Synthesis,Bifunctionalization, and Remarkable Adsorption Performance of Benzene‐Bridged Periodic Mesoporous Organosilicas Functionalized with High Loadings of Carboxylic Acids

Highly ordered benzene‐bridged periodic mesoporous organosilicas (PMOs) that were functionalized with exceptionally high loadings of carboxylic acid groups (COOH), up to 80 mol % based on silica, have been synthesized and their use as adsorbents for the adsorption of methylene blue (MB), a basic dye pollutant, and for the loading and release of doxorubicin (DOX), an anticancer drug, is demonstrated. These COOH‐functionalized benzene? silicas were synthesized by the co‐condensation of 1,4‐bis(triethoxysilyl) benzene (BTEB) and carboxyethylsilanetriol sodium salt (CES), an organosilane that contained a carboxylic acid group, in the presence of non‐ionic oligomeric surfactant Brij 76 in acidic medium. The materials thus obtained were characterized by a variety of techniques, including powder X‐ray diffraction (XRD), nitrogen‐adsorption/desorption isotherms, TEM, and ¹³C and ²⁹Si solid‐state NMR spectroscopy. Owing to the exceptionally high loadings of COOH groups, their high surface areas, and possible π? π‐stacking interactions, these adsorbents have very high adsorption capacities and extremely rapid adsorption rates for MB removal and for the controlled loading/release of DOX, thus manifesting their great potential for environmental and biomedical applications.     

Quantitative 1H NMR analysis of reacted silanol groups in silica nanoparticles chemically modified with monochlorosilanes

Quantitative analysis of reacted silanol groups in silica nanoparticles modified chemically with monochlorosilanes was performed by ¹H NMR after treatment with cesium fluoride. Silica nanoparticles were modified chemically by the reaction between the silanol groups and monochlorosilanes, and the structure of the organic moiety anchored onto the silica surface was confirmed with solid‐state ¹³C NMR. As monochlorosilanes react with silanol groups at 1:1 ratio unlike di‐ or trichlorosilanes, the number of the silanes introduced into silica nanoparticles equals that of reacted silanol groups. Organically modified silica nanoparticles were dissolved using cesium fluoride, and the amount of the soluble organic compounds originated from the introduced silanes was determined by a ¹H NMR internal standard method using pyrene as the reference. Those values determined by ¹H NMR were in good agreement with those determined by elemental analysis. Thus, the number of reacted silanol groups per one particle was calculated on the basis of the results obtained by the ¹H NMR method, and the values were highly dependent on the steric structure of the introduced silanes. Copyright © 2010 John Wiley & Sons, Ltd.     

Dendrimer modified silica gel for anion exchange chromatography: synthesis, characterization and application

The novel grafted silica supports were investigated. The anion exchanger was prepared by chemical modification of a bare silica gel surface. The support was coated with a polymeric moiety formed by condensation polymerization of primary amine with diepoxide. The synthesized copolymer of methylamine (MA) and 1,4-butanedioldiglycidyl ether (BDDE) exhibited a dendrimer structure. The prepared materials were characterized by elemental analysis, FT-IR spectroscopy and solid state (13)C and (29)Si NMR CP-MAS spectroscopy. The porous structure of the adsorbents was investigated using the low temperature nitrogen adsorption (LTNA) method. It allows determination of the influence of the topology of packing materials on their chromatographic properties. Imaging was also carried out on the surfaces of the synthesized materials by scanning electron microscopy (SEM). The obtained stationary phase was applied in ion chromatography for the separation of inorganic anions (F(-), Cl(-), NO(2)(-), Br(-), NO(3)(-), HPO(4)(2-), SO(4)(2-), ClO(4)(-)). Bicarbonate buffer was used as a mobile phase.     

A new thermally immobilized fluorinated stationary phase for RP‐HPLC

A new fluorinated stationary phase was prepared through thermal immobilization of poly(methyl‐3,3,3‐trifluoropropylsiloxane) onto 5 μm Kromasil silica particles. The best conditions of immobilization time and temperature were determined through a central composite design and response surface methodologies. Physical–chemical characterization using solid‐state ²⁹Si NMR measurements, infrared spectroscopy and elemental analysis showed that the immobilization process was effective to promote a coating of the support that corresponds to a monolayer of polymer. The stationary phase presents selectivity for positional isomers and good peak shape for basic compounds.     

Deactivation of silica surfaces with a silanol-terminated polysiloxane; structural sharacterization by inverse gas chromatography and solid-state NMR

Retention gape deactivated with Silicone OV-1701-OH show good chromatographic performance and remarkable stability against water induced stationary phase degradrdation. In an attempt to better understand the findamentals off the deactivation process using silanol terminated polysiloxanes, a fumed silica was deactivated with Silicon OV-1701-OH. In contrast to fused silic capillaries, fumed silica (Aerosil A-200) can be studied by ²⁹Si cross-polarization magic-angle-spinning (CPMAS) NMR, thus serving as a model substrate for fused silica. Retention data from inverse gas chromatography at infinite dilurion and ²⁹Si CP MAS NMR data of five Aerosil phases, differing in residual silanol surface concentration, are correlated with the aim of validating this approach for stationary phase characterization. A comparatively detailed model of the deactivating polymer layer that explains the observed absorption activities is deduced. Surface silanols are shown to play a key role in the polymer layer, the structure of which is of primary importance for the absorption behavior after deactivation. Contrary to common belief, the absolute silanol surface concentration after deativation is only of secondary importance for the overall absorption activity. High silanol surface concentrations enhance degradation of the polysiloxane chains into small cyclic fragments as well as subsequent absorption and immobolization to the silica substrate surface. The mobility of linear polysiloxane chains in the kHz regime (as determined bby NMR cross-polarization dynamics) appears to determine the extent which the residual silanols are accessible for analytes. It is therefore anticipated that there is an optimum silanol surface concentration of fused silica surfaces to be deactivated with silanol terminated polysiloxanes; it should be lazrge enough to adsord polymer fragments, but not large to avoid excessive residual silanol activity.     

Design of In Vitro Bioactive Hybrid Materials from the First Generation of Amine Dendrimers as Nanobuilding Blocks

In this work, the first generation of poly(propyleneimine) dendrimers were functionalized with alkoxysilane terminal groups and subjected to one of two different sol–gel process that followed two different catalytic pathways, that is base‐ or acid‐catalyzed pathways. Thus, two series of new organic–inorganic hybrid materials were obtained in the form of monolithic pieces with differences in terms of both morphology and silanol content, which originated from the different sol–gel pathway that was followed. Moreover, calcium ions were added into the hybrid composition to promote in vitro bioactivity and phosphorous sources were used during the sol–gel step to obtain an earlier bioactive response. Characterization of these organic–inorganic hybrid materials was performed by means of thermogravimetric and elemental analyses, Fourier transform infrared spectroscopy (FTIR), solid state ¹³C, ²⁹Si and ³¹P magic‐angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, N₂‐adsorption isotherms, mercury‐intrusion porosimetry, and ζ‐potential measurements. The in vitro bioactivity of the dendritic hybrid networks was evaluated by soaking the materials in simulated body fluid and the results were explained in terms of the composition of the hybrids and the sol–gel route that was followed to prepare them.     

Preparation and Characterization of a Microwave-Immobilized Fluorinated Stationary Phase for RP-LC

A fluorinated stationary phase was prepared through the immobilization of poly(methyl-3,3,3-trifluoropropylsiloxane) onto 5 μm Kromasil silica by microwave irradiation. The best conditions of immobilization time and temperature were determined by central composite design and response surface methodology. Physical–chemical characterizations (IR, ²⁹Si NMR and elemental analysis) confirmed that the polymer was attached onto the chromatographic support by different mechanisms that resulted in a percent carbon loading of 10%. Some pharmaceuticals were completely separated with the fluorinated stationary phase using a simple mobile phase while the same separation was not possible with a C18 stationary phase.     

Base‐deactivated and alkaline‐resistant chromatographic stationary phase based on functionalized polymethylsilsesquioxane microspheres

Vinyl, chloropropyl, and mercaptopropyl functionalized particles were prepared by a two‐step acidic/alkaline catalyzed co‐hydrolysis/condensation of methyltrimethoxysilane with a different silane precursor that carries chemically reactive functional group including vinyl, chloropropyl, and mercaptopropyl, respectively. The morphology, pore structure, and functional groups of the synthesized packings were studied by SEM, nitrogen adsorption‐desorption measurements, and solid‐state ¹³C ²⁹Si NMR spectroscopy, respectively. The particles show ordered sphere, narrow particle size distribution, and mesoporous structure. The carbon contents of the microspheres are in the range of 17–19%, comparable to those of octadecyl‐bonded silica packings. The three‐kind of microspheres were directly used as packing materials for high‐performance liquid chromatography without size classification. The chromatographic performance of the columns was evaluated and compared with a commercially available C₁₈ phase. The results revealed that these columns possess typical reversed‐phase chromatographic properties with increased hydrophobicity than polymethylsilsesquioxane and symmetric peaks for basic compounds. They were applied to the simultaneous separation of combination bendazol hydrochlorothiazide capsules containing polar and basic drugs with peaks identified by tandem with mass spectrometry. In general, a novel method is provided for the synthesis of different methyltrimethoxysilane‐derived microspheres for high‐performance liquid chromatography, which are advantageous for separating basic compounds.     

Stationary Phases 21: A New Polar Substituted Triazine Stationary Phase for HPLC

A method for preparing a new polar substituted triazine stationary phase is described. The structure of the triazine phase on silica was characterized by elemental analysis, and by FTIR, solid state FT-¹³C NMR, and ²⁹Si NMR spectral analysis. The chromatographic properties of this packing material have been evaluated by using a number of different solutes, and the properties compared with those of a commercial stationary phase RP-18. It is found that this triazine phase has weak π-donor ligands on the silica surface.     

Polar-copolymerized approach based on horizontal polymerization on silica surface for preparation of polar-modified stationary phases

A new approach for preparation of polar-modified reversed-phase liquid chromatography stationary phases was developed by using horizontal polymerization technique on silica surface, which was defined as “polar-copolymerized” approach. Based on this new approach, a representative polar-copolymerized stationary phase composed of mixed n-octadecyl and chloropropyl (C18–C3Cl) was synthesized. The resulting stationary phase named C18HCE was characterized with elemental analysis and solid phase ¹³C and ²⁹Si NMR, which proved the chemistry of polar-copolymerized stationary phases. Chromatographic evaluation and application of the C18HCE were also investigated. The results of preliminary chromatographic evaluation demonstrated that the C18HCE stationary phase exhibited 100% aqueous mobile phase compatibility, low silanol activity. In addition, the application results demonstrated that the C18HCE had superior separation performance in alkaloids separation at acidic conditions compared to some commercial stationary phases.     

High‐Temperature Chlorination‐Reduction Sequence for the Preparation of Silicon Hydride Modified Silica Surfaces

A general method for the functionalization of silica surfaces with silicon hydride (Si–H) groups is described for four different preparations of silica. The silica surface is reduced in a two‐step chlorination–reduction procedure within a simple gas‐flow system at high temperatures. After initial dehydroxylation of the silica surface, silicon chloride groups are formed by the reaction with thionyl chloride. The chlorination activates otherwise inaccessible surface siloxane moieties. A high silicon–hydride surface concentration results from the subsequent reduction of the chlorinated surface with hydrogen. The physical properties of the resulting silica are analyzed using scanning electron microscopy, as well as dynamic light scattering and Brunauer–Emmet–Teller measurements. The chlorination–reduction sequence has no significant impact on the structure, surface area and mesopore size of the silica materials used. The surface of the materials is characterized by diffuse reflectance infrared Fourier transform (DRIFT) and ²⁹Si CP/MAS NMR spectroscopy. The silicon–hydride groups are mostly of the ‐type. The use of high temperatures (>800 °C) results in the condensation of internal and surface silanol groups. Therefore, materials with both a fully condensed silica matrix as well as a surface free of silanol groups are obtained. The materials are ideal precursors for further molecular silica surface modification, as demonstrated with a ferrocene derivative.     

A protophilic solvent‐assisted solvothermal approach to Cu‐BTC for enhanced CO2 capture

Cu‐BTC–ethylenediamine (EDA)/polyethyleneimine (PEI) adsorbents were synthesized using a protophilic solvent‐assisted solvothermal method. EDA was introduced to enhance the degree of activation due to its lower boiling point allowing it to be removed easily compared with dimethylformamide. A contrast experiment was done by introducing PEI to the solvothermal solution considering its higher boiling point. Powder X‐ray diffraction, scanning electron microscopy and Raman spectroscopic characterizations were performed to investigate the effect of EDA/PEI on crystallinity and morphology of the adsorbents. ¹H NMR characterization and elemental analysis were performed to study the removal rate of organic guest molecules and the degree of activation. Nitrogen physical adsorption and CO₂ adsorption isotherms were used to measure the surface area and CO₂ adsorption capacities. The CO₂ adsorption mechanism of the synthesized adsorbents is mainly dependent on physisorption determined by surface area. Furthermore, open metal sites generated by the enhancement of degree of activation also promote the CO₂ adsorption performance. Therefore, adsorbents synthesized using the protophilic solvent‐assisted solvothermal method exhibit excellent CO₂ adsorption performance. Copyright © 2015 John Wiley & Sons, Ltd.     

Formation of an in situ nanosilica nanomatrix via graft copolymerization of vinyltriethoxysilane onto natural rubber

Natural rubber (NR) with an in situ nanosilica nanomatrix was characterized in present work. The in situ nanosilica nanomatrix was prepared via graft copolymerization of a silane monomer, vinyltriethoxysilane (VTES), onto deproteinized NR (DPNR) in latex stage using tetrapentamine (TEPA)/tert‐butylhydroperoxide (TBHPO) as initiators. VTES conversion of more than 80% was obtained, and it depended on VTES concentration. The graft copolymer structure was characterized by Fourier transform infrared (FT‐IR), solution‐state proton nuclear magnetic resonance (¹H‐NMR), and solid‐state ²⁹Si‐NMR spectroscopy. FT‐IR analysis of the graft copolymer confirmed the formation of in situ silica particles, while solution‐state ¹H‐NMR and solid‐state ²⁹Si‐NMR revealed the partial hydrolysis of the ethoxy groups and polycondensation of the silanol groups. The formation of nanosilica particles enhanced thermal and mechanical properties of the graft copolymer. Morphology observations of the in situ nanosilica nanomatrix through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the spherical nanosilica particles form a nanomatrix surrounding NR particle. The formation of the nanomatrix was proved to enhance mechanical properties for NR materials.     

Molecular‐Level Insights into the Oxidative Degradation of Grafted Amines

The oxidative degradation of CO₂ adsorbents consisting of amine‐grafted pore‐expanded mesoporous MCM‐41 silica was investigated. The adsorbents were treated under flowing air at various temperatures, and the degree of deactivation was evaluated through the measurement of their CO₂ adsorption capacity prior and subsequent to exposure to air. To decipher the chemical structure of surface species upon air‐deactivation of grafted amines, a solvent extraction procedure was developed using a deuterated basic solution. The obtained solutions were analyzed by a variety of 1D and 2D NMR spectroscopy techniques, such as ²⁹Si, ¹³C, ¹H, [¹H,¹⁵N] HMBC, [¹H,¹³C] HMQC, COSY and DOSY. The surface species generated by oxidative degradation of amine‐grafted silica were found to contain functional groups such as imine, amide and carboxylic groups. Several structural units were conclusively demonstrated.     

Synthesis and Application of Hydride Silica Composites for Rapid and Facile Removal of Aqueous Mercury

The adsorption of ionic mercury(II) from aqueous solution on functionalized hydride silicon materials was investigated. The adsorbents were prepared by modification of mesoporous silica C‐120 with triethoxysilane or by converting alkoxysilane into siloxanes by reaction with acetic acid. Mercury adsorption isotherms at 20 °C are reported, and maximum mercury loadings were determined by Langmuir fitting. Adsorbents exhibited efficient and rapid removal of ionic mercury from aqueous solution, with a maximum mercury loading of approximately 0.22 and 0.43 mmol of Hg g^?1 of silica C‐120 and polyhedral oligomeric silsesquioxane (POSS) xerogel, respectively. Adsorption efficiency remained almost constant from pH 2.7 to 7. These inexpensive adsorbents exhibiting rapid assembly, low pH sensitivity, and high reactivity and capacity, are potential candidates as effective materials for mercury decontamination in natural waters and industrial effluents.     

A study of the adsorption activities of silanol surface structures on a fused silica model substrate by combining 29Si CP MAS NMR and inverse gas chromatographic data

The possibilities of inverse gas-solid chromatography (IGC) in obtaining chromatographic data on fumed silica were examined. Aerosil A-200, a fused silica model substrate in ²⁹Si nuclear magnetic resonance analysis, was trimethylsilylated to different degrees. IGC was used to very reproducibly determine the free specific energies of adsorption of several functionalized probe solutes. Hydrogen bonding solutes have a free specific energy of adsorption that is at least about 50% higher than that of non-hydrogen bonding probe solutes. NMR was used in combination with elemental analysis to calculate surface concentrations of the different chemical surface structures. IGC data and surface concentrations were combined in order to determine the contribution of each type of surface structure to the total free specific adsorption energy. It could be concluded that residual silanols from the reaction of dihydroxydi-siloxysiloxane (Q₂ groups) with trimethylchlorosilane possess a higher adsorption activity than the silanols initially present.     

New Stationary Phase Prepared by Immobilization of a Copper-Amine Complex on Silica and Its Use for High Performance Liquid Chromatography

Chromatographic silica (10 μm) was chemically modified with the silylating agent: [3-(2-aminoethyl)aminopropyl]trimethoxysilane (AEAPTS). The reaction product was characterized by elemental analysis and infrared and ¹³C and ²⁹Si NMR spectra. The chemically modified silica was treated with Cu(II) in methanol medium. This cation was strongly adsorbed through complexation by the pendant ethylenediamine groups attached to the silica surface. The complex formed on the silica surface was shown to be stable in both aqueous and non-aqueous media. The aim of Cu(II) immobilization is to use this new material as a stationary phase in High Performance Liquid Chromatography (HPLC). Separations of synthetic mixtures of aromatic amines and of polyaromatic hydrocarbons were undertaken using 150×3.9 mm HPLC columns packed with the modified silica, with and without copper ions, to follow the influence of the cation on the chromatographic separation and to verify the efficiency of the new stationary phase for HPLC.     

Emulsion polymerization of ethylene from mesoporous silica nanoparticles with vinyl functionalized monolayers

Emulsion polymerization of ethylene from vinyl functionalized mesoporous silica nanoparticles (V‐MSNs) was reported. V‐MSNs were synthesized via deposition of vinyl monolayers on the pore walls, and the relative surface coverage of the vinyl monolayers was 74%. A fluorinated P‐O‐chelated nickel catalyst coordinated to the vinyl groups. These V‐MSNs hosting catalysts were full dispersed in water assisted by ultrasonic processor in the presence of surfactants. After addition of ethylene, polyethylene (PE) chains grew from the pores of V‐MSNs, formation of stable nanocomposite latices with solid content up to 17.3%. Our method made V‐MSNs well‐dispersed in the PE matrix. Especially, because of a strong interaction between PE and nanoparticles, a stable V‐MSNs core/PE shell structure was formed upon thermal treatment above melting temperature of the PE. Samples were analyzed by a number of techniques including TEM, N₂ adsorption‐desorption, FTIR, and solid state ²⁹Si NMR, DLS, ¹H NMR, GPC, and DSC. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1393–1402, 2009     

Adsorption of Metallocenes on Silica

The adsorption of the metallocenes ferrocene, doubly deuterated ferrocene, cymantrene and nickelocene, as well as molybdenum hexacarbonyl, proceeds in the absence of a solvent. Large single pieces of silica gel were placed in contact with the solid metallocenes and the adsorption process was visualized on a macroscopic scale and the maximal loadings were determined. ¹H, ²H, and ¹³C solid‐state NMR studies confirmed fast isotropic reorientation of the surface‐adsorbed metallocene molecules within the pores of the silica. All prevalent anisotropic solid‐state interactions were averaged out. The solid diamagnetic and paramagnetic materials were amenable to measurements with a standard solution NMR instrument. All metallocenes adsorbed in a monolayer. In the case of ferrocene and cymantrene, different ¹³C MAS signals were obtained for the cyclopentadienyl ring carbon nuclei and assigned to one ring interacting with the surface and one ring pointing away from it. The relative adsorption strengths of ferrocene on different silica supports, nanotubes, and activated carbon were determined by a novel straightforward method recording the desorption temperature. The reversibility of adsorption has been demonstrated by competition experiments using ferrocene, doubly deuterated ferrocene, and cymantrene. Adsorbed nickelocene could be reduced to small Ni⁰ aggregates on the surface and the catalytic activity of the resulting material for the cyclotrimerization of phenylacetylene was proven.     

Study of adsorption and preconcentration by using a new silica organomodified with [3‐(2,2′‐dipyridylamine)propyl] groups

In this work, a silica surface chemically modified with [3‐(2,2′‐dipyridylamine)propyl] groups, named [3‐(2,2′‐dipyridylamine)propyl]silica (Si‐Pr‐DPA) was prepared, characterized, and evaluated for its heavy metal adsorption characteristics from aqueous solution. To our knowledge, we are the first authors who have reported the present modification. The material was characterized using infrared spectroscopy, SEM, and NMR ²⁹Si and ¹³C solid state. Batch and column experiments were conducted to investigate for heavy metal removal from dilute aqueous solution by sorption onto Si‐Pr‐DPA. From a number of studies the affinity of various metal ions for the Si‐Pr‐DPA sorbent was determined to follow the order Fe(III) > Cr(III) >> Cu(II) > Cd(II) > Pb(II) > Ni(II). Two standard reference materials were used for checking the accuracy and precision of the method. The proposed method was successfully applied to the analysis of environmental samples. This ligand material has great advantage for adsorption of transition‐metal ions from aqueous medium due to its high degree of organofunctionalization associated with the large adsorption capacity, reutilization possibility, and rapidity in reaching the equilibrium.