Showing papers on "Mesoporous material published in 2001"
TL;DR: A critical review of adsorption methods that are currently used in the characterization of ordered organic−inorganic nanocomposite materials is presented in this paper, where the authors compare and evaluate the available methods for mesopore size analysis.
Abstract: A critical review of adsorption methods that are currently used in the characterization of ordered organic−inorganic nanocomposite materials is presented, and the adsorption methodology that is potentially useful for this characterization, but has not yet been applied, is discussed. The ordered organic−inorganic nanocomposites include surface-functionalized ordered mesoporous materials (OMMs) with siliceous frameworks (synthesized either via postsynthesis surface modification or via direct co-condensation method), periodic mesoporous organosilicas, and surfactant-containing OMMs. This review covers the methods for determination of the specific surface area and pore volume. The available methods for mesopore size analysis are critically compared and evaluated, with special emphasis on the recent developments related to the application of advanced computational methods for studying adsorption in porous media and to the direct modeling of adsorption using highly ordered surface-functionalized OMMs as model a...
2,987 citations
TL;DR: A general strategy for the synthesis of highly ordered, rigid arrays of nanoporous carbon having uniform but tunable diameters is described, which gives rise to promising electrocatalytic activity for oxygen reduction and could prove to be practically relevant for fuel-cell technologies.
Abstract: Nanostructured carbon materials are potentially of great technological interest for the development of electronic1,2, catalytic3,4 and hydrogen-storage systems5,6. Here we describe a general strategy for the synthesis of highly ordered, rigid arrays of nanoporous carbon having uniform but tunable diameters (typically 6 nanometres inside and 9 nanometres outside). These structures are formed by using ordered mesoporous silicas as templates, the removal of which leaves a partially ordered graphitic framework. The resulting material supports a high dispersion of platinum nanoparticles, exceeding that of other common microporous carbon materials (such as carbon black, charcoal and activated carbon fibres). The platinum cluster diameter can be controlled to below 3 nanometres, and the high dispersion of these metal clusters gives rise to promising electrocatalytic activity for oxygen reduction, which could prove to be practically relevant for fuel-cell technologies. These nanomaterials can also be prepared in the form of free-standing films by using ordered silica films as the templates.
2,352 citations
TL;DR: Ordered mesoporous carbons have been synthesized using ordered mesopore silica templates as discussed by the authors, where the template needs to exhibit three-dimensional pore structure in order to be suitable for the ordered mesophorous carbon synthesis, otherwise disordered microporous carbon is formed.
Abstract: Ordered mesoporous carbons have recently been synthesized using ordered mesoporous silica templates. The synthesis procedure involves infiltration of the pores of the template with appropriate carbon precursor, its carbonization, and subsequent template removal. The template needs to exhibit three-dimensional pore structure in order to be suitable for the ordered mesoporous carbon synthesis, otherwise disordered microporous carbon is formed. MCM-48, SBA-1, and SBA-15 silicas were successfully used to synthesize carbons with cubic or hexagonal frameworks, narrow mesopore size distributions, high nitrogen Brunauer–Emmett–Teller (BET) specific surface areas (up to 1800 m2 g–1), and large pore volumes. Ordered mesoporous carbons are promising in many applications, including adsorption of large molecules, chromatography, and manufacturing of electrochemical double-layer capacitors.
1,467 citations
TL;DR: Mesoporous semiconducting films consisting of preferentially orientated monoclinic-phase nanocrystals of tungsten trioxide have been prepared using a novel version of the sol-gel method, combining excellent photoresponse to the blue region of the solar spectrum, up to 500 nm, with good transparency at wavelengths larger than 550 nm.
Abstract: Mesoporous semiconducting films consisting of preferentially orientated monoclinic-phase nanocrystals of tungsten trioxide have been prepared using a novel version of the sol−gel method. Transformations undergone by a colloidal solution of tungstic acid, stabilized by an organic additive such as poly(ethylene glycol) (PEG) 300, as a function of the annealing temperature have been followed by means of a confocal Raman microscope. The shape and size of WO3 nanoparticles, the porosity, and the properties of the films depend critically on preparation parameters, such as the tungstic acid/PEG ratio, the PEG chain length, and the annealing conditions. Well-crystallized WO3 films combine excellent photoresponse to the blue region of the solar spectrum, up to 500 nm, with good transparency at wavelengths larger than 550 nm. Particular applications of these nanocrystalline WO3 films include photoelectrochemical and electrochromic devices.
961 citations
TL;DR: The area of periodic mesoporous materials prepared by cooperative assembly in the presence of amphiphile molecules underwent dramatic growth as discussed by the authors, and many types may be regrouped in the future.
Abstract: The area of periodic mesoporous materials prepared by cooperative assembly in the presence of amphiphile molecules underwent dramatic growth. Among the silica-based materials, many types may be reg...
810 citations
TL;DR: In this paper, the synthesis and properties of non-siliceous ordered mesoporous materials, covering oxidic, non-oxidic, metallic, and pure carbon frameworks, are addressed.
Abstract: Siliceous ordered mesoporous materials are well-investigated and -covered by several excellent reviews. Less work has been directed to non-siliceous materials, although these could have more wide-ranging applications. This review will address the synthesis and properties of non-siliceous ordered mesoporous materials, covering oxidic, non-oxidic, metallic, and pure carbon frameworks. Organometallic frameworks, which are typically not synthesized in the presence of surfactants, are beyond the scope of this paper.
782 citations
TL;DR: In this article, a review of the techniques used to produce optically functionalized mesostructured and mesoporous materials and the characterization of the final composites is presented.
Abstract: Mesostructured and mesoporous materials are emerging as a new class of optical materials. For mesostructured materials (inorganic/surfactant composites), prepared using a one-step synthesis procedure where the inorganic/surfactant/optically active species coassemble, the unique architecture provided by the surfactant-inorganic phase separation allows for higher concentrations compared to traditional sol-gel glasses and protective packaging of uniform three-dimensional arrays of optical species. The corresponding regularly arranged pores found in mesoporous materials (inorganic only) provide a high surface area to better disperse optically active components and allow for rapid diffusion for optical sensor applications. In this review, we discuss recent research results on the techniques used to produce optically functionalized mesostructured and mesoporous materials and the characterization of the final composites.
609 citations
TL;DR: Carbon nanotubes are useful materials for introduction of nanopores with a controlled diameter into zeolite single crystals as discussed by the authors, where the intracrystalline nanopores are created by crystallization of the zeolites around the carbon nanotube that are subsequently removed by combustion.
Abstract: Carbon nanotubes are shown to be useful materials for introduction of nanopores with a controlled diameter into zeolite single crystals. The intracrystalline nanopores are created by crystallization of the zeolite around the carbon nanotubes that are subsequently removed by combustion.
430 citations
TL;DR: In this paper, a model based on hexagonal mesopores connected by micropores was proposed to evaluate the porosity of SBA-15 silicas and elucidation of the literature problems on the subject.
Abstract: A model based on hexagonal mesopores connected by micropores allows evaluation of the porosity of SBA-15 silicas and elucidation of the literature problems on the subject. The presence of micropores in the walls between the mesopores renders unreliable the surface area determination by the Brunauer−Emmett−Teller equation and the microporosity assessment by the t-plot method. A geometrical model allows calculation of the true surface area, as well as the real mesoporous and microporous pore volumes, the wall thickness and the wall density from the total pore volume, the pressure of pore-filling, and the cell parameter. The increase of synthesis temperature leads to a continuous increase of mesopore size and a continuous decrease of microporous volume until the disappearance of micropores for materials synthesized at nearly 130 °C. The results are discussed on the basis of the collective properties of nonionic surfactants.
398 citations
TL;DR: Aerogels, which are nanoscale mesoporous materials of low density and high surface area, have been well studied as thermal insulators, heterogeneous catalysts, and novel particle or radiation detectors as mentioned in this paper.
Abstract: Aerogels, which are nanoscale mesoporous materials of low density
and high surface area, have been well studied as thermal insulators, heterogeneous
catalysts, and novel particle or radiation detectors. Now, electrically conducting
oxide aerogels are being explored as new materials in electrochemistry and
for their innate ability to amplify the nature of the surfaces of technologically
relevant conducting oxides in batteries, ultracapacitors, and fuel cells.
Recent results are reviewed in which the mixed electron- and cation-conducting
transition metal oxides of vanadium, molybdenum, ruthenium, and manganese
have been prepared as low density, highly porous, and high surface area aerogels
and then studied as charge-storage electrode materials. These materials challenge
the standard ways in which electrochemically active oxides are conceived,
studied, and used.
391 citations
TL;DR: In this paper, strong acidic and high-temperature hydrothermally stable mesoporous aluminosilicates with well-ordered hexagonal structure have been synthesized from the assembly of preformed precursors with cetyltrimethylammonium bromide (CTAB) surfactant.
Abstract: Publisher Summary This chapter discusses strong acidic and high-temperature hydrothermally stable mesoporous aluminosilicates with well-ordered hexagonal structure. These mesoporous aluminosilicates have been successfully synthesized from the assembly of preformed aluminosilicate precursors with cetyltrimethylammonium bromide (CTAB) surfactant. The MAS-5 shows extraordinary stability both in boiling water and in steam. Temperature-programmed desorption of ammonia (NH3) shows that the acidic strength of MAS-5 is much higher than that of MCM-41.
TL;DR: The results suggest thatMAS-5 consists of both mesopores and micropores and that the pore walls of MAS-5 contain primary and secondary structural building units, similar to those of microporous zeolites, which might be responsible for the observed strong acidity and high thermal stability of the mesoporous aluminosilicates with well-ordered hexagonal symmetry.
Abstract: Highly ordered hexagonal mesoporous aluminosilicates (MAS-5) with uniform pore sizes have been successfully synthesized from assembly of preformed aluminosilcate precursors with cetyltrimethylammonium bromide (CTAB) surfactant. The aluminosilicate precursors were obtained by heating, at 100−140 °C for 2−10 h, aluminasilica gels at the Al2O3/SiO2/TEAOH/H2O molar ratios of 1.0/7.0−350/10.0−33.0/500−2000. Mesoporous MAS-5 shows extraordinary stability both in boiling water (over 300 h) and in steam (800 °C for 2 h). Temperature-programmed desorption of ammonia shows that the acidic strength of MAS-5 is much higher than that of MCM-41 and is comparable to that of microporous Beta zeolite. In catalytic cracking of 1,3,5-triisopropylbenzene and alkylation of isobutane with butene, MAS-5 exhibits greater catalytic activity and selectivity, as compared with MCM-41 and HZSM-5. The MAS-5 samples were characterized with infrared, UV−Raman, and NMR spectroscopy and numerous other techniques. The results suggest that ...
TL;DR: In this article, an improved ZnCl 2 -chemical activation method was proposed to produce highly porous activated carbons from lignocellulosic materials, such as coconut shells and palm seeds.
TL;DR: In this article, the authors summarize recent significant progress in synthesis of microporous and dense inorganic membranes with the help of the results obtained in the author's laboratory or reported in the literature.
TL;DR: In this article, the same authors used a hexagonal mesoporous SBA-15-type molecular sieves with pore sizes in the range 51-56 A for immobilization of trypsin using non-ionic block copolymers.
Abstract: Functionalised hexagonal mesoporous SBA-15-type molecular sieves with pore sizes in the range 51–56 A have been prepared using non-ionic block copolymers and used for immobilisation of the enzyme trypsin. Thiol, chloride, amine, and carboxylic acid functional groups were attached by siloxypropane tethers to the siliceous surface of SBA-15 via two methods, post-synthesis grafting and in situ synthesis. Phenylsiloxane groups were also incorporated using these two methods. The resulting solids were rendered porous and used to immobilise trypsin, giving variable but in general higher retention of the enzyme molecules than was observed on unfunctionalised, purely siliceous SBA-15. The resulting supported enzyme catalysts were shown to be active and stable catalysts for the hydrolysis of N -α-benzoyl-DL-arginine-4-nitroanilide (BAPNA). The solids prepared by supporting the enzyme on thiol-functionalised SBA-15 prepared by in situ synthesis were found to be the most promising. Trypsin supported on thiol-functionalised SBA-15 was shown to be recyclable.
TL;DR: Novel open framework molecular sieves, titanium(IV) phosphates named TCM-7 and -8, with new mesoporous cationic framework topologies obtained by using both cATIONic and anionic surfactants are reported, suggesting the tetrahedral state of P and Ti is suggested.
Abstract: Novel open framework molecular sieves, titanium(IV) phosphates named, i.e., TCM-7 and -8 (Toyota Composite Materials, numbers 7 and 8), with new mesoporous cationic framework topologies obtained by using both cationic and anionic surfactants are reported. The 31P MAS NMR, UV−visible absorption, and XANES data suggest the tetrahedral state of P and Ti, and stabilization of the tetrahedral state of Ti in TCM-7/8 is due to the incorporation of phosphorus (at Ti/P = 1:1) vis-a-vis the most stable octahedral state of Ti in the pure mesoporous TiO2. Mesoporous TCM-7 and -8 show anion exchange capacity due to the framework phosphonium cation and cation exchange capacity due to defective P−OH groups. The high catalytic activity in the liquid-phase partial oxidation of cyclohexene with a dilute H2O2 oxidant supports the tetrahedral coordination of Ti in these materials.
01 Jan 2001
TL;DR: Functionalised hexagonal mesoporous SBA-15-type molecular sieves with pore sizes in the range 51–56 A have been prepared using non-ionic block copolymers and used for immobilisation of the enzyme trypsin, showing the most promising solids prepared by supporting the enzyme on thiol-functionalised Sba-15 prepared by in situ synthesis.
Abstract: Abstract Functionalised hexagonal mesoporous SBA-15-type molecular sieves with pore sizes in the range 51–56 A have been prepared using non-ionic block copolymers and used for immobilisation of the enzyme trypsin. Thiol, chloride, amine, and carboxylic acid functional groups were attached by siloxypropane tethers to the siliceous surface of SBA-15 via two methods, post-synthesis grafting and in situ synthesis. Phenylsiloxane groups were also incorporated using these two methods. The resulting solids were rendered porous and used to immobilise trypsin, giving variable but in general higher retention of the enzyme molecules than was observed on unfunctionalised, purely siliceous SBA-15. The resulting supported enzyme catalysts were shown to be active and stable catalysts for the hydrolysis of N -α-benzoyl-DL-arginine-4-nitroanilide (BAPNA). The solids prepared by supporting the enzyme on thiol-functionalised SBA-15 prepared by in situ synthesis were found to be the most promising. Trypsin supported on thiol-functionalised SBA-15 was shown to be recyclable.
TL;DR: In this paper, a system of terms applicable to ordered microporous and mesoporous materials is proposed, and rules for writing a standardized crystal chemical formula for such materials are presented.
Abstract: A system of terms applicable to ordered microporous and mesoporous materials is proposed, and rules for writing a standardized crystal chemical formula for such materials are presented. The recommendations are based both on common usage and on a systematic classification scheme. The nomenclature has been developed to encompass all inorganic materials with ordered, accessible pores with free diameters of less than 50 nm. The crystal chemical formula describes the chemical composition of both the guest species and the host, the structure of the host, the structure of the pore system, and the symmetry of the material. This formula can be simplified or expanded to suit the user's requirements.
TL;DR: In this article, the authors outline advanced synthetic concepts of their intraporous surface organometallic chemistry involving alkyl, (silyl)amide, and alkoxide reagents.
Abstract: Periodic mesoporous silicas (PMSs) give enormous stimulus to the field of nanostructured organic−inorganic composite materials, opening new horizons for selective organic transformations and material science. This article outlines advanced synthetic concepts of their intraporous surface organometallic chemistry involving alkyl, (silyl)amide, and alkoxide reagents. Conclusive methods of characterization, elaborating the importance of spectroscopic probe ligands and nitrogen physisorption, reinforce the excellent capacity of PMS materials as a model support of, for example, amorphous silica. Particular emphasis is placed on tailor-made hybrid materials, highlighting unexpected reaction behavior due to surface and pore confinement. Accordingly, surface silylation as an efficient method for designing the microenvironment is surveyed in detail.
TL;DR: In this paper, the size of mesopores was controlled by means of the combination of the alkyl chain lengths of surfactants and a swelling agent (triisopropyl benzene).
TL;DR: In this article, a mesoporous SBA-15 molecular sieve has been successfully prepared at 373 K by direct synthesis under microwave−hydrothermal conditions within about 2 h.
Abstract: Titanium-substituted mesoporous SBA-15 molecular sieve has been successfully prepared at 373 K by direct synthesis under microwave−hydrothermal conditions within about 2 h. By means of X-ray diffraction, nitrogen adsorption, infrared, UV−vis diffuse reflectance, and Raman spectroscopies, a successful isomorphous substitution of titanium in the silica framework of SBA-15 samples with Si/Ti ratios of 20, 30, and 40 has been reported. The substitution of Ti for Si did not change the textural properties. The higher titanium loading leads to the formation of extraframework titanium species. These results show that microwave-assisted synthesis is an ideal approach to prepare Ti-substituted SBA-15, which is expected to be useful as a selective oxidation catalyst for reactions involving large molecules.
TL;DR: Hollow microspheres with ordered mesoporous walls are synthesised under ambient conditions by a simple procedure involving dilution and neutralisation of an aqueous tetraethoxysilane/cetyltrimethylammonium bromide reaction mixture.
TL;DR: In this article, the authors compared the properties of disordered silica xerogels with respect to their long range and short range order, their specific surface area, pore structure and pore structural parameters and their surface hydroxyl group concentration.
TL;DR: A new class of bifunctional periodic Mesoporous organosilicas (BPMOs) containing two differently bonded organic moieties in a mesoporous host has been synthesized and characterized by incorporating bridge-bonded ethylene groups into the walls and terminally bonded vinyl groups protruding into the channel space, both the chemistry and physical properties of the resulting BPMO could be modified.
Abstract: A new class of bifunctional periodic mesoporous organosilicas (BPMOs) containing two differently bonded organic moieties in a mesoporous host has been synthesized and characterized. By incorporating bridge-bonded ethylene groups into the walls and terminally bonded vinyl groups protruding into the channel space, both the chemistry and physical properties of the resulting BPMO could be modified. The materials have periodic mesoporous structures in which the bridging ethylene plays a structural and mechanical role and the vinyl groups are readily accessible for chemical transformations. The vinyl groups in the material underwent hydroboration with BH3·THF and the resulting organoborane in the BPMO was quantitatively transformed into an alcohol using either H2O2/NaOH or NaBO3·4H2O. The materials retained ordered structures after subsequent in situ reactions with largely unchanged pore volumes, specific surface areas and pore size distributions. Other organic functionalized BPMO materials may be synthesized i...
TL;DR: An existing model that relates the annihilation lifetime of positronium trapped in sub-nanometer pores to the average size of the pores was extended to account for positronsium in any size pore and at any pore as mentioned in this paper.
Abstract: An existing model that relates the annihilation lifetime of positronium trapped in subnanometer pores to the average size of the pores is extended to account for positronium in any size pore and at...
TL;DR: A survey on these new solid bases, their applications in heterogeneous catalysis and new spectroscopic techniques allowing a more detailed investigation of base sites and adsorbates on working catalysts is given in this paper.
TL;DR: In this paper, the mesopore capacity and porosity were investigated by adsorption experiments using adsorbates with different molecular sizes (viz., phenol, methylene blue and erythrosine red).
TL;DR: The block copolymer template used in the synthesis was removed by solvent and calcination methods, leading to mesoporous tungsten oxides which range from amorphous to crystalline depending on the removal treatment.
Abstract: The electrochromic properties of mesoporous tungsten oxide are
described and compared to standard sol–gel films of WO3.
The block copolymer template used in the synthesis was removed by solvent
extraction and calcination methods, leading to mesoporous tungsten oxides
which range from amorphous to crystalline depending on the removal treatment.
The pores are not ordered but do exhibit a fairly regular diameter with an
average size of 4 to 5 nm. The mesoporous tungsten oxides exhibit a
well behaved electrochromic response and their electrochemical and optical
reversibilities are better than those of the analogous sol–gel film.
In addition, the mesoporous films exhibit higher rates for coloration and
bleaching. The high surface area of these materials is responsible for this
behavior and also leads to multiple peaks in the voltammetric scans.
TL;DR: In this paper, the mesoporous structure of vanadia supported on MCM-41 catalysts has been investigated and it was shown that vanadium is mainly in a tetrahedral environment.