Unique Mesoporous Structure Research Articles

Synthesis and characterization of nylon-6/mesoporous silica nanocomposites via in situ synchronous hydrolytic polymerization of tetraethylorthosilicate and ε-caprolactam

Nylon 6 (N6)/mesoporous silica (MS) nanocomposites (NMSNs) were synthesized via in situ synchronous hydrolytic polymerization of tetraethylorthosilicate (TEOS) and ε-caprolactam. The novelty of this technique lies in that the nanosilica generated in situ has unique mesoporous structure and ultrahigh-specific surface area (SSA). Mechanical test showed that, compared to conventional precipitated silica (PS) nanofillers, the MS generated in situ shows better reinforcing efficiency on N6. At a loading of only 3.0 wt % MS, the tensile modulus, flexural modulus, and the heat distortion temperature of NMSNs exhibit increase of 54.8%, 77.9%, and 55.9°C, respectively. The effects of MS on the crystallization behaviors of N6 have been studied by differential scanning calorimetry (DSC), which shows that the incorporation of MS influences the crystallization behaviors of N6 obviously: (1) increases crystallization temperature (Tc) by serving as heterogonous nucleating agent; (2) favors the formation of γ-phase by hindering the mobility of N6 chains. Dynamic mechanical analysis confirmed that, compared ti that of neat N6, the temperature of the main α-relaxation (Tα) and the secondary β-relaxation (Tβ) of NMSNs is shifted 6.1°C and 5.3°C toward higher temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

A novel approach to titania nanowire arrays as photoanodes of back-illuminated dye-sensitized solar cells

Titania nanowire arrays have been deposited on Ti foils through direct oxidizing the Ti substrate with aqueous hydrogen peroxide solutions containing melamine and nitric acid, and the applicability of such nanowire arrays to back-illuminated dye-sensitized solar cells studied in parallel with titania nanotube arrays on Ti foils. The low-temperature nitrogen adsorption measurement reveals that the film with nanowires 25 nm in diameter and 1 μm in length possesses a BET specific surface area of 59.0 m 2 g −1, a value much larger than 26 m 2 g −1 calculated for the nanotube with an inner diameter of 80 nm, an outer diameter of 120 nm and a total length of 3 μm. Assuming an indirect transition between band gaps, the nanowire film exhibits a bandgap of 3.1 eV, slightly larger than that of 3.0 eV for the nanotube one. A detailed electrochemical study suggests that, in comparison with the nanotube film, the nanowire one exhibits much lower saturated photocurrent and poorer conductivity under the Xe-lamp irradiation. However, when utilized to construct back-side illuminated dye-sensitized solar cells, the cell with the 2 μm-thick nanowire photoanode possesses significantly higher efficiency than the one with the 3 μm-thick nanotube photoanode. The relatively high energy conversion efficiency is contributed to the high specific surface area and the unique mesoporous structure of the titania nanowire arrays, which favors the adsorption of dye molecules.

Using shell-tunable mesoporous Fe 3O 4@HMS and magnetic separation to remove DDT from aqueous media

1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) is of concern in water treatment because of its persistence and health effects. A new concept is proposed to synthesize hexagonal mesoporous silica (HMS) with magnetic functionalization for DDT removal from aqueous media. Fe 3O 4 nanocrystals were synthesized by a low-temperature solvothermal process, and then encapsulated in mesoporous silica through a packing approach, forming core–shell structured Fe 3O 4@HMS microspheres. The synthesized materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen adsorption–desorption techniques. The results indicate that the silica shell conserves mesoporous structure after the removal of surfactant templates. Different from previous studies, the thickness, pore volume and surface area of silica shell can be controlled by adjusting the reaction condition. These Fe 3O 4@HMS materials show high adsorption capacity and fast adsorption rate for DDT. Because of the useful magnetic property and unique mesoporous structure, the synthesized materials provide a fast, convenient and highly efficient means to remove DDT from aqueous media.

Mesoporous mesocrystal Ce 1−xZr xO 2 with enhanced catalytic property for CO conversion

Novel mesoporous mesocrystal Ce 1− x Zr x O 2 was synthesized using acetate salt as inorganic species and P123 as surfactant. Transmission electron microscopy reveals that the wall framework consists of a single phase based on the face-centered cubic CeO 2 and the nanocrystals are highly oriented with the crystal axis [001] parallel to the pore channel if the Zr 4+ molar fraction x is 0.3 or less. However, when the Zr 4+ molar fraction is larger than 0.3, a mixture of cubic and tetragonal phases forms and the preferential crystal orientation disappears as revealed by XRD and Raman measurements. The formation mechanism is ascribed to the oriented attachment following the manner of coherent interface. The single phase solid solution at Zr 4+ molar fraction 0.3 demonstrates the best catalytic performance for CO conversion due to the unique mesoporous mesocrystal structure with dominant exposure of highly active {200} planes and an enhanced redox property caused by adequate Zr 4+ incorporation.

Shape Selective Chemistries with Modified Mordenite Zeolites

This is a review of work carried at Dow Chemical on the design and characterization of novel mordenite catalysts with a unique micro and meso-porous structure characterized by a variety of methods including, TEM, BET surface area and pore size distribution, and n-decane hydro-conversion. The catalytic performance of these catalysts in shape selective reactions is illustrated with results from n-decane hydro-conversion and applications to alkylation and trans-alkylation reactions of mono and polynuclear aromatic hydrocarbons and other chemistries.

Preparation of Mesoporous Nanosized KF/CaO–MgO Catalyst and its Application for Biodiesel Production by Transesterification

A mesoporous nanosized KF/CaO–MgO catalyst was prepared by coprecipitation method, and was characterized by transmission electron microscopy, X-ray diffraction, nitrogen adsorption and laser confocal Raman microspectroscopy. The catalyst possessed a unique mesoporous structure with pore size of ca. 34 nm and the average particle size of ca. 35 nm. In comparison with CaO and KF/CaO catalyst, the as-prepared catalyst exhibited higher catalytic activity, higher resistance to saponification, and better acidoresistance (10 mg KOH/g oil). The factors affecting on transesterification were also investigated, and a desired biodiesel yield over 95% was obtained under an optimal preparation conditions.

Phosphonic Acid Functionalized Periodic Mesoporous Organosilicas and Their Potential Applications in Selective Enrichment of Phosphopeptides

Phosphonic acid functionalized periodic mesoporous organosilicas were synthesized by co-condensation of 1,2-bis(trimethoxysilyl)ethane and diethoxyphosphorylethyl-triethoxysilane in acidic medium using Brij-76 as a template. Structural characterizations showed that the mesoporous materials with 2-D hexagonal mesostructures could be obtained in the presence of an inorganic salt, NaCl. The results of transmission electron microscopy revealed that the materials synthesized with NaCl/Brij-76 mass ratios of 3 and 4 had extensive structural defect holes in the nanochannels. After coordinating metal ions (Zr4+ and Fe3+) with phosphonic acid in the mesopore, the materials were applied as the potential immobilized metal affinity chromatographic adsorbent for the selective enrichment of phosphopeptides. Because of the stronger affinity interaction between the coordinated metal ions and the phosphoryl groups of phosphopeptides, the higher surface area, and the unique mesoporous structure, the capture of the phosphop...

Nanochain-structured mesoporous tungsten carbide and its superior electrocatalysis

A unique nanochain-structured mesoporous tungsten carbide (m-NCTC) was synthesized through a simple combined hydrothermal reaction–post heat-treatment approach. When loaded with Pt, the nanostructure (Pt/m-NCTC), as a catalyst, demonstrates high unit mass electroactivity (323 A (g Pt)−1) and high resistance to CO poisoning for methanol oxidation, and is much superior to Pt/C, one of the known excellent electrocatalysts. Its high reaction activity and strong poison-resistivity is very likely due to the unique mesoporous nanochain structure and high specific surface area (113 m2 g−1). This work provides a universal and economic method to synthesize novel mesoporous structured materials and provides scientific insight of mesoporous structured electrocatalysis, thus leading to various important applications as a catalyst in fuel cells, solar cells, sensors and in organic synthesis reactions.

Synthesis and high catalytic properties of mesoporous Pt nanowire array by novel conjunct template method

A novel conjunct template method for fabricating mesoporous Pt nanowire array through direct current (DC) electrodeposition of Pt into the pores of anodic aluminum oxide (AAO) template on Ti/Si substrate from hexagonal structured lyotropic liquid crystalline phase is demonstrated in this paper. The morphology and structure of as-prepared Pt nanowire array are characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The electrocatalytic properties of Pt nanowire array for methanol are also investigated in detail. The results indicate that Pt nanowire array has the unique mesoporous structure of approximate 40–50 nm in diameter, which resulted in the high surface area and greatly improved electrocatalytic activity for methanol. The mesoporous Pt nanowire array synthesized by the new conjunct template method has a very promising application in portable fuel cell power sources.

Interface synthesis of mesoporous MnO 2 and its electrochemical capacitive behaviors

Mesoporous MnO 2 has been synthesized by means of a novel, facile, and template-free method by virtue of a soft interface between CCl 4 and H 2O without any surfactants or organometallic precursors or ligands. X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy analysis, scanning electron microscopy, and an ASAP2010 autoadsorption analyzer were applied to investigate the composition and microstructure of the as-synthesized MnO 2. The structure characterizations indicated a good mesoporous structure for as-prepared MnO 2 with an adsorption average pore diameter of 9.7 nm, mesoporous volume of 0.58 cm 3 g −1, and Brunauer–Emmett–Teller specific surface area of 239 m 2 g −1. Electrochemical properties of the mesoporous MnO 2 were elucidated by cyclic voltammograms, galvanostatic charge–discharge, and electrochemical impedance spectroscopy in 1 M Na 2SO 4 electrolyte. Electrochemical data analysis demonstrated that as-synthesized MnO 2 had good capacitive behavior due to its unique mesoporous structure. A specific capacitance of ca. 220 F g −1 could still be delivered for the mesoporous MnO 2 even at a scan rate of 100 mV s −1.

Ordered Mesoporous Thin Films of Rutile TiO2 Nanocrystals Mixed with Amorphous Ta2O5

Ordered mesoporous thin films of composites of rutile TiO2 nanocrystals with amorphous Ta2O5 are fabricated by evaporation-induced self-assembly followed by subsequent heat treatment beyond 780 degrees C. Incorporation of selected amounts of Ta2O5 (20 mol %) in the mesoporous TiO2 film, together with the unique mesoporous structure itself, increased the onset of crystallization temperature which is high enough to ensure the crystallization of amorphous titania to rutile. The ordered mesoporous structure benefits from a block-copolymer template, which stabilizes the mesostructure of the amorphous mixed oxides before crystallization. The surface and in-depth composition analysis by X-ray photoelectron spectroscopy suggests a homogeneous intermixing of the two oxides in the thin film. A detailed X-ray absorption fine structure measurement on the composite film containing 20 mol % Ta2O5 and heated to 800 degrees C confirms the amorphous nature of the Ta2O5 phase. Photocatalytic activity evaluation suggests that the rutile nanocrystals in the synthesized ordered mesoporous thin film possess good ability to assist the photodegradation of rhodamine B in water under illumination by UV light.

MCM-41 Supported Cu−Mn Catalysts for Catalytic Oxidation of Toluene at Low Temperatures

Complete catalytic oxidation of toluene was investigated on Cu-Mn doped mesoporous and microporous catalysts, i.e., Cu-Mn/MCM-41, Cu-Mn/beta-zeolite, Cu-Mn/ZSM-5 (where SiO2/Al2O3 is either 25 or 38), and Cu-Mn/porous silica, in the presence of excess oxygen. The result shows that mesoporous catalysts have exhibited the highest catalytic activity among these catalysts above. The less amount of coke formation due to the unique mesoporous structures could play a key role in the high activity on the mesoporous catalyst. In addition, the bimetallic Cu-Mn-MCM-41 supported catalyst shows higher oxidation activity than either single metal catalyst, i.e., Cu-MCM-41 and Mn-MCM-41. The highly dispersed Cu-Mn mixed oxides on mesoporous structures probably provide active sites for the complete oxidation of toluene on these mesoporous catalysts.

Templated Carbon Nanofiber with Mesoporosity and Semiconductivity

We have newly fabricated a long one-dimensional (1D) mesoporous carbon nanofiber by using a mesoporous silica nanofiber template. The resulting mesoporous carbon nanofiber shows the unique mesoporous structure of circularly wound nanochannel alignment perpendicular to the long fiber axis and the high gas sorption property, which interestingly presents the p-type semiconducting behavior.

Nanostructures and Optical Properties of Mesoporous Composite Nanofibers Containing CdS Quantum Dots

Mesoporous silica nanofibers containing CdS quantum dots (QDs) were fabricated by the confined self-assembly of a lyotropic mesophase within the nanochannels of porous alumina. The resulting mesoporous nanofibers show unique internal mesostructures that depend on the size of the incorporated CdS QDs. Porous nanochannels of the composite nanofibers are shown to form a circularly wound assembly perpendicular to the long fiber axis with small QDs incorporated. As the diameter of the CdS QDs within the silica nanofibers increases, the circularly wound nanochannels become disordered. This unique mesoporous structure is further perturbed by increasing the amount of incorporated CdS QDs. The perturbed mesostructure inside the nanofibers results in an enhanced efficiency of nitrogen gas adsorption and spectral changes of the incorporated QD emissions. Such perturbed nanochannels inside the nanofibers can be utilized as a preferred mesostructure for adsorbing gas molecules and removing surface emission states of the CdS QDs.

Synthesis and electrochemical properties of mesoporous nickel oxide

Mesoporous Ni(OH) 2 is synthesized using sodium dodecyl sulfate as a template and urea as a hydrolysis-controlling agent. Mesoporous NiO with a centralized pore-size distribution is obtained by calcining Ni(OH) 2 at different temperatures. The BET specific surface area reaches 477.7 m 2 g −1 for NiO calcined at 250 °C. Structure characterizations indicate a good mesoporous structure for the nickel oxide samples. Cyclic voltammetry shows the NiO to have good capacitive behaviour due to its unique mesoporous structure when using a large amount of NiO to fabricate the electrode. Compared with NiO prepared by dip-coating and cathodic precipitation methods, mesoporous NiO with a controlled pore structure can be used in much larger amounts to fabricate electrodes and still maintain a high specific capacitance and good capacitive behaviour.

Mesoporous carbon-containing MoS 2 materials formed from the in situ decomposition of tetraalkylammonium thiomolybdates

Molybdenum disulfide with unique mesoporous structure was synthesized from tetraalkylammonium thiometallate precursors in situ decomposed in a batch reactor in the presence of dibenzothiophene (DBT). The precursors used in this study were tetraalkylammonium thiomolybdates with alkyl groups ranging from propyl to octyl. Molybdenum disulfide thus prepared presents high surface area (from 255 up to 329 m 2/g), high content of carbon (C/Mo=2.7–4.0) and type IV nitrogen adsorption–desorption isotherms when decomposed from tetrahexyl-, tetraheptyl- or tetraoctylammonium thiomolybdates. The as-formed materials are poorly crystallized with a very weak intensity of the (0 0 2) peak of the 2HMoS 2 structure. Such diffraction patterns are characteristic of exfoliated samples. Characterization by TEM shows a disordered layered structure with no long range order for the MoS 2 catalysts. Therefore, the nature of the alkyl group in the precursor affects both the surface area and the pore size distribution of the final MoS 2 catalysts with a progressive morphological modification up to a mesoporous organization.

Morphology of electrically conductive grades of carbon black

In recent years, several new types of highly electrically conductive (HEC) carbon blacks have been commercially introduced for use in plastic. Morphological features of these HEC carbon blacks are directly related to polymer melt rheology, proper loading concentration, resistivity and overall performance of the plastic composite. It was found that the unique mesoporous structure of these new HEC carbon blacks are primarily responsible for their success in Polyvinylchloride formulations.