircraft

 Crystal growth rates in colloidal alloy crystallization of binary mixtures of monodispersed polystyrene and/or silica spheres having different sizes and densities are studied in microgravity by parabolic flights of an aircraft. The crystal growth rates are obtained by time-resolved reflection spectroscopy with a continuous circulating-type stopped-flow-cell system. The growth rates of alloy crystallization increase substantially in microgravity up to about 1.7 times those in normal gravity, which is in contrast to the retarding microgravity effect on the crystallization of single-component spheres. The disappearance of the segregation effect in microgravity is the main cause for the enhancing effect. The absence of convection of the suspension and the lack of downward sedimentation of colloidal spheres are also important. Received: 19 July 1999/Accepted in revised form: 1 September 1999     

Adsorption of three selected flavonoids with humic fraction-modified silica gel in hexane: A mechanism study

Three selected flavonoids, commonly found in spices, red-purple fruits, and vegetables, were adsorbed on humic fraction-modified silica gel in hexane. The percentage of adsorption in hexane for all examined analytes was nearly 100% after 1 hr, as a result of the strong dipole–dipole interaction. The increasing amount of adsorbent involved in the process improved the percentage of adsorption, which in turn shortened the time needed to reach the maximum by providing more binding sites. However, adsorption was not observed in other liquid phases under the same conditions, such as acetonitrile and ethyl ether. The mechanism leading to the adsorption was explored chromatographically, as well as by fourier transform infrared spectroscopy (FTIR) and theoretical simulations.     

Structural analysis of water adsorbed in silica gel

The melting point, T _f of water in a pore decreases as the surface area to pore volume ratio of the pore decreases. Analysis of water absorbed in the pores of silica gels using differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS) shows that the thickness of the bound, non-freezing water layer adjacent to the pore surface increases as its temperature increases, but that it is independent of the surface silanol concentration, [Si_sOH]. In contrast, the thickness decreases as the cylindrical pore radius r _H decreases. Thus, the increase in the bound water thickness from 0.45 nm for gels with r _H =1.2 nm to 1.2 nm for gels with r _H =7.5 nm is due to the increase from –53°C to –7°C of the temperature (e.g., the melting point T _f ) at which the bound water thickness was measured, and not due to the increase in t _H or the decrease in [Si_sOH]. The T _f of bulk water measured in a DSC was –0.3°C. The boiling point T _v of bulk water measured in a DSC was 81.3°C. T _v increased to 94°C in 7.5 nm pores and to 109°C K in 1.2 nm pores.     

Kinetics of vesicle formation

 The kinetics of vesicle formation from a hydrotrope (sodium xylenesulfonate) solution of a surfactant (Laureth 4) is studied by the use of a stopped-flow apparatus combined with a dynamic light scattering device to determine vesicle size in the system. The hydrotrope system studied presents a system with a high surfactant solubilization combined with vesicle formation simply by dilution with water. The kinetic results show a single exponential decay time. The kinetic analysis indicates that the vesicles are formed from a molecular solution which resulted from the shear in the stopped-flow device and grow by monomeric association. Received: 1 October 1996 Accepted: 22 November 1996     

液态29Si NMR研究TEOS/DDS混合体系的氨催化水解动力学

原位引入有机组分对氧化硅体系改性是合成有机-无机杂化硅材料的重要方法.利用原位的29Si液体核磁,研究了甲醇为溶剂、氨水催化条件下的四乙氧基硅烷（TEOS）和二甲基二乙氧基硅烷（DDS）原位共水解的动力学过程.通过改变反应体系中氨和水的浓度,拟合出单体及中间产物浓度随时间的变化曲线,得到了TEOS和DDS各自的水解速率常数以及相应各反应物的反应级数.与单前驱体水解一致的是,在双前驱体系中TEOS和DDS自身的反应级数仍保持一级,但是氨和水的反应级数都有不同程度的增大.与单前驱体水解速率方程相比,混合体系中TEOS的水解速率常数增大.同时,DDS在双前驱体中比单前驱体中的水解速率常数有很大程度的减少.水解动力学表明,TEOS和DDS在双前驱体体系中显示出更平行的水解速率.利用固体29SiMAS NMR,XPS及小角X射线散射（SAXS）手段对双前驱体体系研究得到的信息显示,碱催化条件下原位的TEOS水解中间物与DDS中间产物的原位共缩聚程度很弱.     

Application of solid-state NMR (13C and 29Si CP/MAS NMR) spectroscopy to the characterization of alkenyltrialkoxysilane and trialkoxysilyl-terminated polyisoprene grafting onto silica microparticles

The solid-state Nuclear Magnetic Resonance (NMR) was used to characterize surfaces of silica gels chemically modified by alkenyltrialkoxysilanes and trialkoxysilyl terminated 1,4-polyisoprenes. The formation of covalent bonds created between alkoxy functional groups from alkenyltrialkoxysilane or trialkoxysilyl-terminated 1,4-polyisoprene and silanol groups on silica was clearly demonstrated by means of ¹³C and ²⁹Si CP/MAS NMR spectroscopy. Quantitative data, including calculation of the grafting yields in relation with the initial silanol concentrations, were also obtained by using solid-state ²⁹Si-NMR leading to a final well-defined characterization of the silica surfaces. A relatively good agreement was noticed between the grafting yields calculated from ²⁹Si-NMR spectra and those determined from other analytical techniques such as Wijs titration or elementary analysis. The reactivity of the various silica silanols towards each coupling agent was clearly characterized and estimated, as were the proportions of the various grafted structures formed at the silica surface. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36 : 437–453, 1998