Mesocellular Foam Research Articles

Efficient Palladium‐Catalyzed Aminocarbonylation of Aryl Iodides Using Palladium Nanoparticles Dispersed on Siliceous Mesocellular Foam

A highly dispersed nanopalladium catalyst supported on mesocellular foam (MCF), was successfully used in the heterogeneous catalysis of aminocarbonylation reactions. During the preliminary evaluation of this catalyst it was discovered that the supported palladium nanoparticles exhibited a "release and catch" effect, meaning that a minor amount of the heterogeneous palladium became soluble and catalyzed the reaction, after which it re-deposited onto the support.

Synthesis of hierarchical linearly assembled graphitic carbon nanoparticles via catalytic graphitization in SBA-15

Graphitic carbon nanoparticles have received a great deal of attention due to their high electrical conductivity and excellent thermal and chemical stability. Although various synthesis methods have been proposed for the preparation of graphitic carbon nanoparticles, their assembled synthesis has rarely been studied. Here, we report the synthesis of hierarchical, linearly assembled hollow graphitic nanoparticles via catalytic graphitization in SBA-15, hexagonally ordered mesoporous silica. Carbonization of phenol–formaldehyde resin in the presence of impregnated cobalt salts in SBA-15 followed by the removal of the silica template resulted in carbon composites consisting of CMK-3-type amorphous carbon and graphitic carbon nanoparticles. Subsequent chemical oxidation of the amorphous carbon resulted in a bundle of necklace-like carbon nanowires with a length of a few micrometers, where each nanowire consisted of individual ∼50nm sized hollow graphitic carbon nanoparticles. By contrast, a catalytic graphitization using MCF, mesocellular foam without mesoscopic pore ordering, resulted in randomly assembled graphitic carbon nanoparticles. These findings demonstrate that SBA-15 acted as a macroscopic template for the linear assembly of graphitic carbon nanoparticles during graphitization.

Synthesis of Hierarchical Micro/Mesoporous Structures via Solid–Aqueous Interface Growth: Zeolitic Imidazolate Framework-8 on Siliceous Mesocellular Foams for Enhanced Pervaporation of Water/Ethanol Mixtures

A new hierarchical micro/mesoporous composite is synthesized via direct growth of microporous zeolitic imidazolate framework-8 (ZIF-8) on siliceous mesocellular foams (MCF). Depending on different synthetic conditions, ZIF-8 with two different particle sizes, i.e., ZIF-8 microparticles and ZIF-8 nanoparticles, were successfully formed on the external surface of amine-functionalized MCF (denoted as microZIF-8@MCF and nanoZIF-8@MCF, respectively). The synthesized hierarchical micro/mesoporous ZIF-8@MCF structures were characterized with several spectroscopic techniques including X-ray diffraction (XRD), solid-state NMR, and FT-IR and electron microscopic techniques (scanning electron microscope, SEM, and transmission electron microscopy, TEM). In addition, the pervaporation measurements of the liquid water/ethanol mixture show that nanoZIF-8@MCF/PVA (poly(vinyl alcohol) mixed-matrix membrane exhibits enhanced performance both on the permeability and separation factor. Compared to conventional routes for chemical etching, this study demonstrates a promising and simple strategy for synthesizing novel hierarchical porous composites exhibiting both advantages of mesoporous materials and microporous materials, which is expected to be useful for gas adsorption, separation, and catalysis.

Studies of Hg2+ adsorption and desorption by mesocellular foams silica

MCFs (mesocellular foams) silica, a mesoporous material, was synthesized by the hydrothermal method using tri-block copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (Pluronic P123, EO20-PO20-EO20) as a structuring agent and 1, 3, 5-trimethylbenzene as a pore-expanding agent and the product was characterized by powder X-ray diffraction and scanning electron microscopy. The prepared MCFs was employed as the adsorbent for a study of the adsorption of Hg2+. The adsorptive experimental results showed that the optimal adsorptive conditions were: pH = 5.0, MCFs amount 0.10 g, temperature 20°C, and adsorption time 40 min, when the initial concentration of Hg2+ is 1.0 mg mL−1. The maximum adsorptive amount of Hg2+ was 124.5 mg Hg2+ g−1 MCFs. The desorption studies found that the best desorbing agent is 0.10 M hydrochloric acid. The highest desorption rate of 80.61 % could be reached at a desorption duration of 3 h. The cost of the adsorbent used in this study is lower than that of activated carbon with a higher value of application.

Demonstrating the Benefits and Pitfalls of Various Acidity Characterization Techniques by a Case Study on Bimodal Aluminosilicates

A new combination of a volumetric with a dynamic method to investigate the acidity properties of aluminosilicates is introduced. In the first step, the total acidity is determined volumetrically by the measurement of two-cycle adsorption (TCA) isotherms with ammonia as a probe, directly followed by a dynamic temperature-programmed desorption (TPD) experiment to define the acid strength distribution. Furthermore, the results obtained by the new direct combination of TCA and TPD are validated by comparison with an in-situ FTIR (Fourier transform infrared) study with the same probe molecule on the same materials. Both acidity characterization techniques are compared, and we comment on their complementarity, benefits, and pitfalls. The material under investigation is a new type of bimodal microporous and mesoporous material with zeolitic characteristics, synthesized by a mesotemplate-free method. The acidic nature of the novel material is compared to two reference materials: a crystalline zeolite and a mesoporous aluminum incorporated mesocellular foam (Al-MCF) with amorphous characteristics.

Preparation, characterization and lysozyme immobilization studies on siliceous mesocellular foams: Effect of precursor chemistry on pore size, wall thickness and interpore spacing

Three homologous series of siliceous meso-cellular foams (MCFs) were synthesized using microemulsion templating by incremental variation of ratio of organic pore expander, trimethyl benzene (TMB), and silica precursor (TEOS) concentrations using Pluronic™ block co-polymer (P123) as the surfactant. The calcined materials were tested for lysozyme immobilization to relate the adsorption capacities to meso-structure. Small angle X-ray scattering (SAXS) shows a short range ordering of pores. The pore size and wall thickness were determined from Porod analysis of the SAXS data combined with gas adsorption data. The pore size and lysozyme loading both increase systematically with TMB/P123 ratio, and decrease with increasing TEOS/P123 ratio. By comparing gas adsorption and SAXS data, we show that the BET method overestimates the mesopore specific surface area and therefore leads to an underestimate of the pore size. The effective pore size determined by the BdB-FHH method on the other hand is consistent with that determined by SAXS surface area analysis. The wall thickness (4.4±0.5nm), interpore distance (23.9±1.5nm) and meso-pore volume fraction (0.82±0.04) are independent of synthesis conditions. The mean pore size (33±8nm, spherical equivalent) is generally larger than the interpore distance, which forces the system to adopt a more cylindrical pore morphology at large pore and window sizes, which is confirmed by SAXS and TEM. TEM shows worm-like pores intermixed along with the familiar cellular foam phase.

Cycloisomerization of Acetylenic Acids to γ-Alkylidene Lactones using a Palladium(II) Catalyst Supported on Amino-Functionalized Siliceous Mesocellular Foam

Cycloisomerization of various γ-acetylenic acids to their corresponding γ-alkylidene lactones by the use of a heterogeneous Pd(II) catalyst supported on amino-functionalized siliceous mesocellular foam is described. Substrates containing terminal as well as internal alkynes were cyclized in high to excellent yields within 2–24 h under mild reaction conditions. The protocol exhibited high regio- and stereoselectivity, favoring the exo-dig product with high Z selectivity. Moreover, the catalyst displayed excellent stability under the employed reaction conditions, as demonstrated by its good recyclability and low leaching.

Synthesis of hierarchically porous silicas with mesophase transformations in a four-component microemulsion-type system and the catalytic performance for dibenzothiophene hydrodesulfurization

Hierarchical porous materials especially the silica-based ones are undergoing rapid development due to potential applications in the fields of catalysis, adsorption, separation, and biomedical processes. Although various synthesis methods involving emulsions, colloids, and surfactants have been reported, synthesis of hierarchical porous silicas (HPS) with complex mesophase transformations by using a four-component microemulsion (surfactant/cosurfactant/oil/water) templating approach is still challenging. Herein, we have successfully synthesized porous silica materials by introducing n-butanol (Bu) as the cosurfactant and 1,3,5-trimethylbenzene (TMB) as the oil component in a four-component P123–n-butanol–1,3,5-trimethylbenzene–water system. By simply increasing the molar ratio of Bu to TMB continuously while keeping a fixed mass of TMB in the mean time, mesophase transformations, progressing from mesocellular foam (MCF) via a vesicle-like structure to an ordered 2D hexagonal structure (SBA-15), can be observed. Moreover, an opposite phase transformation process was also proved by gradually increasing the molar ratio of TMB to Bu by maintaining a certain value for the Bu content in the initial system. All the mixed phase silica materials including hexagonal–vesicle, MCF–vesicle–hexagonal, and MCF–disordered-SBA-15-type show hierarchically porous structures. The mechanism for the mesophase transformation was proposed and a micelle/microemulsion method with bimodal templates was put forward to form hierarchical porous silicas with a mixed phase of the MCF–disordered-SBA-15-type structure. Furthermore, a series of Al-containing mesoporous silicas with different structures (hexagonal, vesicle, MCF, MCF–vesicle–hexagonal, and MCF–disordered-SBA-15-type) were used as catalyst supports for dibenzothiophene hydrodesulfurization. The NiMo/Al-hierarchical porous silica catalyst with pore structures of MCF–disordered-SBA-15-type displayed the best hydrodesulfurization performance among all the studied catalysts.

CO2 capture on easily regenerable hybrid adsorbents based on polyamines and mesocellular silica foam. Effect of pore volume of the support and polyamine molecular weight

Mesocellular foams (MCFs) with a wide range of pore volumes and pore sizes were prepared and impregnated with PEI. CO2 adsorption on these adsorbents was studied.

Polymer-coated spherical mesoporous silica for pH-controlled delivery of insulin

We report a pH-controlled insulin release system to provide an oral administration route. Mesoporous silica was chosen as a drug carrier, and pH-sensitive polymers were coated onto spherical mesocellular foam with pre-adsorbed insulin. We evaluated the insulin release in both acidic and neutral solutions to compare how this system behaves under different pH conditions.

介孔碳泡沫分子筛的制备及其对葡萄糖氧化酶的吸附行为

以添加氟化铵改性的介孔二氧化硅泡沫分子筛为模板，糠醇为碳源，运用硬模板法制备不同孔结构的介孔碳泡沫分子筛。采用SEM观察、TEM观察及氮气吸附等手段对介孔碳泡沫分子筛的粒径及孔结构进行了表征。结果表明，经氟离子改性的介孔泡沫分子筛具有较小的颗粒粒径及较大的窗口孔径、胞体孔径和孔容，但比表面积较小。将所制备的介孔碳泡沫分子筛和介孔二氧化硅泡沫分子筛分别用于葡萄糖氧化酶的负载，介孔碳泡沫分子筛对葡萄糖氧化酶的吸附量远远大于相应的硅模板，表明酶分子和载体表面间的静电作用对负载过程有很大影响；同时，拥有较小粒径、较大胞体孔径和孔容的介孔碳泡沫分子筛表现出更大的葡萄糖氧化酶负载量，有望成为优良的酶载体材料。 By using fluorine-modified and original mesostructured cellular foam silica as templates, furfuryl alcohol as carbon precursors, carbonaceous mesocellular foams with different pore sizes were prepared, and then the grain sizes and pore structures of the samples were characterized by scanning electron microscope (SEM), Transmission Electron Microscopy (TEM) and nitrogen adsorption. It was found that fluorine-modified mesostructured cellular foams possessed the smaller particle sizes and specific surface area, but the larger windows and cell diameters and the larger pore volumes. All prepared samples were used as the carriers for immobilization of glucose oxidase. The loading amounts on carbonaceous mesocellular foams were much higher than on corresponding silicon templates, indicating that the immobilization process might be affected strongly by the electrostatic repulsion between the glucose oxidase molecules and carrier surface. Furthermore, carbonaceous mesocellular foam with smaller particle size, larger window size and pore volume showed the highest glucose oxidase loading amounts. It might be served as the prospective enzyme carrier material.

CO2 adsorption on APTES functionalized mesocellular foams obtained from mesoporous silicas

The CO2 adsorption capacity of different APTES-grafted mesoporous silicas of SBA-15 type has been investigated and the influence of support textural properties and the role of the presence of silanol groups on the adsorption capacity are analyzed. Four adsorbents based on SBA-15 were prepared using tetraethyl orthosilicate (TEOS) as silicon source, with and without the addition of trimethyl-benzene (TMB) and n-heptane as swelling agents, and adding in some cases ammonium fluoride as a solubility enhancer. 3-(triethoxysilyl)propylamine (APTES) was then used as grafting agent by reaction with free silanol groups on the silica surface so as to provide pending amino groups for CO2 capture. The adsorption behavior for all supports was adequately described by a Freundlich model, whereas for the APTES-grafted silica, a dual-site Langmuir model was applied, which allowed us to quantify and qualify two different adsorption sites. The addition of n-heptane as swelling agent led to pore sizes beyond 10nm and improved significantly the grafting efficiency, leading to higher CO2 uptakes as compared to the starting supports. At 1bar and 25°C and anhydrous conditions, CO2 uptakes of 2.4mmolg−1 or 0.64mol CO2 per molN were achieved (which reveals a significant contribution of physisorption). This sample could be successfully regenerated at 100°C, maintaining a constant capacity for 3 adsorption–desorption cycles. At 0.15bar and 60°C, anhydrous conditions, CO2 uptake reaches 1.5mmolg−1. This value may be theoretically doubled in the presence of humidity, and there is room for further improvement if supports with the same pore size (13nm) and higher surface areas (e.g. 1000m2/g) are successfully synthesized.

Guanidinylated poly(allylamine) supported on mesoporous silica for CO2 capture from flue gas

The CO2 adsorption performance of aminosilica adsorbents prepared by the impregnation of poly(allylamine) (PAA) and guanidinylated poly(allylamine) (GPAA) into silica mesocellular foam supports is evaluated. The effect of amine loading on the CO2 capacity is consistent with previous reports of poly(allylamine) impregnated adsorbents, whereby the capacity increases initially with increasing amine loading and then drops at very high amine loadings, due to restricted access to the amine sites at high loadings. The CO2 capacity of the new GPAA impregnated adsorbents decreases with an increase in adsorption temperature, showing comparable capacities to those for PAA impregnated adsorbents at low to moderate temperatures. However, at adsorption temperature higher than 75°C, the CO2 capacities of GPAA adsorbents are higher than those for PAA adsorbents, ∼70% higher at the highest temperature studied, 140°C. CO2 adsorption–desorption cycling experiments show that the GPAA adsorbents have a better stability and regenerability at higher temperatures, making this class of materials suited for temperature swing cycles operating in a higher temperature regime than traditional aminosilica adsorbents based on PEI.

Interactions between biomolecules and an iron-silica surface

An iron-silica adsorbent (1:1 ratio by mass) with a pore cell size of 11.4nm and BET surface area of 610m2g−1 was synthesized and compared to a mesocellular foam (MCF) silica and iron oxide for amino acid (alanine, aspartic acid, lysine and histidine) and lysozyme adsorption. Amino acid batch adsorption loadings did not exceed estimated monolayer coverage and were generally quantitatively similar on iron-silica and MCF silica; the observed loadings followed the trend alanine>lysine/aspartic acid≫histidine. Multilayers were observed on the strongly positive iron oxide surface. The dynamic heat of biomolecule adsorption was directly measured with flow microcalorimetry (FMC); the enthalpies of adsorption of alanine, aspartic acid, lysine, and histidine on iron-silica were −0.046, −0.73, −5.3 and −14.3kJmol−1, respectively. Alanine adsorption was mediated by the surrounding water, aspartic acid adsorbed through weak electrostatic attractions, and lysine and histidine formed bonds during adsorption. Lysozyme monolayer loading was higher on iron-silica than on MCF silica, calorimetric studies indicate a different lysozyme adsorption mechanism on iron-silica and MCF silica.

Co‐immobilization of an Enzyme and a Metal into the Compartments of Mesoporous Silica for Cooperative Tandem Catalysis: An Artificial Metalloenzyme

Co‐immobilization of an Enzyme and a Metal into the Compartments of Mesoporous Silica for Cooperative Tandem Catalysis: An Artificial Metalloenzyme

Nanopalladium on Amino‐Functionalized Mesocellular Foam as an Efficient and Recyclable Catalyst for the Selective Transfer Hydrogenation of Nitroarenes to Anilines

AbstractHerein, we report on the use of nanopalladium on amino‐functionalized siliceous mesocellular foam as an efficient heterogeneous catalyst for the transfer hydrogenation of nitroarenes to anilines. In all cases, the protocol proved to be highly selective and favored the formation of the desired aniline as the single product in high yields with short reaction times if naturally occurring and renewable γ‐terpinene was employed as the hydrogen donor. Furthermore, the catalyst displayed excellent recyclability over five cycles and negligible leaching of metal into solution, which makes it an eco‐friendly and economic catalyst to perform this transformation. The scalability of the protocol was demonstrated with the reduction of 4‐nitroanisole on a 2 g scale, in which p‐anisidine was isolated in 98 % yield.

ChemInform Abstract: Highly Dispersed Palladium Nanoparticles on Mesocellular Foam: An Efficient and Recyclable Heterogeneous Catalyst for Alcohol Oxidation.

AbstractPalladium on siliceous mesocellular foam is a highly active and stable catalyst for oxidation of primary and secondary (benzylic) alcohols.

Cytotoxicity and potency of mesocellular foam-26 in comparison to layered clays used as hemostatic agents

Uncontrolled hemorrhage is a leading cause of potentially preventable death. The most effective commercial hemostatic products employ layered clays. Due to safety concerns only a product containing kaolin is currently recommended by the U. S. Department of Defense. A problem related to layered clays, including kaolin, is their cytotoxicity. Also, material left in the wound can lead to thrombosis and other adverse effects. Recently, it has been shown that pure silica mesocellular foams (MCF) with cell window sizes >20 nm are effective in promoting blood clotting. Here, we tested the potency and cytotoxicity of layered clays in comparison to MCF with a cell window size of 26 nm (MCF-26) in vitro. The results showed that the potencies of MCF-26 and layered clays in promoting clotting were comparable. Effects on cell viability were assessed with relevant primary human cell types. The cytotoxic effects of all compounds were cell type-specific and most sensitive were endothelial cells. The IC50 values of MCF-26 were in the mg ml−1 range and its cytotoxicity was ∼1–2 orders of magnitude lower than the cytotoxicity of layered clays. Further, MCF-26 did not adhere strongly to cell surfaces and was not taken up by cells as observed for the layered clays. This suggests that it would be easier to remove MCF-26 from wounds. Altogether, the results suggest that MCF-26 would be effective and safer than currently used hemostatic agents.

ChemInform Abstract: Magnetic Nanoparticles Entrapped in Siliceous Mesocellular Foam: A New Catalyst Support.

AbstractA new catalyst support is prepared by immobilization of γ‐Fe2O3 nanoparticles in the cage‐like pores of siliceous mesocellular foam.

Nanopalladium on Amino‐Functionalized Mesocellular Foam: An Efficient Catalyst for Suzuki Reactions and Transfer Hydrogenations

AbstractThe applications of a heterogeneous Pd0‐AmP‐MCF nanoparticle catalyst in Suzuki cross‐coupling reactions and transfer hydrogenations of alkenes are described. The catalyst was highly efficient for both transformations, resulting in 1) coupling of a wide range of aryl halides with various boronic acids in high yields and 2) chemoselective reduction of a variety of alkenes with the use of 1‐methyl‐1,4‐cyclohexadiene as hydrogen donor. Moreover, the catalyst can be recycled several times without any significant decrease in activity or leaching of metal into solution, making the protocol economical and environmentally friendly. In the case of the Suzuki cross‐coupling, a 15‐fold increase in reaction rate was observed if the reaction was performed under microwave irradiation compared to conventional heating in an oil bath.