Controlled Pore Size Distribution Research Articles

Aerosol synthesis of nanoporous silica particles with controlled pore size distribution

Spherical porous silica particles with well-defined mesoscopic pore structures were synthesized by spray drying of nanocolloidal SiO2, using polyvinylpyrrolidone (PVP) as pore template. During droplet drying, the surface tension of the water leads to spherical close-packed agglomerates of PVP coated silica nanoparticles. After removal of the PVP by calcination, well-defined porous particles were obtained which were characterized by SEM, TEM and nitrogen adsorption–desorption isotherms. Pore size distribution and porosity could be tailored by using colloidal nanosuspensions with different silica particle sizes and by adding different amounts of template (PVP) into the colloidal silica solution. By adding Co3O4 nanoparticles as active phase into the starting suspension, porous catalytic particles were produced by spray drying and calcination. These particles, after reduction to metallic cobalt, are intended to be used as catalyst for the Fischer–Tropsch synthesis, where the product selectivity can be adjusted by tuning the pore size distribution.

Sulfur-infiltrated porous carbon microspheres with controllable multi-modal pore size distribution for high energy lithium–sulfur batteries

Sulfur has received increasing attention as a cathode material for lithium-sulfur (Li-S) batteries due to its high theoretical specific capacity. However, the commercialization of Li-S batteries is limited by the challenges of poor electrical conductivity of sulfur, dissolution of the polysulfide intermediates into the electrolyte, and volume expansion of sulfur during cycling. Herein, we report the fabrication of novel-structured porous carbon microspheres with a controllable multi-modal pore size distribution, i.e., a combination of interconnected micropores, mesopores and macropores. Cathodes made of sulfur infiltrated in such a hierarchical carbon framework provide several advantages: (1) a continuous and high surface area carbon network for enhanced electrical conductivity and high sulfur loading; (2) macropores and large mesopores bridged by small mesopores to provide good electrolyte accessibility and fast Li ion transport and to accommodate volume expansion of sulfur; and (3) small mesopores and micropores to improve carbon/sulfur interaction and to help trap polysulfides. An initial discharge capacity at 1278 mA h g(-1) and capacity retention at 70.7% (904 mA h g(-1)) after 100 cycles at a high rate (1 C) were achieved. The material fabrication process is relatively simple and easily scalable.

Controlling the Effective Surface Area and Pore Size Distribution of sp2 Carbon Materials and Their Impact on the Capacitance Performance of These Materials

A series of sp(2) carbon materials with different specific surface area (SSA) and controlled pore size distribution (PSD) were synthesized at large scale through a facile and low-cost method. The SSA and PSD of these carbon materials were controlled by using different carbon sources and preparation methods. With different total and effective SSA (E-SSA) and PSD, the impacts on their capacitance performance were investigated thoroughly, which demonstrated that both E-SSA and PSD played the most important roles in their capacitance performance. Furthermore, theoretical modeling was performed, and the results are in agreement with the experimental results for the influence of E-SSA and PSD on their capacitance performance. Based on these, a general model using the slit/cylindrical NL-DFT approach is proposed for the estimation of the specific capacitance of sp(2) carbon materials, which offers a simple but reliable method to predict the capacitance performance of these materials, thus speeding up the design and screening of the materials for high-performance supercapacitor and other surface area related devices.

Photocrosslinkable Kappa‐Carrageenan Hydrogels for Tissue Engineering Applications

Kappa carrageenan (κ-CA) is a natural-origin polymer that closely mimics the glycosaminoglycan structure, one of the most important constituents of native tissues extracellular matrix. Previously, it has been shown that κ-CA can crosslink via ionic interactions rendering strong, but brittle hydrogels. In this study, we introduce photocrosslinkable methacrylate moieties on the κ-CA backbone to create physically and chemically crosslinked hydrogels highlighting their use in the context of tissue engineering. By varying the degree of methacrylation, the effect on hydrogel crosslinking was investigated in terms of hydration degree, dissolution profiles, morphological, mechanical, and rheological properties. Furthermore, the viability of fibroblast cells cultured inside the photocrosslinked hydrogels was investigated. The combination of chemical and physical crosslinking procedures enables the formation of hydrogels with highly versatile physical and chemical properties, while maintaining the viability of encapsulated cells. To our best knowledge, this is the first study reporting the synthesis of photocrosslinkable κ-CA with controllable compressive moduli, swelling ratios and pore size distributions. Moreover, by micromolding approaches, spatially controlled geometries and cell distribution patterns could be obtained, thus enabling the development of cell-material platforms that can be applied and tailored to a broad range of tissue engineering strategies.

Synthesis and characterization of bimodal mesoporous silica

Mesoporous silica with controllable bimodal pore size distribution was synthesized with cetyltrimethylammonium bromide (CTAB) as chemical template for small mesopores and silica gel as physical template for large mesopores. The structure of synthesized samples were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2 adsorption-desorption measurements. The experimental results show that bimodal mesoporous silica consists of small mesopores of about 3 nm and large mesopores of about 45 nm. The small mesopores which were formed on the external surface and pore walls of the silica gel had similar characters with those of MCM-41, while large mesopores were inherited from parent silica gel material. The pore size distribution of the synthesized silica can be adjusted by changing the relative content of TEOS and silica gel or the feeding sequence of silica gel and NH4OH.

Template-free environmentally friendly synthesis and characterization of unsupported tungsten carbide with a controllable porous framework

Tungsten carbide (WC) with controlled pore size distribution was synthesized using a novel “precursor reassembly” method. The precursor crystal was assembled by mixing ammonium metatungstate (AMT) and ammonium carbonate (AC) in distilled water, followed by hydrothermal treatment. The mesostructure, crystal phase, and amount of deposited graphitic carbon can be conveniently tuned by controlling carburizing atmosphere (CO or a CO/H 2 mixture). Moreover, the influence of precursor preparation (AMT/AC mass ratio and hydrothermal temperature) on the materials was also investigated. The resultant materials with low carbon content were mesoporous WCs, which showed high specific surface areas (11.3–20.4 m 2 g −1) and adjustable pore-size distributions (average pore size: 15.3–22.3 nm). A mechanism for the formation of WC with a controllable porous framework is proposed. Finally, cyclic voltammetry was used to investigate the inference of different mesoporous structure.

Sequential Vapor Infiltration of Metal Oxides into Sacrificial Polyester Fibers: Shape Replication and Controlled Porosity of Microporous/Mesoporous Oxide Monoliths

The preparation of microporous and mesoporous metal oxide materials continues to attract considerable attention, because of their possible use in chemical separations, catalyst support, chemical sensors, optical and electronic devices, energy storage, and solar cells. While many methods are known for the synthesis of porous materials, researchers continue to seek new methods to control pore size distribution and macroscale morphology. In this work, we show that sequential vapor infiltration (SVI) can yield shape-controlled micro/mesoporous materials with tunable pore size, using polyesters as a sacrificial template. The reaction proceeds by exposing polymer fiber templates to a controlled sequence of metal organic and co-reactant vapor exposure cycles in an atomic layer deposition (ALD) reactor. The precursors infuse sequentially and thereby distribute and react uniformly within the polymer, to yield an organic–inorganic hybrid material that retains the physical dimensions of the original polymer template. Subsequent calcination in air results in an inorganic microporous/mesoporous material that again retains the macroscopic physical shape of the starting polymer matrix. The microporous/mesoporous structure is confirmed by microscopy and nitrogen adsorption/desorption analysis, and the resulting pore size is controlled by the size of the starting polymer repeat unit and by the kinetics of the infiltration/annealing process steps. In situ infrared transmission and quartz crystal microbalance results confirm the chemical reaction mechanisms. The chemical transformation that occurs during SVI could be important for a range of applications that utilize well-defined porous nanostructures.

Production of Porous Polymeric Films with Unimodal or Bimodal Pore-Size Distributions via Depressurization- and Photopolymerization-Induced Bubble Nucleation in Low-Viscosity UV-Curable Monomer/High-Pressure CO2 Solutions

The control of pore-size distribution in porous films is essential in many applications. Here, we report the development of a process facilitating the production of polymeric porous films with bimo...

FAU-Type Zeolite Nanocasted Carbon Replicas for CO2 Adsorption and Hydrogen Purification

Microporous ordered carbon have been synthesized by the nanocasting process from zeolite Y using acetylene and furfuryl alcohol as carbon precursors. If the proper synthesis conditions are chosen, these materials retain the long-range order of the zeolite mold. The resulting carbons possess a large surface area (≥2200 m2/g), a high microporosity (≥1.0 cm3/g), and a controlled pore size distribution, which was tailored by the wall thickness of the zeolite template. Because of their high micropore volume, the carbon replicas of zeolite Y are attractive adsorbent materials and might be used to replace conventional activated carbons as adsorbents in pressure swing adsorption processes (PSAs) for H2 purification. In the present contribution, we evaluate the adsorption capacity of the carbon replicas in a H2-PSA based on their single-component adsorption isotherms of CO2, CH4, and N2 measured at room temperature. The ideal adsorbed solution theory (IAST) was used to predict the co-adsorption of CO2/CH4/N2 gas m...

Importance of pore size in high-pressure hydrogen storage by porous carbons

Abstract Development of high-capacity hydrogen-storage systems utilizing physisorption at high pressure and low temperature is hindered by poor understanding of the pore size/shape requirements for achieving the maximum hydrogen uptake. Tuning the carbon structure and pore size of carbide-derived carbons (CDCs) with high accuracy by using different starting carbides, chlorination temperatures and activation temperatures allows rational design of carbon materials with increased hydrogen-storage capacity. Systematic experimental investigation of a large number of CDCs with controlled pore size distributions and specific surface area (SSA) shows that pores larger than ∼1.5 nm contribute little to hydrogen storage. It has been experimentally demonstrated that, just as at ambient pressure, pores of 0.6–0.7 nm in diameter provide the largest H 2 uptake per unit SSA at elevated pressures and liquid nitrogen temperatures. The effect of pore size was stronger than the effect of surface chemistry on the hydrogen uptake.

Osteogenic differentiation of dura mater stem cells cultured in vitro on three-dimensional porous scaffolds of poly(ε-caprolactone) fabricated via co-extrusion and gas foaming

A novel scaffold fabrication method utilizing both polymer blend extrusion and gas foaming techniques to control pore size distribution is presented. Seventy-five per cent of all pores produced using polymer blend extrusion alone were less than 50 μm. Introducing a gas technique provided better control of pore size distribution, expanding the range from 0–50 to 0–350 μm. Varying sintering time, annealing temperature and foaming pressure also helped to reduce the percentage of pore sizes below 50 μm. Scaffolds chosen for in vitro cellular studies had a pore size distribution of 0–300 μm, average pore size 66 ± 17 μm, 0.54 ± 0.02% porosity and 98% interconnectivity, measured by micro-computed tomography (microCT) analysis. The ability of the scaffolds to support osteogenic differentiation for subsequent cranial defect repair was evaluated by static and dynamic (0.035 ± 0.006 m s −1 terminal velocity) cultivation with dura mater stem cells (DSCs). In vitro studies showed minimal increases in proliferation over 28 days in culture in osteogenic media. Alkaline phosphatase expression remained constant throughout the study. Moderate increases in matrix deposition, as assessed by histochemical staining and microCT analysis, occurred at later time points, days 21 and 28. Although constructs cultured dynamically showed greater mineralization than static conditions, these trends were not significant. It remains unclear whether bioreactor culture of DSCs is advantageous for bone tissue engineering applications. However, these studies show that polycaprolactone (PCL) scaffolds alone, without the addition of other co-polymers or ceramics, support long-term attachment and mineralization of DSCs throughout the entire porous scaffold.

Geometric control and tuneable pore size distribution of buckypaper and buckydiscs

The fabrication of buckypaper from unfunctionalised multi-walled carbon nanotubes (MWCNTs) without the aid of surfactants or surface modification techniques is accomplished through a novel and quick frit compression method. The dimensions can be controlled through the size of the syringe housing and the through the mass of carbon nanotubes added. Their thicknesses are typically much larger than surfactant-cast buckypaper and range from 120 μm up to 650 μm; buckypaper with thicknesses larger than 500 μm we call buckydiscs. Buckypaper and buckydiscs are mechanically robust to handle, flexible, stable in solvents and possess larger porosities than Triton-X100 cast buckypaper. They also exhibit a memory effect when bending wetted samples, returning to their former geometry on drying. Buckypaper and buckydiscs were studied by mercury intrusion porosimetry to reveal a defined distribution of mesopores and small macropores that is, along with their density and apparent free volume, dependant on the casting solvent and therefore tuneable. Moreover, the frit compression system also allows control over the 3-dimensional geometry of the buckydiscs during the casting process.

Prussian blue nanoparticles doped nanocage for controllable immobilization and selective biosensing of enzyme

A conductive nanocage composed of Prussian blue (PB) nanoparticles doped mesocellular silica–carbon foam was prepared. This nanocage possessed ink-bottlelike structure with narrow and controllable pore-size distribution, good biocompatibility and favorable conductivity. The Prussian blue nanoparticles dispersed homogeneously on the mesowalls and provided the nanocage with highly catalytic ability toward the reduction of hydrogen peroxide. The nanocage could be used for volume-selective entrapment of enzyme to prepare a biosensor. The use of the Prussian blue nanoparticles doped nanocage would open new horizons for fabrication of biosensors and biocatalysts.

Conductive and Highly Catalytic Nanocage for Assembly and Improving Function of Enzyme

A conductive nanocage composed of PdNPs-doped (PdNPs = palladium nanoparticles) mesocellular carbon−silica foam was prepared using a designed wet chemical process followed by electrochemical reduction. This nanocage possessed a 3-D interconnected bottleneck mesostructure with large surface area, narrow and controllable pore-size distribution, good biocompatibility, and favorable conductivity and hydrophilicity. The produced PdNPs dispersed homogeneously on the mesowalls and provided the nanocage with a high degree of catalytic ability for the electrooxidation of hydrogen peroxide at an extremely low overpotential, and they offer the possibility to selectively detect oxidase substrates. The nanocage was size-controllable and could be used for volume-selective entrapment of enzymes without aggregation and a change of structure, which preserved good bioactivity of the entrapped enzyme and produced a highly sensitive biosensor with excellent operational and storage stability. Using glucose oxidase as a model,...

Synthesis of nanoporous carbon with controlled pore size distribution and examination of its accessibility for electric double layer formation

A new template approach is reported for the synthesis of nanoporous carbon. In contrast with previous template methods, the present one combines the synthesis of template, the introduction and formation of carbon into one step. This is achieved by simultaneous pyrolysis of Fe(CO) 5 and C 2H 2 to form the Fe template in situ with the formation of carbon. Additionally, by simply supplying Fe(CO) 5 and C 2H 2 at different ratios, the proportion and particle size of the Fe template can be altered. Consequently, nanoporous carbons with different pore sizes can be prepared after the Fe particles have been removed by HCl treatment. Under the present experimental conditions, a microporous carbon is demonstrated having a surface area of 602 m 2/g and pore sizes mainly in the range of 0.5–1.2 nm, and a mesoporous carbon having a surface area of 880 m 2/g and pore sizes mainly in the range of 2–10 nm. As an example for potential applications, the presence of mesopores in the mesoporous carbon is shown to have larger capacitance values than the microporous carbon. This may result from the fact that the presence of mesopores facilitates the electrolyte migration into the carbon interior.

Layered microporous tin(iv) bisphosphonates

This article reports the hydrothermal synthesis and characterization of two new series of porous tin(IV) phosphonophenoxyphenylphosphonates with controlled pore size distributions, using as precursor the 4-(4'-phosphonophenoxy)phenyl phosphonic acid, [H2O3P-C6H4]2-O. Supermicroporous solids (S(BET), 300-400 m2 g(-1)) were obtained employing n-alcohol (C1-C6)-water mixtures (solvents ratio 1 : 1), in the presence of hydrofluoric acid. X-Ray powder diffraction shows that these compounds are semi-crystalline and the local environments around the phosphorus and tin elements have been studied by 31P and 119Sn MAS-NMR spectroscopy, respectively. The microstructure (particle sizes and shapes) of these phosphonates has been analyzed by scanning and transmission electron microscopy. This study shows that the microstructures of single-ligand (for instance tin(IV) phenylphosphonate) and cross-linked tin(IV) bisphosphonates are different. Tin(IV) phenylphosphonate crystallizes as micron-sized spheres, theta approximately 1-2 microm, formed by the aggregation of nanospheres, whereas tin(IV) bisphosphonates crystallize as microparticles larger than 20 microm. The textural properties of these porous solids were characterized by N2 and CO2 sorption isotherms. The key result of this work is that maxima of pore size distributions smoothly shift from 12 to 16 angstroms upon increasing the chain length of the alcohol. The microporosity of tin(IV) bisphosphonates is compatible with a double role played by the phosphonate groups acting as a pillar between adjacent layers and as a component of the hybrid organic-inorganic layers.

A nanostructured titania bioceramic implantable device capable of drug delivery to the temporal lobe of the brain

A new TiO 2 nanostructured bioceramic device was synthesized using a sol–gel process in order to control pore size distribution and particle size. The objective was to obtain a constant drug release rate for antiepileptic drugs directly into the central nervous system (CNS). Point defects were generated in the titania network in order to obtain the desired interaction between a highly polar drug and the titania device. Difficulties in the control of epileptic seizures and common side effects have led us to study the possibility of using an implantable nanostructured bioceramic device in the brain of a rat. This device contains an anticonvulsant drug (valproic acid, VPA) which can be released directly into the temporal lobe of the brain at a constant rate. This rate should be constant over an extended period of time. Epilepsy is a disease that occurs in approximately 4% of the world population. Normally it can be treated using systemic therapy. The area covered by drug diffusion should include the amygdale, hippocampus and cortex of the temporal lobe. To study the efficiency of the drug release “in vivo”, epileptic conditions were generated using the chemical Kindling method.

Synthesis and Characterization of Nanosized ZrTiO<sub>4</sub> Powders Prepared by the Sol-Gel Method

Ceramic ZrTiO4 powders were prepared by a modified sol-gel method using zirconium oxychloride and titanium tetraisopropoxide. In situ high temperature X-ray diffraction results show that crystallization of the amorphous gel starts at 400 °C. Singlephase ZrTiO4 nanoparticles were obtained after heat treatment at 450 oC for 1 h. An average particle size of 46 nm has been determined by nitrogen adsorption analysis. After pressing these sinteractive powders, pellets with controlled pore size distribution were obtained by sintering at temperatures as low as 400 oC. The analysis of pores by mercury porosimetry shows an average porosity of 45 %. Pressing and sintering the nanosized powders prepared by that modified sol-gel technique produced pellets that are good candidates to be used in humidity sensing devices.

Carbide-Derived Carbons: Effect of Pore Size on Hydrogen Uptake and Heat of Adsorption

Cryoadsorption is a promising method of enhancing gravimetric and volumetric onboard H2 storage capacity for future trans- portation needs. Inexpensive carbide-derived carbons (CDCs), produced by chlorination of metal carbides, have up to 80% open-pore volume with tunable pore size and specific surface area (SSA). Tuning the carbon structure and pore size with high sensitivity by using different starting carbides and chlorination temperatures allows rational design of carbon materials with en- hanced C-H2 interaction and thus increased H2 storage capacity. A systematic experimental investigation of a large number of CDCs with controlled pore size distributions and SSAs shows how smaller pores increase both the heat of adsorption and the total volume of adsorbed H2. It has been demonstrated that increasing the average heat of H2 adsorption above 6.6 kJmol -1 substantially enhances H2 uptake at 1 atm (1 atm=101325 Pa) and -196°C. The heats of adsorption up to 11 kJmol -1 exceed values reported for metal-organic framework compounds and carbon nanotubes.

Low-Temperature Sol-Gel Synthesis of Single-Phase ZrTiO4 Nanoparticles

Ceramic ZrTiO4 powders were prepared by a sol-gel method using zirconium oxychloride and titanium tetraisopropoxide. In situ high temperature X-ray diffraction results show that crystallization of the amorphous gel starts at 400 ∘C. Single-phase ZrTiO4 nanoparticles were obtained after heat treatment at 450 ∘C for one hour. An average particle size of 46 nm has been determined by nitrogen adsorption analysis. After pressing these sinteractive powders, pellets with controlled pore size distribution were obtained by sintering at temperatures as low as 400 ∘C. The analysis of pores by mercury porosimetry gives an average porosity of 45%. The electrical resistivity, determined by impedance spectroscopy measurements at 24 ∘C under different humidity environments, shows the ability of these pellets to adsorb water vapor in the porous surfaces. Pellets fabricated with the nanosized powders prepared by the sol-gel technique are proposed as good candidates to be used in humidity sensing devices.