Matthew L. Jorgensen

Bio: Matthew L. Jorgensen is an academic researcher from Connecticut College. The author has contributed to research in topics: Birnessite & Cryptomelane. The author has an hindex of 3, co-authored 3 publications receiving 357 citations.

Sol−Gel Synthesis of Layered Birnessite-Type Manganese Oxides

Abstract: Layered birnessite-type manganese oxides have been synthesized by sol−gel reactions involving KMnO4 or NaMnO4 with glucose. These microporous manganese oxides are designated as octahedral layer materials, K-OL-1 and Na-OL-1, because their layered structure consists of edge-shared MnO6 octahedra. The interlayer regions are occupied by alkali metal cations and water molecules. K-OL-1 and Na-OL-1 have been characterized by elemental analysis, powder X-ray diffraction, scanning electron microscopy, FT-IR spectroscopy, and Auger electron spectroscopy. The empirical formula of K-OL-1 has been determined to be K0.28MnO1.96(H2O)0.19. An interlayer spacing of 7 A, typical of natural and synthetic birnessites, has been measured by X-ray diffraction. The sol−gel synthesis of K-OL-1 is carried out with concentrated aqueous solutions of glucose and KMnO4 in a 1.5:1 mole ratio. Diluted reaction mixtures produce flocculent gels or precipitates which yield other manganese oxide phases such as cryptomelane and Mn2O3. The ...

Sol-gel synthesis of birnessite from KMnO4 and simple sugars

Abstract: Birnessite is a naturally occurring manganese oxide that has been identified as a major constituent of deep sea manganese nodules. The mineral consists of layers of edge- and corner-linked MnO{sub 6} octahedra with water molecules and alkali-metal cations in the interlayer voids. A generalized elemental composition of birnessite is A{sub x}MnO{sub 2{plus_minus}y}{sm_bullet}zH{sub 2}O, in which A represents an alkali-metal cation. Natural and synthetic birnessites with an octahedral layered (OL) structure have attracted significant interest because of their potential as heterogeneous catalysts and materials for secondary batteries. Birnessites are also precursors for tunnel structure manganese oxides such as cryptomelane and todorokite. Sol-gel processing of birnessites potentially offers numerous advantages over traditional methods of synthesis such as high-purity, particle-size homogeneity, and film-casting capability. However, very few sol-gel routes have been developed for materials with near-MnO{sub 2} stoichiometry such as birnessite. Early reports of manganese oxide gels described {open_quotes}MnO{sub 2} jellies{close_quotes} formed from reactions of KMnO{sub 4} with simple sugars. However, until now these systems remained poorly characterized. The authors have reinvestigated these manganese oxide gels and in the process discovered a new sol-gel method of preparing birnessite with interlayer potassium cations, K-OL-1. 26 refs., 3 figs.

Synthesis and formation mechanism of manganese dioxide nanowires/nanorods.

Abstract: Alpha-, beta-, gamma-, and delta-MnO(2) single-crystal nanowires/nanorods with different aspect ratios have been successfully prepared by a common hydrothermal method based on the redox reactions of MnO(4)(-) and/or Mn(2+). The influences of oxidant, temperature, and inorganic cation (NH(4)(+) and K(+)) template concentrations on the morphology and crystallographic forms of the final products are discussed in this paper. It is interesting to find that all the MnO(2) one-dimensional nanostructures have a similar formation process: delta-MnO(2), which has a layer structure, serves as an important intermediate to other forms of MnO(2), and is believed to be responsible for the initial formation of MnO(2) one-dimensional nanostructures. A rolling mechanism has been proposed based on the results of the series of TEM images and XRD patterns of the intermediate.

Ultrathin MnO2 nanofibers grown on graphitic carbon spheres as high-performance asymmetric supercapacitor electrodes

Abstract: Growing MnO2 nanofibers on graphitic hollow carbon spheres (GHCS) is conducted by refluxing GHCS in a KMnO4 aqueous solution aimed to enhance the electrochemically active surface area of MnO2. The stoichiometric redox reaction between GHCS and MnO4− yields GHCS–MnO2 composites with controllable MnO2 content. It is found that these ultrathin MnO2 nanofibers are vertically grown on the external surface of the GHCS, yielding a composite electrode showing good electron transport, rapid ion penetration, fast and reversible Faradic reaction, and excellent rate performance when used as supercapacitor electrode materials. An asymmetric supercapacitor cell with GHCS–MnO2 as the positive electrode and GHCS as the negative electrode can be reversibly charged/discharged at a cell voltage of 2.0 V in a 1.0 mol L−1 Na2SO4 aqueous electrolyte, delivering an energy density of 22.1 Wh kg−1 and a power density of 7.0 kW kg−1. The asymmetric supercapacitor exhibits an excellent electrochemical cycling stability with 99% initial capacitance and 90% coulombic efficiency remained after 1000 continuous cycles measured using the galvanostatic charge–discharge technique.

Photochemical Water Oxidation by Crystalline Polymorphs of Manganese Oxides: Structural Requirements for Catalysis

Abstract: Manganese oxides occur naturally as minerals in at least 30 different crystal structures, providing a rigorous test system to explore the significance of atomic positions on the catalytic efficiency of water oxidation. In this study, we chose to systematically compare eight synthetic oxide structures containing Mn(III) and Mn(IV) only, with particular emphasis on the five known structural polymorphs of MnO2. We have adapted literature synthesis methods to obtain pure polymorphs and validated their homogeneity and crystallinity by powder X-ray diffraction and both transmission and scanning electron microscopies. Measurement of water oxidation rate by oxygen evolution in aqueous solution was conducted with dispersed nanoparticulate manganese oxides and a standard ruthenium dye photo-oxidant system. No Ru was absorbed on the catalyst surface as observed by XPS and EDX. The post reaction atomic structure was completely preserved with no amorphization, as observed by HRTEM. Catalytic activities, normalized to ...

A Review of Porous Manganese Oxide Materials

Abstract: This review concerns the synthesis, characterization, and applications of porous manganese oxides during the last two years The synthesis of porous tunnel structures, layered structures, and related materials is discussed Both microporous and mesoporous systems materials are covered here Characterization discussed here focuses around structural studies The focus of the application sections include electrochemical and catalytic studies