Mesostructured Solids Research Articles

Immobilization of D-Amino Acid Oxidase (DAAO) Enzyme on Hybrid Mesoporous MCF, SBA-15 and MCM-41 Nanomaterial.

Hybrid mesoporous materials as carriers for immobilization of D-amino acid oxidase (DAAO) were prepared via three steps: (i) hydrothermal synthesis of nanoporous MCF, SBA-15 and MCM-41 powders, (ii) functionalization with 3-aminopropyltriethoxysilane (APTES) by post-synthesis grafting; and (iii) activation with glutardialdehyde. The resulting mesostructured solids were characterized by various techniques: XRD, IR, TGA-DTA and N2 adsorption–desorption (BET). The characterization results indicated that these materials still maintained their structure after functionalization. IR data and TGA-DTA analysis demonstrated the existence of amine functional groups on the surface of APTES-functionalized samples. The DAAO immobilized on these materials exhibited higher catalytic activity and stability of enzyme for conversion of cephalosporin C (CPC) as compared to those of the non-functionalized ones. The catalytic activity and stability of enzyme decreased in the order MCF > SBA-15 > MCM-41.

Asymmetric benzoylation of hydrobenzoin by copper(ii) bis(oxazoline) anchored onto ordered mesoporous silicas and their carbon replicas

A copper(II) complex with a commercial chiral bis(oxazoline) was anchored onto ordered mesoporous silica materials and their respective carbon replicas. The amount of transition metal complex loaded onto the mesostructured solids was determined by ICP-AES and the materials were also characterized by elemental analysis, FTIR, TG/DSC and isotherms of N2 adsorption at −196 °C. For the first time the asymmetric benzoylation of a 1,2-diol was performed in the heterogeneous phase by using an anchored commercial bis(oxazoline) ligand. The effect of the type of mesoporous material on the catalytic parameters, as well as on the reutilization of catalysts in several catalytic cycles, was checked. All the composites prepared were active, selective and enantioselective in this asymmetric organic transformation. Using the two ordered mesoporous silicas as supports good selectivities, with comparable yields and TONs to the homogeneous phase reaction, were obtained. Furthermore these two heterogeneous catalysts are more stable upon reuse than the corresponding ordered carbon replica materials. One of the former heterogeneous catalysts, with mesoporous silica as a support, could be further reused for 4 consecutive cycles without significant loss of selectivity, the TON or enantioselectivity.

Mesoporous materials and electrochemistry

Ordered mesoporous materials prepared by the template route have attracted increasing interest from the electrochemists community due to their plenty of unique properties and functionalities that can be effectively exploited in electrochemical devices. This review will cover the whole field of the intersection between electrochemistry and ordered mesoporous materials. The latter are either electronically insulating (silica and some other metal oxides, as well as silica-based organic-inorganic hybrid materials), semi-conducting (metal oxides), or conducting (metals, carbons). The three main intersection areas are: (1) the development/use of electrochemical methods to characterize the properties of mesoporous materials (i.e., charge and mass transfer processes); (2) the generation of mesostructured solids by electro-assisted deposition using appropriate templates; and (3) the application of these novel materials for electrochemical purposes. The most common devices to date are based on a bulk composite or thin film configuration and the resulting electrodes modified with such mesoporous materials have been successfully applied in various fields, including mainly electrochemical sensing and biosensing as well as energy conversion and storage (620 references).

Designed synthesis and characterization of ordered mesoporous materials with high micropore content

Highly ordered mesoporous material SBA-15 with rich micropores has been successfully prepared by changing the hydrothermal treatment acidity and temperature to adjust the interaction between silanols and block copolymers at the inorganic/organic interface in the self-assembled mesostructured solids, so that the amount of hydrophilic PEO blocks inserted into the silica walls can be adjusted. The characterization results show that when the hydrothermal treatment pH value and temperature are 2.2 and 100 °C, respectively, the sample calcined at 300 °C shows a micropore volume as high as 0.176 cm3/g, which is 21.6% of the total pore volume.

A silanol protection mechanism: Understanding the decomposition behavior of surfactants in mesostructured solids

Abstract

ChemInform Abstract: Mesostructured Non-oxidic Solids with Adjustable Worm-Hole Shaped Pores: M-Ge-Q (Q: S, Se) Frameworks Based on Tetrahedral [Ge4Q10]4- Clusters.

The discovery of MCM-41 and its relatives has spawned a revolution in the design and synthesis of tailored mesostructured oxide-based materials. By comparison, non-oxidic solids such as sulfides or selenides are only very little exploredÐpartly because of difficulties in handling or obtaining relevant precursors (e.g., [SiS4] 4± units). Direct sulfur and selenium analogs of MCM-41 type materials would be the thioand selenoaluminosilicates. However, these systems are expected to be very unstable to hydrolysis. Therefore, one needs a working analog for the sulfides and selenides to mimic some of the characteristics of the [SiO4] 4± unit. A suitable such building unit with tetrahedral topology and similar charge is the adamantane thioanion [Ge4S10] 4± (or its selenium analog) (Scheme 1), which is made of four corner-linked [GeS4] 4± tetrahedra. We have already studied in detail their corresponding salts (RNMe3)4[Ge4Q10] (abbrev. as CnGeQ) with various surfactants. Reports on mesostructured chalcogenides have begun to appear, such as CdS and ZnS prepared through the incorporation of surfactants. Also, initial studies on mesostructured tin sulfides and a brief report on the synthesis of mesostructured thiogermanates resulting from the hydrothermal treatment of amorphous GeS2 and C16H33NMe3 Br, (CTA), are noteworthy. Various microstructured metal sulfides resembling those of zeolites have been forecast and important first steps have been made in recent years. The adsorption and sensing behavior of some structurally well-defined microporous lamellar tin sulfides (cation)2Sn3S7 have been explored. [15] Small guests such as NH3, H2S, and alcohols were found to interact with these materials. A recent exciting development toward producing well-defined mesostructured materials is the discovery of ASU-32, a novel indium sulfide that features pore diameters of ~14.5 Š.

Analytical study on the pyrolytic behaviour of cellulose in the presence of MCM-41 mesoporous materials

The effect of different mesoporous materials of the MCM-41 type on the pyrolytic behaviour of cellulose was evaluated by off-line analytical pyrolysis followed by GC–MS analysis of the evolved products trapped onto a XAD-2 resin. Siliceous MCM-41 (Si-MCM-41) and Me-MCM-41 catalysts containing different metals, namely Al, Mg, Ti, Sn or Zr, were synthesised and investigated utilising the same catalyst/cellulose mass ratio 1:3. The effect of the catalysts was evaluated by quantifying the yields of the following pyrolysis products: (2H)-furan-3-one, 2-furaldehyde, 5-methyl-2-furaldehyde, 4-hydroxy-5,6-dihydro-pyran-2-one, levoglucosenone, 1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one (LAC), 1,4:3,6-dianhydro-α- d-glucose and levoglucosan. All the examined mesostructured solids decreased the yields of levoglucosan with respect to uncatalysed cellulose, and increased the production of levoglucosenone and LAC. The effect was higher with doped MCM-41 in comparison to Si-MCM-41. The formation of other pyrolysis products was less influenced by the catalyst. The activity of Sn-MCM-41 was further investigated by preparative pyrolysis with a fixed bed quartz reactor. This catalyst gave rise to a pyrolytic liquid enriched in LAC and depleted in levoglucosan, and could be re-used six times after regeneration without apparent loss of activity.

Analysis of Products Generated from the Thermal and Catalytic Degradation of Pure and Waste Polyolefins using Py-GC/MS

The possibility of transforming waste plastics into valuable hydrocarbons via catalytic cracking and reforming is attracting increasing interest. Pyrolysis coupled with Gas Chromatographic separation and Mass Spectrometry detection (Py-GC/MS) has been used in this work to study the product selectivity of various catalysts in the conversion of pure and residual polyethylene samples into hydrocarbon products. Five acid solids of comparable aluminium contents but different textural and acid properties were tested as catalysts, including three zeolites (standard ZSM-5, nanocrystalline n-ZSM-5 and Beta) and two mesostructured solids (Al-MCM-41 and Al-SBA-15). Thermal cracking of the pure and residual polymers generated a similar range of products to each other, with a high proportion of linear paraffins and olefins of varying lengths. The presence of zeolitic materials resulted in complete elimination of heavy linear products, an increase in the light hydrocarbon fraction and a marked selectivity towards the formation of single-ring aromatic species, particularly benzene, toluene and xylene. Aromatic formation was particularly notable with the small crystal size n-ZSM-5 (aromatic selectivity up to 53.9%) and less marked in the case of standard ZSM-5 (up to 36.4%) and Beta zeolite (up to 35.0%). Mesostructured catalysts like Al-MCM-41 and Al-SBA-15 favoured the production of light C2–C5 hydrocarbons (up to 57.9%) while the formation of aromatic products was significantly lower than with zeolitic materials. The paper examines the extent and the causes for this product selectivity and discusses its connection with the acid and textural properties of each catalyst. It was also observed that, under the experimental conditions employed, the products generated were not significantly affected by the nature and origin of the polymers employed.

Catalytic activity of zeolitic and mesostructured catalysts in the cracking of pure and waste polyolefins

Six acid solids of varying acid and textural characteristics has been investigated for their catalytic activity in the degradation of plastic polymers using thermogravimetric and differential thermal analysis. The polymers included pure low-density polyethylene, pure high-density polyethylene and two samples of recycled polyethylene of urban and agricultural origins. The catalysts were three zeolitic materials (standard ZSM-5, nanocrystalline n-ZSM-5 and Beta) and three mesostructured solids (sol–gel Al-MCM-41 (sg), hydrothermal Al-MCM-41 (hy) and Al-SBA-15). The catalytic activity of each acid solid has been related to its capacity to shift the degradation reaction to lower temperatures. Despite showing strong acid properties, standard ZSM-5 zeolite exhibited a very low catalytic activity on most plastics, which was attributed to diffusional impediments that affected the access of the bulky polymer molecules to its internal active sites. These impediments were partly overcome in the case of Beta zeolite and even more markedly with nanocrystalline n-ZSM-5, which exhibited the strongest catalytic activity due to a combination of strong acid properties and large external surface area. Owing to their non-crystalline nature, mesostructured solids showed weaker acid properties than their zeolitic counterparts. However, this disadvantage was partly compensated by the presence of larger pores that reduced diffusional hindrances. Thus, Al-MCM-41 (hy) exhibited one of the highest catalytic activities, largely surpassing the performance of crystalline solids with stronger acid properties. The catalytic activity of all the acid solids tested in this work was significantly reduced when they were used on waste plastics. This deactivating effect was more notable in mesostructured solids.

Organized mesoporous solids: mechanism of formation and use as host materials to prepare carbon and oxide replicas

Since the discovery of organized mesoporous solids by Mobil Oil Co. scientists, numerous patents and papers dealing with the synthesis, mechanism of formation, properties and applications of these exciting solids have been published. In this context, our research group has focused its activities on two research area: ( i) the understanding of the formation of silica and alumina mesostructured solids using in situ probing techniques such as fluorescence, and ( ii) the development of new synthesis routes such as nanocasting, with the aim of preparing ordered mesoporous carbons and oxides with tailored properties. This short review reports the main results that we have obtained in recent years on these topics. To cite this article: B. Lebeau et al., C. R. Chimie 8 (2005).

Ortho-chalcogenostannates as ligands: syntheses, crystal structures, electronic properties, and magnetism of novel compounds containing ternary anionic substructures [M4(mu4-Se)(SnSe4)4]10- (M=Mn, Zn, Cd, Hg), 3(infinity)[[Hg4(mu4-Se)(SnSe4)3]6-], or 1(infinity)[[HgSnSe4]2-

By reaction of K4[SnSe4].1.5 MeOH with CdCl2 or Hg(OAc)2 in water/methanol it was possible to prepare single crystals of four novel compounds that contain ternary anionic coordination oligomers and polymers: [K10(H2O)16(MeOH)(0.5)][M4(mu4-Se)(SnSe4)4] (4: M=Cd, 5: M=Hg), [K6(H2O)3][Hg4(mu4-Se)(SnSe4)3].MeOH (6), and K2[HgSnSe4] (7), which were structurally characterized by single-crystal X-ray diffraction. The optical absorption properties of the isostructural compounds 4 and 5, as well as those of the recently reported Zn (2) and Mn (3) analogues, were studied by UV-visible spectroscopy. These investigations showed the quaternary phases to have relatively small optical gaps for their molecular size (2.2-2.6 eV), which are similar to the excitation energies that were observed for mesostructured solids of the respective combination of elements. According to DFT investigations on the ternary anions, an experimentally observed difference between the absorption behavior of the d10 compounds 2, 4, and 5 and the open-shell d(5) compound 3 is in line with different characters of the frontier orbitals in the two cases. Both the calculations and a magnetic measurement on 3 demonstrated antiferromagnetic coupling between the mu(4)-Se-bridged Mn centers.

The anion sequence in the phase transformation of mesostructures templated by non-ionic block copolymers.

A p6m to Ia3d mesophase evolution is achieved by simply adjusting the acidity and/or anion species in the presence of block copolymers; the unusual anion sequence that affects the phase behavior of block copolymer templated mesostructured solids is revealed to be SO(4)(2-)(HSO(4)(-)) > NO(3)(-) > Br(-) > Cl(-).

Surfactant Templated Assembly of Cubic Mesostructured Semiconductors Based on [Sn2Se6] 4- and Pt2+ in Single-Crystal Form.

ABSTRACTMesostructured non-oxidic materials with cubic Ia-3d symmetry were prepared by linking [Sn2Se6] 4- clusters with Pt2+ in the presence of surfactant molecules. The use of long chain pyridinium-based surfactants (octadecyl- and eicosadecyl) afforded materials with exceptionally high cubic pore order and single-crystal particle morphology. By contrast trimethylammonium-based surfactants produced cubic mesostructured solids with inferior overall quality. We have also synthesized materials with significantly lower surfactant content by increasing the Pt2+:[Sn2Se6] 4- molar ratio, while maintaining the cubic pore symmetry. All materials are semiconductors with energy band-gap in the range 0.9<Eg<1.8 eV.

Investigations by fluorescence techniques of the mechanism of formation of silica- and alumina-based MCM-41-type materials

Silica- and alumina-based mesostructured MCM-41-type materials were obtained at low temperature in the presence of cationic (cetyltrimethylammonium bromide (CTAB) or chloride) and anionic (sodium dodecylsulfate) surfactants, respectively, by modifying the pH of the corresponding clear precursor solutions.In situ fluorescence techniques were used to study the first steps of formation of these mesostructured solids prior to precipitation. For the silica-based system using CTAB, only a small fraction of micelle-bound bromide ions is exchanged by OH− and/or silicate ions and there is hardly any micelle growth in the presence of these additives and upon lowering the pH to a value close to that where the mesostructured solid precipitates out. A similar result was observed for the alumina-based systems. For both types of systems the micelles remain close to spherical in the precursor solution.

Synthesis of cubic mesoporous MCM-48 materials from the system SiO2:CTAOH/Br:H2O

By a detailed study of the pH of the synthesis gel, CTA+ concentration, temperature and time of crystallization in the formation of the different mesophases in the system SiO2:CTAOH/Br:H2O, it was found that the driving force for the different phase formation is the negative charge of the silicate oligomers formed during crystallization of the mesostructured solids which have to be balanced by the CTA+ surfactant cations. The more appropriate packing of cationic surfactant species in terms of energy minimization provokes the formation of the different phases observed by working at different pHs, temperatures or crystallization times of synthesis.

Interface Charge Density Matching as Driving Force for New Mesostructured Oxovanadium Phosphates with Hexagonal Structure, [CTA]xVOPO4·zH2O

Hexagonal mesostructured mixed-valence oxovanadium phosphates [CTA]xVOPO4·zH2O, in short ICMUV-2, have been synthesized through a S+I- cooperative mechanism using cationic surfactant (cetyltrimethylammonium, CTAB) rodlike micelles as a template. On the lines of the hypothesis that the driving force leading to the formation of mesostructured solids is the charge density matching at the interface between the supramolecular−organic and supramolecular−inorganic moieties, the self-assembling process between CTA+ micelles and VOPO4q- planar anions can be thought of as consequence of the adequate adjustment of the metal mean oxidation state. X-ray powder diffraction and TEM techniques show that the solids consist of hexagonal arrays of mesopores filled with surfactant, whereas spectroscopic results allow us to propose an oxovanadium phosphate bond topology similar to that observed in the NaxVOPO4·nH2O layered derivatives. The thermal behavior of the mesostructured materials has also been investigated, given that...

Nanostructure synthesis using surfactants and copolymers

Self-assembled structures of surfactants and block copolymers provide a valuable tool for controlling nanostructure formation in polymers and inorganic solids. The past year has seen a huge number of different new nanoparticles and mesostructured solids. A high level of control of the mesoscopic and macroscopic morphologies has been reached for both polymer nanostructures and mesoporous inorganic materials. © 1999 Elsevier Science Ltd.