Mesoporous Arrays Research Articles

Direct synthesis of ordered mesoporous polymer and carbon materials by a biosourced precursor

Ordered mesoporous polymer and carbon materials were prepared with a one-pot green chemistry synthesis using tannin as a biosourced carbon precursor. The process is based on the evaporation-induced self-assembly of the tannin with an amphiphilic surfactant. Tannin self-condensation polymerization reactions were used to avoid any carcinogenic cross-linkers such as formaldehyde and to improve the thermal stability of the intermediate ordered mesophase. The calcinations of the mesophase lead to polymer and carbon materials having a hexagonal array of mesopores beside micropores.

In-Situ Preparation of Boron-Doped Carbons with Ordered Mesopores and Enhanced Electrochemical Properties in Supercapacitors

Boron-doped ordered mesoporous carbons (B-OMCs) were successfully prepared using an in-situ approach via organic-inorganic co-assembly, in which, laboratory-made boron-modified phenolic resins were selected as the carbon precursor, tetraethyl orthosilicate as the inorganic precursor and reverse amphiphilic triblock copolymer as the soft template. Their structures and electrochemical properties were investigated in detail. The results showed that the B-OMCs possessed highly ordered mesoporous structures and large surface areas ranging from 1367 to 1657 m2/g. The pore diameters of B-OMCs increased due to the restraint of B to the contraction of the carbon framework during carbonization process. The obtained OMC (0.12% B doped) sample exhibited superior electrochemical performance with large specific capacitance of 196 F/g in 6 M KOH electrolyte at the current density of 50 mA/g, which was mainly owing to the pseudocapacitance offered by the heteroatom-containing functional chemical groups. Simultaneously, the OMC (0.12% B doped) was able to maintain the ordered pore structure with hexagonal arrays of mesopores.

Mesoporous Co3O4 and CoO@C Topotactically Transformed from Chrysanthemum‐like Co(CO3)0.5(OH)·0.11H2O and Their Lithium‐Storage Properties

AbstractIn this work, a novel hydrothermal route is developed to synthesize cobalt carbonate hydroxide, Co(CO3)0.5(OH)·0.11H2O. In this method, sodium chloride salt is utilized to organize single‐crystalline nanowires into a chrysanthemum‐like hierarchical assembly. The morphological evolution process of this organized product is investigated by examining different reaction intermediates during the synthesis. The growth and thus the final assembly of the Co(CO3)0.5(OH)·0.11H2O can be finely tuned by selecting preparative parameters, such as the molar ratio of the starting chemicals, the additives, the reaction time and the temperature. Using the flower‐like Co(CO3)0.5(OH)·0.11H2O as a solid precursor, quasi‐single‐crystalline mesoporous Co3O4 nanowire arrays are prepared via thermal decomposition in air. Furthermore, carbon can be added onto the spinel oxide by a chemical‐vapor‐deposition method using acetylene, which leads to the generation of carbon‐sheathed CoO nanowire arrays (CoO@C). Through comparing and analyzing the crystal structures, the resultant products and their high crystallinity can be explained by a sequential topotactic transformation of the respective precursors. The electrochemical performances of the typical cobalt oxide products are also evaluated. It is demonstrated that tuning of the surface texture and the pore size of the Co3O4 products is very important in lithium‐ion‐battery applications. The carbon‐decorated CoO nanowire arrays exhibit an excellent cyclic performance with nearly 100% capacity retention in a testing range of 70 cycles. Therefore, this CoO@C nanocomposite can be considered to be an attractive candidate as an anode material for further investigation.

Ordered Mesoporous Carbon Nitrides with Graphitic Frameworks as Metal-Free, Highly Durable, Methanol-Tolerant Oxygen Reduction Catalysts in an Acidic Medium

Developments of high-performance cost-effective electrocatalyts that can replace Pt catalysts have been a central theme in polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs). In this direction, nitrogen-doped carbon nanostructures free of metallic components have attracted particular attention. Here we show that directing graphitic carbon nitride frameworks into mesoporous architecture can generate a highly promising metal-free electrocatalyst for an oxygen reduction reaction (ORR) in an acidic medium. The ordered mesoporous carbon nitride (OMCN) was synthesized with a nanocasting strategy using ordered mesoporous silica as a template. A variety of characterizations revealed that the OMCN is constructed with graphitic carbon nitride frameworks and ordered arrays of uniform mesopores. The OMCN showed significantly enhanced electrocatalytic activity for ORR compared to bulk carbon nitride and ordered mesoporous carbon in terms of the current density and onset potential. A high surface area and an increased density of catalytically active nitrogen groups in the OMCN appear to contribute concomitantly to the enhanced performance of the OMCN. Furthermore, the OMCN exhibited superior durability and methanol tolerance to a Pt/C catalyst, suggesting its widespread utilization as an electrocatalyst for PEMFCs and DMFCs.

Surfactant-Templated Synthesis of Ordered Silicas with Closed Cylindrical Mesopores

Ordered mesoporous silicas with 2-dimensional hexagonal arrays of closed cylindrical pores were synthesized via templating with block copolymer surfactant followed by calcination at appropriately high temperatures. Precursors to closed-pore silicas, including SBA-15 silicas and organosilicas, were selected based on the existence of narrow passages to the mesopores. The increase in calcination temperature to 800–950 °C led to a dramatic decrease in nitrogen uptake by the materials, indicating the loss of accessible mesopores, whereas small-angle X-ray scattering (SAXS) indicated no major structural changes other than the framework shrinkage. Since SAXS patterns for ordered mesoporous materials are related to periodic arrays of mesopores, the existence of closed mesopores was evident, as additionally confirmed by TEM. The formation of closed-pore silicas was demonstrated for ultralarge-pore SBA-15 and large-pore phenylene-bridged periodic mesoporous organosilicas. The increase in the amount of tetraethyl orthosilicate in standard SBA-15 synthesis also allowed us to observe the thermally induced pore closing. It is hypothesized that the presence of porous plugs in the cylindrical mesopores and/or caps at their ends was responsible for the propensity to the pore closing at sufficiently high temperatures. The observed behavior is likely to be relevant to a variety of silicas and organosilicas with cylindrical mesopores.

Study on the Pyrolysis of Cellulose for Bio-Oil with Mesoporous Molecular Sieve Catalysts

Mesoporous materials possess a hexagonal array of uniform mesopores, high surface areas, and moderate acidity. They are one of the important catalysts in the field of catalytic pyrolysis. In this paper, mesoporous materials of Al-MCM-41, La-Al-MCM-41, and Ce-Al-MCM-41 were synthesized, characterized, and tested as catalysts in the cellulose catalytic pyrolysis process using a fixed bed pyrolysis reactor. The results showed that mesoporous materials exhibited a strong influence on the pyrolytic behavior of cellulose. The presence of these mesoporous molecular sieve catalysts could vary the yield of products, which was that they could decrease the yield of liquid and char and increase the yield of gas product, and could promote high-carbon chain compounds to break into low-carbon chain compounds. Mesoporous molecular sieve catalysts were benefit to the reaction of dehydrogenation and deoxidation and the breakdown of carbon chain. Further, La-Al-MCM-41 and Ce-Al-MCM-41 catalysts can produce more toluene and 2-methoxy-phenol, as compared to the non-catalytic runs.

Preparation and luminescence of (SBA-15)–Eu 2O 3 composite materials

In this study, (SBA-15)–Eu 2O 3 host-guest composites have been prepared with SBA-15 mesoporous sieve as host and Eu 2O 3 as guest via the solid-phase ultrasonic method and liquid-phase medium ultrasonic method. The host–guest composite materials showed the properties of luminescence. Four excitation peaks appeared in the excitation spectra of the samples. The excitation peaks are located at 397, 415, 466, 537 nm; 392, 408, 464, 532 nm and 393, 406, 465, 533 nm for the nano-Eu 2O 3, the liquid-phase medium ultrasonic method (LPMUM) and the solid-phase ultrasonic method (SPUM) samples, respectively. SBA-15 has the well-ordered hexagonal arrays of mesopores, which makes centrosymmetry of Eu 3+ higher in the prepared (SBA-15)–Eu 2O 3 samples. The intensity of 5D 0→ 7F 1 transition strengthens, and the intensity of 5D 0→ 7F 2 transition weakens.

The synthesis and characterization of aluminum loaded SBA-type materials as catalyst for polypropylene degradation reaction

The performance of pure and aluminum containing SBA-type catalysts prepared using different aluminum sources and different Al/Si ratios were investigated in the polypropylene degradation reaction using a thermogravimetric analyzer. For the synthesis of catalysts, aluminum isopropoxide and aluminum sulphate were used as the aluminum sources. Synthesized materials had high surface areas and exhibited nitrogen adsorption isotherms of type IV. EDS results showed that the aluminum incorporation into the structure was very effective. 27Al MAS NMR spectra of the catalysts exhibited tetrahedrally and octahedrally coordinated aluminum species in the structure. TEM images of synthesized catalysts showed well-ordered hexagonal arrays of uniform mesopores with cylindrical channels. With the aluminum loading, DRIFTS analysis of the pyridine adsorbed materials revealed the existence of Brönsted acid sites in the synthesized catalysts in addition to Lewis acid sites. Thermogravimetric analysis results showed a marked reduction in the degradation temperature in the presence of aluminum containing SBA-type catalysts. The activation energy value of the degradation reaction decreased to about 51–70 kJ/mole in the presence of catalysts synthesized using aluminum sulphate as the aluminum source and when aluminum isopropoxide was used as the aluminum source activation energy value of the reaction decreased to 82–89 kJ/mol.

Lysine-assisted rapid synthesis of crack-free hierarchical carbon monoliths with a hexagonal array of mesopores

The rapid and scalable synthesis of hierarchical carbon monoliths with an ordered mesostructure and fully interconnected macropores has been demonstrated. Resorcinol and formaldehyde based polymers were used as the carbon precursor, triblock copolymer Pluronic F127 as the structural directing agent, and organic base lysine as both the polymerization catalyst and mesostructure assembly promoter. In the presence of lysine, homogeneous and crack-free polymer monoliths can be obtained through rapid gelation in 15 min at 90 °C. The polymer monoliths have a robust framework, which can be directly dried at 50 °C in air and carbonized at high temperature under a nitrogen atmosphere. The carbon monoliths are crack-free and have an ordered mesostructure with fully interconnected macropores. The surface area and the macropore volume are high with values up to 600 m 2 g −1 and 3.52 cm 3 g −1, respectively. Further steam activation of the carbon monolith can significantly improve the surface area to 2422 m 2 g −1 while still maintaining the ordered mesostructure.

(2-Hydroxyethyl)-trimethylammonium hydroxide as an organic base for the synthesis of highly ordered MCM-41

MCM-41material was synthesized using various ratios of (2-Hydroxyethyl)-trimethylammonium hydroxide and sodium hydroxide. The calcined samples were characterized by powder XRD, scanning electron microscopy, nitrogen physisorption, 29Si MAS NMR spectroscopy and transmission electron microscopy. The XRD pattern of all calcined samples shows at least four distinct peaks that indicates long range order of them. The nitrogen adsorption/desorption isotherm of all samples exhibits type IV isotherm which is the typical characteristic of mesoporous materials. When (2-Hydroxyethyl)-trimethylammonium hydroxide was used alone as a base for the synthesis of MCM-41, the highest value of surface area was obtained. Results also reveal that the pore size distribution of this sample is so narrow. The SEM images show that wiry MCM-41 samples were obtained when (2-Hidroxyethyl)-trimethylammonium hydroxide was used in the synthesis process. 29Si MAS NMR spectroscopy proves that the presence of pure organic base in synthesis medium improves framework condensation of MCM-41. TEM images illustrate well-ordered hexagonal array of mesopores in all samples.

Hydrophobic mesoporous silica applied in GC separation of hexene isomers

A novel CH3-functionalized mesoporous silica material (PTM) with nearly spherical morphology was synthesized by a one-step synthesis route using polymethylhydrosiloxane and tetraethoxylsilane in the presence of triblock copolymer P123 as structure-directing agent. Thus-obtained material possessed highly-ordered mesopore arrays and texture with highly CH3-functionalized surface. As compared with pure siliceous SBA-15, PTM showed the high performance for gas chromatographic separation of hexene isomers.

Highly ordered mesoporous carbon arrays from natural wood materials as counter electrode for dye-sensitized solar cells

Highly ordered mesoporous carbon arrays are prepared by a facile carbonization of the natural bamboo and oak wood in argon atmosphere. The as-prepared oak mesoporous carbon arrays have good electrocatalytic activity and high conductivity, based on their well connected framework, highly ordered microtexture, wider mesopores and larger surface area. Consequentially, the photovoltaic performance of the DSSC with the oak mesoporous carbon array film as counter electrode is excellent and comparable to that of the DSSC with FTO/Pt counter electrode. In addition, it is a simple method for a mass production of mesoporous carbon arrays with natural wood materials.

Highly stable aluminosilicates with a dual pore system: Simultaneous formation of meso- and microporosities with zeolitic BEA building units

Highly stable Al-MCM-48-type mesoporous materials with zeolitic secondary building units (SBUs) of BEA zeolite in the framework (hereafter denoted as Al-MCM-48-BEA) were synthesized by direct hydrothermal methods. The synthesis involves simultaneous introduction of two types of structure directing agents, namely, tetraethylammonium hydroxide (TEAOH) for controlling the fabrication of SBU of BEA and a mixture of cetyltrimethylammonium bromide (CTMABr) and Brij-30 for directing the formation of cubic mesophase. The results of X-ray diffraction (XRD) and fourier-transform infrared (FT-IR) spectroscopy revealed the coexistence of mesoporous Al-MCM-48-type arrays with Ia–3 d cubic structure zeolitic SBUs in the materials. In addition, two distinct types of pore systems with characteristics of meso- and micropores were identified in Al-MCM-48-BEA materials by using variable-temperature (VT)-hyperpolarized (HP) 129Xe NMR spectroscopy. Thus, Al-MCM-48-BEA materials possess SBUs of BEA in the walls of highly ordered cubic mesoporous arrays and therefore exhibit much higher thermal, hydrothermal, and mechanical stabilities in comparison to conventional Al-MCM-48 materials. Consequently, these novel materials were found to have strong acidic sites, rendering them highly active and selective catalysts for the formation of α-tocopherol (vitamin E) in the alkylation–condensation of isophytol with trimethylhydroquinone under supercritical CO 2 media.

Synthesis and characterization of mesoporous Gd2O3 nanotube and its use as a drug-carrying vehicle

Gd2O3 nanotubes were constructed for the first time by assembling highly crystalline Gd2O3 nanoparticles through the use of combined soft template and sol-gel methods. Amphiphilic block copolymer was used as structure-directing agent and gadolinium isopropoxide as inorganic precursor in non-aqueous solution. The amphiphilic copolymer molecules are known to undergo self-organization above a critical micelle concentration, forming micellular architecture that further provides a structurally ordered active site for the nucleation and growth of Gd monomers. The resulting self-assembly of the Gd2O3 nanocrystals led to the formation of Gd2O3 tubular nanostructure after pyrolytic removal of the template. Transmission electron microscopy analysis indicated a mesoporous channel array along the [110] direction of the nanotubes where the wall of nanotube is well organized by the assembly of a highly crystalline framework of Gd2O3 nanocrystals. This Gd2O3 nanotube exhibited weak superparamagnetic property and was found to be able to carry and elute a model molecule, i.e. ibuprofen (IBU), in a controllable manner via an external magnetic field. The mechanism of IBU release from the nanotubes with and without the use of magnetic stimulus was proposed.

Highly ordered mesoporous carbon nanofiber arrays from a crab shell biological template and its application in supercapacitors and fuel cells

Mesoporous carbons with large uniform pore sizes and high surface areas are of great interest due to their potential applications in electrochemical double layer capacitors (EDLCs), hydrogen storage, separation and catalysis. Here, we report a facile synthesis approach to highly ordered mesoporous carbon nanofiber arrays (MCNAs) by combining surfactant-templating self-assembly of organic resols with a natural crab shell hard-templating process. The obtained materials consist of a mesoporous carbon nanofiber (70 nm in mean diameter and 11 nm in mesopore), an interspacing void of 70 nm between nanofibers, and 1 micrometre of pores between nanofiber arrays. The unique structure (ordered mesopores, macroporous voids and partially graphitic framework) provides a more favorable path for electrolyte penetration and transportation, good electronic conductivity, as well as possess a large specific surface area (1270 m2 g−1) and more vacancies or defects in a graphite plane, which facilitate uniform distribution of metal nanoparticles and a synergistic effect between the nanoparticles and MCNAs, and give rise to promising electrocatalytic activity as a supporting medium for Pt in direct methanol fuel cells. The resultant materials also have excellent capacitive performance for supercapacitor application.

Pore-lattice deformations in ordered mesoporous matrices: experimental studies and theoretical analysis

The sorption of fluids in mesoporous silica is an important physical phenomenon with a wide range of applications. Traditionally, mesoporous materials have been considered as inert scaffolds for the sorption and condensation reaction of the fluid. Here we present in situ small angle X-ray diffraction experiments providing evidence for a sorption strain induced in the solid that manifests itself as a change in the lattice parameter of the ordered mesopore array as the pores gradually adsorb fluid material. The experimental data are analyzed by means of Monte Carlo simulations carried out in a grand canonical ensemble describing a fluid confined by deformable substrates. We show that-in agreement with experimental data-sorption of a nonpolar fluid causes the pores to expand initially, to shrink abruptly when capillary condensation sets in, and to expand again as more liquid-like fluid is adsorbed subsequently. We show that the pore pressure can be extracted from a thermodynamic analysis of sorption isotherms in the liquid-like regime and that this information can be used for an estimation of the Young's modulus of the porous silica material. In addition, our Monte Carlo simulations indicate that the phase behavior of confined fluids is considerably changed by the deformability of the confining solid. This is reflected by a change of the location of phase boundaries at sufficiently subcritical temperatures.

A facile method for the preferential alignment of mesochannels in silica films by solution flow

We report a simple and one-step processing method to prepare mesoporous silica films with preferential alignment of cylindrical mesochannels during the condensation of TEOS in the presence of Pluronic P123 (EO 20PO 70EO 20, M w = 5800) triblock copolymer, employed as a structure-directing agent. The alignment of mesochannels in a mesoporous silica film is achieved by the directional solution flow without additional complex treatments on the substrate. It is shown that the hexagonal arrays of cylindrical mesopores are oriented parallel to the direction of solution flow when the film is thin enough (∼200 nm). Above the critical film thickness, the effect of the directional solution flow is not significant enough such that the orientation near the substrate does not propagate across the entire film, yielding the mixed orientation of mesochannels. In-plane and out-of-plane XRD measurements along with FE-SEM measurements were used to characterize the degree of alignment of mesochannels.

Mechanism of heavy metal uptake by a hybrid MCM-41 material: Surface complexation and EPR spectroscopic study

A novel hybrid MCM-41-based material was synthesized by incorporation of AEDTC [ N-(2-aminoethyl)dithiocarbamate] in the MCM-41 pores. The derived MCM-41 ⊗ AEDTC material possesses high AEDTC loading 35% [w:w], and a well-defined array of regular mesopores with a specific surface area of 632 m 2/g. Heavy metal, Cd, Pb, Cu, and Zn, uptake was studied in detail at physiological pH values 6–8, by a combination of analytical and electron paramagnetic resonance (EPR) spectroscopic techniques. The analytical data show a significant improvement, i.e., 200–500%, for Pb, Cu, and Zn uptake by the MCM-41 ⊗ AEDTC hybrid vs the unmodified MCM-41. In contrast, Cd shows an exceptional behavior: (a) Cd uptake by MCM-41 ⊗ AEDTC is very low. (b) Competitive metal uptake experiments reveal that Cd ions cause a characteristic inhibition of Cu or Pb uptake by the MCM-41 ⊗ AEDTC while Cd binding itself always remained low. The present findings are analyzed by a combination of surface complexation modeling and EPR spectroscopy. Accordingly, in the MCM-41 ⊗ AEDTC the sulfur atoms of AEDTC provide strong binding sites for metal binding, with a stoichiometry [ S AEDTC]:[Metal] = 1:1. Cd inhibits accessibility of Cu or Pb ions in the AEDTC sites.

Self-Assembly of Shape Controlled Hierarchical Porous Thin Films: Mesopores and Nanoboxes

Hierarchical porous thin films with well-defined pore dimensions and topologies have been obtained through an evaporation induced self-assembly process. The films show a cubic ordered array of mesopores together with the presence of well-defined nanoboxes that appear homogeneously dispersed in the material. The nanoboxes are formed by controlled crystallization of NaCl during the evaporation of the solvent when the film is deposited. The pores can be selectively emptied by thermal treatment and water washing allowing the preparation of a new generation of hierarchical porous materials.

Single Crystalline Mesoporous Silicon Nanowires

Herein we demonstrate a novel electroless etching synthesis of monolithic, single-crystalline, mesoporous silicon nanowire arrays with a high surface area and luminescent properties consistent with conventional porous silicon materials. These porous nanowires also retain the crystallographic orientation of the wafer from which they are etched. Electron microscopy and diffraction confirm their single-crystallinity and reveal the silicon surrounding the pores is as thin as several nanometers. Confocal fluorescence microscopy showed that the photoluminescence (PL) of these arrays emanate from the nanowires themselves, and their PL spectrum suggests that these arrays may be useful as photocatalytic substrates or active components of nanoscale optoelectronic devices.