Β-manganese Dioxide Research Articles

Insights of annealed PCz/β-MnO2 nanocomposites as potent material for high temperature applications

In the present work, the polycarbazole (PCz)/β-manganese dioxide (MnO2) nanocomposite (PMO) was prepared by facile in-situ polymerization approach. The thermal stability of as synthesized material was annealed and monitored upto 1200 °C by TGA analysis and found that the material exhibited no significant weight loss (4.1%). Thus, the annealed material exhibits excellent thermal stability which indicates its great potential for various high temperature applications such as concentrated solar power trough system, high thermal energy storage material, turbine engines, hot and high speed aircraft structures, etc.

Tribological properties of α-, and β-manganese dioxide/polytetrafluoroethylene composites under the dry sliding condition

Nano-sized α-manganese dioxide (α-MnO2) and β-manganese dioxide (β-MnO2) powders synthesized by a hydrothermal approach were employed to improve the tribological property of polytetrafluoroethylene (PTFE). The wear resistances of α-MnO2/PTFE and β-MnO2/PTFE composites are both far better than that of the original PTFE. Compared with α-MnO2/PTFE composite, β-MnO2/PTFE composite always exhibits a better wear performance. Of all the α-, and β-MnO2/PTFE composites, the composite with the β-MnO2 addition of 10wt% shows the best tribological properties, due to the existences of the uniform PTFE-based transfer film and the continuous worn surface of this composite produced during the friction process.

An enzymatic glucose biosensor based on a glassy carbon electrode modified with manganese dioxide nanowires

A glassy carbon electrode was modified with β-manganese dioxide (β-MnO2), and glucose oxidase (GOx) was immobilized on its surface. The β-MnO2 nanowires were prepared by a hydrothermal method and characterized by scanning electron microscopy and powder X-ray diffraction. They were then dispersed in Nafion solution and cast on the glassy carbon electrode (GCE) to form an electrode modified with β-MnO2 nanowires that exhibits improved sensitivity toward hydrogen peroxide. If GOx is immobilized in the surface, the β-MnO2 acts as a mediator, and Nafion as a polymer backbone. The fabrication process was characterized by electrochemical impedance spectroscopy, and the sensor and its materials were characterized by cyclic voltammetry and amperometry. The biosensor enables amperometric detection of glucose with a sensitivity of 38.2 μA · mM−1 · cm−2, and a response time of < 5 s. This study also demonstrates the feasibility of realizing inexpensive, reliable, and high-performance biosensors using MnO2 nanowires.

Hydrogen peroxide sensor based on glassy carbon electrode modified with β-manganese dioxide nanorods

A novel sensor for hydrogen peroxide (H2O2) was fabricated using β-MnO2 nanorods on a glassy carbon electrode (GCE). The nanorods were obtained by a hydrothermal method and characterized by scanning electron microscopy and X-ray diffraction. Cyclic voltammetry was used to evaluate the electrochemical performance of the modified GCE. The sensor exhibits excellent catalytic activity toward the oxidation of H2O2 and displays a rather wide linear range (from 2.5 μM to 42.9 mM), high sensitivity (21.74 μA·mM−1), a low detection limit (2.45 μM at an S/N of 3), and a response time of <5 s.

A study on non-isothermal kinetics of the thermal decompositions of β-manganese dioxide

In this research, the thermal decompositions of β-manganese dioxide (β-MnO 2) under different atmospheres of dynamic nitrogen and air were investigated by TG, DTG, DSC and XRD techniques. Non-isothermal studies clearly indicate that two decomposition stages occur over the temperature regions of 30–1100 °C: the decomposition of β-MnO 2 to Mn 2O 3 and of this oxide to Mn 3O 4 in both nitrogen and air. β-MnO 2 decomposes at higher temperatures in air. The model-free kinetic analysis method together with the minimum deviation approach was employed to determine the activation energy ( E a) and the kinetic model function (mechanism) of the thermal decomposition process from a series of thermogravimetric experiments. The results show that β-MnO 2 exhibits higher values of the activation energy ( E a) and the pre-exponential factor ( A) in air. Compared with various solid state reaction models, the reactions are best described by the random nucleation and nuclei growth models.

Decomposition of H 2O 2 over manganese-chromium oxide catalyst in aqueous and alkaline solutions

β-manganese dioxide with 0.1 chromic anhydride was thermally treated at different temperatures (250, 500, 750 and 1000 °C). The decomposition products were characterized by X-ray diffraction measurements. The catalytic activity of the thermal products for H 2O 2 decomposition was tested in aqueous and alkaline solutions. X-ray diffraction analysis revealed that the addition of 0.1 M CrO 3 stabilizes the β-MnO 2 crystalline form at 500 °C. The transformation of β-MnO 2 into cubic Mn 2O 3 was detected after heating at 750 °C. At 1000 °C a crystalline Mn 3O 4 was produced. The addition of 0.1 M CrO 3 to β-MnO 2 decreased the catalytic activity for H 2O 2 decomposition in aqueous solution. The addition of sodium hydroxide to the solution of H 2O 2 much enhanced the rate of decomposition. The activity of the mixed catalysts was found to be higher than that for pure β-MnO 2. This effect can be attributed to the intrinsic instability of H 2O 2 in alkaline medium and to the base catalysis by OH −.

Chemically activated manganese dioxide for dry batteries

The present investigation has enabled us to convert inactive β-manganese dioxide to high electrochemically active types by chemical processes. Natural and chemically prepared β-manganese dioxides were roasted at 1050 °C to from Mn 2O 4. This compound was subjected to activation treatment using hydrochloric and sulfuric acid under various reaction conditions. The manganese dioxide so obtained was examined by X-ray diffraction, thermogravimetric, differential thermal and chemical analyses. The structure of the dioxide obtained was found to be greatly dependent on the origin of MnO 2 and type of acid used. Treatement with hydrochloric acid yield the so-called γ-variety while sulfuric acid tended to produce γ- or α-MnO 2. In addition, waste manganese sulfate obtained as by-product from sulfuric acid digestion treatment was recycled and electrolytically oxidized to γ-MnO 2. The discharge performance of the above-mentioned MnO 2 samples as battery cathodic active material was evaluated and compared with the ordinary battery grade.

XRD Studies on the conversion from several manganese oxides to β-manganese dioxide during acid digestion in MnSO 4H 2SO 4 system

The wet method to change crystal structure from several manganese oxides to β-manganese dioxide, iso-structural with rutile, was reported. Manganese oxides such as Mn 2O 3 and Mn 3O 4 gave the same XRD profiles as an electrolytic MnO 2 (EMD) on boiling in dilute H 2SO 4 solution at 90–100°C for several hours and finally gave the XRD pattern of β-MnO 2 for a prolonged reaction period. Interesting finding was that several MnO 2s such as δ-MnO 2, α-MnO 2, EMD and heat-treated EMD could be converted into β-MnO 2 by using the proton-assisted rearrangement reaction in a boiling dilute H 2SO 4 solution containing Mn 2+ ion at 90–110°C for several hours to several weeks depending on starting materials. The complex situations on classifying artificial manganese dioxides especially EMDs in terms of crystal structure are discussed.

Adsorption of barium ions by β-manganese dioxide and its activation in oleate flotation

The Ba 2+ ion adsorption isotherms on β-MnO 2 were of the Langmuir type. The endothermic heat of adsorption (40 kJ mol −1) is ascribed to entropy contributions associated with the Na + Ba 2+ ion-exchange mechanism. The Ba 2+ ion adsorption density was higher at pH 10 than that at pH 7, due to the more negative surface charge at the higher pH. Ba 2+ ions were found to reverse the sign of the ζ potential of the MnO 2 particles. More oleate was adsorbed by β-MnO 2 in the presence of Ba 2+ ions than in their absence. The oleate adsorption isotherms on Ba 2+-activated MnO 2 were of the Freundlich type and indicated an exothermic process. Hallimond flotation recovery of Ba 2+-activated MnO 2 was higher at pH 10 than at pH 7, although less oleate was adsorbed at the higher pH. At pH 7, Mn 2+-activation led to higher recoveries than Ba 2+-activation. It seems that the attraction between the surface and the activator plays an important rôle in determining the flotation recovery.

Manganese dioxide electrode. Part 2.—Hydrogen ion response in the presence of manganese(II) ions

Potential-pH and proton release-pH measurements were made in manganese(II) chloride solutions for a “hydrogen form” electrodeposited γ-manganese dioxide and for a “hydrogen form”β-manganese dioxide. The slope of all potential against pH plots was –0.118 V/pH. Proton release data showed that at least the surface of the manganese dioxide varied throughout these potential against pH plots due to reaction with the solution. When the extent of this reaction was kept constant or made zero by an extrapolation procedure, slopes were –0.059 V/pH. No direct response to manganese(II) ions was observed.

Manganese dioxide electrode. Part 1.—Hydrogen ion response in the absence of other cations

Potential against pH plots have been obtained for a “hydrogen form” electrodeposited γ-manganese dioxide and for a “hydrogen form”β-manganese dioxide ore. The electrolyte solution was hydrochloric acid; no cations other than hydrogen ions were present. The plots were straight lines with a slope of –0.059 V/pH and changes of pH caused no hysteresis. Changing the electrolyte to sulphuric acid did not affect the potential against pH relationship. When other cations are present, the effects on the potential against pH plot caused by ion exchange between the manganese dioxide and these cations, can be minimised by an extrapolation procedure.The potential determining reaction for manganese dioxide is most probably MnO2+ H++ e ⇌ MnOOH.

Standard electrode potential of ?-manganese dioxide and its relation to other properties

Further measurements are reported for the standard potentials of variously prepared and treated samples of β-manganese dioxide. Values lie in the range 1.231–1.244 V except for a highly crystalline autoclaved sample (1.196 V). A discrepancy in the ion-exchange behaviour of these almost stoichiometric β-MnO2 samples, compared with that of less stoichiometric forms of manganese dioxide, has been traced to a reaction between manganese dioxide and dilute acids which is rate controlled by diffusion in the oxide.