Size-Exclusion "capture and release" separations using surface-patterned poly(N-isopropylacrylamide) hydrogels

Micrometer-scale poly(N-isopropylacrylamide) (poly-NIPAAm) hydrogel monolith patterns were fabricated on solid surfaces using soft lithography. At sufficiently high aspect ratios, the hydrogel monoliths swell and contract laterally with temperature. The spaces between the monoliths form a series of trenches that catch, hold, and release appropriately sized targets. A series of poly-NIPAAm monoliths were fabricated with dry dimensions of 40 microm height, 12 microm diameter, and a spacing of 12 microm between monoliths. Above the lower critical solution temperature (LCST), the monoliths collapse to their dry dimensions and the spacing between monoliths is 12 microm. Below the LCST, the monoliths swell by 70% in the lateral direction, reducing the gap size between monoliths to 3 microm. The potential use of the hydrogel monoliths as size-selective "catch and release" structures was demonstrated with a mixture of 6 and 20 microm polystyrene microspheres, where the 6 microm diameter particles were selectively concentrated and separated from the larger particles.     

Voltage-assisted capillary LC of peptides using monolithic capillary columns prepared by ring-opening metathesis polymerization

We examined the use of monolithic capillary columns prepared via ring-opening metathesis polymerization (ROMP) for peptide separation in voltage-assisted capillary LC (voltage-assisted CLC). In order to demonstrate their potential for peptide separation, ROMP-derived monoliths with RP properties were prepared. The preparation procedure of monoliths was transferred from ROMP monoliths optimized for CLC. ROMP monoliths were synthesized within the confines of 200 microm id fused-silica capillaries with a length of 37 cm. After optimization of the chromatographic conditions, the separation performance was tested using a well-defined set of artificial peptides as well as two peptidic mixtures resulting from a tryptic digest of BSA as well as a collagenase digest of collagen. ROMP monoliths showed comparable performance to other monolithic separation media in voltage-assisted CLC published so far. Therefore, we conclude that by optimizing the composition of the ROMP monoliths as well as by using the controlled manner of their functionalization, ROMP monoliths bear a great potential in CLC and CEC.     

Facile approach to glycidyl methacrylate-based polyHIPE monoliths with high epoxy-group content

This paper reports a facile approach to glycidyl methacrylate (GMA)-based polyHIPE monoliths with high epoxy-group content, which are fabricated using a high internal phase emulsion (HIPE) template via radiation-induced polymerization at room temperature. The effects of the polymerization temperature and the pore sizes of polyHIPE monoliths on the content of epoxy groups are investigated. Results show that the polymerization temperature is the most important factor in influencing the content of epoxy groups in GMA-based polyHIPE monoliths. To prove their superiority over monoliths with low epoxy-group contents, the as-prepared polyHIPE monoliths are applied in phenol removal from cigarette smoke through a reaction between the epoxy group and phenol. The results show that the higher the content of epoxy groups in the polyHIPE monoliths, the higher the rate of phenol removal, indicating their high performance in these specific applications for the polyHIPE monoliths with high epoxy-group contents.     

Silica Monolith for the Removal of Pollutants from Gas and Aqueous Phases

This study focused on the application of mesoporous silica monoliths for the removal of organic pollutants. The physico-chemical textural and surface properties of the monoliths were investigated. The homogeneity of the textural properties along the entire length of the monoliths was assessed, as well as the reproducibility of the synthesis method. The adsorption properties of the monoliths for gaseous toluene, as a model of Volatile Organic Compounds (VOCs), were evaluated and compared to those of a reference meso-structured silica powder (MCM-41) of commercial origin. Silica monoliths adsorbed comparable amounts of toluene with respect to MCM-41, with better performances at low pressure. Finally, considering their potential application in water phase, the adsorption properties of monoliths toward Rhodamine B, selected as a model molecule of water soluble pollutants, were studied together with their stability in water. After 24 h of contact, the silica monoliths were able to adsorb up to the 70% of 1.5 × 10⁻² mM Rhodamine B in water solution.     

Liquid-phase synthesis and application of monolithic porous materials based on organic–inorganic hybrid methylsiloxanes, crosslinked polymers and carbons

Our recent progress in porous materials based on organic–inorganic hybrids, organic crosslinked polymers, and carbons is summarized. Flexible aerogels and aerogel-like xerogels with the polymethylsilsesquioxane (PMSQ) composition are obtained using methyltrimethoxysilane (MTMS) as the sole precursor. Preparation process and the flexible mechanical properties of these aerogels/xerogels are overviewed. As the derivative materials, hierarchically macro- and mesoporous PMSQ monoliths and marshmallow-like soft and bendable porous monoliths prepared from dimethyldimethoxysilane /MTMS co-precursors have been obtained. Organic crosslinked polymer monoliths with well-defined macropores are also tailored using gelling systems of vinyl monomers under controlled/living radical polymerization. The obtained polymer monoliths are carbonized and activated into activated carbon monoliths with well-defined pore properties. The activated carbon monoliths exhibit good electrochemical properties as the monolithic electrode. Some possibilities of applications for these porous materials are also discussed.     

Polymer monoliths synthesized by radiation co-polymerization in solution

Hydrophilic co-polymer monoliths were prepared by irradiating alcoholic solutions containing diethyleneglycol dimethacrylate (DEGDMA) and 2-hydroxyethylacrylate (HEA) monomers. The effect of monomer ratio, solvent properties and radiation dose on the porous properties of the monoliths was studied in detail and compared to the monolith prepared from DEGDMA. Increase of the HEA content in the co-monomer mixture (up to 18 vol%) resulted in monoliths with increased pore size and hydrophilic character. The biggest pores were obtained when methanol was used as solvent.The use of the monoliths as chromatographic columns for separation of proteins, amino and nucleic acids is also reported.     

Sponge-nested polymer monoliths: Versatile materials for the solid-phase extraction of bisphenols

Polymer monoliths are promising materials for sample preparation due to their high porosity, pH stability, and simple preparation. The use of melamine formaldehyde foams has been reported as an effective support to prepare highly robust silica and polymer monoliths. Herein, divinylbenzene monoliths based on a 50:50 (%, w/w) crosslinker/porogen ratio have been nested within a melamine-formaldehyde sponge, resulting in monoliths with a surface area higher than 400 m²/g. The extraction performance of these monoliths was evaluated for the extraction of endocrine-disrupting bisphenols from aqueous solutions. We evaluated for the first time the versatility of sponge-nested polymer monoliths by comparing three different extraction modes (vortex mixing, magnetic stirring, and orbital shaking). Vortex mixing showed a comparable recovery of bisphenols (39%–81%) in a shorter extraction time (30 min, instead of 2 h). In addition, the robustness of the sponge-nested polymer monoliths was demonstrated for the first time by reshaping a larger monolithic cube (0.125 cm³) into four smaller pieces (4 × 0.03125 cm³) leading to a 16%–21% increase in extraction efficiency. This effect was attributed to an increase in the effective contact area with the sample, obtaining a higher analyte extraction capacity.     

Mutual consistency between simulated and measured pressure drops in silica monoliths based on geometrical parameters obtained by three-dimensional laser scanning confocal microscope observations

The geometrical properties of co-continuous macroporous silica monoliths have been studied by laser scanning confocal microscopy (LSCM) and a comparison has been made with those obtained by conventional mercury intrusion method. Tetrahedral skeleton model (TMS), which mimics the gel skeleton shape of monoliths, was compared with real monoliths in terms of macropore and porosity using the geometrical parameters extracted from the LSCM observations. Liquid flow behavior through the macroporous silica monoliths was examined in comparison with those simulated using TSM, based on the geometrical properties obtained from LSCM observations. Heterogeneity in macropore topology and connectivity in pores and skeletons are suggested to contribute to the improvement of the model structure for macroporous monoliths.     

Recent strategies to enhance the performance of polymer monoliths for analytical separations

This review summarizes recent developments made in the incorporation of functional materials into organic polymer monoliths, together with new monolithic forms and formats, which enhance their application as supports and stationary phase materials for sample preparation and chromatographic separations. While polymer monoliths are well‐known supports for the separation of large molecules, recent developments have been made to improve their features for the separation of small molecules. The selectivity and performance of organic polymer monoliths has been improved by the incorporation of different materials, such as metal‐organic frameworks, covalent organic frameworks, or other types of nanostructured materials (carbon nanohorns, nanodiamonds, polyoxometalates, layered double hydroxides, or attapulgite). The surface area of polymer monoliths has been significantly increased by polymer hypercrosslinking, resulting in increased efficiency when applied to the separation of small molecules. In addition, recent exploration of less conventional supports for casting polymer monoliths, including photonic fibres and 3D printed materials, has opened new avenues for the applications of polymer monoliths in the field of separation science. Recent developments made in these topics are covered, focusing on the strategies followed by the authors to prepare the polymer monoliths and the effect of these modifications on the developed analytical applications.     

Chiral silica-based monoliths in chromatography and capillary electrochromatography

Chiral-modified silica-based monoliths have become well-established stationary phases for both high performance liquid chromatography (HPLC) and capillary electrochromatography (CEC). The silica-based monoliths were fabricated either in situ in the capillaries for nano-HPLC and CEC or in a mould for “conventional” HPLC. The present review summarizes the chiral modification of silica monoliths and the recent development in the field of enantioselective separations by nano-HPLC and CEC.     

Hierarchically porous Fe_2O_3 /CuO composite monoliths:Synthesis and characterization

In this paper,hierarchically porous Fe2O3 /CuO composite monoliths were first successfully synthesized by a mild method using silica monoliths as templates.The structure of composite monoliths was characterized by X-ray diffraction,scanning electron microscopy,nitrogen adsorption-desorption.The results indicated that the molar ratio of Fe to Cu had a great influence on the crystal phase of Fe2O3,pore size and the structure of the macroporous wall.The Fe2O3 /CuO composite monoliths consist of hierarchically macroporous and mesoporous structure,while the sample with the Fe/Cu molar ratio of 2:1 possesses tighter wall structure than other samples.It is expected that asprepared Fe2O3/CuO composite monoliths have potential applications in several fields as catalysts,catalyst supports,chemical sensors and high-performance liquid chromatography (HPLC).     

Synthesis and theoretical study of molecularly imprinted monoliths for HPLC

Molecularly imprinted monoliths integrate the high permeability of monolithic materials and the high selectivity and affinity of molecularly imprinted polymers (MIP). Thus, in recent years, development of this novel MIP format in HPLC has expanded quickly, particularly use of organic materials. This review focuses on the principal aspects of good practice in polymerization, theoretical studies, and recent developments in molecularly imprinted monoliths. Some thoughts on perspectives of MIP monoliths are also expressed.     

Affinity chromatography with monolithic capillary columns. II. Polymethacrylate monoliths with immobilized lectins for the separation of glycoconjugates by nano-liquid affinity chromatography

Monolithic capillary columns with surface bound lectin affinity ligands were introduced for performing lectin affinity chromatography (LAC) by nano-liquid chromatography (nano-LC). Two kinds of polymethacrylate monoliths were prepared, namely poly(glycidyl methacrylateco-ethylene dimethacrylate) and poly(glycidyl methacrylate-co-ethylene dimethacrylate-co-[2-(methacryloyloxy)ethyl]trimethyl ammonium chloride) to yield neutral and cationic macroporous polymer, respectively. Two lectins including concanavalin (Con A) and wheat germ agglutinin (WGA) were immobilized onto the monolithic capillary columns. The neutral monoliths with immobilized lectins exhibited lower permeability under pressure driven flow than the cationic monoliths indicating that the latter had wider flow-through pores than the former. Both types of monoliths with immobilized lectins exhibited strong affinity toward particular glycoproteins and their oligosaccharide chains (i.e., glycans) having sugar sequences recognizable by the lectin. Due to the strong binding affinity, the monoliths with surface bound lectins allowed the injection of relatively large volume (i.e., several column volumes) of dilute samples of glycoproteins and glycans thus allowing the concentration of the glycoconjugates and their subsequent isolation and detection at low levels (approximately 10(-8) M). To further exploit the lectin monoliths in the isolation of glycoconjugates, two-dimensional separation schemes involving LAC in the first dimension and reversed-phase nano-LC in the second dimension were introduced. The various interrelated methods established in this investigation are expected to play a major role in advancing the sciences of "nano-glycomics".     

UV-LED photopolymerised monoliths

For the first time photopolymerisation of polymer monoliths has been realised with UV-light emitting diodes (LEDs) as light source and demonstrated with polymethacrylate monoliths created in fused silica capillaries and plastic chips.     

Hierarchically porous Fe2O3/CuO composite monoliths: Synthesis and characterization

In this paper, hierarchically porous Fe2O3/CuO composite monoliths were first successfully synthesized by a mild method using silica monoliths as templates. The structure of composite monoliths was characterized by X-ray diffraction, scanning electron microscopy, nitrogen adsorption-desorption. The results indicated that the molar ratio of Fe to Cu had a great influence on the crystal phase of Fe2O3, pore size and the structure of the macroporous wall. The Fe2O3/CuO composite monoliths consist of hierarchically macroporous and mesoporous structure, while the sample with the Fe/Cu molar ratio of 2 : 1 possesses tighter wall structure than other samples. It is expected that as-prepared Fe2O3/CuO composite monoliths have potential applications in several fields as catalysts, catalyst supports, chemical sensors and high-performance liquid chromatography (HPLC).     

Hydrophobic polymer monoliths as novel phase separators: Application in continuous liquid–liquid extraction systems

Hydrophobic macroporous polymer monoliths are shown to be interesting materials for the construction of “selective solvent gates”. With the appropriate surface chemistry and porous properties the monoliths can be made permeable only for apolar organic solvents and not for water. Different poly(butyl methacrylate-co-ethylene dimethacrylate) (BMA-EDMA) and poly(styrene-co-divinylbenzene) (PS-DVB) monoliths prepared with tailored chemistries and porosities were evaluated for this purpose. After extensive characterization, the PS-DVB monoliths were selected due to their higher hydrophobicity and their more suitable flow characteristics. BMA-EDMA monoliths are preferred for mid-polarity solvents such as ethyl acetate, for which they provide efficient separation from water. Breakthrough experiments confirmed that the pressures necessary to generate flow of organic solvents through PS-DVB monoliths were substantially lower than for water. A phase separator was constructed using the monoliths as the flow selector. This device was successfully coupled on-line with a chip-based continuous liquid–liquid-extraction (LLE) system with segmented flow. Efficient separation of different solvents was obtained across a wide range of flow rates (0.5–4.0 mL min⁻¹) and aqueous-to-organic flow ratios (β = 1–10). Good robustness and long life-time were also confirmed. The suitability of the device to perform simple, cheap, and reliable phase separation in a continuous LLE system prior to gas-chromatographic analysis was proven for some selected real-life applications.     

Specially Treated Aramid Fiber Stabilized Gel‐Emulsions: Preparation of Porous Polymeric Monoliths and Highly Efficient Removing of Airborne HCHO

Porous polymeric monoliths with densities as low as ≈0.060 g cm⁻³ are prepared in a gel‐emulsion template way, of which the stabilizer employed is a newly discovered acidified aramid fiber that is so efficient that 0.05% (w/v, accounts for continuous phase) is enough to gel the system. The porous monoliths as obtained can be dried at ambient conditions, avoiding energy‐consuming processes. Importantly, the monoliths show selective adsorption to HCHO, and the corresponding adsorption capacity ( M6 ) is ≈2700 mg g⁻¹, the best result that is reported until now. More importantly, the monoliths can be reused after drying.     

Addition of N-carbobenzyloxy-L-tryptophan as a co-template molecule to molecularly imprinted polymer monoliths for (+)-nilvadipine

Molecularly imprinted polymer (MIP) monoliths for (+)-nilvadipine have been prepared using 4-vinylpyridine as a functional monomer and toluene/1-dodecanol as a porogen without or with addition of N-carbobenzyloxy-L-tryptophan (Cbz-L-Trp) as a co-template molecule. The MIP monoliths prepared with (+)-nilvadipine as a sole template molecule had no macro through-pores, while those could be formed by addition of Cbz-L-Trp as the co-template molecule. Furthermore, on the former nilvadipine enantiomers could not be separated, but on the latter they could. The presence of Cbz-L-Trp affected the polymerization process and resulted in forming macro through-pores of the MIP monoliths for (+)-nilvadipine and attaining separation of nilvadipine enantiomers. These results suggest that co-addition of Cbz-L-Trp could be effective for preparing MIP monoliths for (+)-nilvadipine, whose preparation is difficult.     

SYNTHESIS OF MACROPOROUS POLYACRYLAMIDE AND POLY(NISOPROPYLACRYLAMIDE) MONOLITHS VIA FRONTAL POLYMERIZATION AND INVESTIGATION OF PORE STRUCTURE VARIATION OF MONOLITHS

A novelty method,frontal polymerization(FP),was employed to directly produce a series of polyacrylamide (PAM),poly(N-isopropylacrylamide)(PNIPAM) and acrylamide-N-isopropylacrylamide copolymer macroporous monoliths. Field emission scanning electronic microscope and mercury intrusion method were adopted to measure some parameters of these monoliths,such as frame,pore size distribution as well as porosity.Effects of types of monomer,thicker and surfactant on porous structure of monoliths were studied.A var...