Siliceous Mesocellular Foam Research Articles

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.

In situ synthesis of phosphate binding mesocellular siliceous foams impregnated with iron oxide nanoparticles

Large cavities embedded with iron oxide nanoparticles within mesocellular siliceous foams (MCFs) uptake phosphate ions from water effluent.

CO2 adsorption by amine modified siliceous mesostructured cellular foam (MCF) in humidified gas

A set of branched and linear polyethyleneimine (PEI) modified mesocellular siliceous foams (MCF) were evaluated as adsorbents for CO2 capture at modestly elevated temperatures under conditions that simulate the vacuum swing adsorption (VSA) process in humidified gas. Increasing the temperature was found to be beneficial for achieving reversible CO2 adsorption/desorption with reasonable capacities and rates. Under humid conditions, the materials lost 0–15% of their adsorption capacities in 0.5atm CO2 compared to under dry conditions at 105–115°C. The working capacity (0.025–0.15atm CO2) at 105°C was 2–17% higher under humid than under dry conditions. During cycling, the branched PEI adsorbent showed a gradual decrease in CO2 adsorption–desorption capacity under dry conditions, but the reduction in capacity was significantly reduced under wet conditions. The reduction in CO2 adsorption capacity was attributed to by-product formation, confirmed by IR, 13C CP-MAS NMR and EDS. In a humid environment, the formation of by-product was significantly reduced.

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.

Highly Selective Macrocycle Formations by Metathesis Catalysts Fixated in Nanopores

Ruthenium-based metathesis catalysts immobilized on mesocellular siliceous foam (MCF) bearing large nanopores proved highly efficient and selective for macrocyclic ring-closing metathesis (RCM). Kinetic studies revealed that the homogeneous counterpart exhibited far higher activity that accounted for more oligomerization pathways and resulted in less macrocyclization products. Meanwhile, the immobilized catalysts showed lower conversion rates leading to higher yields of macrocyclic products in a given reaction time, with conversion rates and yields dependent upon pore size, catalyst loading density, and linker length. The macrocycle formations via RCM were accelerated by increasing the pore size and decreasing the catalyst loading density while retaining the comparably high yield. The catalysts immobilized on MCF, of which silica surface is rigid and pores are relatively large, showed high conversion rates and yields compared with an analogue immobilized on TentaGel resins, of which backbone becomes flexible upon swelling in the reaction medium. It is noteworthy that the selectivity for the macrocyclic RCM can be significantly improved by tuning the catalyst initiation rates via immobilization onto the support materials in which well-defined three-dimentional network of large nanopores are deployed.

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.

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.

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

γ-Fe(2)O(3) nanoparticles were formed inside the cage-like pores of mesocellular foam (MCF). These magnetic nanoparticles showed a uniform size distribution that could be easily controlled by the MCF pore size, as well as by the hydrocarbon chain length used for MCF surface modification. Throughout the entrapment process, the pore structure and surface area of the MCF remained intact. The resulting magnetic MCF facilitated the immobilization of biocatalysts, homogeneous catalysts, and nanoclusters. Moreover, the MCF allowed for facile catalyst recovery by using a simple magnet. The supported catalysts exhibited excellent catalytic efficiencies that were comparable to their homogeneous counterparts.

Catalase immobilized on siliceous mesocellular foam with controlled window size

Siliceous mesocellular foam (MCF) with tunable cell and window size was synthesized by the acid catalyzed sol–gel reaction of tetraethoxysilane in the presence of triblock copolymer Pluronic P123 (EO20PO70EO20) as structure-directing agent. The cell’s size of MCF is increased with the increase of 1,3,5-trimethylbenzene amount, while the window’s size of MCF could be tailored between 4 and 18.2 nm without affecting the cells size by adding of NH4F. The obtained MCF materials were employed as carriers for catalase immobilization. FT-IR spectra and N2 sorption show that the catalase is immobilized into the mesopores of MCF. MCF with window size of 12.9 nm shows high catalase loading and activity, suggesting that matching the window’s size with enzyme molecular diameter is a critical factor in attaining efficient immobilization since smaller window size prevents larger enzyme from entering the pore and larger window size causes the leakage of enzyme. The thermal and storage stabilities of the immobilized catalase were also improved due to the shield of the mesopores of MCF.

Polyethylenimine-impregnated siliceous mesocellular foam particles as high capacity CO2 adsorbents

Siliceous mesostructured cellular foams (MCF) impregnated with polyethylenimine (PEI) of various molecular weights and structures were evaluated as CO2 adsorbents. The MCF solid support consisted of a well-defined interconnected three-dimensional mesoporous structure with large cell diameter of 30.3 nm and large window diameter of 11.3 nm, filled with polyethylenimine up to 70 weight percent or about 22.3% nitrogen atom by weight of the adsorbents. While other mesoporous solid supports lost their porosity after PEI impregnation, our MCF solid support maintained its pore volume over the range of 1.12 to 1.64 cm3 g−1. The importance of the porosity of PEI-impregnated MCF adsorbents for high capacity CO2 adsorbents was demonstrated. The highest CO2 sorption capacity (180.6 mg-CO2/g-adsorbent or 393.6 mg-CO2/g-PEI at 75 °C) was obtained for silica supports loaded with 50 weight percent branched PEI with average molecular weight of 600 g mol−1. Under dry atmospheric CO2 gas, this adsorbent reached the theoretical CO2 capacity of 0.50 mole-CO2 per mole-nitrogen within less than about 8 min, making this adsorbent one of the most effective CO2 adsorbents reported. Repeated multiple sorption cycles demonstrated good stability of this adsorbent for CO2 capture. The initial sorption kinetics determined the overall CO2 sorption capacity, which was limited by the formation of a carbamate layer as a result of the CO2–PEI complexation that due to inhibition of CO2 diffusion; the kinetics of “ionic” gelation of the impregnated PEI by CO2 controlled the overall performance of the CO2 adsorbents. At 75 °C, the operating temperature favored the molecular mobility of PEI and unrestricted diffusion of CO2 to allow the theoretical CO2 capacity of the PEI to be attained. Lower temperatures limited the mobilities of PEI and CO2 and the kinetics of “ionic” gel formation dominated, causing a lowered overall performance of the CO2 adsorbents. Overall, this study points to the importance of interconnected porous channel networks to optimize the performance of PEI-impregnated mesoporous silica particles.

Ultra-low-cost route to mesocellular siliceous foam from steel slag and mesocellular carbon foam as catalyst support in fuel cell

A large- and uniform-pore-sized mesocellular siliceous foam with a high surface area is successfully synthesized, using blast-furnace slag as an ultra-low-cost silica source, under neutral pH conditions. A high-purity silica source can be easily prepared from blast-furnace slag by extraction using an acid leaching process, followed by dissolution in NaOH solution. The mesocellular siliceous foam is synthesized by the interaction of these silicate precursors with P123 ((EO) 20(PO) 70(EO) 20) block copolymers in the presence of trimethylbenzene (TMB) used as a pore expander, followed by calcination at 550 °C in air. The resulting mesocellular siliceous foam denoted as MSU-F–SP has ∼30 nm sized large pores and high BET surface area of 554 m 2 g −1. The structure of MSU-F–SP is very similar to MSU-F silica synthesized from sodium silicate mixtures in the presence of P123 and TMB. Mesocellular carbon foam is easily synthesized through the direct carbonization of a tri-block copolymer in the as-synthesized mesostructured materials after acid-catalyzed polymerization using sulfuric acid. The sulfuric acid is used as a dehydration catalyst and the amount of sulfuric acid is controlled to optimize the pore structure. The mesocellular carbon foam synthesized using 0.16 mL of sulfuric acid per gram of composite material has the most uniform pore structures. A mesocellular carbon foam with high surface area and large mesopores allows good dispersion of Pt nanoparticles, leading to a higher methanol electro-oxidation activity in fuel cells compared to that of Pt nanoparticles on Vulcan XC-72.

Hydrophobic Surface Induced Activation of Pseudomonas cepacia Lipase Immobilized into Mesoporous Silica

Lipase from Pseudomonas cepacia (PCL) was successfully immobilized into siliceous mesocellular foams (MCFs) with various hydrophobic/hydrophilic surfaces. The catalytic performances of immobilized PCL were investigated using the transesterification reaction and hydrolytic reaction as model reactions. The specific activity of immobilized PCL greatly increased with enhanced surface hydrophobicity of MCFs, mainly because of lipase activation via hydrophobic interaction between alkyl groups in MCFs and the surface loop (so-called "lid") of PCL. Conformational changes of immobilized PCL were further investigated using time-resolved fluorescence spectroscopy with Trp as an intrinsic probe. When the immobilized PCL was suspended in phosphate buffer, short-lived τ(1) shortened and the fractional contribution of τ(1) significantly increased with the increasing level of surface hydrophobicity of MCFs. These results revealed that Trp(s) of the immobilized PCL were surrounded by a hydrophilic microenvironment because of the fact that the opened "lid" permitted the diffusion of water to the active site cleft. However, for the immobilized PCL suspended in n-hexane, long-lived τ(3) increased with the increase of surface hydrophobicity of MCFs. The reduced interaction between Trp(s) and the surrounding protein matrix was due to intercalation of n-hexane into the active site cleft when the lipase was in open conformation. The above results demonstrated that PCL immobilized into MCF with hydrophobic surfaces were in an activated open conformation.

Amine modified mesocellular siliceous foam (MCF) as a sorbent for CO 2

Adsorption is considered a promising method for carbon capture. CO 2 adsorbents take a variety of forms – but one approach is to fill mesoporous substrates with a polymeric CO 2 selective sorbent. SBA-15 and mesocellular siliceous foam (MCF) are high pore volume, high surface area ordered mesoporous materials for which modification with amine should result in high capacity, highly selective adsorbents. SBA-15 and MCF were separately loaded with approximately one pore volume equivalent of linear polyethyleneimine (PEI) ( M w = 2500) or branched PEI ( M n = 1200). CO 2 adsorption/desorption isotherms under dry CO 2 were obtained at 75, 105 and 115 °C. The CO 2 adsorption/desorption kinetics were improved with temperature, though the CO 2 capacities generally decreased. The adsorption capacity for MCF loaded with branched PEI at 105 and 115 °C were 151 and 133 mg/g adsorbent, respectively (in 50% CO 2/Ar, 20 min adsorption time). These are significantly higher than the adsorption capacity observed for SBA-15 loaded with branched PEI under same conditions, which were 107 and 83 mg/g adsorbent, respectively. Thus the results indicate that, on a unit mass basis, amine modified MCF's are potentially better adsorbents than amine modified SBA-15 for CO 2 capture at modestly elevated temperature in a vacuum swing adsorption process.

PEI modified mesocellular siliceous foam: A novel sorbent for CO2

Abstract A series of materials based on mesocellular siliceous foam (MCF) and SBA-15, but modified with branched and linear polyethyleneimine (PEI) were synthesized and investigated as CO 2 adsorbents. PEI modified MCFs, have higher PEI loadings than SBA-15 and, consistent with this exhibit higher CO 2 capacities on both a volume % and weight % basis. Performing CO 2 adsorption at modestly elevated temperatures is beneficial for achieving good adsorption and desorption rates.

Photocatalytic hydroxylation of benzene to phenol over titanium oxide entrapped into hydrophobically modified siliceous foam

The selective photocatalytic conversion of benzene to phenol was achieved on titania incorporated in hydrophobically modified mesocellular siliceous foam (MCF). Titanium oxide nanoparticles entrapped into mesocellular siliceous foam (TiO2@MCF) were prepared by “co-condensation” method using block copolymer as a template. TiO2@MCF was further modified by surface organo-grafting with silylation agent to make it hydrophobic (TiO2@MCF/CH3) and the grafted organic functional groups on the surface of TiO2 were selectively removed by post UV-irradiation to obtain the catalyst (TiO2@MCF/CH3/UV) that has a higher selective activity for benzene oxidation. By modifying the hydrophobicity of the mesoporous siliceous cage environment, both the adsorption of reactants (benzene) and the desorption of the desired products (phenol) on photocatalytic sites can be facilitated with an increase in selectivity and yield of phenol production. The titania nanoparticles incorporated into MCF cage were characterized by X-ray diffraction, nitrogen adsorption–desorption, high-resolution transmission electron microscopy, energy-dispersive X-ray analysis, and UV–visible diffuse reflectance spectroscopy. The hydrophobic modification of the catalysts was confirmed by Fourier transform infrared spectroscopy, water contact angle measurement, and thermo-gravimetric analysis. The adsorption isotherms of benzene and phenol on various catalysts suspended in aqueous solution were measured to investigate the effect of hydrophobic MCF cage. The hydrophobically modified TiO2@MCF/CH3/UV sample showed the highest selectivity and yield for the photocatalytic hydroxylation of benzene to phenol in aqueous solution. This could serve as an efficient and green photocatalyst for the selective oxidative conversion of a hydrophobic reactant to a hydrophilic product.

Stable and efficient immobilization technique of aldolase under consecutive microwave irradiation at low temperature

To establish a stable and efficient immobilization technique under microwave irradiation, a focused microwave reaction system was used, where the temperature was set appropriately in the microwave system and cooling module to produce consecutive microwave irradiation. 2-Deoxy-D-ribose-5-phosphate aldolase (DERA) was rapidly and efficiently immobilized in mesocellular siliceous foams (MCFs) under microwave irradiation. When the output power in the microwave system was set to 30 W, after 3 min, 88.4% of the enzyme protein was coupled to the wall of the support pores and the specific activity of the immobilized enzyme was 2.24 U mg(-1), 149.2% higher than that of the free enzyme and 157.0% higher than that of the non-microwave-assisted immobilized enzyme. In catalysis, microwave-assisted immobilized DERA tolerated a wider range of both pH and temperature than other DERA preparations. The thermal and storage stabilities were also significantly improved. This focused; microwave-assisted immobilization technique has proven to be simple, stable and highly efficient. This technique could also be applied to other enzyme immobilizations.

ChemInform Abstract: Mesocellular Siliceous Foams with Uniformly Sized Cells and Windows.

Molecular sieves with uniform large pores are desirable for chemical reactions and for use in separations involving large molecules.1 Periodic cubic and hexagonal mesoporous silica phases with uniform large pores have been synthesized by using nonionic triblock and star diblock copolymers as templates.2 Control over the pore size is achieved by adjusting the hydrophobic volumes of the self-assembled aggregates.2,3 In this paper, we describe how adding a sufficiently large amount of an organic cosolvent induces a phase transformation from the highly ordered p6mm mesostructure of SBA-15-type mesoporous silicas to remarkable mesostructured cellular foams (mesocellular foams, MCFs) composed of uniformly sized, large spherical cells that are interconnected by uniform windows to create a continuous 3-D pore system. The interconnected nature of the large uniform pores makes these new mesostructured silicas promising candidates for supports for catalysts and in separations involving large molecules, and they may be of interest in low-dielectric applications. The MCFs have been synthesized in aqueous acid by using dilute Pluronic P123 solutions in the presence of 1,3,5-trimethylbenzene (TMB) as organic cosolvent.4 X-ray diffraction (XRD) experiments5 reveal well-resolved peaks at small angles, as shown in Figure 1 for a sample with a cell diameter of 33 nm. Careful analyses of the scattering data for MCFs show that the higher order peaks cannot be indexed to any plane or space group (e.g., p6mm) or to a lamellar diffraction pattern. In fact, after subtraction of the background,6 the X-ray data are in good agreement with simulated scattering7 due to monodisperse spheres (cells) of diameter D (see Table 1), while attempts to fit the X-ray data to

Post-immobilization of modified macromolecular reagents using assembled penicillin acylase for microenvironmental regulation of nanopores and enhancement of enzyme stability

Penicillin acylase (PA) is known to regulate the microenvironment of nanospores. In this study, nanopores containing chemically-modified macromolecules co-assembled with immobilized PA were constructed. We also investigated the various types of functionalized mesocellular siliceous foams (MCFs) commonly used for the immobilization of PA by measuring the catalytic performance and stability of each PA preparation. Amino-MCF activated by p-benzoquinone was chosen as the optimum support for PA immobilization. Successful modification of macromolecules was verified by FT-IR and ultraviolet (UV) spectroscopy. The specific activity of PA co-assembled with dextran 10 k was 99.1 U/mg, which was 1.5-fold that of pristine immobilized PA, while the optimum pH was shifted to neutral. Compared to pristine immobilized and free PA, the optimum temperatures for the modified PA were 5 and 10°C higher, respectively. The residual activity of the ficoll derivative of PA after treatment at 50°C for 6 h was 70%, and this was later increased to 214.5% compared to that of pristine immobilized PA. The dextran 10 k derivative of PA exhibited 90.2% residual activity after 25 times of continuous use. The results show that chemically-modified macromolecules co-assembled with PA in amino-MCF provided a suitable microenvironment for enzyme stability.

Siliceous mesocellular foam for high-performance liquid chromatography: Effect of morphology and pore structure

Spherical siliceous mesocellular foam (MCF) particles with an average particle size of 4.8 μm have been successfully prepared. These spherical particles were tailored in pore sizes and surface areas. They were functionalized with C 8 or C 18 groups, and applied towards reversed phase high-performance liquid chromatography (HPLC) column separations. Their high surface areas gave rise to very good retention characteristics, as illustrated in the separation of a series of alkylbenzene solutes with increasing chain length. The highly interconnected porous structure and ultralarge pore size of MCF allowed the columns to be used at high flow rates without much loss in column efficiency. The column efficiency and peak symmetry were further improved by eliminating the micropores of the stationary phase. The reversed phase column packed with C 18-modified spherical MCF particles provided for excellent separation of different deoxynucleosides, illustrating the broad applicability of these materials due to their controlled pore size.