Macroporous Particles Research Articles

Hierarchically Porous Carbon Networks Derived from Chitosan for High-Performance Electrochemical Double-Layer Capacitors.

Activated carbon (AC) compounds derived from biomass precursors have garnered significant attention as electrode materials in electric double-layer capacitors (EDLCs) due to their ready availability, cost-effectiveness, and potential for mass production. However, the accessibility of their active sites in electrochemistry has not been investigated in detail. In this study, we synthesized two novel macro/micro-porous carbon structures prepared from a chitosan precursor using an acid/potassium hydroxide activation process and then examined the relationship between their textural characteristics and capacitance as EDLCs. The material characterizations showed that the ACs, prepared through different activation processes, differed in porosity, with distinctive variations in particle shape. The sample activated at 800 °C (Act-chitosan) was characterized by plate-shaped particles, a specific surface area of 4128 m2/g, and a pore volume of 1.87 cm3/g. Assessment of the electrochemical characteristics of Act-chitosan showed its remarkable capacitance of 183.5 F/g at a scan rate of 5 mV/s, and it maintained exceptional cyclic stability even after 10,000 cycles. The improved electrochemical performance of both chitosan-derived carbon structures could thus be attributed to their large, well-developed active sites within pores < 2 nm, despite the fact that interconnected macro-porous particles can enhance ion accessibility on electrodes. Our findings provide a basis for the fabrication of biomass-based materials with promising applications in electrochemical energy storage systems.

Kinetic model describing self-limiting CO2 diffusion in supported amine adsorbents

A reaction–diffusion shrinking core model describing the decay in diffusivity of supported amine sorbents upon CO2 sorption under both simulated direct air capture and point source capture conditions is described. The decay in CO2 diffusivity is associated with crosslinking in the aminopolymer samples and general pore blockage in the amino-silane derived samples, which occurs as CO2 is adsorbed. The model is used to extract four kinetic parameters that govern the CO2 uptake kinetics and working capacity: an apparent reaction rate constant, an initial effective diffusivity, and two dimensionless decay parameters. Ideally, an initially reaction limited system would allow for direct determination of the intrinsic reaction rate constant; however, sorption experiments suggest mass transfer resistances related to gas mixing, external boundary layers and intraparticle diffusion are present. Reaction rate constants are determined and agree well with theoretical values predicted with the Eyring equation parameterized using density functional theory energies from literature sources. The kinetic performance is expressed as the average effective diffusivity as a function of average conversion, which can be correlated to the dispersion of sorption sites on the support and the morphology of the active sorbent phase. Four supports are impregnated or grafted with amines, SBA-15, single-walled zeolite nanotubes (ZNT), Syloid SiO2, and γ-Al2O3. Due to its pore structure, γ-Al2O3 supported amines can be modeled at the μm scale or at the nm scale, where the shell balance is on the μm-sized macroporous particle aggregate or on the nm-sized amine film on the surface of the Al2O3 nanoparticles, which comprise the spherical particle aggregates. Faster diffusion rates are maintained under 400 ppm rather than 10% CO2 due to a slower reaction rate giving a slower decay in diffusivity. This work provides a first principles kinetic analysis of CO2 sorption where previous models are semi-empirical and use arbitrary kinetic parameters.

Microspherical polystyrene-divinylbenzene particles hybridized with eremomycin stabilized gold nanoparticles as a stationary phase for chiral liquid chromatography

A novel enantioselective adsorbent was obtained by hybridization of microspherical polystyrene-divinylbenzene (PS-DVB) macroporous particles with eremomycin-stabilized gold nanoparticles (GNPs). Macrocyclic antibiotic eremomycin was used as a stabilization agent to obtain GNPs which were then characterized by transmission electron microscope. The average diameter of obtained nanoparticles is about 16.6 nm. Eremomycin-stabilized nanoparticles were successfully embedded into the porous polymer structure with a resulting chiral selector content of 37.5 pmol/g. The obtained PS-DVB composite containing GNPs with immobilized eremomycin was studied by scanning electron microscopy and diffuse reflectance spectroscopy. The values of the specific surface area (500 m2/g) and porosity of the adsorbent (0.39 cm3/g) are measured using nitrogen adsorption at low temperatures. The obtained composite material was used as a chiral stationary phase of liquid chromatography. A good separation enantio-selectivity to amino acids, their derivatives and beta-blockers under RPC (reversed-phase) and HILIC (Hidrophilic Interaction Liquid Chromatography) mode is demonstrated. The results obtained revealed that the prepared Eremo@GNP@PS-DVB composite is promising for use as a stationary phase in HPLC.

Versatility of the Preparation Method for Macroporous Cryogel Particles Utilizing the Inverse Leidenfrost Effect.

We have investigated the versatility of a two-step preparation method, without a detergent, that combines both the inverse Leidenfrost effect and the cryogelation technique by using the macroporous particles of different kinds of monomers (four vinyl monomers) or a natural polymer (agarose). First, the precursor of polymers was dropped into liquid nitrogen to prepare the spherical frozen droplet by the inverse Leidenfrost effect. Second, the frozen droplets were cryo-polymerized at the frozen temperature; then, cryogel particles were prepared after thawing. Subsequently, the basic characteristics of the macroporous polymer particles obtained above were compared, focusing on the appearances, porous morphologies, and mechanical properties. It was found that the similar polymer particles could be obtained by the two-step preparation method, while there was a slight difference in their characteristics, depending on the type of monomers. Especially for the mechanical properties, the cryogel particles of the hydrophilic polymer exhibited a shape memory function with sponge-like elasticity, whereas the hydrophobic polymer particles were observed to be cracked after compression (i.e., no shape memory function). This work provides a versatile method of adopting various kinds of monomers and natural polymers for the preparation of macroporous particles. Hence, the method possibly has a potential to prepare and design "tailor-made" macroporous polymer particles for the application purpose.

Synthesis of macroporous three-way catalysts via template-assisted spray process for enhancing mass transfer in gas adsorption

Catalyst particles with macroporous structures have been attracting much attention because of their high molecular diffusions and catalytic activities. In this study, macroporous-structured three-way catalyst (TWC) particles were synthesized via a template-assisted spray process followed by an additional heating process. Several process parameters, i.e., carrier-gas type, template size, and reaction temperature, were investigated to enable preparation of macroporous particles with controllable porous structures and interconnected pore networks. The mass transfer coefficients of the obtained macroporous TWC particles were assessed using the Linear Driving Force approximation to understand the effects of the macroporous structure on the mass transfer improvement. The results showed that the introduction of macropores into TWC particles enhances the mass transfer coefficient.

The Novel Polymethacrylate Based Hydrophilic Stationary Phase for Ion Chromatography.

Ion chromatography is widely used as a useful and powerful tool for the analysis of anionic and cationic components found in waters and aqueous media. The performance and selectivity of ion chromatography are based on the stationary phase column packed material. In this study, it is aimed to develop new column material with quaternary ammonium functional group based on monodisperse polymeric particles for ion chromatography and to investigate their chromatographic performance. For the analysis of inorganic anions by ion chromatography, new stationary phases macroporous monodisperse particles based on 3-chloro-2-hydroxy propylmethacrylate-co-ethylene dimethacrylate are obtained as column packing material. 3-chloro-2-hydroxy propylmethacrylate and ethylene glycol dimethacrylate are transformed to porous monodisperse particle form by using glycidyl methacrylate as the seed latex and ethyl benzene as the porogen solvent via micro-suspension polymerization technique. Then macroporous monodisperse particles surface is functionalized by triethylamine so strong anion exchange is obtained for ion chromatography packing material. A series of stationary phases prepared from polymer particles containing different amounts of porogen solvent were tested. The results show that column packing material is successful to separate inorganic anions mixture such as F-, Cl-, NO2-, Br-, NO3- by using the carbonate and bicarbonate solutions as mobile phases.

Enhanced Protein Adsorption Capacity of Macroporous Pectin Particles with High Specific Surface Area and an Interconnected Pore Network.

There has been much interest in developing protein adsorbents using nanostructured particles, which can be engineered porous materials with fine control of the surface and pore structures. A significant challenge in designing porous adsorbents is the high percentage of available binding sites in the pores owing to their large surface areas and interconnected pore networks. In this study, continuing the idea of using porous materials derived from natural polymers toward the goal of sustainable development, porous pectin particles are reported. The template-assisted spray drying method using calcium carbonate (CaCO3) as a template for pore formation was applied to prepare porous pectin particles. The specific surface area was controlled from 177.0 to 222.3 m2 g-1 by adjusting the CaCO3 concentration. In addition, the effects of a macroporous structure, the specific surface area, and an interconnected pore network on the protein (lysozyme) adsorption capacity and adsorption mechanism were investigated. All porous pectin particles performed rapid adsorption (∼65% total capacity within 5 min) and high adsorption capacity, increasing from 1543 to the highest value of 2621 mg g-1. The results are attributed to the high percentage of available binding sites located in the macropores owing to their large surface areas and interconnected pore networks. The macroporous particles obtained in this study showed a higher adsorption capacity (2621 mg g-1) for lysozyme than other adsorbents. Moreover, the rapid uptake and high performance of this material show its potential as an advanced adsorbent for various macromolecules in the food and pharmaceutical fields.

Synthesis of High Specific Surface Area Macroporous Pectin Particles by Template-Assisted Spray Drying.

Many types of porous particles containing inorganic and organic substances, such as carbon, metals, metal oxides, inorganic-organic hybrids, and polymers, have been developed. However, natural polymer-derived particles are relatively rare. To our knowledge, this report describes the first synthetic method for obtaining meso-/macroporous particles made from pectin, which is a natural polymer with a wide range of biological activities suitable for active substance support applications. These porous particles were prepared using a template-assisted spray-drying method, followed by a chemical etching process. An organic template [i.e., poly(methyl methacrylate) (PMMA)] or an inorganic template [i.e., calcium carbonate (CaCO3)] was used to evaluate the resulting formation of macroporous structures in the pectin particles. Furthermore, the concentration of the templates in the precursor solution was varied to better understand the mechanism of porous pectin particle formation. The results showed that the final porous particles maintained the characteristic properties of pectin. The differences between the two templates resulted in two distinct types of porous particles that differed in their particle morphologies (i.e., spherical or wrinkled), particle sizes (ranging from 3 to 8 μm), pore sizes (ranging from 80 to 350 nm), and pore volume (ranging from 0.024 to 1.40 cm3 g-1). Especially, the porous pectin particles using the CaCO3 template have a significantly high specific surface area of 171.2 m2 g-1, which is 114 times higher than that of nonporous pectin particles. These data demonstrated the potential for using PMMA and CaCO3 templates to control and design desired porous materials.

Synthesis of Porous Silica Particles for the Adsorption of Organic Dye in Aqueous Medium

This study investigated the removal of the organic dye like methylene blue using porous particles in a batch adsorption process. Porous silica microparticles were synthesized with macropores or meso-macropores and used as adsorbent particles. The hierarchically porous structures with additional mesopores were found to be more effective adsorbent than simple macroporous particles. The size of the macropores affected the adsorption capacity of the porous particles, and smaller pore size resulted in a larger amount of organic dye being adsorbed on the particle surface, due to increased surface area. Silica microparticles with wrinkled surfaces were also tested, and their adsorption capacities were studied in relation to their morphologies. Unlike previous studies using mesoporous silica as adsorbents, in this study the methylene blue adsorption kinetics could be explained by the second to fourth order reaction, implying that faster removal of dye molecules is possible compared to photocatalytic reactions, with first order kinetics. The higher order kinetics can be advantageous, providing a faster removal rate, compared to the conventional photocatalytic removal of dyes and other adsorbents.

Hierarchical Macroporous Particles for Efficient Whole-Cell Immobilization: Application in Bioconversion of Greenhouse Gases to Methanol.

A viable approach for methanol production under ambient physiological conditions is to use greenhouse gases, methane (CH4) and carbon dioxide (CO2), as feed for immobilized methanotrophs. In the present study, unique macroporous carbon particles with pore sizes in the range of ∼1-6 μm were synthesized and used as support for the immobilization of Methylocella tundrae. Immobilization was accomplished covalently on hierarchical macroporous carbon particles. Maximal cell loading of covalently immobilized M. tundrae was 205 mgDCM g-1 of particles. Among these particles, the cells immobilized on 3.6 μm pore size particles showed the highest reusability with the least leaching and were chosen for further study. After immobilization, M. tundrae showed up to 2.4-fold higher methanol production stability at various pH and temperature values because of higher stability and metabolic activity than free cells. After eight cycles of reuse, the immobilized cells retained 18.1-fold higher relative production stability compared to free cells. Free and immobilized cells exhibited cumulative methanol production of 5.2 and 9.5 μmol mgDCM-1 under repeated batch conditions using simulated biogas [CH4 and CO2, 4:1 (v/v)] as feed, respectively. The appropriate pore size of macroporous particles favors the efficient M. tundrae immobilization to retain better biocatalytic properties. This is the first report concerning the covalent immobilization of methanotrophs on the newly synthesized macroporous carbon particles and its subsequent application in repeated methanol production using simulated biogas as a feed.

Synthesis of Macroporous Silica Particles by Continuous Generation of Droplets for Insulating Materials.

We report on the synthesis of porous silica particles by self-assembly routes in a continuous manner for application to thermal insulators. A continuous process was employed to produce tiny droplets containing precursor materials such as silica and organic templates for self-organization to fabricate particles with well defined pores. A rotating cylinder system or a spray drying process was adopted to form emulsions or aerosol droplets as micro-reactors for self-assembly, and the physical properties including the thermal conductivity of the resulting porous particles were compared between the two methods. The porous particles could be coated as a thick film by solution dripping, and the fluorination treatment using a silane coupling agent was performed to produce superhydrophobic surfaces of insulating layers by a lotus effect.

Vortex Fluidic Mediated Synthesis of Macroporous Bovine Serum Albumin-Based Microspheres.

Macroporous bovine serum albumin (BSA) nanoparticles with controllable diameter were readily fabricated in a rapidly rotating angled glass tube in a vortex fluidic device (VFD). Systematically varying the rotational speed and the ratio of BSA, ethanol, and glutaraldehyde led to conditions for generating ca. 600 nm diameter macroporous particles that have intrinsic fluorescence emission at 520 nm when excited at 490 nm. The presence of the macropores increased the absorption efficiency of rhodamine B with potential applications for drug delivery purpose, compared with BSA nanoparticles having surfaces devoid of pores. Further control over the size of BSA nanoparticles occurred in the presence of C-phycocyanin protein during the VFD processing, along with control of their shape, from spheres to pockets, as established in exploring the parameter space of the microfluidic device.

Development and application of a biocatalyst-filter reactor for the continuous production of caseinate hydrolysate surfactants

Abstract A novel continuous process for enzymatic production of sodium caseinate hydrolysates with a low degree of hydrolysis (DH) and increased interfacial behaviour was developed. Retention of free peptidase in the reactor (separation of the peptidase from the product via an ultra-filtration membrane) was not possible because the peptidase used (thermolysin-like peptidase from Geobacillus stearothermophilus; Sternzym BP 25201; 34 kDa, approximately 4.3 nm) was smaller than the hydrolysate product (up to 90 μm). Thus, the peptidase was immobilized on macroporous particles (Sepabeads EC-EP/M; 200–500 μm) and applied for the process consisting of a stirred reactor vessel and a metal filter (150 μm) as the separation unit. A consistent DH of 2.2–2.6% was obtained by adding about 1/3 of the initial peptidase activity per day or adjusting the residence time. This DH resulted in improved foam and emulsion behaviours (foam stability increased to 139 ± 2.3%; emulsion stability increased to 162 ± 9%) of the filtrate compared to substrate and was like a hydrolysate produced in a batch hydrolysis using the free enzyme. However, the continuous process was superior to the batch process because it resulted in an increased space-time yield (155%) and enzyme productivity (695%).

Preparation of Macroporous Mn3O4 Microspheres via Thermal Decomposition in Water Vapor

AbstractMacroporous materials are in constant demand for use in environmental purification filters. Although the preparation of porous materials by a thermal decomposition route without templates and surfactants is simple, low‐cost, and scalable, the pore size of the resulting materials is limited to micropore or mesopore regions. Herein, I report the preparation of macroporous Mn3O4 microspheres from MnCO3 spheres via thermal decomposition in water vapor. The accelerated decomposition of MnCO3 by water vapor facilitates vermicular growth of Mn3O4 primary particles at a low temperature, leading to the formation of a maze‐like pore structure. The characteristic microstructure of macroporous Mn3O4 microspheres exhibits nanoparticle capture properties and inherited its pore structure of Mn3O4 during conversion to Mn2O3 by reheating. This study reveals new possibilities for the application of the thermal decomposition method to prepare macroporous particles.

One-step Preparation of Monodisperse Multifunctional Macroporous Particles through a Spontaneous Physical Process.

Macroporous particles that combine the property features of spherical structures and porous materials are expected to find use over micro- and macroscopic length scales from miniaturized systems such as cell imaging, drug and gene delivery to industrial applications. However, the capacity for de novo design of such materials is still limited. Here, a spontaneous process to fabricate monodisperse multifunctional macroporous particles (MMMPs) by high internal phase emulsion templating is reported. An interesting physical phenomenon involving self-emulsification and synergistic effects between nanoparticles and amphiphilic diblock copolymers is observed in this process. These MMMPs, featured with tailor-made pore structures, pH responsiveness, and magnetic response, could be used as stimuli-responsive carriers for multiple functional molecules with a high loading and releasing efficiency. This new understanding regarding the underlying phenomena that control self-emulsification behavior and synergistic action in emulsion systems provides a unique outlook and a novel approach to the design of potentially multifunctional porous materials for controllable release and delivery processes.

Macroporous microspheres and microspheroidal particles from polyhydromethylsiloxane

Polysiloxane macroporous microspheres and macroporous spheroidal particles were generated from a linear siloxane polymer using a simple emulsion procedure. Osmotic pressure produced by nano-dispersed ionic salt solution in polysiloxane droplets formed in aqueous emulsion is proposed as a mechanism of macropore formation. The competition between cross-linking of the polymer and osmotic swelling of the microspheres governs the shape and porosity of the particles which were characterized by SEM, 29Si MAS NMR, mercury intrusion porosimetry, and X-ray computed tomography.

Preparation of macroporous replica particles using stereocomplex of isotactic poly(methyl methacrylate) and syndiotactic poly(methacrylic acid)

Macroporous silica gel was employed for layer-by-layer (LbL) film preparation of isotactic- (it-) poly(methyl methacrylate) (PMMA) and syndiotactic- (st-) poly(methacrylic acid) (PMAA). The extraction of macroporous silica gel by fluorine hydride resulted in macroporous replica particles, confirmed by SEM. The further extraction of st-PMAA from their particles gave the macroporous replica consisting of porous it-PMMA films. The obtained porous it-PMMA films as macroporous replica particles showed the re-incorporation of st-PMAA. Therefore, the structure of the porous it-PMMA film was stabilized by the macroporous particle structure, although they did not include substrate. The physically crosslinked network structures maintained the molecular porous structures, without a chemically crosslinked reaction.

Nucleic acid separations using superficially porous silica particles

Ion pair reverse-phase liquid chromatography has been widely employed for nucleic acid separations. A wide range of alternative stationary phases have been utilised in conjunction with ion pair reverse-phase chromatography, including totally porous particles, non-porous particles, macroporous particles and monolithic stationary phases. In this study we have utilised superficially porous silica particles in conjunction with ion pair reverse-phase liquid chromatography for the analysis of nucleic acids. We have investigated a range of different pore-sizes and phases for the analysis of a diverse range of nucleic acids including oligonucleotides, oligoribonucleotides, phosphorothioate oligonucleotides and high molecular weight dsDNA and RNA. The pore size of the superficially porous silica particles was shown to significantly affect the resolution of the nucleic acids. Optimum separations of small oligonucleotides such as those generated in RNase mapping experiments were obtained with 80Å pore sizes and can readily be interfaced with mass spectrometry analysis. Improved resolution of larger oligonucleotides (>19mers) was observed with pore sizes of 150Å. The optimum resolution for larger dsDNA/RNA molecules was achieved using superficially porous silica particles with pore sizes of 400Å. Furthermore, we have utilised 150Å pore size solid-core particles to separate typical impurities of a fully phosphorothioated oligonucleotide, which are often generated in the synthesis of this important class of therapeutic oligonucleotide.

Effect of Solvents on the Surface Modification of Hydrophilic Macro-Porous Particles with an Ion-Exchange Monomer Having Both Anion and Cation Exchange Groups

Effect of Solvents on the Surface Modification of Hydrophilic Macro-Porous Particles with an Ion-Exchange Monomer Having Both Anion and Cation Exchange Groups

Macroporous zirconia particles prepared by subcritical water in batch and flow processes

Porous zirconia particles were synthesized through a low-temperature hydrothermal synthesis process. Under hydrothermal conditions, water can control the direction of crystal growth, morphology, particle size, and size distribution because thermodynamics and transport properties can be controlled by pressure and temperature. In a batch process, the hydrothermal synthesis was conducted at 200–300 °C and 30 MPa with an SUS-304 tube as the reactor. At the same reaction pressure, experiments were also performed for a flow process with temperatures of 180–200 °C. The synthesized products were calcined and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results showed that the macroporous zirconia particles that were formed had pore diameters around 419 nm. The XRD pattern indicated that the products were composed of zirconium oxide particles with monoclinic, tetragonal, and cubic structures.