Hybrid Monolith Research Articles

Photopatternable Di-ureasil−Zirconium Oxocluster Organic−Inorganic Hybrids As Cost Effective Integrated Optical Substrates

Organic−inorganic hybrids containing methacrylic acid (McOH, CH2═C(CH3)COOH)) modified zirconium tetrapropoxide, Zr(OPrn)4, classed as di-ureasil−zirconium oxo-cluster hybrids, have been prepared and structurally characterized by X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), Fourier transform infrared (FT-IR) and Raman (FT-Raman) spectroscopies, 29Si and 13C nuclear magnetic resonance (NMR), and atomic force microscopy (AFM). XRD and SAXS results have pointed out the presence of Si- and Zr-based nanobuilding blocks (NBBs) dispersed into the organic phase. Inter-NBBs correlation distances have been estimated for the pure di-ureasil and a model compound obtained by hydrolysis/condensation of Zr(OPrn)4:McOH (molar ratio 1:1): dSi ≈ 26 ± 1 Å and dZr ≈ 16 ± 1 Å, respectively. In the case of the di-ureasil−zirconium oxo-cluster hybrids, these distances depend on the Zr relative molar percentage (rel. mol. Zr %) (dSi ranges from 18 to 25 Å and dZr from 14 to 23 Å, as the rel. mol. Zr % increases from 5 to 75), suggesting that the Si- and Zr-based clusters are interconstrained. Complementary data from FT-IR, FT-Raman, 29Si and 13C NMR, and AFM support to a structural model where McOH-modified Zr-based NBBs (Zr-OMc) are present over the whole range of composition. At low Zr-OMc contents (rel. mol. Zr % <30) the clusters are well-dispersed within the di-ureasil host, whereas segregation occurs at the 0.1 µm scale at high Zr-OMc concentration (rel. mol. Zr % = 50). No Zr−O−Si heterocondensation has been discerned. Monomode waveguides, diffractions gratings, and Fabry−Perot cavities have been written through the exposure of the hybrid monoliths to UV light. FT-Raman has shown that the chemical process that takes place under illumination is the polymerization of the methacrylate groups of the Zr-OMc NBBs. The guidance region in patterned channels is a Gaussian section located below the exposed surface with typical dimensions of 320 µm wide and 88 µm deep. The effective refractive index is 1.5162 (maximum index contrast on the order of 1 × 10−4) and the reflection coeficient of the Fabry−Perot cavity (formed by a grating patterned into a 0.278 cm channel) is 0.042 with a free spectral range value of 35.6 GHz.

Preparation, characterization and analytical application of a hybrid organic–inorganic silica-based monolith

In the present study, a mercapto groups-incorporated hybrid silica-based monolith, which consists of a continuous porous silica backbone, was successfully synthesized by sol–gel technology. The hybrid silica monolith was characterized by various techniques, such as elemental analysis, scanning electron microscopy, diffused infrared spectroscopy and low temperature nitrogen desorption/adsorption measurements. The results showed that the monolith contains high sulfur content (up to 3.05%) with a hierarchical porous structure (throughpores and mesopores) and large specific surface area (467 m 2/g). Due to the favorable chemical reactivity of mercapto pendant moieties, the hybrid monolith can be facilely derivatized to yield various functional groups. In this study, they were oxidized by hydrogen peroxide (30%, w/w) to produce sulfonic acid groups, which exhibited excellent cation-exchange capability. The application of this material is demonstrated by in-tube microextraction of anaesthetics followed by capillary electrophoretic separation. The monolith can be effectively applied to purify and enrich the target analytes in human urine.

Colloidal Gelation as a General Approach to the Production of Porous Materials

A versatile means for preparing (nano)porous materials from arbitrary colloids and resins is presented. Aqueous gelation under mild conditions followed by ambient drying gives robust organic (image shown) and hybrid monoliths, with independent variations in structure and composition demonstrated. Novel, previously inaccessible porous materials may be prepared via this technique.

Fabrication of molecularly imprinted hybrid monoliths via a room temperature ionic liquid‐mediated nonhydrolytic sol–gel route for chiral separation of zolmitriptan by capillary electrochromatography

A room temperature ionic liquid (RTIL)-mediated nonhydrolytic sol-gel (NHSG) protocol was explored for the fabrication of new molecularly imprinted silica-based hybrid monoliths for chiral separation of a basic template zolmitriptan by CEC. The RTIL-mediated NHSG protocol involved free-radical copolymerization and NHSG process. Three carboxylic acids (trifluoromethyl acrylic acid, cinnamic acid, and methacrylic acid (MAA)) were examined as both the functional monomers and the catalysts for the NHSG condensation of methacryloxypropyltrimethoxysilane (MPTMS) to form silica-based framework. RTIL was incorporated to reduce gel shrinkage and also to act as the pore template. The effects of carboxylic acids and RTIL on the performance of the silica-based hybrid molecularly imprinted polymer (MIP) monoliths were investigated in detail to realize excellent chiral recognition and to give new insights into the mechanism of the RTIL-mediated NHSG strategy. Excellent chiral separation of (R)/(S)-zolmitriptan was achieved when the molar ratio of MAA to MPTMS was 1:4 and 1:2 with RTIL involved. The synergism of the free-radical copolymerization of the C=C bond of carboxylic acids and MPTMS with the NHSG condensation of MPTMS catalyzed by the carboxylic acids was demonstrated. The incorporation of RTIL increased porosity, and hence improved selectivity of the prepared hybrid monoliths.

Synthesis of propyl‐functionalized hybrid monolithic silica capillaries and evaluation of their performances in nano‐LC and CEC

During the last decade, silica monolithic capillaries have focused more and more attention on miniaturized separation techniques like CEC, nano-LC, and chip electrochromatography owing to their unique chromatographic properties and to their possible in situ synthesis. Nevertheless, the preparation of conventional silica-based individual monolithic columns is time consuming, owing to the individual steps involved, including the synthesis of the silica matrix and its subsequent on-column chemical grafting. The hybrid organic-inorganic monoliths, whose synthesis is based on the polycondensation of siloxane with organosiloxane precursors, seems to be an attractive alternative since their direct synthesis leads to silica monoliths with organic moieties covalently linked to the inorganic silica matrix through hydrolytically stable Si-C bonds. This study describes the synthesis of hybrid monoliths using propyltrimethoxysilane (C3-TriMOS) as a new kind of silica coprecursor to subsequently increase the hydrophobicity of the stationary phase. The influence of several experimental parameters (pH, gelation temperature, relative proportion of the precursors) on the textural (skeleton and macropore size) and chromatographic properties (efficiency, retention, and electroosmotic mobility) of the obtained monoliths are discussed. The results show that the optimal coprecursor incorporation is obtained after a postgelation step during which the condensation of the C3-TriMOS coprecursor is favored by an increase in the pH medium. Thermal hydrolysis of urea previously added to the polymerization mixture allows this in situ pH increase. These hybrid monoliths present hydrophobic properties and allow the separation of test mixtures in the RP mode without any further modification. Moreover, they present excellent efficiencies since reduced plate height as low as 5 and 15 microm are obtained in the electrodriven mode (CEC) and in the hydrodynamic one (nano-LC), respectively.

One-Pot Syntheses of the First Series of Emulsion Based Hierarchical Hybrid Organic−Inorganic Open-Cell Monoliths Possessing Tunable Functionality (Organo−Si(HIPE) Series)

The elaboration of organo−silica-based hybrid monoliths exhibiting a hierarchical trimodal porous structure (micro-, meso-, and macroporosity) with tunable functionality have been synthesized for the first time via high internal phase emulsion (HIPE) process and lyotropic mesophases. Through one-pot synthesis, many organic functionalities that can act as network modifiers (methyl, dinitrophenylamino, benzyl, and mercaptopropyl) or co-network formers (pyrrol) have been anchored to the amorphous silica porous network. The resulting materials have been thoroughly characterized via a large set of techniques: SEM, TEM, SAXS, mercury porosimetry, nitrogen adsorption isotherms, FTIR, 29Si MAS NMR, and XPS. These sol−gel-derived hierarchical open-cell functional hybrid monoliths exhibit macroscopic void spaces ranging from 5 μm up to 30 μm and their accessible micro-and mesoporosities reveal hexagonal organization for the dinitrophenylamino-, benzyl-, and pyrrol-based hybrids. The average condensation degree for these hybrid networks ranges between 86 and 90%, yielding shaped monoliths with both good integrity and sufficient mechanical properties to be usable as functional catalytic or chromatographic supports. Also, function accessibility has been demonstrated through heterogeneous nucleation of Pd metallic nanoparticles.

Electrohydrodynamics around single ion-permselective glass beads fixed in a microfluidic device

This work demonstrates by direct visualization using confocal laser scanning microscopy that the application of electrical fields to a single-fixed, ion-permselective glass bead produces a remarkable complexity in both the coupled mass and charge transport through the bead and the coupled electrokinetics and hydrodynamics in the adjoining bulk electrolyte. The visualization approach enables the acquisition of a wealth of information, forming the basis for a detailed analysis of the underlying effects (e.g., ion-permselectivity, concentration polarization, nonequilibrium electroosmotic slip) and an understanding of electrohydrodynamic phenomena at charge-selective interfaces under more general conditions. The device used for fixing single beads in a microfluidic channel is flexible and allows to investigate the electrohydrodynamics in both transient and stationary regimes under the influence of bead shape, pore size and surface charge density, mobile phase composition, and applied volume forces. This insight is relevant for the design of microfluidic/nanofluidic interconnections and addresses the ionic conductance of discrete nanochannels, as well as nanoporous separation and preconcentration units contained as hybrid configurations, membranes, packed beds, or monoliths in lab-on-a-chip devices.

Characterization and optical properties of sol–gel processed PMMA/SiO 2 hybrid monoliths

Organic–inorganic hybrid monoliths consisting of poly(methyl methacrylate) and SiO 2 were synthesized by the sol–gel process. Three PMMA/TEOS ratios by weight were prepared, namely PMMA/TEOS = 80/20, 50/50 and 20/80. The effects of the ratio of PMMA/TEOS on thermal stability, microstructure, morphology and optical properties were systematically studied. In particular, scanning electron microscopy (SEM) demonstrated morphological variation corresponding to the degree of miscibility between organic and inorganic components. Energy dispersive spectroscopy (EDS) clearly revealed that the SiO 2 was more uniformly distributed in the hybrids with increasing PMMA content. The refractive index could be adjustable in the range of 1.474–1.486. The 80/20 monolith had the similar transparency to pure PMMA in the visible region and lower absorption than PMMA in the near infrared region, suggesting its potential applications for optical devices.

Ionic conductance of nanopores in microscale analysis systems: Where microfluidics meets nanofluidics

In this tutorial review we illustrate the origin and dependence on various system parameters of the ionic conductance that exists in discrete nanochannels as well as in nanoporous separation and preconcentration units contained as hybrid configurations, membranes, packed beds, or monoliths in microscale liquid phase analysis systems. A particular complexity arises as external electrical fields are superimposed on internal chemical and electrical potential gradients for tailoring molecular transport. It is demonstrated that the variety of geometries in which the microfluidic/nanofluidic interfaces are realized share common, fundamental features of coupled mass and charge transport, but that phenomena behind the key steps in a particular application can be significantly tuned, depending on the morphology of a material. Thus, the understanding of morphology-related transport in internal and external electrical potential gradients is critical to the performance of a device. This addresses a variety of geometries (slits, channels, filters, membranes, random or regular networks of pores, etc.) and applications, e. g., the gating, sensing, preconcentration, and separation in multifunctional miniaturized devices. Inherently coupled mass and charge transport through ion-permselective (charge-selective) microfluidic/nanofluidic interfaces is analyzed with a stepwise-added complexity and discussed with respect to the morphology of the charge-selective spatial domains. Within this scenario, the electrostatics and electrokinetics in microfluidic and nanofluidic channels, as well as the electrohydrodynamics evolving at microfluidic/nanofluidic interfaces, where microfluidics meets nanofluidics, define the platform of central phenomena.

New Generation of Hybrid Organic-Inorganic Macrocellular Foams: Integrative Chemistry Toward Reaching Multifunctional Materials

ABSTRACTThe elaboration of organosilica based hybrid monoliths exhibiting a hierarchically structured bimodal porous structure with tunable functionality have been processed via High Internal Polymeric Emulsion (HIPE) process for the first time. Through one pot synthesis, many organic functionalities that can act as network modifiers (Methyl, Dinitrophenylamino, Benzyl, Mercaptopropyl) or co-network formers (Pyrrol) have been anchored to the amorphous silica porous network. The resulting materials have been thoroughly characterized via a large set of techniques SEM, TEM, SAXS, mercury porosimmetry, nitrogen adsorption isotherms, FTIR, 29Si MAS NMR. These sol-gel derived hierarchical open cell functional hybrid monoliths exhibit macroscopic void spaces ranging from 5 up to 30 [.proportional]m and their accessible micro-mesoporosity, reveal hexagonal organisation for the dinitrophenylamino, benzyl, and pyrrol based hybrids. The average condensation degree for these hybrid networks ranges between 86 and 90% yielding shaped monoliths with both good integrity and sufficient mechanical properties to be usable as functional catalytic or chromatographic supports.

Periodic mesoporous hybrid monolith with hierarchical macro–mesopores

We describe the synthesis of hybrid monolith with hierarchically macro–mesoporous structure by a sol–gel process from the mixture of 1,4-bis(triethoxysilyl)benzene (BTEB) and tetraethoxysilane (TEOS) using poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (P123) as structure directing agent under acid medium. The ordered mesoporous structure is embedded in the skeleton of the well-defined co-continuous macropore of the hybrid monolith. The influence of aging condition, acidic concentration, P123/Si ratio and TMB/P123 ratio on the macro- and meso-structure of the resultant monolith was investigated in details. The three-successive aging processes are necessary for the mesostructural order of the monolith to survive the surfactant removing process. The well-defined co-continuous macropore could be formed with the aid of TMB, which probably delays the phase separation rate during the sol–gel process through enhancing the interaction between the hydrophobic BTEB with P123 surfactant micelles. The macro–mesoporous hybrid monolith with phenylene bridged in the mesoporous framework may have potential application as a novel kind of stationary phase for high performance liquid chromatography (HPLC).

A Room Temperature Ionic Liquid (RTIL)‐Mediated, Non‐Hydrolytic Sol–Gel Methodology to Prepare Molecularly Imprinted, Silica‐Based Hybrid Monoliths for Chiral Separation

A Room Temperature Ionic Liquid (RTIL)‐Mediated, Non‐Hydrolytic Sol–Gel Methodology to Prepare Molecularly Imprinted, Silica‐Based Hybrid Monoliths for Chiral Separation

Glycol-modified organosilanes in the synthesis of inorganic-organic silsesquioxane and silica monoliths

Highly porous inorganic-organic hybrid monoliths with mesopores in a macroporous network have been prepared from tris-(2-hydroxyethoxy)methylsilane (MeGMS), tris-(2-hydroxyethoxy)phenylsilane (PhGMS), 1,2-bis[tris-(2-hydroxyethoxy)silyl]ethane (bEtGMS) and 1,4-bis[tris-(2-hydroxyethoxy)silyl]benzene (bPhGMS) with or without the presence of tetrakis(2-hydroxyeth-oxy)silane (EGMS) and a structure-directing agent (P123).

Mechanical and thermal properties of SiO2–PMMA monoliths

Organic–inorganic hybrid monoliths of cross-linked polymethylmethacrylate (PMMA) and silica (SiO2) were prepared by sol–gel, using tetraethoxysilane (TEOS) and methylmethacrylate (MMA) as precursors and 3-(trimethoxysilyl) propylmethacrylate (TMSPM) to make compatible the organic and inorganic components. Two types of monoliths were prepared, H1-type using a molar ratio composition of 16:1:4 for water:TEOS:ethanol and 1:0.1:0.1 for TEOS:TMSPM:MMA and H2-type using 6.3:1:2.52 for water:TEOS:ethanol and 1:0.25:0.25 for TEOS:TMSPM:MMA. Semi-transparent monoliths were obtained in both cases after the gelation–solidification and drying processes, which took about seven days. Thermal properties of the samples were obtained by applying thermal lens spectroscopy and their mechanical properties were measured by depth sensing indentation and Vickers microhardness. FTIR spectroscopy measurements were performed to complement the characterization. We found that the hardness of the hybrid monoliths have values between those of commercial PMMA and a sol–gel SiO2 monolith. This result is a consequence of the reinforcement produced by the SiO2 component in the organic–inorganic hybrid matrix. The thermal diffusivity of the hybrid monoliths shows an appreciable increasing in the hybrid system with respect to the pure SiO2 monolith. Mechanical behavior of monoliths is strong influenced by the SiO2–PMMA ratio or changing the water:TEOS:ethanol contents.

High-pressure catalytic combustion of gasified biomass in a hybrid combustor

Catalytic combustion of synthetic gasified biomass was conducted in a high-pressure facility at pressures ranging from 5 to 16 bars. The catalytic combustor design considered was a hybrid monolith (400 cpsi, diameter 3.5 cm, length 3.6 cm and every other channel coated). The active phase consisted of 1 wt.% Pt/γ-Al 2O 3 with wash coat loading of total monolith 15 wt.%. In the interpretation of the experiments, a two-dimensional boundary layer model was applied successfully to model a single channel of the monolith. At constant inlet velocity to the monolith the combustion efficiency decreased with increasing pressure. A multi-step surface mechanism predicted that the flux of carbon dioxide and water from the surface increased with pressure. However, as the pressure (i.e. the Reynolds number) was increased, unreacted gas near the center of the channel penetrated significantly longer into the channel compared to lower pressures. For the conditions studied ( λ = 4–6, T in = 218–257 °C and residence time ∼5 ms), conversion of hydrogen and carbon monoxide were diffusion limited after ignition, while methane never ignited and was kinetically controlled. According to the kinetic model surface coverage of major species changed from CO, H and CO 2 before ignition to O, OH, CO 2 and free surface sites after ignition. The model predicted further that for constant mass flow combustion efficiency increased with pressure, and was more pronounced at lower pressures (2.5–10 bar) than at higher pressures (>10 bar).

Fibrous Crystalline Hydrogels Formed from Polymers Possessing A Linear Poly(ethyleneimine) Backbone

Novel thermoreversible physical hydrogels formed from polymers with linear and star architectures possessing a linear poly(ethyleneimine) (PEI) backbone have been investigated. The hydrogelation occurred simply upon natural cooling of hot aqueous solutions of PEIs to room temperature. The X-ray diffraction and differential scanning calorimetry measurements for the resultant hydrogels unambiguously indicated that the hydrogelation originated from the formation of dihydrate crystalline structures of PEI. These crystalline hydrogels are structurally unique and hierarchical. Microscopic images revealed that the morphologies of the crystalline hydrogels depend on their molecular architectures. The linear PEI resulted in branched fibrous bundles organized by unit crystalline nanofibers with a width of ca. 5-7 nm. The six-armed star with benzene ring core produced fanlike fibrous bundles while the four-armed star with porphyrin core assembled into asterlike aggregates. The critical concentration of gelation (C(G)) was low (about 0.2 approximately 0.3%) and the thermoreversible gel-sol transition temperatures (T(G)) were controllable from approximately 43 to approximately 79 degrees C. The hydrogels formed in the presence of the various aqueous additives including organic solvents, hydrophilic polymers, physical cross-linker, chemical cross-linker, and base enabling modification and functionalization during synthesis. The mechanical properties of the hydrogels could be improved by chemical cross-linking of preformed hydrogels by glutaraldehyde. Physically and physical/chemical cross-linked hydrogels served as excellent template roles in biomimetic silicification, which produced silica-PEI hybrid powder or monolith constructed by nanofibers.

Organic–inorganic hybrid poly(silsesquioxane) monoliths with controlled macro- and mesopores

Siloxane-based organic–inorganic hybrid monoliths with well-defined macropores and/or mesopores have been synthesized by a sol–gel process, accompanied by polymerization-induced phase separation. Using aklyltrialkoxysilanes and alkylene-bridged alkoxysilanes, two different categories of organosiloxane networks have been characterized in view of macroporosity (based on phase separation) and mesoporosity (supramolecularly templated by surfactants). While the alkyl-terminated poly(siloxane) networks exhibit substantial surface hydrophobicity accompanied by mechanical flexibility, the alkylene-bridged networks behave much more similarly to those prepared from tetraalkoxysilanes with regard to surface hydrophilicity, mechanical rigidness and mesopore-forming ability. The supramolecular templating of mesopores embedded in the gel skeletons (which comprise well-defined macroporous networks) has proven to give a wide variety of hierarchically-designed macro–mesoporous hybrid materials.

有機‐無機ハイブリッド多孔体による光散乱制御

The tuning of light scattering strength has been demonstrated for organic-inorganic hybrid monoliths with well-defined through-pores in micrometer range. Macroporous gels having interconnected pores and skeletons are obtained in a system containing methyltrimethoxysilane, water, nitric acid, and methanol using an alkoxy-derived sol-gel method combined with the phase separation. The sizes of pores and skeletons can be controlled by varying molar ratios of water and methanol in the starting compositions which mostly affect the onset of polymerization-induced phase separation in the system. The mercury porosimetry shows that the resultant gels have a sharp pore size distribution, and the average pore diameter increases with increasing the amount of water and methanol. The coherent backscattering measured for the gels formed in between two slide glasses reveals that the transport mean free path of light decreases with decreasing the sizes of pores and skeletons. Pore size dependence of the scattering strength can be qualitatively explained by a Mie scattering calculation using a model in which spherical pores are randomly distributed in methylsiloxane matrix. The results indicate that the scattering strength can be tuned by controlling the sizes of the pores.

Inorganic-Organic Hybrid Hierarchically Structured Methyl-modified Silica Monoliths

ABSTRACTHighly porous inorganic-organic hybrid monoliths with mesopores in a macroporous network have been prepared from methyltris(2-hydroxyethoxy)silane (MeGMS) and tetrakis(2-hydroxyethoxy)silane (EGMS) in the presence of an amphiphilic block copolymer. The amount of methyltris(2-hydroxyethoxy)silane (MeGMS) in the gel has been varied from 0 to 100 %. These glycol-modified silanes have the advantage of being water-soluble and thus allowing for a direct templating of liquid-crystalline surfactant mesophases without the presence of a homogenizing organic solvent such as ethanol. The wet gels have been dried by supercritical extraction with carbon dioxide.In the present work, the sol-gel behaviour of these glycol-modified silanes is discussed especially with a focus on the formation of the meso- and macrostructure. In addition, the influences of the varying ratios of methyltris(2-hydroxyethoxy)silane on the structural features of the gels are investigated by various analytical techniques such as small angle X-ray scattering, nitrogen sorption, and scanning electron microscopy.

Leaching of anchored Rh and Pd species from thiourea-functionalized monolithic silica xerogel catalysts

Abstract Hybrid monoliths able to bind metal species were prepared by sol–gel method using different catalysts and solvents. Starting materials were the “double” thioureas 1,4-[(EtO) 3 Si(CH 2 ) 3 NHC(S)NH] 2 (C 6 H 4 ) (Siphen) and 1,12-[(EtO) 3 Si(CH 2 ) 3 NHC(S)NH] 2 (C 12 H 24 ) (SiC12). Rh(I) and Pd(II) species were anchored through sulphur co-ordination on the surface of the monoliths obtained from Siphen. In the case of Rh(I), anchored metal complexes were spectroscopically identified by FTIR microspectrometry. The metal leaching was determined in the hydroformylation (Rh) and hydrogenation (Pd) of styrene. The metal species present in reaction solutions were quantified using plasma atomic emission spectrometry.