Siliceous Mesostructured Cellular Foams Research Articles

Improved biocatalytic cascade conversion of CO2 to methanol by enzymes Co-immobilized in tailored siliceous mesostructured cellular foams

CO2 can be enzymatically reduced to methanol in a cascade reaction involving three enzymes: formate-, formaldehyde- and alcohol dehydrogenase (FateDH, FaldDH, ADH).

Vanadium Phosphorus Oxide/Siliceous Mesostructured Cellular Foams: efficient and selective for sustainable acrylic acid production via condensation route

A new type of supported vanadium phosphorus oxide (VPO) with self-phase regulation was simply fabricated (organic solvent free) for the first time by depositing the specific VPO precursor NH4(VO2)HPO4 onto the Siliceous Mesostructured Cellular Foams (MCF) with controlled activation. The resulting materials were found to be highly efficient and selective for sustainable acrylic acid (AA) plus methyl acrylate (MA) production via a condensation route between acetic acid (HAc) and formaldehyde (HCHO). A (AA + MA) yield of 83.7% (HCHO input-based) or a (AA + MA) selectivity of 81.7% (converted HAc-based) are achievable at 360 °C. The systematic characterizations and evaluations demonstrate a unique surface regulation occurring between the MCF and the NH4(VO2)HPO4 precursor. NH3 release upon activation of NH4(VO2)HPO4 precursor together with adsorption of NH3 by MCF automatically induces partial reduction of V5+ whose content is fine-tunable by the VPO loading. Such a functionalization simultaneously modifies phase constitution and surface acidity/basicity of catalyst, hence readily controls catalytic performance.

Förster Resonance Energy Transfer Study of the Improved Biocatalytic Conversion of CO2 to Formaldehyde by Coimmobilization of Enzymes in Siliceous Mesostructured Cellular Foams

By combining two enzymes, formate dehydrogenase (FateDH) and formaldehyde dehydrogenase (FaldDH), it is possible to drive the thermodynamically unfavorable conversion of CO2 to formaldehyde. For this purpose, the enzymes were coimmobilized in siliceous mesostructured cellular foams (MCFs). A high degree of adsorption of both enzymes was achieved by coimmobilizing the enzymes sequentially, i.e., first FateDH and then FaldDH. The highest conversion rate was obtained with an enzyme mass ratio of 1:15 (FateDH/FaldDH). Using MCF functionalized with mercaptopropyl groups (MCF-MP), the activity increased ∼4 times compared to the enzymes free in solution. To probe the distance between the two enzymes, they were separately labeled with either Cy3 or Cy5 dyes and studied with Förster resonance energy transfer (FRET). An increased energy transfer was observed when the enzymes were coimmobilized in MCF-MP, suggesting that the two enzymes are in close proximity, resulting in higher conversion of CO2 to formaldehyde.

Immobilization of formaldehyde dehydrogenase in tailored siliceous mesostructured cellular foams and evaluation of its activity for conversion of formate to formaldehyde

Formaldehyde dehydrogenase (FaldDH) is used as a catalyst to reduce formate to formaldehyde in a cascade reaction to convert CO2 to methanol. This enzyme, however, has low activity and is sensitive to substrate/product concentration and pH. To improve the performance of FaldDH, it can be immobilized through physical adsorption in siliceous mesostructured cellular foams (MCF), which physical properties are suitable for the immobilization of large molecules as FaldDH (molecular size of 8.6 × 8.6 × 19 nm). In this work two MCF materials were synthesized: MCF1 with a pore size of 26.8 nm and window size of 10.5 nm; and MCF2 with a pore size of 32.9 nm and window size of 13.0 nm. The surfaces of the materials were functionalized with octyl, mercaptopropyl or chloromethyl groups. FaldDH was successfully immobilized inside all the materials, yielding enzyme loadings of about 300 mg g‐1 in MCF1 and more than 750 mg g−1 in MCF2. However, the enzyme was inactive upon immobilization on MCF1, whereas on MCF2 the enzyme retained its catalytic activity presumably owing to the larger pores of this material and the need for the enzyme to undergo configurational changes during the reaction. Using MCF2 functionalized with mercaptopropyl groups the activity of FaldDH was enhanced beyond that of the free enzyme. Additionally, low leakage of the enzyme from the MCF2 was observed during the reactions. Thus, tailored MCF is a highly attractive material for employment of the FaldDH enzyme.

Influence of operating conditions and immobilization on activity of alcohol dehydrogenase for the conversion of formaldehyde to methanol

Improved activity of alcohol dehydrogenase by immobilization in octyl-functionalized siliceous mesostructured cellular foams and tuning of pressure and formaldehyde concentration.

Siliceous mesostructured cellular foams/poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) composite biomaterials for bone regeneration.

Osteoinductive and biodegradable composite biomaterials for bone regeneration were prepared by combining poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) with siliceous mesostructured cellular foams (SMC), using the porogen leaching method. Surface hydrophilicity, morphology, and recombinant human bone morphogenetic protein 2 adsorption/release behavior of the SMC/PHBHHx scaffolds were analyzed. Results of scanning electron microscopy indicated that the SMC was uniformly dispersed in the PHBHHx scaffolds, and SMC modification scaffolds have an interconnected porous architecture with pore sizes ranging from 200 to 400 μm. The measurements of the water contact angles suggested that the incorporation of SMC into PHBHHx improves the hydrophilicity of the composite. In vitro studies with simulated body fluid show great improvements to bioactivity and biodegradability versus pure PHBHHx scaffolds. Cell adhesion and cell proliferation on the scaffolds was also evaluated, and the new tools provide a better environment for human mesenchymal stem cell attachment, spreading, proliferation, and osteogenic differentiation on PHBHHx scaffolds. Moreover, micro-computed tomography and histological evaluation confirmed that the SMC/PHBHHx scaffolds improved the efficiency of new bone regeneration with excellent biocompatibility and biodegradability and faster and more effective osteogenesis in vivo.

Synthesis of task-specific ionic liquids with grafted diglycolamide moiety. Complexation and stripping of lanthanides

Task-specific ionic liquids (TSILs) of a novel class, with the diglycolamide moietity grafted in the alkyl chain of imidazolium cation, were synthesized and characterized. Lanthanide complexation capabilities of TSILs as active components of solid phase extractants were evaluated by studies on the adsorption of lanthanides from aqueous solutions. The TSIL-based solid adsorbents prepared by immobilization of long-alkyl-chain TSILs in siliceous mesostructured cellular foams adsorb trivalent lanthanides. No extraction of lanthanides from aqueous solution into 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C6mim][Nf2T]) was observed at any acidity in the presence of these TSILs in the aqueous phase. This implies that TSILs suppress the extraction of lanthanides by formation of water-soluble complexes. The TSILs added to solvent extraction systems consisting of N,N,N′,N′-tetraoctyl-3-oxapentanediamide (TODGA) in [C6mim][Nf2T] and aqueous HNO3 solutions show very good stripping properties for lanthanides.

Magnetic Fe3O4@mesoporous silica composites for drug delivery and bioadsorption

Magnetic Fe3O4@mesoporous silica (MS) composites were synthesized by generating Fe3O4 nanoparticles in the mesoporous silica matrix using the sol–gel method in nitrogen atmosphere. The mesoporous silica hosts include SBA-15 particles owning highly ordered p6mm mesostructure, siliceous mesostructured cellular foams (MCFs), and fiber-like mesoporous silica (FMS) with unique pore structures. The X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 adsorption/desorption results show that Fe3O4 functionalized MCFs and FMS possess suitable mesoporous structure for the adsorption of both small-molecular drug and large biomolecules. The biocompatibility tests on L929 fibroblast cells using MTT assay reveal low cytotoxicity of these systems. These Fe3O4@mesoporous silica composites show sustained release properties for aspirin in vitro. The release of the aspirin molecules from the pores of the Fe3O4@mesoporous silica composites is basically a diffusive process. Fe3O4@MCFs and Fe3O4@FMS owning larger pore size are good candidates for the adsorption of bovine serum albumin (BSA). These magnetic composites can be potential vectors for drug delivery and bioadsorption.

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.

Covalent immobilization of trypsin on to siliceous mesostructured cellular foams to obtain effective biocatalysts

The properties of siliceous mesostructured cellular foams (MCF) with the surface functionalised using different organosilanes to immobilize covalently trypsin have been studied. Four organosilanes were applied: 3-aminopropyltriethoxysilane, 2-aminoethyl-3-aminopropylmethyldimethoxysilane, 2-aminoethyl-3-aminopropyltrimethoxysilane and 3-glicydoxypropyl-triethoxysilane. The samples modified using alkylamines were further activated with glutaraldehyde (GLA), a cross-linker. Commercially available silica gels and Eupergit C were used for comparison. Activity of MCF-based biocatalysts expressed in BAPNA and casein conversion, was significantly higher than of the silica gel- and Eupergit C-based counterparts. In the best systems the determined activity of trypsin was higher than of a free enzyme. The GLA-amino linkages appeared the most effective systems for the covalent immobilization of trypsin. The MCF-based preparations were notably more stable than a native enzyme at 333 K and they also showed good storage stability at 277 K. A unique porous structure of MCF was found to be a critical factor which renders siliceous mesostructured foam a very promising material for immobilization of enzymes.

Application and properties of siliceous mesostructured cellular foams as enzymes carriers to obtain efficient biocatalysts

The application of siliceous mesostructured cellular foams (MCF) with the surface functionalised using different organosilanes to immobilize covalently invertase and glucoamylase have been studied. Four organosilanes were applied: 3-aminopropyltriethoxysilane (APTS), 2-aminoethyl-3-aminopropylmethyldimethoxysilane (AEAPMDS), 2-aminoethyl-3-aminopropyltrimethoxysilane (AEAPTS) and 3-glicydoxypropyl-triethoxysilane (GPTS). The samples modified using alkylamines were further functionalised with glutaraldehyde (GLA), a cross linker. Commercially available silica gels and Eupergit C were used for comparison. Activity of MCF-based biocatalysts was significantly higher than of the silica gel and Eupergit C based counterparts. In the best systems the determined activity of both immobilized enzymes was even higher than that of the free enzymes. The glutaraldehyde (GLA)-amino linkage formed by organosilanes with two amino groups was the most effective system for MCF-bound invertase and that formed by APTS in the covalent immobilization of glucoamylase. A unique porous structure of MCF was found to be a critical factor which renders siliceous mesostructured foam a very promising material for immobilization of enzymes.

Continuous Fixed-Bed Gas-Phase Hydroformylation over PPh3-Modified Mesostructured Cellular Foam-Supported Rh Catalyst

siliceous mesostructured cellular foams (mcfs) are a new class of three-dimensional hydrothermally robust materials with ultralarge mesopores. the open system of large pores and the controllable pore size give mcfs unique advantages as catalyst supports. in this paper, mcfs were employed as supports in developing the pph3-rh/mcf catalyst for propylene hydroformylation in a fixed-bed reactor. the pph3-rh/mcf catalyst shows high activity (propylene conversion of 21.6% and butyraldehyde tof of 160.6 h(-1)), high selectivity (n-butyraldehyde/i-butyraldehyde = 10.4), and excellent stability under mild conditions of p = 1.0 mpa, t 393 k, and sv = 2 000 h(-1).

SBS as template to synthesize 3D siliceous mesostructured cellular foams

A mesostructured cellular foam (MCF) with three-dimensional (3D) disordered strutlike structure is prepared by using triblock copolymer (poly(styrene-b-butadiene-b-styrene), SBS, M W=140K) as template under strong acid conditions. It is the first report to use triblock copolymer with both hydrophobic head and tail groups instead of hydrophilic head and hydrophobic tail copolymers to synthesize siliceous mesostructured cellular foams. The resulted materials have high pore volume (0.92 cm 3/g) and relatively narrow pore size distributions with a large pore size of 7.9 nm, which will allow for the fixation of large active complexes, reduce diffusional restriction of reactants and enable reactions involving bulky molecules to take place, especially.

Microemulsion Templating of Siliceous Mesostructured Cellular Foams with Well-Defined Ultralarge Mesopores

Siliceous mesostructured cellular foams (MCFs) with well-defined ultralarge mesopores and hydrothermally robust frameworks are described. The MCFs are templated by oil-in-water microemulsions and are characterized by small-angle X-ray scattering, nitrogen sorption, transmission electron microscopy, scanning electron microscopy, thermogravimetry, and differential thermal analysis. The MCFs consist of uniform spherical cells measuring 24−42 nm in diameter, possess BET surface areas up to 1000 m2/g and porosities of 80−84%, and give, because of their pores with small size distributions, higher-order scattering peaks even in the absence of long-range order. Windows with diameters of 9−22 nm and narrow size distribution interconnect the cells. The pore size can be controlled by adjusting the amount of the organic swelling agent that is added and by varying the aging temperature. Adding ammonium fluoride selectively enlarges the windows by 50−80%. In addition, the windows can be enlarged by postsynthesis treatm...

Siliceous Mesostructured Cellular Foams with Uniformly Sized and Shaped Pores

ABSTRACTMesostructured siliceous cellular foams (mesocellular foams, MCFs) with homogeneous ultra-large mesopores are described. MCFs consist of uniform spherical cells 21–36 nm in diameter and possess surface areas up to 900 m2/g. Uniform windows, 7–18 nm in diameter, interconnect the cells to form a continuous 3-D pore system, which makes the MCFs attractive candidates for supports for catalysis and in separation and immobilization involving large molecules. They may be of interest in low-dielectric applications. The size of the cells can be controlled by the concentration of the added organic cosolvent. Adding small amounts of NH4F selectively enlarges the windows. We propose that the MCFs are templated by oil-inwater microemulsion droplets. The large-pore MCF materials resemble aerogels, with the benefit of a facilitated synthesis procedure in combination with well-defined pores and wall structure.