Preparation Of Monoliths Research Articles

Lightweight and strong exfoliated graphite/polyvinyl alcohol monoliths with highly thermo/electro conductivity for advanced thermal/EMI management

Preparation of lightweight polymer monoliths with highly thermo/electro conductivity for advanced thermal/electromagnetic interference (EMI) management in high-integrated and weight-sensitive electronics remains pending challenges. Here, lightweight porous exfoliated graphite/polyvinyl alcohol (EG/PVA) monoliths with locally layered structure are fabricated via a hypergravity induced self-assembly method (HGSA). Owing to the HGSA method resulting in formation of multiply robust EG networks, the monoliths show an exceptional thermal conductivity of 2.42–8.45 W/mK and a high electrical conductivity of 8.16–230.40 S/m at low density of 0.28–0.64 g/cm3, thus endowing itself with remarkable thermal/EMI management capability. To the best of our knowledge, this is probably first time to achieve high thermal conductivity (>5 W/mK) into porous polymer composites with such low density. Besides, an impressive specific compression modulus of 338.2–689.4 MPa cm3/g is achieved in the monoliths, which is basically comparable to most carbon foams after heat treatment. The results we provided in this research open new possibilities for fabricating lightweight polymer composites with multiple functions for advanced thermal/EMI management.

Preparation of composite monoliths of quaternized chitosan and diatom earth for protein separation.

In this study, composite monoliths with porous structures were prepared using quaternized chitosan and diatom earth for protein separation. Quaternized chitosan (N-[(2-hydroxy-3-trimethylammonium)propyl] chitosan chloride) dissolved in water was mixed with diatom earth and crosslinked with glutaraldehyde under low-temperature conditions to form a cryogel. Interconnected porous monoliths were obtained after removing ice crystals from the cryogel. The monoliths adsorbed bovine serum albumin selectively from the solution mixture of bovine serum albumin and bovine ɤ-globulin, and bovine ɤ-globulin was recovered in the flow-through fraction. The adsorption selectivity was enhanced by changing the solution pH from 6.8 to 5.5. The adsorption of bovine serum albumin by the monolith was replicated at least five times following its washing with a buffer containing 400mM NaCl and subsequent regeneration with a 10mM acetate buffer. The composited monolith is a promising adsorbent for the removal of acidic proteins, such as serum albumin contamination in neutral proteins, for example, ɤ-globulins, in bioproduction processes.

Enabling Solution Processable COFs through Suppression of Precipitation during Solvothermal Synthesis.

Covalent organic frameworks (COFs) are crystalline, nanoporous materials of interest for various applications, but current COF synthetic routes lead to insoluble aggregates which precludes processing for practical implementation. Here, we report a COF synthesis method that produces a stable, homogeneous suspension of crystalline COF nanoparticles that enables the preparation of COF monoliths, membranes, and films using conventional solution-processing techniques. Our approach involves the use of a polar solvent, diacid catalyst, and slow reagent mixing procedure at elevated temperatures which altogether enable access to crystalline COF nanoparticle suspension that does not aggregate or precipitate when kept at elevated temperatures. On cooling, the suspension undergoes a thermoreversible gelation transition to produce crystalline and highly porous COF materials. We further show that the modified synthesis approach is compatible with various COF chemistries, including both large- and small-pore imine COFs, hydrazone-linked COFs, and COFs with rhombic and hexagonal topologies, and in each case, we demonstrate that the final product has excellent crystallinity and porosity. The final materials contain both micro- and macropores, and the total porosity can be tuned through variation of sample annealing. Dynamic light scattering measurements reveal the presence of COF nanoparticles that grow with time at room temperature, transitioning from a homogeneous suspension to a gel. Finally, we prepare imine COF membranes and measure their rejection of polyethylene glycol (PEG) polymers and oligomers, and these measurements exhibit size-dependent rejection and adsorption of PEG solutes. This work demonstrates a versatile processing strategy to create crystalline and porous COF materials using solution-processing techniques and will greatly advance the development of COFs for various applications.

Treating Waste with Waste: Facile Preparation of Elastic Thermoplastic Polyurethane Monolith for Efficient Oil/Water Separation

Abstract An auspicious thermoplastic polyurethane (TPU) monolith has been prepared by a facile and cost-effective method of thermally induced phase separation (TIPS). With superb porous structure, excellent hydrophobicity/oleophilicity, and superior elasticity, the obtained TPU monolith exhibits an outstanding adsorption capacity, high oil/water separation efficiency, and good recycling performance, achieving the goal of treating waste with waste.

Preparation of nickel-chelated iminodiacetate-functionalized macroporous agarose monolith using modular and clickable building blocks for affinity separation of histidine-tagged recombinant proteins

Selective separation and purification of protein from complex medium is required to completely investigate the structure and function of the target protein. In this study, a composite macroporous agarose monolith containing iminodiacetate-chelated Ni2+ ligands was synthesized for selective separation and purification of histidine-tagged recombinant proteins. The large and interconnected pores in the monolith enabled fast binding of proteins with high matrix tolerance in treating complex mediums. To realize the selective protein binding, the iminodiacetate was directly conjugated to epoxy-functionalized agarose monolith via simple chemical reactions between epoxy and imino groups. After chelated Ni2+, the composite monolith could bind histidine-tagged recombinant proteins through the coordination interaction between transition metal ions and the imidazole ring of histidine. To further increase the binding capacities of the monolith, a hydrophilic intermediate polymer chain containing multiple iminodiacetate immobilization sites was conjugated to the azide-functionalized agarose monolith via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The morphology and chemical composition of the composite agarose monolith were characterized systematically. The protein binding capacities of the obtained composite agarose monolith were subsequently investigated. The binding capacities of the composite agarose monolith towards the model proteins Gp10 and Lys84 were 0.93 and 0.51 mg/mL, respectively. The protein binding of the composite agarose monolith could be manipulated by adjusting the temperature and concentrations of imidazole. These results demonstrate that the composite agarose monolith could be used as an affinity medium for rapid separation and purification of histidine-tagged recombinant proteins from biological samples.

Rapid fabrication of zwitterionic sulfobetaine vinylimidazole-based monoliths via photoinitiated copolymerization for hydrophilic interaction chromatography

Zwitterionic sulfobetaine-based monolithic stationary phases have attracted increasing attention for their use in hydrophilic interaction chromatography. In this study, a novel hydrophilic polymeric monolith was fabricated through photo-initiated copolymerization of 3-(3-vinyl-1-imidazolio)-1-propanesulfonate (SBVI) with pentaerythritol triacrylate using methanol and tetrahydrofuran as the porogenic system. Notably, the duration for the preparation of this novel monolith was as little as 5 min, which was significantly shorter than that required for previously reported sulfobetaine-based monoliths prepared via conventional thermally initiated copolymerization. Moreover, these monoliths showed good morphology, permeability, porosity (62.4%), mechanical strength (over 15 MPa), column efficiency (51,230 plates/m), and reproducibility (relative standard deviations for all analytes were lower than 4.6%). Mechanistic studies indicated that strong hydrophilic and negative electrostatic interactions might be responsible for the retention of polar analytes on the zwitterionic SBVI-based monolith. In particular, the resulting monolith exhibited good anti-protein adhesion ability and low nonspecific protein adsorption. These excellent features seem to favor its application in bioanalysis. Therefore, the novel zwitterionic sulfobetaine-based monolith was successfully employed for the highly selective separation of small bioactive compounds and the efficient enrichment of N-glycopeptides from complex samples. In this study, we prepared a novel zwitterionic sulfobetaine-based monolith with good performance and developed a simpler and faster method for preparation of zwitterionic monoliths.

Hydrophilic macroporous monoliths with tunable water uptake capacity fabricated by water‐in‐oil high internal phase emulsion templating

AbstractIn this contribution, a series of well‐defined amphiphilic di‐block copolymers poly(ethylene oxide)‐b‐polystyrene (PEO43‐b‐PSx) with different PS segment lengths of x = 41, 78, and 130 units were synthesized through activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP). The as‐prepared block copolymers successfully stabilized the water‐in‐oil (W/O) high internal phase emulsions (HIPEs) containing pH responsive monomers 2‐(dimethylamino)ethyl methacrylate (DMAEMA) and 2‐(diethylamino)ethyl methacrylate (DEAEMA). The effect of macro‐surfactant loading, PS segment length, and DMAEMA/DEAEMA content on the stability of HIPEs and the corresponding polyHIPE structure were investigated. Results show that the average void size of polyHIPE decreases with the increase of surfactant concentration. Macroporous morphologies with closed‐cell or open‐cell can be manipulated by surfactant loading as well. The openness of polyHIPE decreases as the increase in hydrophobic PS segment length. Compared to DMAEMA containing HIPE systems, stable DEAEMA containing HIPEs are more easily obtained by using the as‐prepared macro‐surfactant. Stable HIPE with a relatively large amount of DEAEMA, up to 70 vol% of oil‐phase has been achieved. The obtained PDEAEMA‐co‐PS polyHIPEs derived from 0.116 mol% PEO43‐b‐PS41 stabilized emulsion templates show pH responsiveness towards water absorption and the highest acidic water uptake capacity can be up to 6.6 times its weight at equilibrium state. This work paves the way for the preparation of hydrophilic macroporous monolith from stable W/O HIPE template, and confirms the strength of macro‐surfactant in such an approach.

Facile Preparation of Porous Low Density Polyethylene Monolith for Efficient Oil/Water Separation

Abstract A promising porous low-density polyethylene (LDPE) monolith has been successfully prepared for the first time via a facile thermally induced phase separation (TIPS) method, followed by vacuum drying. The obtained LDPE monolith, with excellent hydrophobicity, shows highly efficient and selective adsorption of oil from oil/water mixtures including oil-in-water emulsion.

Preparation of lignin-based carbon foam monoliths with high strength and developed micrometer-sized cell/nano-sized porous structures using a self-bubbling method

Lignin is an attractive renewable feedstock used for the production of carbon materials because of its abundance and high carbon content. This work aims to explore a scalable technology to produce carbon foams from lignin. A lignin self-bubbling method has been developed in this study using zinc chloride as the catalyst for the thermal decomposition of lignin, resole as a cross-linking agent and a surfactant as the foaming assistant agent. The effects of dosage of zinc chloride and resole, type and dosage of surfactant, foaming temperature, heat treatment on the structure and properties of the materials have been investigated. The results show that the structure and properties of the resultant lignin-based carbon foams without any fractures is highly tunable depending on the amount of zinc chloride, resole and surfactants used, the foaming temperature in the self-bubbling process and post-heat treatment step. It is found that the non-ionic surfactant Tween-80 can significantly improve the mechanical strength and porosity of monolithic lignin-based carbon foams. The lignin-based carbon foams prepared using a self-bubbling method under ambient pressure not only exhibit a compressive strength of ˃4 MPa and an electric conductivity of 0.79 S cm−1, but also bear a developed structure of micrometer-sized cells with a low density of 0.3 g cm−3 and nanometer-sized pores with surface area of ˃175 m2 g−1. Furthermore, the lignin-based carbon foams have high thermal and structural stability to resist burning for various applications and exhibit excellent performance in oil/water separation, which retain 91% of the adsorption capacity toward oils even after being recycled 20 times.

Current trends in the development of polymer-based monolithic stationary phases.

This review focuses on the development and applications of organic polymer monoliths, with special attention to the literature published in 2021. The latest protocols in the preparation of polymer monoliths are discussed. In particular, tailored surface modification using nanomaterials, the development of chiral stationary phases and development of stationary phases for capillary electrochromatography are reviewed. Furthermore, the optimization of pore forming solvents composition is also discussed. Finally, the use of monolithic stationary phases in sample treatment using solid-phase extraction and enrichment methods, molecularly imprinted polymers and enzymatic reactors is mentioned.

Aesthetic Aerogel Window Design for Sustainable Buildings

Transport of heat through windows accounts for more than 25% of heating and cooling losses in residential buildings. Silica-based aerogels are translucent with extremely low thermal conductivity, which make them attractive for incorporation into the interspaces of glazing units. Widespread incorporation of monolithic-silica-aerogel-based windows could result in significant energy savings associated with the heating and cooling of buildings. However, monolithic silica aerogels do not have the optical clarity of vision glass, due to light scattering by the solid matrix, and often have surface imperfections, both of which render these materials less appealing for glazing applications. Here, we demonstrate a variety of approaches to preparing aesthetically pleasing monolithic silica aerogel by a rapid supercritical extraction method for incorporation into glazing units, including: (1) process improvements that result in monoliths with higher visible light transmission; (2) innovative mold design for the preparation of uniform aerogel monoliths; (3) glazing designs that use thinner monoliths; and (4) the incorporation of artistic effects using dyes and laser etching to prepare glazing units with mosaic- or stained-glass-like patterns in which surface imperfections are perceived as features of the design rather than flaws.

Monolithic Materials-Based RPLC-MS for Proteoform Separation and Identification.

High-performance separation of proteoforms plays an important role in top-down proteomic ananlysis due to high complexity of the proteome. To this end, the functionalized ethylene-bridged hybrid monolithic materials have been developed for reversed-phase liquid chromatographic separation of proteoforms followed by online combination with high-resolution mass spectrometry (MS) for top-down proteomic analysis. Such monoliths have advantages of homogenously distributed functional groups in the framework, good chemical stability, and high permeability and, thus, show high resolution, good reproducibility, and low backpressure for proteoform separation. This chapter describes in detail the preparation of such monoliths and online combination with high-resolution MS for proteoform separation and identification.

Preparation of Polystyrene Microsphere-Templated Porous Monolith for Wastewater Filtration.

Porous monoliths prepared using templates are highly sought after for filtration applications due to their good mass transport properties and high permeability. Current templates, however, often lead to the formation of dead-end pores and irregular pore distributions, which reduce the efficiency of the substrate flow across the monolith column. This study focused on the preparation of a microsphere-templated porous monolith for wastewater filtration. The optimal template/monomer ratio (50:50, 60:40, 70:30) was determined, and appropriate template removal techniques were assessed for the formation of homogenous pores. The physicochemical characteristics and pore homogeneity of the monoliths were examined. The 60:40 ratio was determined to result in monoliths with homogeneous pore distributions ranging from 1.9 μm to 2.3 μm. SEM and FTIR investigations revealed that solvent treatment was effective for removing templates from the resulting solid monolith. The water quality assessments revealed reductions in the turbidity and the total number of suspended particles in the tested wastewater of up to 96–99%. The findings of this study provide insightful knowledge regarding the fabrication of monoliths with homogenous pores that are beneficial for wastewater treatment.

CO2 Capture by Reduced Graphene Oxide Monoliths with Incorporated CeO2 Grafted with Functionalized Polymer Brushes

The monolithic materials of reduced graphene oxide (rGO) can be used successfully in CO2 adsorption. Here, the incorporation of CeO2 particles with and without polymer brushes grafted from the particles showed that the structural properties could be changed, affecting the adsorption of CO2. Polymer brushes of (1) poly(acrylic acid) (PAA), (2) poly(vinyl caprolactam) (PVCL) and (3) poly[(2-(methacryloyloxy)ethyl) trimethylammonium chloride] (PMETAC) were grafted from CeO2 via reversible addition−fragmentation chain transfer (RAFT) polymerization. The preparation of monoliths of rGO with different modified CeO2 particles led to different thermal properties (TGA), structural changes (BET isotherms) and CO2 adsorption. The responsive character of the CeO2@polymer was proven by the DLS and UV results. The responsive character of the particles incorporated into the rGO monolith affected not only the adsorption capacity but also the microstructure and values of the surface volume of the pores of the monolith. Monoliths with porosity values for better adsorption were affected by the responsive character of the polymer.

Lyophilization‐Free Engineering of Polyelectrolyte Monolith by an Ice‐Dissolving‐Complexation Method

AbstractIce templating is a versatile strategy for structural engineering of hydrophilic polymers and composites, yet the removal of ice templates requires lengthy lyophilization, and the prepared materials need further crosslinking for use in water. This study introduces an ice‐dissolving‐complexation (IDC) method to prepare ice templating monolith in an hour without the need for ice sublimation under a vacuum. The aqueous solution of sodium carboxymethyl cellulose (CMCNa) is frozen, immersed in ethanol/Cu2+ bath (−20 °C). Ice templates dissolved in ethanol, whereby the CMC‐Cu2+ complexation occurred simultaneously to stabilize CMC microstructures. The IDC method enables the preparation and stabilization of CMC monolith with pores and/or aligned channels in one step that is 30–50 times more efficient than lyophilization in terms of the time consumed for ice removal. The IDC method is applicable to various polyelectrolytes and hybrids for straightforward use in water, as exemplified by a proof‐of‐concept CMC‐Cu2+‐carbon nanotubes monolith, which exhibits high performance solar‐steaming under one sun irradiation.

Formulation and characterization of hydroxyapatite-based composite with enhanced compressive strength and controlled antibiotic release.

A composite based on hydroxyapatite (HA) and chitosan (CS) combined with ciprofloxacin (CIP) was formulated by the solid-liquid mixing method. The optimization of the solid to the liquid ratio and the use of chitosan in a small amount (≤5wt%) promoted the preparation of stable and rigid monoliths. A synergistic effect of CS and CIP contents on the compressive strength of the CIP-loaded composite was evidenced. The compressive strength of the fabricated biocomposite ranged in values from 1 to 6MPa, comparable to those reported for cancellous bone. The improvement of the mechanical properties with the increase of the rate of organic components was correlated with the diminution of the surface area and the reduction in the pore volume of the specimens. On the other hand, the in vitro release experiments of the antibiotic indicated a sustained and controlled release of CIP over 10 days. Moreover, in vitro antibacterial tests performed on the biocomposite HA-CS5-CIP showed significant inhibition of Staphylococcus aureus and Escherichia coli pathogens. According to the showed results, the formulated composite with three-phase components could be a promising material for bone repair and local antibiotic release for the treatment of bone infections.

Online specific recognition of mycotoxins using aptamer-grafted ionic affinity monolith with mixed-mode mechanism

Herein, a facile and practical aptamer-grafted ionic affinity monolith with mixed-mode mechanism was explored as a versatile platform for online specific recognition of polar and non-polar mycotoxins. The mixed-mode mechanism including molecular affinity adsorption (between aptamers and targets), hydrophilic interaction and ionic interaction (between stationary phase and targets) were adopted and provided a better flexibility in adjusting separation selectivity to reduce nonspecific adsorption with respect to the single mode. Preparation and characterization of aptamer-based affinity monoliths were investigated, The characterization of pore size distribution, Brunauer-Emmett-Teller (BET) surface area and the specificity and cross-reaction were also evaluated. As a result, the hydrophilic nature and negative charge on affinity monolith were obtained. Multiple interactions including aptamer affinity binding, hydrophilic interaction (HI) and ion exchange (IE) could be adopted for online selective extraction. Specific recognitions of polar ochratoxin A (OTA), non-polar zearalenone (ZEN) and aflatoxin B1 (AFB1) was fulfilled with LODs as 0.03, 0.05 and 0.05 μg/L, respectively. Applied to real cereals, good recoveries of the fortified OTA, AFB1 and ZEN were achieved as 92.6 ± 1.3% ~ 95.6 ± 1.3% (n=3), 93.9 ± 2.3% ~ 98.2 ± 3.4% (n=3) and 92.7 ± 2.0% ~ 96.9 ± 3.5% (n=3) in corn, wheat and rice, respectively. The results displayed that Apt-MCs with hydrophilic and ionic interaction mixed-mode mechanism were efficient enough and competent for the online recognition of mycotoxins in cereals.

Air activation of charcoal monoliths for capacitive energy storage.

Charcoal monoliths derived from waste wood were activated with air for the application of electrochemical capacitor electrodes and an insight was given into the activation mechanism. The mild air activation is effective and pollution-free compared to the common chemical activation using KOH etc. for the preparation of crack-free carbon monoliths. The activation process was controlled by altering the activation temperature and time, and their effects on the nanostructure of charcoal monoliths were studied. As the activation temperature or time increased, air eroded the defective surface of charcoal layer-by-layer, with the oxygen atoms being introduced by chemisorption and oxidation reactions and removed by dehydration and decomposition reactions. Meanwhile, micro-pores were produced. The electrode activated at 300 °C for 1 h, with a specific surface area of 567 m2 g−1 and a high micro-porosity of 86%, exhibited a specific capacitance of 203 F g−1 and 35.5 F cm−3. Moreover, it presented a higher total capacitance of 3.6 F cm−2 than most reported pellet electrodes. These findings give a reasonable picture of the air activation process and are instructive to prepare activated carbon monoliths under an oxidizing environment.

Preparation of Lignin-Based Carbon Foam Monoliths with High Strength and Developed Micrometer-Sized Cell/Nano-Sized Porous Structures Using a Self-Bubbling Method

Preparation of Lignin-Based Carbon Foam Monoliths with High Strength and Developed Micrometer-Sized Cell/Nano-Sized Porous Structures Using a Self-Bubbling Method

(Invited) Development of Ionic Porous Polymer for Sensing Applications

Porous polymers with macr/micro- sized pores have potential applications in separation, batteries, fuel cells and sensors [1, 2]. Thiol-ene "click" is a widespread method for monolith preparation owing to its exceptional versatility, simplicity and facile tunability. In our previous work, we reported on the fabrication of extremely soft type thiol-ionic gels (T-IGs) incorporating ionic liquid (IL) (70–85 wt%) in the thiol–ene network of thiol-based end-crosslinker and acrylate monomers [3, 4]. The T-IGs exhibited tunable mechanical and conductive properties and conductivity as high as 5.40 mS cm−1 is attained for longer acrylate group containing gels at room temperature. In this work we developed a series of porous polymers through polymerization induced phase separation by utilizing thiol-ene reaction between multi-functional thiol monomers and diacrylate crosslinkers in ionic Liquid solvent medium. The matrix of the polymers constructed of interconnected micro-globules forming a three-dimensional network. These microporous polymers exhibited tunable mechanical prosperities and morphology. In contrary to the ionic gels, the porous structure with entrapped ILs exhibited high ionic conductivity possibly due to relatively unperturbed transport of ions within the interconnected polymer particles compared to the bulk polymeric network. Physical properties of these porous ionic polymers have been investigated to optimize suitable condition for best performance in piezoresistive sensors (enabling sensing of both pressure and strain). This work is expected to add potential functionality in the applied field of the polymer materials.References Sakakibara, K., Kagata, H., Ishizuka, N., Sato, T., Tsujii, Y. Fabrication of surface skinless membranes of epoxy resin-based mesoporous monoliths toward advanced separators for lithium ion batteries. J. Mater. Chem. A, 5, 6866–6873 (2017).Liu, Z., Ou, J., Zou, H., Click polymerization for preparation of monolithic columns for liquid chromatography. Trends Anal. Chem., 82, 89–99 (2016).Ahmed, K., Naga, N., Kawakami, M. & Furukawa, H. Development of ionic gels using thiol-based monomers in ionic liquid. 9800,980005 (2016).Ahmed K, Naga N., Kawakami M. and Furukawa H., Extremely Soft, Conductive and Transparent Ionic Gels by 3D Optical Printing, Macromol. Chem. Phys., 1800216 (2018).