Tailored Pore Size Research Articles

Fine tuning the hydrophobicity of counter‐anions to tailor pore size in porous all‐poly(ionic liquid) membranes

AbstractCharged porous polymer membranes (CPMs) emerging as a multifunctional platform for diverse applications in chemistry, materials science and biomedicine have been attracting widespread attention. Fabrication of CPMs in a controllable manner is of particular significance for optimizing their function and maximizing practical values. Herein, we report the fabrication of CPMs exclusively from poly(ionic liquid)s (PILs), and their pore size and wettability were precisely tailored by rational choice of counter‐anions. Specifically, a stepwise subtle increase in hydrophobicity of the counter‐anions by extending the length of fluorinated alkyl substituents, i.e. from bis(trifluoromethane sulfonyl)imide to bis(pentafluoroethane sulfonyl)imide and bis(heptafluoropropane sulfonyl)imide, decreased the average pore size gradually from 1546 to 157 and 77 nm, respectively. Meanwhile, the corresponding water contact angles increased from 90° to 102° and 120°. The sensitive control over the porous architectures and surface wettability of CPMs by systematic variation of anion hydrophobicity provides solid proof of the impact of PIL anions on CPM structure. © 2019 Society of Chemical Industry

High specific surface area ordered mesoporous silica COK-12 with tailored pore size

Abstract Ordered mesoporous silica materials such as COK-12, analogous to the well-known SBA-15, are characterized by high surface areas and unique features such as defined pore sizes in the meso-size range and high pore ordering. The aim of this work was to prove the washing step and choice of calcination and aging temperature during the COK-12 synthesis as effective tools in tailoring, markedly improving the specific surface area, pore size, and pore volume. By controlling the aging temperature, the pore size was linearly adjusted between 5.7 and 8.1 nm, while preserving the hexagonal ordering of the pores. The synthesized COK-12 powders possess pore volumes and specific surface areas up to 1.23 cm3 g−1 and 860 m2 g−1, respectively, which is markedly higher than what has previously been reported about COK-12. The presented results and the environmentally friendly character of the synthesis will make COK-12 more interesting for future adaption to the industrial processes, for example in catalysis, adsorption, or drug delivery.

Metal-Organic Frameworks Based Nano/Micro/Millimeter-Sized Self-Propelled Autonomous Machines.

Synthetic nano/micro/millimeter-sized machines that harvest energy from the surrounding environment and then convert it to motion have had a significant impact on many research areas such as biology (sensing, imaging, and therapy) and environmental applications. Autonomous motion is a key element of these devices. A high surface area is preferable as it leads to increased propellant or cargo-loading capability. Integrating highly ordered and porous metal-organic frameworks (MOFs) with self-propelled machines is demonstrated to have a significant impact on the field of nano/micro/millimeter-sized devices for a wide range of applications. MOFs have shown great potential in many research fields due to their tailorable pore size. These fields include energy storage and conversion; catalysis, biomedical application (e.g., drug delivery, imaging, and cancer therapy), and environmental remediation. The marriage of motors and MOFs may provide opportunities for many new applications for synthetic nano/micro/millimeter-sized machines. Herein, MOF-based micro- and nanomachines are reviewed with a focus on the specific properties of MOFs.

Hybrid Organic-Inorganic Materials Containing a Nanocellulose Derivative as Chiral Selector.

Hybrid organic-inorganic materials (HOIM), with high mechanical stability, large surface area, tailored pore size, controlled morphology, and organic loading have shown superior chiral separation performance. In this chapter, the preparation of hybrid organic-inorganic materials of core-shell silica microspheres by a layer-by-layer self-assembly method is described. The enantioseparation performance by high-performance liquid chromatography is illustrated by various types of chiral compounds under normal- and reversed-phase elution conditions. The chiral selector of nanocrystalline cellulose derivative hybrid organic-inorganic materials showed good performance in the separation of enantiomers.

Quasi-static and dynamic in vitro mechanical response of 3D printed scaffolds with tailored pore size and architectures

Scaffold-based Tissue Engineering represents the most promising approach for the regeneration of load bearing skeletal tissues, in particular bone and cartilage. Scaffolds play major role in this process by providing a physical template for cells to adhere and proliferate whilst ensuring an adequate biomechanical support at the defect site. Whereas the quasi static mechanical properties of porous polymeric scaffolds are well documented, the response of these constructs under high strain compressive rates remain poorly understood. Therefore, this study investigates, for the first time, the influence of pore size and geometry on the mechanical behaviour of Polycaprolactone (PCL) scaffolds under quasi static and dynamic conditions. 3D printed scaffolds with varied pore sizes and geometries were obtained using different filament distances (FD) and lay-down patterns, respectively. In particular, by fixing the lay-down pattern at 0/90° and varying the FD between 480 and 980 μm it was possible to generate scaffolds with square pores with dimensions in the range of 150–650 μm and porosities of 59–79%. On the other hand, quadrangular, hexagonal, triangular and complex pore geometries with constant porosity (approx. 70%) were obtained at a fixed FD of 680 μm and imposing four different lay-down patterns of 0/90, 0/60/120, 0/45/90/135 and 0/30/60/90/120/150°, respectively. The mechanical response of printed scaffolds was assessed under two different compression loading regimes spanning five distinct strain rates, from 10−2 to 2000 s−1, using two different apparatus: a conventional screw-driven testing machine (Instron 4483) and a Split Hopkinson pressure bar (SHPB) equipped with a set of A201 Flexi-force™ (FF) force sensors and a pulse shaper. Our results show that the mechanical properties of PCL scaffolds are not strain rate sensitive between 1300 and 2000 s−1 and these strongly depend on the pore size (porosity) rather than pore geometry. Those findings are extremely relevant for the engineering of bone tissue scaffolds with enhanced mechanical stability by providing new data describing the mechanical response of these constructs at high strain rates as well as the at the transition between quasi static and dynamic regimes.

Fabrication of dual‐layer poly(styrene‐b‐4‐vinyl pyridine)–poly(vinylidene fluoride) membranes with tailored pore sizes under 10 nm via surface quaternization

ABSTRACTBlock copolymer membranes can be applied to precise size‐based separation because of their highly ordered surface morphology and adjustable pore sizes. However, there is a lower limit of the scale of block copolymer self‐assembly; this makes it a challenge to tailor the pore size down to below 10 nm. In this study, poly(styrene‐b‐4‐vinyl pyridine) membranes were modified to quaternized selective layers with pores smaller than 10 nm and were supported by poly(vinylidene fluoride) hollow fibers as the substrate to provide a high mechanical strength. Two reactants, methyl iodide and 2‐chloroacetamide, were used in the quaternization. With this one‐step chemical modification, the molecular weight cutoff was reduced from 190 to 8 kDa, and the surface pore sizes were narrowed down from 20–30 to 3 nm; this bridged the gap of tailored pore sizes down to below 10 nm. Such membranes are promising candidates for low‐molecular‐weight separation with high resolution. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47137.

Magnetic ordered mesoporous carbon materials for adsorption of minocycline from aqueous solution: Preparation, characterization and adsorption mechanism.

In this paper, the effect of cyanoguanidine (CNGE) for tailoring pore size during the soft-templating preparation of mesoporous carbon materials was studied. In consideration of cyclic utilization, the surface of the mesoporous carbon materials were doped with magnetic Fe3O4 particles. The characterization results (including TEM, XRD, BET, TGA and FT-IR) showed that adding CNGE did not destroy the ordered porous structure; instead, it changed the pore size from 2.98 nm to 9.42 nm. Besides, the mesoporous carbon materials exhibited a strong magnetic response owing to the dopant of Fe3O4 particles. With the increase in CNGE, some functional groups were added to the surface of the mesoporous carbon materials, which partly promoted the adsorption effect. The results indicated that adsorption approached equilibrium in the first 10 min and reached the maximum when the pore size was 5.89 nm. The kinetic of minocycline adsorption on magnetic ordered mesoporous carbon material could be interpreted by a pseudo-first-order model. The adsorption isotherms showed that the adsorption process was complex, combining physical and weak chemical adsorption, in good agreement with the Sips model.

Biocompatible Porous Scaffolds of Chitosan/Poly(EG-ran-PG) Blends with Tailored Pore Size and Nontoxic to Mesenchymal Stem Cells: Preparation by Controlled Evaporation from Aqueous Acetic Acid Solution.

The preparation of porous films (average size variation from 1 to 32 μm) of a 1:1 blend of chitosan with poly(EG-ran-PG) by the controlled evaporation of water from a 2 wt % aqueous acetic acid solution is reported. Interestingly, the blend exhibited porosity that could be tailored from 1 to 32 μm with the temperature of preparation of the blend film. The powder X-ray diffraction, Fourier transform infrared, and differential scanning calorimetry analyses of the films suggested the formation of partially miscible blends. Temperature-induced phase separation of the blend appears to be the mechanism of pore formation. The tensile strength, cytotoxicity, and biocompatibility of the blend films for the growth of mesenchymal stem cells were assessed vis-a-vis chitosan. The 1:1 blend film was observed to lack cytotoxicity and was also viable for the growth of mesenchymal stem cells. The tensile properties of the 1:1 blend were superior to those of the chitosan film. The simple preparation of porous, nontoxic, and biocompatible films could find use as a scaffold in the growth of tissue, and especially bone tissue, in wound dressing, and in filtration if a better control over pore size is achieved.

Synthesis and characterization of novel dendritic macroporous monoliths

The monoliths have changed the paradigm of the supports for applications in different fields, such as chromatography, catalysis, combinatorial chemistry, enzymatic bioreactors, among other. Particularly, the dendronized monoliths are a good alternative of hybrid material due to multivalency. Dendronized macroporous monoliths were prepared from a Newkome-type dendron (Beherás amine) and classical monomers such as NAT, AAm, AAc, and (BIS) as cross-linker. The monoliths have been thoroughly characterized using infrared microscopy, scanning electron microscopy (SEM), thermogravimetric analysis and swelling index. For the reaction, several factors such as monomer, solvent, porogen and their ratios were analysed. The morphological characteristics of monoliths were mainly managed by the conditions of the synthesis way, offering the opportunity to tailor pore size, surface characteristics and porosity. The results demonstrated a compromise between both the dendronized degree and the dynamic in the formation of globules and clusters during the polymerization reaction. It was also demonstrated that the porosity properties were governed by the dendritic moiety of the monoliths.

Synthesis of Silica Xerogels Obtained in Organic Catalyst via Sol Gel Route

Citric acid is an organic acid catalyst and content carbon that is templated into silica network. The mixture between these materials is gratefully useful to tailor pore size of silica-carbon mixtures in the form of silica-carbon sols which robust and good hydrostability properties. This fabricated materials is applied for coated membrane layers (thin film) coated onto membrane substrates for water desalination. This study was aimed to utilize sol gel process to synthesize the functionalization of organic catalyst in silica matrices. Silica xerogels was prepared from TEOS (Tetraethyl orthosilicate) with a two-step organic acid and base catalyst via sol gel method. The hydrolysis and condensation reactions were applied within 3 hours at 50 °C. IR spectra shows that.

Ultrathin nanofilm with tailored pore size fabricated by metal-phenolic network for precise and rapid molecular separation

Abstract The tailored nanofilms have attracted a rapidly growing interest in various separation processes. Recently, microporous materials have provided a promising way to meet this requirement due to their distinct structures. However, suffering from the uncontrollable heterogeneous nucleation, crystalline materials are difficult to form the ultrathin and defect-free nanofilms. Herein, tannic acid (TA)/Fe3+ complex, which was microporous amorphous material, was fabricated on the ultrafiltration membrane via the layer-by-layer technique. Interestingly, in addition to the pH value mentioned in the literature, the aggregation of Fe3+ in the aqueous solution was also found to have significant influence on chemical composition and physical structure of the complex. Through the strict control on the Fe3+ aggregation, the defect-free TA/Fe3+ nanofilm has an average pore size of 0.7 nm, which was the smallest among the reported TA/Fe3+ nanofilms. More importantly, the pore size of nanofilm was in accordance with our expectation, and the molecular dynamic simulation further confirmed the result. It demonstrated that the tailored pore structure of the nanofilm can be designed on the basis of the molecular structure. Moreover, the nanofilm has an ultrathin thickness of 5 nm. To the best of our knowledge, the nanofilm was the thinnest nanofilm used for liquid separation. Compared with the nanofilms made by various materials, the TA/Fe3+ nanofilm obviously broke through the selectivity-permeability trade-off of the nanofilms, with the ultrathin thickness and the narrow pore size distribution. Additionally, the TA/Fe3+ nanofilm can precisely separate molecules that were close in size. This work provides a facile method to fabricate tailored nanofilms with high performance designed at a molecular level.

Adsorption and Detection of Hazardous Trace Gases by Metal-Organic Frameworks.

The quest for advanced designer adsorbents for air filtration and monitoring hazardous trace gases has recently been more and more driven by the need to ensure clean air in indoor, outdoor, and industrial environments. How to increase safety with regard to personal protection in the event of hazardous gas exposure is a critical question for an ever-growing population spending most of their lifetime indoors, but is also crucial for the chemical industry in order to protect future generations of employees from potential hazards. Metal-organic frameworks (MOFs) are already quite advanced and promising in terms of capacity and specific affinity to overcome limitations of current adsorbent materials for trace and toxic gas adsorption. Due to their advantageous features (e.g., high specific surface area, catalytic activity, tailorable pore sizes, structural diversity, and range of chemical and physical properties), MOFs offer a high potential as adsorbents for air filtration and monitoring of hazardous trace gases. Three advanced topics are considered here, in applying MOFs for selective adsorption: (i) toxic gas adsorption toward filtration for respiratory protection as well as indoor and cabin air, (ii) enrichment of hazardous gases using MOFs, and (iii) MOFs as sensors for toxic trace gases and explosives.

Construction of a thermoresponsive magnetic porous polymer membrane enzyme reactor for glutaminase kinetics study.

Fabrication of polymer membranes with nanopores and a confinement effect toward enzyme immobilization has been an enabling endeavor. In the work reported here, an enzyme reactor based on a thermoresponsive magnetic porous block copolymer membrane was designed and constructed. Reversible addition-fragmentation chain transfer polymerization was used to synthesize the block copolymer, poly(maleic anhydride-styrene-N-isopropylacrylamide), with poly(N-isopropylacrylamide) as the thermoresponsive moiety. The self-assembly property of the block copolymer was used for preparation of magnetic porous thin film matrices with iron oxide nanoparticles. By covalent bonding of glutaminase onto the surface of the membrane matrices and changing the temperature to tune the nanopore size, we observed enhanced enzymolysis efficiency due to the confinement effect. The apparent Michaelis-Menten constant and the maximum rate of the enzyme reactor were determined (Km = 32.3 mM, Vmax = 33.3 mM min-1) by a chiral ligand exchange capillary electrochromatography protocol with L-glutamine as the substrate. Compared with free glutaminase in solution, the proposed enzyme reactor exhibits higher enzymolysis efficiency, greater stability, and greater reusability. Furthermore, the enzyme reactor was applied for a glutaminase kinetics study. The tailored pore sizes and the thermoresponsive property of the block copolymer result in the designed porous membrane based enzyme reactor having great potential for high enzymolysis performance. Graphical abstract ᅟ.

Porous ceramics with tailored pore size and morphology as substrates for coral larval settlement

The growing demand for stony corals as ornamental aquarium animals requires defined aquacultural breeding strategies. For the sexual propagation of corals, material substrates are needed, that attract larvae and support their settlement and development. In this study, five types of highly porous ceramic materials were developed following the example of coral skeleton. The applicability of these settlement substrates was tested using larvae of the stony coral Pocillopora damicornis. Partial sintering of pressed clay pellets, freeze casting of clay and alumina-mullite based slurries and direct foaming of high alkane phase emulsified suspensions (HAPES) using alumina were employed. By the addition of mm-sized spherical polystyrene beads as sacrificial templates during freeze casting (alumina-mullite), superficial pores in the size of the larvae were created. The inorganic substrates featured open porosities between 35% (pressed clay) and 83% (foamed alumina), pore sizes ranging from nm to mm-scale and pore morphologies dominated by interparticle porosity (pressed), lamellar pores (freeze casting) and cellular pore types (direct foaming). The ceramic substrates were incubated in artificial sea water for 3 months to induce necessary biofilm formation and algae growth. Afterwards, individual substrates were exposed to 5 coral larvae, and their settlement behavior was monitored over 14 days. At the end of this period, all ceramic materials were successfully accepted as settlement substrates, with a mean settlement rate of 46.2%, and no significant differences between the substrate types. On samples with large surface superficial pores, a significantly reduced survival of settled larvae (79%) compared to the other porous materials (93–98%) was determined, suggesting a non-ideal surface topography. While alumina foam samples (HAPES) exhibit the most promising results in terms of settlement and survival of larvae, clay-based substrates provide a more economic solution for the sexual propagation of corals in aquaculture.

Facile Synthesis of Mixed Metal–Organic Frameworks: Electrode Materials for Supercapacitors with Excellent Areal Capacitance and Operational Stability

Electrode materials with high surface area, tailored pore size, and efficient capability for ion insertion and enhanced transport of electrons and ions are needed for advanced supercapacitors. In the present study, a mixed metal-organic framework (MOF) (cobalt- and manganese-based MOF) was synthesized through a simple one-pot solvothermal method and employed as the electrode material for the supercapacitor. Notably, a Co-Mn MOF electrode displayed a large surface area and excellent cycling stability (over 95% capacitance retention after 1500 cycles). Also, superior pseudocapacitive behavior was observed for the Co-Mn MOF electrode in the KOH electrolyte with an exceptional areal capacitance of 1.318 F cm-2. Moreover, an asymmetric supercapacitor was assembled using Co-Mn MOF and activated carbon electrode as positive and negative electrodes, respectively. The fabricated supercapacitor showed a specific capacitance of 106.7 F g-1 at a scan rate of 10 mV s-1 and delivered a maximum energy density of 30 W h kg-1 at 2285.7 W kg-1. Our studies suggest the Co-Mn MOF as promising electrode materials for supercapacitor applications.

Three-dimensional printing of porous carbon structures with tailorable pore sizes

• Porous carbon structures with tailorable pore sizes fabricated via 3D printing. • Monodispersed SiO 2 spheres were used as hard template as well as viscosifier. • The surface areas and porous structures can be precisely controlled. • The printed catalyst shows good performance for oxidation of benzyl alcohol. Structured porous carbon materials have been extensively applied for catalyst, sensor, adsorbent, energy storage materials and many others. However, the preparation of such carbon materials in a controllable way remains a significant challenge. In this work, 3D printing has been employed to prepare porous carbon structures with tailorable pore sizes. A starch/gelatin ink has been applied as carbon source with SiO 2 monodispersed spheres as hard template. The process exhibits an excellent printing accuracy. Controllable meso and macro structures can be thereby obtained. The printed monolithic structures have been used as metal-free catalysts for the selective oxidation of benzyl alcohol, as an illustration. The monolithic and meso/macro-porous structure has a remarkable influence on the reaction rate. A high conversion with high benzaldehyde selectivity has been achieved. The 3D printing strategy provides us a simple, low cost and reliable way of fabricating carbon structures with designable meso/macro-pores, which is promising for many other applications beyond catalysis.

"Novel Adsorbent for Wastewater Treatment: Tailored Pore Size for Hazards from Aqueous Solution"

"Novel Adsorbent for Wastewater Treatment: Tailored Pore Size for Hazards from Aqueous Solution"

Tailoring the pore size distribution of self-cross-linked 4,4′-bis(chloromethyl)-1,1′-biphenyl polymers using reactive and non-reactive co-solvents

Self-cross-linked 4,4′-bis(chloromethyl)-1,1′-biphenyl (BCMBP) polymers with tailored pore size distribution (PSD) and average pore width (Wavg) were synthesized via the Friedel-Crafts reaction in 1,2-dichloroethane (DCE) with reactive (benzene) or non-reactive (hexane and cyclohexane) co-solvents. Compared to using only DCE, Wavg increases (up to 450%) with increasing benzene:DCE ratio due to decreases in cross-linking degree. Hexane and cyclohexane induce phase separation and co-solvent trapping in developing polymers, changing PSD and Wavg without altering cross-linking degree. Findings provide a simple technique to synthesize hyper-cross-linked polymers with user-defined PSDs.

Tailoring Pore Size, Structure, and Morphology of Hierarchical Mesoporous Silica Using Diblock and Pentablock Copolymer Templates

Mesoporous materials of tailored pore size, structure, and morphology are of interests for a wide range of applications. It is important to develop synthetic methods that will allow for easy proces...

High-Throughput Computational Screening of the Metal Organic Framework Database for CH4/H2 Separations.

Metal organic frameworks (MOFs) have been considered as one of the most exciting porous materials discovered in the last decade. Large surface areas, high pore volumes, and tailorable pore sizes make MOFs highly promising in a variety of applications, mainly in gas separations. The number of MOFs has been increasing very rapidly, and experimental identification of materials exhibiting high gas separation potential is simply impractical. High-throughput computational screening studies in which thousands of MOFs are evaluated to identify the best candidates for target gas separation is crucial in directing experimental efforts to the most useful materials. In this work, we used molecular simulations to screen the most complete and recent collection of MOFs from the Cambridge Structural Database to unlock their CH4/H2 separation performances. This is the first study in the literature, which examines the potential of all existing MOFs for adsorption-based CH4/H2 separation. MOFs (4350) were ranked based on several adsorbent evaluation metrics including selectivity, working capacity, adsorbent performance score, sorbent selection parameter, and regenerability. A large number of MOFs were identified to have extraordinarily large CH4/H2 selectivities compared to traditional adsorbents such as zeolites and activated carbons. We examined the relations between structural properties of MOFs such as pore sizes, porosities, and surface areas and their selectivities. Correlations between the heat of adsorption, adsorbility, metal type of MOFs, and selectivities were also studied. On the basis of these relations, a simple mathematical model that can predict the CH4/H2 selectivity of MOFs was suggested, which will be very useful in guiding the design and development of new MOFs with extraordinarily high CH4/H2 separation performances.