Macroporous Monolithic Materials Research Articles

Pickering medium internal phase emulsions based on natural clay particles: Route to a macroporous adsorbent

We synthesized oil-in-water Pickering medium internal phase emulsions (MIPEs) based on (1) natural, unmodified montmorillonite (MMT) nanoparticles as a stabilizer; (2) a trace quantity of Tween-20 (T-20) as a co-stabilizer; and (3) eco-friendly flaxseed oil as the continuous phase. We modulated the stability, rheological properties, and droplet size of the emulsion by adjusting the MMT concentration, Tween-20 concentration, and oil phase volume fraction. We used these emulsions as templates to prepare a macroporous monolithic adsorbent [poly (carboxymethylcellulose-g-acrylamide); PCAM] with a hierarchical pore structure and excellent connectivity that approximates materials derived from Pickering high internal phase emulsions (HIPEs). Even when we decreased the internal phase volume fraction to 30%, there were still interconnecting pores in the material. Compared with Pickering HIPEs, our approach reduced the oil phase volume fraction substantially (approximately 45%), which lowered the production cost of the emulsion. Our Pickering MIPE-derived macroporous monolithic material effectively adsorbed cationic dyes (methyl violet and methylene blue) from water. Our environmentally friendly method of preparing Pickering MIPEs will enable researchers to prepare absorbents with an excellent hierarchical pore structure, which will facilitate rapid mass transport and increased greater specific surface area.

Fabrication of lanthanum and nitrogen – co-doped SrTiO3 – TiO2 heterostructured macroporous monolithic materials for photocatalytic degradation of organic dyes under visible light

Herein, we demonstrate a facile way of fabricating visible-light-active lanthanum and nitrogen – co-doped SrTiO3 – TiO2 heterostructured macroporous monolithic materials with bicontinuous morphology by impregnating strontium and lanthanum ions into a preformed porous TiO2 gel in aqeuous solution containing urea followed by heat treatment in NH3 atmosphere. The SrTiO3 macroporous monolithic materials were formed by a solid-state reaction between the TiO2 gel phase and precipitated SrCO3, while Sr2+ was partially substituted with La3+ ions. The SrCO3 was precipitated within the TiO2 wet gel by the reaction between impregnated Sr2+ and CO2, which was produced by hydrolysis and decarbonation of a chelating agent in the TiO2 wet gels and by hydrolysis of urea at 60 °C. X-ray powder diffraction studies showed that the incorporation of strontium, lanthanum, and nitrogen could effectively retard the phase transformation of TiO2 from anatase to rutile and growth of crystallites. XPS analysis confirmed that lanthanum atoms were incorporated into the SrTiO3 lattice by substituting strontium atoms, and nitrogen was incorporated in the TiO2 lattice (i) substitutionally forming Ti – N-bonds and (ii) interstitially. The resultant lanthanum and nitrogen – co-doped SrTiO3 - TiO2 heterostructured monolithic materials retained a narrow macropore size distribution at the diameter ∼1.7 μm.

Synthesis of macroporous monolithic materials from a waste renewable source

ABSTRACTInterconnected porous monolithic materials can be directly obtained from non‐templating methods by reacting raw Kraft black liquor with epichlorohydrin either in the presence or not of surfactant, whereas extracted lignin leads to non‐porous materials. In the presence of a surfactant, micelles organization takes place and porosity of 40–60% can be achieved. Without surfactant, chemically induced phase separation occurs, giving materials with agglomerated nodules morphology. Carbonization followed by activation with CO2 yield monolithic micro/mesoporous carbons with surface area of 300 m2 g−1. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41215.

Exfoliation of Graphite Oxide in Water without Sonication: Bridging Length Scales from Nanosheets to Macroscopic Materials

Dispersed graphene oxide (GO) nanosheets in water were synthesized via a new approach involving sonication-free exfoliation, as promoted by repetitive simple freeze–thaw cycles. These cycles consist of rapid freezing of an aqueous solution containing graphite oxide and subsequent thawing of the resultant solid. This approach is effective for exfoliation of graphite oxide and yields approximately 80% GO after six repetitive freeze–thaw cycles. The GO synthesized by the new method experiences minimal fragmentation during the exfoliation process and has a lateral size at least 3-fold larger than that of GO prepared by using sonication, as evidenced by atomic force microscopy and dynamic light scattering. We also demonstrate use of the resulting exfoliated GO that is synthesized using this approach as a building block for the synthesis of a low-density (≈0.02 g cm–3) macroporous monolithic material, using directional freezing, which forms ice rods within the solution that served as the template to direct the assembly of the solution-dispersed GO nanosheets into a honeycomb-like morphology with a 10 μm macropore opening and sheet-like walls. Such a unique morphology of the synthesized monolith has broad applicability for advanced functional materials that allow extremely high throughput with minimal pressure drop as well as electronic and energy storage materials.

Degradation of polyribonucleotides: biocatalysis and the monitoring of products

Macroporous monolithic material containing covalently linked ribonuclease A was used to create high-performance flow heterogeneous biocatalysts (bioreactors). The kinetic parameters of the degradation of polycytidylic acid were identified, and the properties of the obtained systems were compared. A HPLC method has been developed for monitoring products of biocatalytic degradation of RNA, and the possibility of using biocatalytic and HPLC columns in RNA degradation processes in a multicomponent mixture of biological molecules was shown.

Synthesis of porous emulsion‐templated monoliths from a pulp mill by‐product

AbstractBlack liquor is a by‐product of the paper mill Kraft process that deserves more valorization than its present use as low‐grade fuel. In this work, we present an original approach allowing the preparation of macroporous interconnected monolithic materials using as‐received black liquor as main raw material. The process involves the formulation of an oil‐in‐water medium internal phase emulsion as soft templating porosity medium. The oil (internal phase) used is castor oil, whereas the continuous phase is constituted of black liquor containing a hydrophilic surfactant and epichlorohydrin as lignin crosslinking agent. Due to the high viscosity of the system, a specially designed emulsifying device was employed. The proper choices of the surfactant and emulsification conditions allow obtaining cellular biopolymers with almost monodisperse, interconnected void structure and satisfactory mechanical properties. These innovative results are promising for the future development of fully bio‐based emulsion‐derived materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Monolithic polymeric sorbents for high-performance chromatography of synthetic polymers

A number of macroporous monolithic materials based on copolymers of butyl methacrylate or lauryl methacrylate with ethylene glycol dimethacrylate is obtained via thermal free-radical polymerization. The effect of polymerization conditions on pore parameters of the synthesized sorbents is studied. Polymer stationary phases obtained for the efficient analysis of synthetic polymers are tested for the separation of a multicomponent mixture containing polystyrene samples of various molecular masses.

Facile preparation of macroporous graphitized carbon monoliths from iron-containing resorcinol–formaldehyde gels

In this report, we demonstrate the facile preparation of macroporous monolithic materials based on graphitized carbon by utilizing catalytic graphitization at relatively low temperature (1000°C). The precursor polymer, macroporous resorcinol–formaldehyde (RF) xerogel, can be obtained without any surfactants or polymeric additives in water/ethanol mixed solvent via the sol–gel reaction accompanied by phase separation. The use of iron chloride as an acid catalyst for polymerization provides the RF monoliths incorporated with Fe, which catalyzes the graphitization. The effects of the starting composition on the morphologies of the resultant RF gels and the characteristics of the graphitized carbon monoliths have been discussed.

Activated carbons and carbon-containing poly(vinyl alcohol) cryogels: characterization, protein adsorption and possibility of myoglobin clearance

Adsorption of myoglobin (Mb), bovine serum albumin (BSA) and γ-globulin (GG) onto activated carbons (ACs) with different pore size distributions, and poly(vinyl alcohol) (PVA) monolithic cryogels containing AC particles was studied. The highest initial rate of Mb adsorption was observed for AC having the largest specific surface area (1939 m(2) g(-1)) and pore volume (1.82 cm(3) g(-1)). The adsorption kinetics of proteins was characterized by a bimodal shape of the distribution f(D) function of an effective diffusion coefficient. Adsorption isotherms of Mb and GG were of Freundlich type within the studied range of equilibrium concentrations (10-150 μg mL(-1)). The distributions of free energy of protein adsorption were bimodal and reflected both interactions with carbon surfaces and self-association of proteins. Adsorbed amounts of Mb were the highest among the proteins studied (up to 700 mg g(-1) carbon), which was attributed to the higher fraction of pores accessible for Mb. Incorporation of carbon particles into PVA-based cryogel resulted in macroporous monolithic composite materials (AC-PVA) exhibiting good flow-through properties. Scanning electron microscopy of the composites showed macroporous aggregates of carbon particles held together by films and bridges of PVA. The rates of adsorption and adsorbed amounts of proteins on AC-PVA were reduced compared to the pristine carbon and depended on the carbon content in the composites. Nevertheless, adsorption of Mb on AC-PVA took place even in the presence of 500-fold higher concentration of BSA. This indicated a possibility of Mb clearance from blood plasma using the PVA-carbon monoliths.

Molecularly imprinted macroporous monolithic materials for protein recognition

Abstract Synthetic materials that can specifically recognize proteins will find wide application in many fields. In this report, bovine serum albumin was chosen as the template protein. Acrylamide and N,N′-methylenebisacrylamide were employed as the functional and cross-linker monomers, respectively. Molecularly imprinted macroporous monolithic materials that can preferentially bind the template protein in an aqueous environment were prepared by combination of molecular imprinting technique and freezing/thawing preparation method. The resulted imprinted macroporous monolithic columns were evaluated by utilizing as stationary phase in high performance liquid chromatography and solid-phase extraction materials. The experimental results indicated that the imprinted macroporous monolithic column exhibited good recognition for template protein, as compared with the control protein (hemoglobin), whereas the non-imprinted polymer (prepared under the same conditions except without addition template protein) had no selective properties.

Hydrophilic methacrylate monoliths as platforms for protein microarray

Hydrophilic macroporous monolithic materials based on a copolymer of 2-hydroxyethyl methacrylate with glycerol dimethacrylate was synthesized by photo-initiated free-radical polymerization of monomers in a presence of the low molecular mass porogens, such as cyclohexanol, dodecanol, toluene and heptane, as well as the solutions of hydrophobic polymers, namely, polystyrene of different molecular weights and concentrations in toluene, and poly(dimethyl siloxane) in heptane. The Hildebrand solubility parameters were used to predict the diluent-polymer compatibility. Pore size distribution and surface area characterization have been assessed by mercury intrusion porosimetry; scanning electron microscopy was used to evaluate the differences in macroporous morphology obtained with different porogenic agents. The monolithic materials were covalently attached to a glass surface directly at polymerization step. Monolithic layers were applied as platforms for microarrays to accomplish highly sensitive solid-phase protein analysis. The efficiency of developed microarrays was demonstrated using mouse IgG and goat anti-mouse IgG as a model affinity pair.

Methacrylate-based monolithic layers for planar chromatography of polymers

A series of macroporous monolithic methacrylate-based materials was synthesized by in situ free radical UV-initiated copolymerization of functional monomers, such as glycidyl methacrylate (GMA), butyl methacrylate (BuMA), 2-aminoethyl methacrylate (AEMA), 2-hydroxyethyl methacrylate (HEMA) and 2-cyanoethyl methacrylate (CEMA), with crosslinking agent, namely, ethylene glycol dimethacrylate (EDMA). The materials obtained were applied as the stationary phases in simple and robust technique – planar chromatography (PLC). The method of separation layer fabrication representing macroporous polymer monolith bound to the specially prepared glass surface was developed and optimized. The GMA–EDMA and BuMA–EDMA matrixes were successfully applied for the separation of low molecular weight compounds (the mixture of several dies), as well as poly(vinylpyrrolidone) and polystyrene homopolymers of different molecular weights using reversed-phase mechanism. The materials based on copolymers AEMA–HEMA–EDMA and CEMA–HEMA–EDMA were used for normal-phase PLC separation of 2,4-dinitrophenyl amino acids and polystyrene standards.

Macroporous Monolithic Polymers: Preparation and Applications

In the last years, macroporous monolithic materials have been introduced as a new and useful generation of polymers used in different fields. These polymers may be prepared in a simple way from a homogenous mixture into a mold and contain large interconnected pores or channels allowing for high flow rates at moderate pressures. Due to their porous characteristics, they could be used in different processes, such as stationary phases for different types of chromatography, high-throughput bioreactors and in microfluidic chip applications. This review reports the contributions of several groups working in the preparation of different macroporous monoliths and their modification by immobilization of specific ligands on the products for specific purposes.

Thermally induced dissolution/precipitation – A simple approach for the preparation of macroporous monoliths from linear aliphatic polyamides

A versatile way of preparing macroporous monolithic materials from linear aliphatic polyamides is presented. Simply, polyamide pellets were treated in benzyl alcohol (BA) at elevated temperature, causing dissolution by interchain hydrogen bond disruption. Subsequent cooling below the upper critical solution temperature (UCST) resulted in precipitation and partial restoration of the semicrystalline polymer, which is organized into network structures. The final steps were a solvent exchange of BA for methanol, followed by drying to form monolithic entities. A number of polyamides ranging from hydrophilic to hydrophobic were tested and under the experimental conditions, poly(1-aza-2-cycloheptanone (PA6) and (poly-[imino-1,6-hexanediylimino{1,10-dioxo-1,10-decanediyl}] (PA610) yielded entities with macroporous properties that were deemed useful for liquid chromatography. The morphological features and porous properties of the monoliths produced by this dissolution-precipitation procedure were studied by scanning electron microscopy, adsorption/desorption of N(2)(g) according to the Brunauer-Emmett-Teller (BET) principle, and mercury intrusion porosimetry. Degradation of the polymer backbone was noticeable when the dissolution time was extended and shortening of the polymer chains was confirmed by MALDI-MS, viscosity measurements, X-ray photoelectron spectroscopy (XPS), and potentiometric titration. When the heating was limited to the time it took to dissolve the polymers, mechanically stable monoliths could be obtained. The dissolution/heat treatment time further seemed to be useful for controlling the macroporous morphology.

Preparation and characterization of sizable macroporous epoxy resin‐based monolithic supports for flow‐through systems

This paper presents further results from our efforts to prepare sizable macroporous monolithic materials from epoxy resins and polyamines by emulsion polymerization. For their uses as supports in flow systems, the study aimed at developing materials possessing maximum fluid permeability, high mechanical stability, and a controlled porosity and surface area. Characterization of the materials has been carried out using different techniques, focusing on morphological and mechanical features, and on the surface chemistry. Morphology and porosity were studied with SEM, nitrogen adsorption/desorption, mercury intrusion porosimetry (MIP), and (2)H NMR cryoporosimetry. The chemical composition of the bulk structures and their surfaces was studied by means of bulk elemental analysis and X-ray photoelectron spectroscopy, and potentiometric titration was used to assess the relative amounts of amines and epoxy groups. Essentially, the morphological features were a high fluid permeability, but rather low specific surface area. Convective flow was facilitated by large, interconnected, and evenly spaced macropores which were formed by nonporous skeletons of the connected-rod type. Despite the interfacial nature of the polymerization, the bulk and the surface of the fully cured materials showed similar elemental compositions. All materials were found to have a high surface density of hydroxyl groups, which facilitates functionalization reactions.

New platforms for 3-D microarrays: Synthesis of hydrophilic polymethacrylate monoliths using macromolecular porogens

Hydrophilic macroporous monolithic material based on poly(glycidyl methacrylate-co-glycerol dimethacrylate) was synthesized by photo-initiated free-radical polymerization. Different pore-forming agents, including low molecular mass cyclohexanol and dodecanol, as well as the solutions of hydrophobic polymers, namely, polystyrene in toluene and poly(dimethyl siloxane) in hexane, were used to obtain the macroporous polymer platforms intended for new type of 3-D microarrays (biochips). The porous characteristics of functional copolymers obtained were investigated by mercury intrusion porosimetry and scanning electron microscopy. Some of developed materials were tested for protein microarray construction. Demonstration of potential of suggested materials, as well as optimization of protein covalent immobilization conditions, were realized using model mouse IgG – goat anti-mouse IgG affinity pair.

Synthesis and investigation of a new macroporous monolithic material based on an N‐hydroxyphthalimide ester of acrylic acid‐co‐glycidyl methacrylate‐co‐ethylene dimethacrylate terpolymer

AbstractA macroporous monolithic material based on an N‐hydroxyphthalimide ester of acrylic acid‐co‐glycidyl methacrylate‐co‐ethylene dimethacrylate terpolymer was synthesized by photoinitiated free‐radical polymerization. Several porogenic solvents, such as cyclohexanol, dodecanol, and poly(ethylene glycol)s, were tested to obtain the monolithic material with an optimal pore size allowing unrestricted penetration of large molecule (proteins) into a three‐dimensional porous space. The new monolithic material was covalently bound to an inert surface (glass) directly in the polymerization step, and it was suggested as a solid matrix for the development of new types of three‐dimensional protein microarrays (biochips). A demonstration of the potential of the suggested microarray platform as well as optimization of microarray performance conditions was realized with a model mouse immunoglobulin G/goat anti‐mouse immunoglobulin G affinity pair. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Preparation of macroporous methacrylate monolithic material with convective flow properties for bioseparation: Investigating the kinetics of pore formation and hydrodynamic performance

The preparation of macroporous methacrylate monolithic material with controlled pore structures can be carried out in an unstirred mould through careful and precise control of the polymerisation kinetics and parameters. Contemporary synthesis conditions of methacrylate monolithic polymers are based on existing polymerisation schemes without an in-depth understanding of the dynamics of pore structure and formation. This leads to poor performance in polymer usage thereby affecting final product recovery and purity, retention time, productivity and process economics. The unique porosity of methacrylate monolithic polymer which propels its usage in many industrial applications can be controlled easily during its preparation. Control of the kinetics of the overall process through changes in reaction time, temperature and overall composition such as cross-linker and initiator contents allow the fine tuning of the macroporous structure and provide an understanding of the mechanism of pore formation within the unstirred mould. The significant effect of temperature of the reaction kinetics serves as an effectual means to control and optimise the pore structure and allows the preparation of polymers with different pore size distributions from the same composition of the polymerisation mixture. Increasing the concentration of the cross-linking monomer affects the composition of the final monoliths and also decreases the average pore size as a result of pre-mature formation of highly cross-linked globules with a reduced propensity to coalesce. The choice and concentration of porogen solvent is also imperative. Different porogens and porogen mixtures present different pore structure output. Example, larger pores are obtained in a poor solvent due to early phase separation.