High-performance porous polyimide (PI) monoliths, including PI aerogels, sponges, and foams, have become one of the hotspots in both researching and applications due to their superior properties such ...as high porosity, outstanding mechanical and thermal stability, low dielectric constant and thermal conductivity. Up to now, various fabricating methods and applicating situations for PI porous monolith materials have been reported. From the viewpoint of molecular chemistry, porous structure construction, as well as the functional modification, the property optimization and adjustment are feasible, endowing PI monoliths with promising potential for different practical applications (e.g. sensors, low-k materials, thermal management, energy field and utilization, absorption and filtration, photonic utilization, etc.). In this review, the recent progress of porous PI monoliths was summarized in detail based on the fabrication methods, functional modifications, as well as multi-functional applications. Besides, the future perspectives of this field were also provided for reference. Apart from presenting an overview of progress made in the field of PI porous monoliths, this review could also be meaningful for those researching topics which have similarity within.
An ice-templating process was used to fabricate polymer/MOF monoliths, specifically chitosan/UiO-66, as adsorbents for water treatment. The ice-templated macropores enhanced mass transport, while the ...monoliths could be easily recovered from solution. This was demonstrated by the adsorption of methylchlorophenoxypropionic acid (MCPP, a herbicide compound) from dilute aqueous solution. To enhance the stability, the freeze-dried monoliths were treated with NaOH solution, solvent exchanged, and dried. The treated chitosan/UiO-66 monolith achieved an adsorption capacity of 34.33 mg g–1 (a maximum theoretic value of 334 mg g–1 by the Langmuir model), closer to the capacity (36.00 mg g–1) of the freshly prepared UiO-66 nanoparticles and much higher than that of the NaOH-washed UiO-66 nanoparticles (18.55 mg g–1), by performing the tests in 60 ppm MCPP solution. The composite monolith could be easily picked up using tweezers and used for recycling tests. Over 80% of the adsorption capacity was retained after three more cycles. The powder X-ray diffraction and N2 sorption studies suggested the crystalline structure of UiO-66 was destroyed during NaOH washing procedure. This, however, provides the potential to improve the adsorption capacity by developing methods to fabricate true polymer/MOF composites.
In this work, we manifested a new approach in designing solid-state colorimetric sensors for the selective optical sensing of As3+. The sensor fabrication is modulated using, (i) a cubic mesopores of ...ordered silica monolith, and (ii) a bimodal macro-/meso-porous polymer monolith, as hosting templates that are immobilized with a tailor-made chromoionophoric probe (DFBEP). The surface morphology and structural dimensions of the monolith templates and the sensor materials are characterized using p-XRD, XPS, FE-SEM-EDAX, HR-TEM-SAED, FT-IR, TGA, and BET/BJH analysis. The sensing components such as pH, probe content, sensor dosage, kinetics, temperature, analyte concentration, linear response range, selectivity, and sensitivity are optimized to arrive at the best sensing conditions. The silica and polymer-based monolithic sensors show a linear spectral response in the concentration range of 2–300 and 2–200 ppb, with a detection limit of 0.87 and 0.75 ppb for As3+, respectively. The real-time ion-monitoring propensity of the sensors is tested with spiked synthetic and real water samples, with a recovery efficiency of ≥99.1% (RSD ≤1.57%). The sensors act as both naked-eye optical sensors and preconcentrators, with a response time of ≤2.5 min. The molecular and photophysical properties of the DFBEP-As3+ complex are studied by TD-DFT calculations, using the B3LYP/6–31G (d,p) method.
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•Ordered pore networks of silica and polymer-based monolith templates are prepared.•An indigenous chromoionophoric molecular probe is synthesized for As3+ ion-sensing.•The probe anchored monolith templates act as solid-state colorimetric ion-sensors.•The optodes offer exclusive selectivity in capturing ultra-trace levels of As3+.•The proposed optical sensors are fast responsive, benign, reusable, and durable.
Applications such as filtration require not only control over the pore structure but also over properties like surface characteristics and mechanical strength. The addition of filler particles to ...solution based freeze casting of preceramic polymers combines the flexibilities of freeze casting and preceramic polymers. Alumina platelets, silica spheres and preceramic filler particles with different compositions were frozen in solution based freeze casting of preceramic polymers with cyclohexane as solvent. Methyl- and methyl-phenyl polysiloxanes as well as (3-aminopropyl)triethoxysilane were used as precursors and cross-linking agent, respectively. The compressive strength increases by factors of up to 1.9 (25 vol% preceramic filler) due to enhanced isotropy of the dendritic pore structure. At lower concentrations (1.7 vol%), alumina platelets are more effective in strengthening than spherical particles. In dependence on the composition of the preceramic filler, BET surface area and the ratio of vapor uptake between water and heptane change by factors of up to 1.19 and 16, respectively. Calculations according to a linear rule of mixture fit very well with the experimental data. In summary, the versatile approach to add differing filler particles to solution based freeze casting allows for tailoring the pore structure as well as surface characteristics of macroporous monolithic samples.
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•Addition of preceramic and ceramic fillers overcomes limitations of solution based freeze-casting of polysiloxanes.•Enhanced isotropy of pore structure increases the compressive strength by factors of up to 1.9.•Different chemical compositions of filler particles allow for altering the BET surface area from 276.4-535.2 m2g-1.•Ratio of water to heptane uptake as a measure of hydrophilicity can be adjusted in a range from 0.13-2.86.•Linear rule of mixture precisely predicts hydrophilicity and BET surface area and allows design of properties.
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•Internal structure of a monolith reconstructed using 3D X-ray tomography images.•Fluid velocity, pressure drop and shear stress modelled using CFD tools.•Tortuosity derived from CFD ...simulated fluid pathways (streamlines).•Modelling validated by experimental residence time distribution (RTD) results.
Highly porous monolithic alumina columns find a wide variety of applications, including in chromatography, due to increased surface area and good accessibility to the ligands and reduced diffusional hindrances. Several modelling approaches have been applied to describe experimentally observed flow behaviour in such materials, which morphology plays a key role in determining their hydrodynamic and mass transfer properties. In this work, a direct computational fluid dynamics (CFD) modelling approach is proposed to simulate flow behaviour in monolithic porous columns. The morphological structure of a fabricated alumina monolith was first reconstructed using 3D X-ray tomography data and, subsequently, OpenFOAM, an open-source CFD tool, was used to simulate the essential parameters for monoliths’ performance characterisation and optimisation, i.e. velocity and pressure fields, fluid streamlines, shear stress and residence time distribution (RTD). Moreover, the tortuosity of the monolith was estimated by a novel method, using the computed streamlines, and its value (∼1.1) was found to be in the same range of the results obtained by known experimental, analytical and numerical equations. Besides, it was observed (for the case of the monolith studied) that fluid transport was dominated by flow heterogeneities and advection, while the shear stress at pore mouths was significantly higher than in other regions. The proposed modelling approach, with expected high potential for designing target materials, was successfully validated by an experimentally obtained residence time distribution (RTD).
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•The HWB-AO adsorbent was a porous, processable and non-biologically toxic monolith.•The HWB-AO exhibited high selectivity and long service life.•The adsorption capacity for uranium ...was 256.4 mg g−1 at pH = 6.
Uranium is not only toxic and radioactive, even more an important resource to ensure the nuclear energy development. This work reported an amidoxime-based hyper-crosslinked polymeric resin adsorbent (HWB-AO) to extract uranium from ocean. The monolithic matrix was prepared by suspension polymerization using styrene (St) and divinylbenzene (DVB), followed by post-polymerization modification to graft diaminomaleonitrile (DAMN) and conduct amidoximation to introduce amidoxime groups (AO) in its interior and surface. AO can enhance the affinity to uranium and hydrophilicity to accelerate the uranium adsorption. The monolithic structure overcome the problem that powder adsorbent is easy to drain in real seawater, so the monolithic is easier to apply. The batch adsorption experiments results showed that HWB-AO has an magnificent uranium removal rate (85%) and the maximum adsorption capacity (qe,max) is 256.4 mg g−1. In addition, HWB-AO still maintains a giant adsorption efficiency after eight times adsorption–desorption cycles and is environmentally friendly. Concurrently, HWB-AO exhibits excellent selectivity and removal rate (greater than88%) in modified seawater. Therefore, HWB-AO is considered as a potential adsorbent to perform uranium extraction from natural seawater.
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•We have developed hierarchically porous carbon-based monoliths with high CO2 capacity.•The high capacity is due to synergistic effects of textural and surface properties.•The ...monolithic form is advantageous over powder adsorbents for easy and safe handling.•The easy regeneration under mild conditions makes them promising for practical application.
Various porous solid sorbents in the form of powder or monoliths have been developed over the last years, as a promising solution for reducing CO2 emissions. Although powder sorbents, due to higher porosities and efficient mass transport, exhibit higher capacities compared with monoliths, several factors limit their suitability for practical application. The most prominent is their low bulk density, which makes them difficult to handle and poses health risks due to dust inhalation. In this work, we prepared robust hierarchically porous carbon-based monoliths based on a simple three-step approach with the focus on combining efficient CO2 adsorption and transport with easy handling for practical applications. The approach is based on incorporation of polystyrene nanoparticles (PS NPs) and expanded graphite (EG) into a nitrogen-rich precursor, which is polymerized to form 3D monoliths. Incorporation of thermally unstable PS NPs or thermally stable EG enables us to control the formation of macropores during a precarbonization step, while variation of KOH concentration and mixing intensity during a subsequent activation step controls the formation of micropores. The resulting hierarchically porous monoliths with high nitrogen contents exhibited CO2 uptake capacities reaching 6.52 mmol g−1 at 273.15 K and 1 bar, which is among the highest reported for porous carbon monoliths. In addition, the materials also exhibited good reversibility of CO2 adsorption over several cycles with simple regeneration under mild conditions. Considering the high CO2 capture performance together with improvements in sorbent properties such as easy handling and reusability, the presented sorbents are promising candidates for practical applications.
Processable microporous organic polymers (MOPs) attract incomparable research interest because their vairous types, such as monoliths and membranes are for practical application. Most processable ...MOPs usually need harsh conditions such as the use of expensive metal catalysts, specialized stereospecific monomers, etc., which restrict the sustainable and real applications of processable MOPs. Therefore, the economical mass production of processable MOPs remains a formidable challenge. Herein, a novel strategy is reported for constructing processable hypercrosslinked polymers (HCPs) need two steps synthesis of pre‐crosslinking and deep‐crosslinking using divinylbenzene (DVB) as a self‐crosslinking monomer under the catalysis of a small amount of FeCl3. The resulting HCPs monoliths possess high BET surface area of 1033–1056 m2 g−1 with hierarchical porosity, and show excellent mechanical strength up to 65 MPa. It is, to the best of authors' knowledge, the first report of using aromatic vinyl monomers as self‐crosslinking monomers to generate HCPs monoliths with high surface area, yielding no by‐products, and high mechanical strength.
A novel strategy for constructing processable hypercrosslinked polymers (HCPs) needs two‐step synthesis of pre‐crosslinking and deep‐crosslinking using divinylbenzene (DVB) as a self‐crosslinking monomer under the catalysis of a small amount of FeCl3. The resulting HCPs monoliths possess high BET surface area of 1033–1056 m2 g−1 with hierarchical porosity, and show excellent mechanical strength up to 65 MPa.
Unidirectional and non-unidirectional freeze cast SiOC monoliths were characterized by means of digital image processing. For this purpose a novel method of pore segmentation in complex dendritic ...pore morphologies was developed. For the first time, the proposed method made it possible to perform an extensive geometrical and structural pore space characterization and analysis on single pore level. The orientation of the primary dendritic channels was obtained from high resolution μCT images. Based on the mean directional vector distribution, the pore space was segmented. As a result, 95% (unidirectional) and 88% (non-unidirectional) of the original binary pore volume could be allocated to individual pores. The pore interconnectivity could be derived from this segmented pore space. It has been shown that the degree of interconnectivity between pores of the same orientation is higher than between pores of different orientation. This could be the reason for peculiar wicking behavior in non-unidirectional samples.
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•Characterization of unidirectional and non-unidirectional freeze cast monoliths.•Pore orientation was obtained from primary dendritic structure.•The pore space was segmented and allocated to individual pores.•Pore interconnectivity was evaluated on single pore level.•Non-unidirectional monoliths show reduced interconnectivity between pore clusters.
Porous nonoxide ceramics have exhibited impressive progress in terms of synthesis and applications over the past few decades because of their unique characteristics distinguished from the oxide ...counterparts. From the synthetic aspect, the preceramic polymer route, where nonoxide ceramics such as carbides and nitrides are produced from molecular precursors, offers exceptional opportunities to elaborate and control the material shape as well as the micro‐ and nanostructures in concert with various techniques. This review presents monolithic ceramic materials based on various reduced phases bearing hierarchical porosity with a focus on those obtained from macroporous preceramic monoliths prepared via the one‐pot sol–gel process accompanied by spinodal decomposition. Here, we highlight two classes of preceramic inorganic–organic hybrid gels: organometallic crosslinked polymers based on poly(silsesquioxane)s and nonorganometallic hybrid networks related to Ti without Ti–C bonds. The polymer‐to‐ceramic conversion processes are discussed with concern for the crystal transition behaviors and the variation of pore properties in different length scales upon heating. In addition, although out of the preceramic polymer category, some examples of inorganic–organic nanocomposite gels with a carbonizable polymer and/or urea for yielding porous metal carbides and nitrides in a monolithic form are introduced as well, which provides extended versatility toward a variety of transition metal systems.
Sol–gel processes accompanied by phase separation provide macroporous monolithic materials with three‐dimensionally interconnected porous structure consisting of a variety of inorganic‐organic hybrids. Calcination of thus obtained preceramic monoliths under inert atmosphere affords hierarchically porous polymer‐derived ceramics with good controllability in terms of pore properties as well as crystal phases.
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