Oxide Molecular Sieve Research Articles

Electronic and Magnetic Structure of LaSr-2×4 Manganese Oxide Molecular Sieve Nanowires

In this study we combine scanning transmission electron microscopy, electron energy loss spectroscopy and electron magnetic circular dichroism to get new insights into the electronic and magnetic structure of LaSr-2×4 manganese oxide molecular sieve nanowires integrated on a silicon substrate. These nanowires exhibit ferromagnetism with strongly enhanced Curie temperature (T c >500 K), and we show that the new crystallographic structure of these LaSr-2×4 nanowires involves spin orbital coupling and a mixed-valence Mn3+/Mn4+, which is a must for ferromagnetic ordering to appear, in line with the standard double exchange explanation.

Chemical synthesis of oriented ferromagnetic LaSr-2 × 4 manganese oxide molecular sieve nanowires

We report a chemical solution based method using nanoporous track-etched polymer templates for producing long and oriented LaSr-2 × 4 manganese oxide molecular sieve nanowires. Scanning transmission electron microscopy and electron energy loss spectroscopy analyses show that the nanowires are ferromagnetic at room temperature, single crystalline, epitaxially grown and self-aligned.

Preparation and Characterization of a Cerium(IV)-incorporated Manganese Oxide OMS-2. Effect of Cerium(IV) Template on Octahedral Molecular Sieves of Manganese Oxide and Characterization of Manganese Oxide Molecular Sieves with Cerium(IV) as Dopant

The manganese oxide material K-OMS-2 was synthesized both via a redox reaction between potassium permanganate and manganese nitrate in an acidic medium (nitric acid) under reflux conditions and by the sol–gel reaction between KMnO4 and maleic acid employed in a 3:1 molar ratio. Cerium(IV) was then added by an ion-exchange method. The structures, morphologies, chemical compositions and thermal stabilities of the resulting materials were studied by X-ray diffraction (XRD), N2 adsorption/desorption, scanning electron microscopy (SEM), Fourier-transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC) and TGA techniques. Both the morphologies and the surface properties of the materials synthesized by these two methods were different. Thus, the material prepared via the sol–gel process possessed a higher surface area and exhibited both a different type of adsorption isotherm and smaller crystallite sizes than the material synthesized by redox reaction under reflux conditions. The physical...

ChemInform Abstract: Structure, Porosity, and Redox in Porous Manganese Oxide Octahedral Layer and Molecular Sieve Materials

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis of todorokite-type manganese oxide from Cu-buserite by controlling the pH at atmospheric pressure

A todorokite-type manganese oxide molecular sieve material was successfully synthesized at atmospheric pressure by refluxing treatment of Cu 2+ exchanged Na-buserite (named as Cu-OMS-1). TEM (transmission electron microscope) and HRTEM (high resolution transmission electron microscope) images revealed that this material has a needle-phase crystal morphology with thickness 0.1–1 μm, and the lattice fringes spacing 1.0 nm corresponding to the [1 0 0] plane of the todorokite structure. Such morphological and intergrowth characteristics were similar to those of hydrothermally synthesized todorokites. The Cu-OMS-1 with a chemical composition of Cu 0.34MnO 2.19 · 1.11H 2O, was stable below 400 °C. The BET surface area was found to be 62.5 m 2/g, and a major micropore size distribution peak centered at 0.70 nm for Cu-OMS-1 by the Horvath–Kawazoe (HK) method. As determined by the t-plot method, 31% of the surface area was contributed by micropores. The pH of reaction solution plays an important role in the sub-structure modification of formed Cu-buserites and the formation of todorokite at atmospheric pressure. A mechanism for the influence of pH on the transformation is discussed.

Study on Ammonia‐Nitrogen and Humic Acid Removal Using Aluminum Oxide Molecular Sieve and Modified Clinoptilolite

AbstractThe removal of ammonia‐nitrogen (NH4+–N) and humic acid (HA) in water by aluminum oxide molecular sieve (AOMS)/modified clinoptilolite (MC) was investigated using a flow system. The study focuses on the effect of AOMS on the removal of NH4+–N and HA. The dependence of ion‐exchange of MC on the organic contaminants was also investigated. The results show that the NH4+–N is difficult to remove by AOMS only. However, the effective removal of HA by AOMS brings about a higher efficiency of NH4+–N removal by AOMS‐MC, so that the NH4+–N and HA are removed simultaneously.

Structure, porosity, and redox in porous manganese oxide octahedral layer and molecular sieve materials

The control of synthesis methods allows the preparation of unique materials such as octahedral layer (OL) and octahedral molecular sieve (OMS) systems. These mixed valent porous materials are excellent semiconductors. Conductivity in porous molecular sieve materials is unusual and leads to more favorable characterization such as less charging in relation to insulating materials like clays and zeolites. Semiconductivity of OL and OMS materials allows potential applications as sensors, redox catalysis, and in fuel cells. This review will focus on the use of composition and redox to control the structure, morphology, porosity, catalytic activity, and conductivity of such materials. A major emphasis in this field has been on the generation of new materials and the mechanism of formation of such systems.

On the location of different titanium sites in Ti–OMS-2 and their catalytic role in oxidation of styrene

Abstract Octahedral manganese oxide molecular sieves (OMS-2) modified by impregnation of TiO 2 exhibit a higher catalytic activity for oxidation of styrene with tert -butylhydroperoxide in comparison to titanium-incorporated OMS-2, where the styrene conversions were ca. 70% and 45–50%, respectively. The framework of titanium species has no effect on the enhancement of catalytic activity, while the non-framework of titanium species induces a synergetic effect that enhances the oxidation of styrene with tert -butylhydroperoxide.

Microwave Synthesis of Nanoporous Materials

Studies in the last decade suggest that microwave energy may have a unique ability to influence chemical processes. These include chemical and materials syntheses as well as separations. Specifically, recent studies have documented a significantly reduced time for fabricating zeolites, mixed oxide and mesoporous molecular sieves by employing microwave energy. In many cases, microwave syntheses have proven to synthesize new nanoporous structures. By reducing the times by over an order of magnitude, continuous production would be possible to replace batch synthesis. This lowering of the cost would make more nanoporous materials readily available for many chemical, environmental, and biological applications. Further, microwave syntheses have often proven to create more uniform (defect-free) products than from conventional hydrothermal synthesis. However, the mechanism and engineering for the enhanced rates of syntheses are unknown. We review the many studies that have demonstrated the enhanced syntheses of nanoporous oxides and analyze the proposals to explain differences in microwave reactions. Finally, the microwave reactor engineering is discussed, as it explains the discrepancies between many microwave studies.

Synthesis of Todorokite at Atmospheric Pressure

A 3 × 3 tunnel-structured manganese oxide, todorokite, or MnO6 octahedral molecular sieve (OMS-1), was synthesized at atmospheric pressure by a refluxing process from birnessite, the layer-structured precursor. The todorokite synthesized by the refluxing process (named as OMS-1-R) consisted of fibers with various lengths and platy trilling patterns, made of fiber crystals twinned with each other at 120°, from which the fibers matted and extended. Intergrowth of different widths of tunnels commonly occurred in a disorderly manner, with a triple octahedral chain width being the most predominant. Such morphological and intergrowth characteristics were similar to those of natural todorokites and a hydrothermally synthesized todorokite. When refluxing time was increased, the crystallinity of OMS-1-R was promoted and small scale twinning in morphology became a relatively large and coarse twinning. However, there was no other crystalline phase produced. The OMS-1-R24, synthesized after 24 h of refluxing, with a ...

The Preparation of Oxide Molecular Sieves. Phosphate‐Based Molecular Sieves: Novel Synthetic Approaches to New Structures and Compositions

The Preparation of Oxide Molecular Sieves. Phosphate‐Based Molecular Sieves: Novel Synthetic Approaches to New Structures and Compositions

Magnesium Manganese Oxide Nanoribbons: Synthesis, Characterization, and Catalytic Application

A todorokite-type magnesium manganese oxide molecular sieve material with a morphology of nanoribbons has been synthesized using a combination of techniques consisting of a sol−gel process to synthesize a nanosized tetraethylammonium manganese oxide layered material, an ion-exchange method to prepare a thin-film Mg−buserite (Mg−OL-1) precursor, and a hydrothermal reaction to transform the Mg−buserite to nanoribbonlike Mg−todorokite (Mg−OMS-1) material. The transformation of the Mg−buserite thin films to Mg−todorokite nanoribbons has been studied using XRD and TEM. XRD data indicate that the structural transformation of Mg−OL-1 to Mg−OMS-1 is completed after hydrothermal heating at 150 °C for about 40 h and at 200 °C for less than 8 h. TEM data show that the nanoribbons form at an early stage of the hydrothermal treatment, followed by the appearance of lattice fringes. TEM data also indicate that the well-formed nanoribbonlike crystals have a uniform tunnel dimension along the a axis and a long-range-order...

Synthesis of a Stable Metallic Niobium Oxide Molecular Sieve and Subsequent Room Temperature Activation of Dinitrogen

Mesoporous niobium oxide was treated at room temperature with bis(toluene) niobium to make a new black material that exhibits metallic properties. The metallic behavior is attributed to low-valent NbII in the walls of the porous structure and is fully supported by strong emissions at the Fermi level, variable temperature resistivity measurements, and temperature-independent paramagnetism. These materials possess higher conductivities than reported for any molecular sieve and also represent the first example of a metallic oxide-based molecular sieve. For comparison, the conductivity is almost 10 000 times greater than the highest value measured for an open structured mesoporous material. Treatment at room temperature with dinitrogen leads to formation of a thin nitride coat on the surface. Cleavage of dinitrogen is an extremely rare and important reaction that typically requires very forcing conditions in the solid state (high temperatures in excess of several hundred degrees, argon plasmas, etc.) or low-valent coordinatively stressed metal centers in the homogeneous phase. This is the first example of a molecular sieve mediating this process and because of the controlled porosity and high surface areas of these materials they are ideal candidates for model studies for nitrogen reduction and catalytic nitrogen incorporation into organic compounds. Since porous materials are often the catalytic support of choice for industrial processes, these materials may lead to the development of commercial nitrogen incorporation processes.

Cytochrome c immobilization into mesoporous molecular sieves

The immobilization of cytochrome c into the mesoporous moleclar sieves MCM-48 (Mobil Composition of Matter) and SBA-15 (Santa Barbara Amorphous), as well as the layered niobium oxide Nb-TMS4 (Niobium Transition Metal Oxide Molecular Sieve) is described. The cytochrome c loading was influenced by the molecular sieve structure, i.e., one-dimensional vs. three-dimensional. Cytochrome c immobilization was accomplished by absorption into the molecular sieves followed by silylation of the pore openings. The molecular sieves containing cytochrome c were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV/Vis, and FT-IR spectroscopy. The protein was found to be stable in the molecular sieve under conditions that would denature the protein in solution. The immobilized cytochrome c retained its redox activity following immobilization for several months as demonstrated by cyclic voltammetry (CV).

Tailored Porous Materials

Tailoring of porous materials involves not only chemical synthetic techniques for tailoring microscopic properties such as pore size, pore shape, pore connectivity, and pore surface reactivity, but also materials processing techniques for tailoring the meso- and the macroscopic properties of bulk materials in the form of fibers, thin films, and monoliths. These issues are addressed in the context of five specific classes of porous materials: oxide molecular sieves, porous coordination solids, porous carbons, sol−gel-derived oxides, and porous heteropolyanion salts. Reviews of these specific areas are preceded by a presentation of background material and review of current theoretical approaches to adsorption phenomena. A concluding section outlines current research needs and opportunities.

Synthesis and Mechanistic Studies of Sulfated Meso- and Microporous Zirconias with Chelating Carboxylate Surfactants

Ligand-assisted templating with carboxylate surfactants is used to produce micro- and mesoporous zirconias in a method where the organic template can be removed with a simple acid treatment obviating the usual harsh calcination conditions required to remove templates from transition metal oxide molecular sieves. A new mechanism is proposed for the mesostructure formation, in which the self-assembly step and the condensation step occur simultaneously with polymer propagation. Applications in shape-selective catalysis are envisaged.

Synthetic zeolites and other microporous oxide molecular sieves.

Use of synthetic zeolites and other microporous oxides since 1950 has improved insulated windows, automobile air-conditioning, refrigerators, air brakes on trucks, laundry detergents, etc. Their large internal pore volumes, molecular-size pores, regularity of crystal structures, and the diverse framework chemical compositions allow "tailoring" of structure and properties. Thus, highly active and selective catalysts as well as adsorbents and ion exchangers with high capacities and selectivities were developed. In the petroleum refining and petrochemical industries, zeolites have made possible cheaper and lead-free gasoline, higher performance and lower-cost synthetic fibers and plastics, and many improvements in process efficiency and quality and in performance. Zeolites also help protect the environment by improving energy efficiency, reducing automobile exhaust and other emissions, cleaning up hazardous wastes (including the Three Mile Island nuclear power plant and other radioactive wastes), and, as specially tailored desiccants, facilitating the substitution of new refrigerants for the ozone-depleting chlorofluorocarbons banned by the Montreal Protocol.

Studies of Decomposition of H2O2over Manganese Oxide Octahedral Molecular Sieve Materials

A series of manganese oxide molecular sieve (OMS) materials has been successfully synthesized. Doping some divalent cations and first row transition metal ions such as Mg2+, Ni2+, Cu2+, Co2+, and Fe3+into the framework of OMS materials to form [M]-OMS materials was also done. The catalytic activities of [M]-OMS materials and commercial MnO2for H2O2decomposition were studied. The experimental results show an activity order sequence as follows: most of [M]-OMS materials > commercial MnO2; [M]-OMS-2 > [M]-OMS-1; and among [M]-OMS-2 samples, [Ni]-OMS-2 > [Cu]-OMS-2 > [Fe]-OMS-2 > [Co]-OMS-2 > [Mg]-OMS-2. The kinetics and a mechanism of H2O2catalytic decomposition over [M]-OMS materials were studied and proposed, as well.

Synthesis of Microporous Transition Metal Oxide Molecular Sieves with Bifunctional Templating Molecules.

Systematic tuning of the micropore size in microporous transition metal oxide molecular sieves can be achieved by varying the length of the hydrocarbon chain of the diamine molecules used as templating agents. The large bifunctional molecules self-assemble with much smaller cross-sectional micellar dimensions than their monofunctional counterparts. The resulting family of porous materials offers exciting new flexibility in designing molecular sieves targeted for size selectivity and chemical functionality.

Octahedral manganese oxide molecular sieves having a (4 × 4) tunnel structure

Octahedral manganese oxide molecular sieves having a (4 × 4) tunnel structure