Preparation Of Monoliths Research Articles

A Facile Strategy for In Situ Fabrication of Covalent Triazine Framework Aerogel with Thermal Insulation Property.

Covalent triazine frameworks (CTFs) have attracted tremendous attention with respect to their rich nitrogen content, functional triazine units, and high porosity. However, efficient and simple preparation of CTF monoliths is still a challenge. Here, we propose a novel and facile approach for the in situ preparation of CTF aerogels. Trifluoromethanesulfonic acid was used as the solvent and catalyst, which could not only promote the polymerization reaction to form a gel but also protonate the CTFs. By virtue of the simplicity and efficiency of the strategy, a series of macroscopic CTF aerogels with tunable density were obtained by adjusting the monomer concentration. Due to the porous and partially crystalline structure, the as-produced macroscopic CTF aerogels behaved with good mechanical and thermal insulation performances. This finding thus offers an effective and easily scalable approach toward fabricating macroscopic CTF aerogels and broadens the applications of CTFs in a variety of domains.

Effect of binary porogen mixtures on polymer monoliths prepared by gamma-radiation initiated polymerization

Gamma-radiation initiated polymerization is an easy-to-use and simple technique for the preparation of porous polymer monoliths widely used as active materials in separation columns. Herein, binary porogen mixtures of ethyl acetate/acetone/acetonitrile with methanol were used to synthesize diethylene glycol dimethacrylate monoliths with this technique. Systematic studies have been performed to determine the effect of the composition of the solvent mixture on the morphology and the reaction kinetics, including the growth mechanism and the growth rate. The irradiation dose-dependent conversion profiles showed that with binary solvents the polymerization is much faster than with the same compounds used as single solvents. Depending on the type and the composition of the solvent one-, two- and three-dimensional, and fractal growth mechanisms were identified.

Preparation of Hierarchical Porous Monoliths With High Surface Areas by a Solvent Knitting Strategy.

Hierarchical porous hypercrosslinked monoliths (PolyHIPE-HCP) with ultrahigh specific surface areas are prepared via a solvent knitting strategy. Compared to previous work, the solvent knitting strategy is carried out in a relatively low air-controlled atmosphere with gradient heating starting from low temperature while using DCM (Dichloromethane) as both a solvent and a cross-linker, allowing for a slow and controlled cross-linking process, thereby achieving a BET surface area ranging from 514 to 728m2g-1. Scanning electron microscopy (SEM) shows that the knitting process does not affect the presence of macroporous structure in the PolyHIPE. With the introduction of mesopores and micropores, these hierarchical porous monoliths exhibit significant potential for applications in gas adsorption and water treatment. Hence, a universal, simple and low-cost method to synthesize polymeric monoliths with hierarchically porous structure and higher surface area is proposed, which has fascinating prospects in industrialization.

Thiol-functionalized MOF modified 3D printed monolithic microextraction array for analysis of trace Cd and Pb in human urine

Controlling the position, size, and shape of pores is a limitation of traditional monolithic preparation methods. The application of 3D printing technology offers high customizability, allowing the precise printing of pore positions, sizes, and shapes according to the designer's 3D model. Herein, by using Projection Microstereolithography (PμSL), we prepared a 3D-printed monolithic array with post-modification of thiol-functionalized metal-organic framework (MOF), and combined it with inductively coupled plasma mass spectrometry (ICP-MS) for the online analysis of trace Cd and Pb in human urine. To achieve array monolithic microextraction, six 3D-printed monolithic columns were modified with thiol-functionalized MOF-808 (MOF-808-SH), and were then assembled in the 3D printed extraction device incorporating gas valve and scaffold. The MOF-808-SH modified 3D-printed monolithic column exhibits excellent extraction performance to Cd2+ and Pb2+ due to rich active adsorption sites and hierarchical porous structure, and has long life span (>100 reused times). Under the optimized conditions, the limits of detection (LODs) are 3.5 and 17.6 ng L−1 for Cd2+ and Pb2+, respectively, with the relative standard deviations of 4.9 % and 8.2 % (0.1 μg L−1, n = 7), and the sample throughput is 11 h−1. To validate the accuracy of the method, the method was used to determine Cd and Pb in Certified Reference Materials of freeze-dried human urine, the determined results agree well with the certified values. This method was also successfully applied to the determination of trace Cd and Pb in real human urine samples. The developed method offers low LODs, robust anti-interference capability, high sample throughput, long reuse cycles, and automation analysis, showing great potential for the analysis of trace heavy metals in biological samples.

Preparation of DNA nanoflower-modified capillary silica monoliths for chiral separation.

Innovative chiral capillary silica monoliths (CSMs) were developed based on DNA nanoflowers (DNFs). Baseline separation of enantiomers such as atenolol, tyrosine, histidine, and nefopam was achieved by using DNF-modified CSMs, and the obtained resolution value was higher than 1.78. To further explore the effect of DNFs on enantioseparation, different types of chiral columns including DNA strand containing the complementary sequence of the template (DCT)-modified CSMs, DNF2-modified CSMs, and DNF3-modified CSMs were prepared as well. It was observed that DNF-modified CSMs displayed better chiral separation ability compared with DCT-based columns. The intra-day and inter-day repeatability of model analytes' retention time and resolution kept desirable relative standard deviation values of less than 8.28%. DNF2/DNF3-modified CSMs were able to achieve baseline separation of atenolol, propranolol, 2'-deoxyadenosine, and nefopam enantiomers. Molecular docking simulations were performed to investigate enantioselectivity mechanisms of DNA sequences for enantiomers. To indicate the successful construction of DNFs and DNF-modified CSMs, various charaterization approaches including scanning electron microscopy, agarose gel electrophoresis, dynamic light scattering analysis, electroosmotic flow, and Fourier-transform infrared spectroscopy were utilized. Moreover, the enantioseparation performance of DNF-modified CSMs was characterized in terms of sample volume, applied voltage, and buffer concentration. This work paves the way to applying DNF-based capillary electrochromatography microsystems for chiral separation.

Effect of crosslinker/porogen ratio on sponge-nested polymer monoliths for solid-phase extraction

Polymer monoliths can be polymerised within different molds, but limited options are available for the preparation of free-standing polymer monoliths for analytical sample preparation, and in particular, solid-phase extraction (SPE). Commercial melamine-formaldehyde sponges can be used as supports for the preparation of polymer monoliths, due its flexibility, giving various shapes to monoliths. Herein, the crosslinker/porogen ratio of highly porous sponge-nested divinylbenzene (DVB) polymer monoliths has been evaluated. Monoliths prepared using different crosslinker/porogen ratios were applied to the extraction of bisphenol F, bisphenol A, bisphenol AF, and bisphenol B. Monoliths containing 50 wt % DVB and 50 wt % porogens presented the highest recovery of bisphenols. Under the optimised conditions, the developed method showed a linear range between 2.5 µg L−1 and 150 µg L−1 for BPA and BPAF, and between 5 µg L−1 and 150 µg L−1 for BPB and BPF. The limits of detection (LOD, S/N = 3) and limits of quantification (LOQ, S/N = 10) ranged from 0.36 µg L−1 to 1.09 µg L−1, and from 1.20 µg L−1 to 3.65 µg L−1, respectively. The recoveries for spiked bisphenols (10 µg L−1) in tap water and water contained in a polycarbonate containers were between 82 % and 114 %.

An Ice‐Dissolving‐Crosslinking Method for Efficient and Large‐Scale Preparation of Polyelectrolyte Monoliths with Ultra‐Stability in Aqueous Environments

AbstractIce‐templating is a versatile method for constructing macro‐porous hydrophilic polymer materials. However, the ice‐templating method is generally limited by high energy cost and low efficiency for large‐scale fabrication. Further, due to its hydrophilic nature, the constructed materials are vulnerable to water swelling and have poor structural stability. Here, an Ice‐Dissolving‐Crosslinking (IDCr) method is developed for efficient and large‐scale preparation of polyelectrolyte monoliths with ultra‐stability in aqueous environment. Specifically, Ice‐Dissolving in water‐miscible organic solvent is responsible for pore creation, while subsequent Crosslinking ensures pore structures stabilization. The macro‐porous architecture of materials, taking sodium carboxymethyl cellulose (CMC) as a polyelectrolyte example and trimesoyl chloride (TMC) as the crosslinker, CMC‐TMCIDCr is made much stabler as compared with the case of conventional Lyophilization‐Crosslinking technique (CMC‐TMCLC). The IDCr method is applicable to various hydrophilic polyelectrolytes and hybrids for long‐time use in water and brines, as exemplified by CMC‐TMC‐carbon nanotubes monolith, which exhibits high performance in solar thermal desalination process. This novel approach opens up new opportunities for the construction of porous monoliths with efficient preparation and excellent water stability.

Preparation of Monolith for Online Extraction and LC-MS Analysis of β-Estradiol in Serum Via a Simple Multicomponent Reaction.

Multicomponent reactions offer efficient and environmentally friendly strategies for preparing monoliths suitable for applications in analytical chemistry. In the described study, a multicomponent reaction was utilized for the one-pot miniaturized preparation of a poly(propargyl amine) polymer inside commercial silica-lined PEEK tubing. The reaction involved only small amounts of reagents and was characterized by atom economy. The resulting monolithic column was incorporated into an autosampler system for the online extraction and cleanup of β-estradiol from human serum. Sample pretreatment was simplified to a simple dilution with methanol and centrifugation to remove proteins. The resulting platform included LC-MS analysis in multiple reaction monitoring for quantitative analysis of β-estradiol. The method was validated in serum, demonstrating practical applicability for the monitoring of fertile women. Recoveries were above 94%, and LOD and LOQ values at 0.008 and 0.18 ng mL-1, respectively. The developed platform proved to be competitive with previous methods for solid-phase microextraction of β-estradiol in serum, with comparable recovery and sensitivity but with the advantage of nearly complete automation. The environmental impact of the process was evaluated as acceptable due to the miniaturization of the monolith synthesis and the automation of extraction. The drawback associated with the LC-MS technique can be reduced by the inclusion of additional analytes in a single investigation. The work demonstrates that multicomponent reactions are versatile, economical, and possibly a green methodology for producing reversed-phase and mixed-mode sorbents, enabling miniaturization of the entire analytical procedure from the preparation of extraction sorbents to analysis.

Facile preparation of lightweight and robust carbon aerogel monoliths for high-temperature thermal insulation and oil-water separation

Lightweight carbon aerogels (CAs) are urgently required for thermal insulation and organics absorption. However, a facile preparation method of ambient pressure drying (APD) remains a challenge since the large surface tension causes severe shrinkage, collapse or even cracking of porous network. Herein, a series of lightweight, robust and large-sized CA monoliths (0.240–0.327 g/cm3) are prepared through sol-gel polymerization of resorcinol-formaldehyde (RF) followed by solvent exchange-free APD using cotton fibers as reinforcement precursor. The deliberate tailoring of synthesis parameters and the appropriate introduction of cotton fibers jointly bring the advantages of facilitating sol-gel of RF solution.reducing drying shrinkage of hydrogels, and improving compatibility of carbonization shrinkage between fibers and matrix. Consequently, for instance, the CA composite with a density of 0.283 g/cm3, have high compressive strength (3.66 MPa), low thermal conductivity (0.070 W/(m·K)), excellent hydrophobicity (water contact angle as high as 145°), and high-volume organic absorption capability (74.8–95.7%). The facile preparation of CA composites through solvent exchange-free APD with monomer polymerization should be a promising approach to their further application in thermal insulation and oil-water separation.

Preparation of chiral monoliths with new modulation of the monolith surface chemistry for the enantioseparation of chiral drugs by nano-liquid chromatography

Here, we report the preparation and application of two new chiral monoliths for the enantioseparation of chiral drugs in nano-LC. Using 3‑chloro-2-hydroxypropylmethacrylate (HPMA-Cl, 2) as a precursor monomer, two different chiral monomers namely, Nα-Boc-Lys-HPMA (3A) and Nα-Fmoc-Lys-HPMA (3B) were synthesized and used for the preparation of chiral polymer monoliths. The first monolithic column (referred to as monolith I) was prepared by an in-situ polymerization of Nα-Boc-Lys-HPMA as the chiral monomer and ethylene dimethacrylate while the second monolithic column (referred to as monolith II) was prepared by an in-situ polymerization of Nα-Fmoc-Lys-HPMA as the chiral monomer and ethylene dimethacrylate as the crosslinker. Methanol and 1-propanol were used as the porogenic solvents. The prepared chiral monoliths were investigated for the enantioseparation of chiral drugs, including β-blockers (e.g., atenolol, propranolol, metoprolol) and anti-inflammatory drugs (e.g., ketoprofen, ibuprofen, flurbiprofen, naproxen, etodolac). The enantioseparation could be achieved via the formation of π-π interactions on the aromate-rich and aromate-poor chiral molecules while enantioseparation mechanism of chiral drugs included mostly π-π interactions and hydrogen bonding. Monolith II showed better enantioselectivity than Monolith I and the resolution values up to 2.12 were successfully achieved.

Shape stability control of a 3D-printed clay/biochar-based monolith to support Fe catalyst for continuous levofloxacin degradation with low metal leaching

Disposing of wet solid waste sludge has become a prominent issue because it has high environmental risks. Herein, a clay/biochar-based monolith (CBM) is prepared using a three-dimensional (3D) printing design method. The CBM is loaded with iron (Fe) and used as a catalyst (Fe/CBM) to activate peroxymonosulfate (PMS) for degrading levofloxacin (LVF) in an aqueous solution. The monolith preparation process is inexpensive, and the monolith has designable flow paths that facilitate improved mass transport and material recycling. ZnCl2, as a chemical activator, is added to the 3D-printed slurry to improve the catalytic performance of Fe/CBM. Oscillatory stress sweep and frequency sweep tests prove that incorporating ZnCl2-containing sludge in the slurry effectively increases the elastic modulus and critical stress, improving structural stability and constructability. The slurry containing 10% sludge (S10%-Zn with 1 M ZnCl2), exhibits 30% higher static yield stress than the slurry containing only clay and water (S0%). Fe/CBM is prepared by loading Fe active sites onto the surface of CBM via an impregnation method, and it leaches very low amounts of Fe (<0.2 mg/L) and other heavy metals (e.g., Cd, and Pd, etc). Fe/CBM-S10%-Zn/PMS with 10% mass fraction of sludge exhibits much higher (∼80% at 20 min) degradation efficiency than Fe/CBM-S0%/PMS (∼15% at 20 min) and Fe/CBM-S10%/PMS (∼43% at 20 min). Combining with XPS results, when ZnCl2 is added to the slurry, the content of Fe2+ in the catalytic material increases, improving the catalytic performance. The PMS activation mechanism of Fe/CBM-S10%-Zn for LVF degradation is also discussed, which is ascribed to the radical and nonradical pathways. This provides new insights on how to recycle solid waste and make high-performance clay/biochar-based monolith catalysts for the continuous wastewater treatment.

Preparation of carbon-based monolith with macroporous-mesoporous structure derived from PVDF hollow fiber membranes for supercapacitors

In this work, a carbon-based monolith with macroporous-mesoporous structure derived from polyvinylidene fluoride (PVDF) hollow fiber membranes is reported. The Co2+ soaked PVDF hollow fiber membranes are treated with vinyltrimethoxysilane (VTMS) and calcined at relatively low temperatures (600 °C) to obtain a carbon-based material with a distinctive honeycomb porous structure. The VTMS treatment is the committed step, which provides a hard SiO2 protective layer for the PVDF hollow fiber membrane during the calcination process to support the skeleton structure and prevent the macrostructure collapse and also plays a role in expanding mesopores. The obtained hierarchically porous structure can improve the electrochemical activity of the carbon-based material. In a three-electrode system, the specific capacitance of 701.0 F g−1 can be achieved at a current density of 1 A g−1, and the retention rate is 112.1 % after 10,000 cycles at 10 A g−1. The assembled quasi-solid-state symmetric supercapacitor can be operated in a 0–1.4 V voltage window, and it demonstrates an energy density of 26.3 Wh kg−1 at the power density of 349.9 W kg−1.

One-pot preparation of bi-functional POSS-based hybrid monolith via photo-initiated polymerization for isolation of extracellular vesicles

Extracellular vesicles (EVs) are important participants in numerous pathophysiological processes, and could be used as valuable biomarkers to detect and monitor various diseases. However, facile EV isolation methods are the essential and preliminary issue for their downstream analysis and function investigation. In this work, a polyhedral oligomeric silsesquioxanes (POSS) based hybrid monolith combined metal affinity chromatography (MAC) and distearoyl phospholipid ethanolamine (DSPE) function was developed via photo-initiated thiol-ene polymerization. This synthesis process was facile, simple and convenient, and the obtained hybrid monolith could be applied to efficiently isolate EVs from bio-samples by taking advantages of the specific bond of Ti4+ and phosphate groups on the phospholipid membrane of EVs and the synergistic effect of DSPE insertion. Meanwhile, the eluted EVs could maintain their structural integrity and biological activity, suggesting they could be used for downstream application. Furthermore, 75 up-regulated proteins and 56 down-regulated proteins were identified by comparing the urinary EVs of colorectal cancer (CRC) patients and healthy donors, and these proteins might be used as potential biomarkers for early screening of CRC. These results demonstrated that this hybrid monolith could be used as a simple and convenient tool for isolating EVs from bio-samples and for wider applications in biomarker discovery.

Review of recent advances in development and applications of organic-silica hybrid monoliths.

Organic-silica hybrid monoliths attracted attention as an alternative to extensively researched organic polymer-based and silica-based counterparts. The development and applications of these materials as extraction and separation media in capillary liquid chromatography and capillary electrochromatography were previously reviewed in several manuscripts. In this review, we will concentrate on work published since mid-2016 focusing on advances in their development using sol-gel chemistry of tetra- and trialkoxysilanes and subsequent surface modification with organic monomers, and "one-pot" strategy incorporating sol-gel chemistry of alkoxysilanes and free-radical polymerization, ring-opening polymerization, or thiol-based click polymerization with organic monomers. Approaches adapted to the preparation of hybrid monoliths made with polyhedral oligomeric silsesquioxanes will be covered as well.

Effect of hydrophilic/lipophilic balance on the porogenic properties of non-ionic surfactants for monolith preparation and chromatographic separation

The effect of hydrophilic/lipophilic balance (HLB) of polyoxyethylene ethers of different chain lengths on the microporogenic properties of the Brij surfactants has been studied. The objective of this work is to help better understand the role of each porogen and to set criteria for selecting the proper non-ionic surfactant, based on the HLB value. Seven recipes of different porogen compositions were first prepared and the highest efficiency was achieved using decane/decanol/dodecanol mixture with Brij® 30. Then, four other Brij surfactants covering the entire HLB scale were tested, and the prepared monoliths were characterized by SEM, BET, FT-IR and chromatography. The results showed that increasing the HLB from 9.72 to 18.84 was accompanied by an increase in monolith density and surface areas. The optimum HLB range was found to be 10 to 15. Surfactants of lower HLB formed either nonporous or less efficient columns, while those of higher HLB formed non-permeable columns. Adjusting the HLB was possible by mixing surfactants of different HLB. The prepared monoliths could be used in the isocratic mode with a mobile phase consisting of a mixture of ACN and water (20:80, v/v) at a flow rate of 1.5 μL min−1 to separate five sulfa drugs. The separation results showed that the elution order of the compounds correlated with their lipophilicity, with sulfamerazine (logp = 0.52) being the first to elute, and sulfaquinoxoline (logp=1.70) being the most retained. The asymmetry factors of the separated compounds ranged between 1.18 and 1.25, and the resolution was found to be in the range 2.92−7.80. The prepared monoliths could be also successfully separate a mixture of four different nonsteroidal anti-inflammatory drugs and a mixture of four benzoic acid derivatives. This work assists in optimizing the surfactant-based porogenic mixture to meet the desired porosity, surface area, morphology and chromatographic separation requirements.

Preparation of carbonaceous monolith from polyacrylonitrile@lignin hybrid composite and its sensing and adsorption capability

Preparation of carbonaceous monolith from polyacrylonitrile@lignin hybrid composite and its sensing and adsorption capability

Nano-Fe3O4 coated on carbon monolith for anode enhancement in microbial fuel cells

Anode materials were vital for power production in microbial fuel cells (MFCs). By freeze-drying and carbonization, porous carbon monolith derived from wax gourd (WGCM) was prepared. WGCM was then coated by nano-Fe3O4 to obtain the nano-Fe3O4/WGCM anode. WGCM anode increased the maximum power density of the MFCs from 430.6 mW/m2 to 906.6 mW/m2, while nano-Fe3O4/WGCM anode further promoted it to 1438.8 mW/m2. WGCM had a three-dimensional (3D) microporous network structure, a hydrophilic surface and good conductivity, which enhanced biofilm formation and reduced internal resistance. Fe3O4 increased Geobacter enrichment on anode surface, a popular electricigen in MFCs. Calculated from anode surface microbial cell density and the relative abundance, Geobacter on the nano-Fe3O4/WGCM increased by 41.4% compared with the WGCM anode. The results demonstrated that the preparation of carbon monolith coated with nano-Fe3O4 was a promising method for anode enhancement in MFCs.

Threedimensionally patterned, hierarchically and anisotropically structured bacterial cellulose

Structuring cellulosic materials is an important step towards realizing emerging technologies, such as so-called engineered living materials, and improving on established ones, such as tissue engineering. In this work, we present a route for the preparation of cellulose monoliths exhibiting a three-dimensional pattern on the macroscopic scale, together with structural anisotropy in the cellulose fiber level. This was achieved by rheotactic growth, i.e. under flowing medium, of bacterial cellulose over a 3D-printed dissolvable template. The surrounding setup was realized using commercially available components. Here, we report on and discuss structural properties of cellulose monoliths obtained by this process, such as shrinkages during processing, the strut densities of 50 mg cm−3, preferred orientations of cellulose within the struts, and the pore size distributions, which were determined from nanoscale-precision silica replica.

Enhancement of supercapacitive performance of carboxymethyl cellulose-derived porous carbon monoliths by the addition of carbon nanotubes

In this study, a simple and eco-friendly fabrication strategy for the preparation of porous carbon monoliths with 3-dimensional conductive networks was demonstrated. Porous carbon/carbon nanotube composite monoliths (PCCMs) with large specific surface area and hierarchical pore structures were prepared via eco-friendly ice-templating followed by carbonization. The resulting PCCMs showed excellent electrochemical performance due to their well-developed hierarchical porosity and high electrical conductivity following the addition of 1-D carbon nanotubes. In a 3-electrode configuration, the PCCM-derived electrode delivered a specific capacitance of 240 F g−1 at 1 A g−1. In a practical application, the PCCM-based symmetric capacitor exhibited the specific capacitance of 47.0 F g−1, rate capability of 72.7%, power density of 9.5 kW kg−1 and a cycling stability of ∼100% after 20,000 cycles, respectively. These results suggested that the PCCMs can be applied as an active material for high-performance electrical double-layer capacitors.

Preparation of Hierarchical Porous Silicon Carbide Monoliths via Ambient Pressure Drying Sol–Gel Process Followed by High-Temperature Pyrolysis

Hierarchical porous silicon carbide (SiC) attracts great attention due to its superior chemical resistance, high thermal shock resistance, and excellent thermal stability. The preparation of a porous SiC monolith via a simple sol-gel method is limited by either the high cost of the raw materials or the special time-consuming drying process. Herein, we report an ambient drying sol-gel approach for the synthesis of organic-inorganic hybrid monolithic gels which can be converted into hierarchical porous SiC monoliths upon pyrolysis at 1400 °C. The as-synthesized SiC monoliths possess hierarchical pores with macropores of 4.5 µm and mesopores of 2.0 nm. The porosities, specific surface areas and compressive strengths of the hierarchical porous SiC monoliths are 71.3%, 171.5 m2/g and 7.0 ± 0.8 MPa, respectively.