Nanostructured MnO Research Articles

Thickness influences on nanostructured MnO thin films, physical properties and sensing performance

This work employed the chemical bath deposition (CBD) technique to fabricate a thin layer of nanostructured MnO. According to XRD measurements, the films have a cubic crystal structure and are polycrystalline, with orientations of (111, 200, 311, and 222), with (200) being the preferred orientation. Although the dislocation density parameters (100.46 to 80.36) and strain decreased from 34.75 to 31.08 and 34.75 to 100.36, respectively, the grain size was largest at (200) nm film thickness and lowest at (300) nm thickness. The deposited films exhibited a smooth surface topography as evidenced by the average surface roughness dropping from 8.70 nm to 4.27 nm, the average particle size observed to be 82.8 nm to 39.2 nm, and a reduction in root mean square (rms) values from 6.82 nm to 3.09 nm in the AFM images. Nanostructured MnO films exhibit a variety of grain morphologies, polycrystalline structure, and uniformity in SEM images. Their optical properties were measured in the 300–900 nm wavelength range. The extinction coefficient ranged from 0.368 to 0.276, whereas the computed refractive indices of the films with varying thicknesses fell between 3.6 and 2.95. The transmittance ranged between 86 and 81% in the VIS-NIR region with a band gap between 3.24 and 3.13 eV, and it was found that the absorption and absorption coefficient increased with film thickness. The thickness of MnO reduces its sensitivity to H2S gas.

The effect of zinc shape on its corrosion mitigation as an anode in aqueous Zn/MnO2 battery

• Developing of Zn powder and dust electrode for aqueous Zn/MnO 2 battery. • Zn powder with grain sizes >500 µm attenuate its corrosion and dissolution in NH 4 Cl solution. • Assembling of Zn powder or dust (anode) with electrolytic (EMD) or nanostructured (NMD) MnO 2 (cathode) in Zn/MnO 2 cell. • Zn powder (>500 µm)/NMD cell yields a highest output voltage of 1.646 V. • Specific energy (109.722 mWh/g) and the lowest voltage drop of 0.7% after 2 h of discharge. This work gives an insight into how zinc (Zn) anode in the Zn/MnO 2 batteries is corroded depending on its shape (in the form of powder or dust), and how such shape can play a role to attenuate the Zn corrosion and dissolution during an electrochemical process. Indeed, the corrosion of Zn anodes in powder and dust shape was investigated in ammonium chloride aqueous NH 4 Cl solution using open circuit potential (OCP) plot, linear polarization (LP), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) methods. The electrodes were also observed by scanning electron microscopy (SEM) and analyzed using X-ray diffraction (XRD). The results show that the corrosion rate significantly depends on Zn grain size and surface area. In addition, the SEM observations showed clearly some corrosion features on the surface of Zn grains. Furthermore, the XRD analysis confirms the formation of a corrosion layer constituted of ZnO and adsorbed Zn(NH 3 ) 2 Cl 2 molecules. These electrodes, with two distinct shapes, were used as anodes in assembled Zn/MnO 2 batteries with two types of MnO 2 cathode namely nanostructured manganese dioxide (NMD) and electrolytic manganese dioxide (EMD). Discharge tests showed high performance for Zn/MnO 2 cell based on Zn powder (>500 µm) as anode and NMD as a cathode in NH 4 Cl electrolyte, with an output voltage of 1.65 V and specific energy of 109.72 mWh/g after 2 h under 1 mA. Moreover, this cell is the most stable with a voltage drop as low as 0.7% after 2 h of continuous discharge. Such results demonstrate that the assembled Zn/MnO 2 can be used for low cost and high-performance battery with a specific structure and shape of both anode and cathode materials.

Synergistic Nanostructured MnOx/TiO2 Catalyst for Highly Selective Synthesis of Aromatic Imines

AbstractThis work reports the development of a synergistic nanostructured MnOx/TiO2 catalyst, with highly dispersed MnOx nanoparticles (4.5±1 nm) on shape‐controlled TiO2 nanotubes (8–11 nm width and 120–280 nm length), for selective synthesis of valuable aromatic imines at industrially important conditions. Pristine TiO2 nanotubes exhibited 97 % imine selectivity at a 38.3 % benzylamine conversion, whereas very low imine selectivity was obtained over commercial TiO2 materials, indicating the catalytic significance of shape‐controlled TiO2 nanotubes. The MnOx nanoparticle/TiO2 nanotube (10 wt% Mn) catalyst calcined at 400 °C showed the best activity with 95.6 % benzylamine conversion and 99.9 % imine selectivity. This catalyst exhibited good recyclability for four times and is effective for converting numerous benzylamines into higher yields of imines. The high catalytic performance of MnOx/TiO2 nanotubes was attributed to higher number of redox sites (Mn3+), high dispersion of Mn species, and shape‐controlled structure of TiO2, indicating that this catalyst could be a promising candidate for selective oxidation reactions.

Removal of NO by Using Sodium Persulfate Solution: Catalyzed by Different Nanostructured MnO2

In this study, MnO2 nanotubes, nanowires, and nanoparticles were synthetized by a hydrothermal method, after which the NO removal process with sodium persulfate solution catalyzed by MnO2 of differ...

Highly Sensitive As3+ Detection Using Electrodeposited Nanostructured MnOx and Phase Evolution of the Active Material during Sensing.

A simple, one-step electrodeposition approach has been used to fabricate MnOx on an indium-doped tin oxide substrate for highly sensitive As3+ detection. We report an experimental limit of detection of 1 ppb through anodic stripping voltammetry with selectivity to As3+ in the presence of 10 times higher concentrations of several metal ions. Additionally, we report the simultaneous phase evolution of active material occurring through multiple stripping cycles, wherein MnO/Mn2O3 eventually converts to Mn3O4 as a result of change in the oxidation states of manganese. This occurs with concomitant changes in morphology. Change in the electronic property (increased charge transfer resistance) of the material due to sensing results in an eventual decrease in sensitivity after multiple stripping cycles. In a nutshell, this paper reports stripping-voltammetry-induced change in morphology and phase of as-prepared Mn-based electrodes during As sensing.

Carbon‐Quantum‐Dot‐Derived Nanostructured MnO2 and Its Symmetrical Supercapacitor Performances

AbstractWe report here synthesis of nanostructured MnO2 by using carbon‐quantum dot (CQD) as reducing agent which is obtained by environmentally benign approach from waste material. The obtained carbon quantum dot‐MnO2 nanohybrid is characterized by various analytical techniques. The spectral studies reveal the characteristic absorption/emission features of nanostructured CQD‐MnO2. The X‐ray‐diffraction and microscopic analysis indicate that the synthesized CQD‐MnO2 is crystalline in nature with the grain size in the range of 250 − 300 nm. Electrochemical studies reveals that the carbon quantum dot‐MnO2 nanohybrid electrode exhibits a high specific capacitance of 189 F g‐1 at 0.14 A g‐1 with an excellent stability over 1200 charge‐discharge cycles. The excellent electrochemical performance is attributed to the large surface area and high conductivity due to the presence of conductive nanonetwork of the CQD in the carbon quantum dot‐MnO2 matrix. The symmetric supercapacitor (CQD‐MnO2|Na2SO4|CQD‐MnO2) constructed using the carbon quantum dot‐MnO2 electrodes delivers high energy and power densities with a wide operating potential window of 0 ‐ 1.6 V.

Synthesis and characterization of nanostructured MnO2-CoO and its relevance as an opto-electronic humidity sensing device.

Metal carboxylates are widely used in science and technology and have been the subject of intense studies due to the practical importance of their products. The present paper reports the synthesis of MnO2–CoO using metal carboxylates as precursors and the effect of humidity on the transmitted power through its thin film at room temperature. The refractive index of the material was found to be 1.445930 and the peak obtained from the photoluminescence spectra lies in the visible region. TEM reported a minimum grain size of ∼5.7 nm and SAED confirmed the crystalline nature of the material, which was further confirmed by XRD. Fluorescence characteristics also confirmed the low dimensionality of the material. The film was then investigated using SEM which exhibited the porous morphology. Through UV-Vis spectroscopy, it was found that the absorption of the film takes place in the UV region and the optical band-gap was observed to be 3.849 eV from the Tauc plot. The film was employed as a transmission based opto-electronic humidity sensor. Average sensitivity was found to be ∼2.225 μW/% RH with response and recovery times of 47 s and 59 s respectively. Experiments were repeated and the reproducibility of result was found to be ∼89%.

Influence of imidazolium-based ionic liquid electrolytes on the performance of nano-structured MnO2 hollow spheres as electrochemical supercapacitor

Activated carbon//MnO2 hollow sphere asymmetric supercapacitor shows an energy density of 163 W h kg−1 in EMIMBF4 ionic liquid as electrolyte.

Study on the electrochemical behavior of nanostructure S-doping manganese oxide as a novel supercapacitor material.

A nanostructure S-doping manganese oxide (MnO(x)S(y)) amorphous powder was prepared by a homogeneous coprecipitation method for supercapacitor application. The structure and surface morphology of the as-prepared MnO(x)S(y) powder were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), elemental analysis and X-ray photoelectron spectroscopy (XPS). The as-prepared nanostructure S-doping manganese oxide powder was confirmed with a chemical composition of MnO1.26S0.23 by elemental analysis, in which the average oxidation state of manganese is about 3.1. The supercapacitive behavior of the as-prepared MnO1.26S0.23 was studied by means of cyclic voltammetry (CV) and constant current charge-discharge cycling (CD) experiments in 1 mol L(-1) Na2SO4 electrolyte. A maximum specific capacitance of 181 F g(-1) was obtained for MnO1.26S0.23. Furthermore, the specific capacitance remained 97.3% of the original value after 500 cycles. The superior capacitive behavior and better cycling stability indicate that the amorphous nanostructure MnO(x)S(y) maybe a promising electrode material for electrochemical capacitors.

High-Performance Asymmetric Supercapacitor Based on Graphene Hydrogel and Nanostructured MnO2

We have successfully fabricated an asymmetric supercapacitor with high energy and power densities using graphene hydrogel (GH) with 3D interconnected pores as the negative electrode and vertically aligned MnO(2) nanoplates on nickel foam (MnO(2)-NF) as the positive electrode in a neutral aqueous Na(2)SO(4) electrolyte. Because of the desirable porous structure, high specific capacitance and rate capability of GH and MnO(2)-NF, complementary potential window of the two electrodes, and the elimination of polymer binders and conducting additives, the asymmetric supercapacitor can be cycled reversibly in a wide potential window of 0-2.0 V and exhibits an energy density of 23.2 Wh kg(-1) with a power density of 1.0 kW kg(-1). Energy density of the asymmetric supercapacitor is significantly improved in comparison with those of symmetric supercapacitors based on GH (5.5 Wh kg(-1)) and MnO(2)-NF (6.7 Wh kg(-1)). Even at a high power density of 10.0 kW kg(-1), the asymmetric supercapacitor can deliver a high energy density of 14.9 Wh kg(-1). The asymmetric supercapacitor also presents stable cycling performance with 83.4% capacitance retention after 5000 cycles.

Graphene and nanostructured MnO 2 composite electrodes for supercapacitors

Graphene-based materials are promising electrodes for supercapacitors, owing to their unique two-dimensional structure, high surface area, remarkable chemical stability, and electrical conductivity. In this paper, graphene is explored as a platform for energy storage devices by decorating graphenes with flower-like MnO 2 nanostructures fabricated by electrodeposition. The as-prepared graphene and MnO 2, which were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), have been assembled into an asymmetric supercapacitor. The specific capacitance of the graphene electrode reached 245 F/g at a charging current of 1 mA after an electro-activation process. This value is more than 60% larger than the one before electro-activation. The MnO 2 nano-flowers which consisted of tiny rods with a thickness of less than 10 nm were coated onto the graphene electrodes by electrodeposition. The specific capacitance after the MnO 2 deposition is 328 F/g at the charging current of 1 mA with an energy density of 11.4 Wh/kg and 25.8 kW/kg of power density. This work suggests that our graphene-based electrodes are a promising candidate for the high-performance energy storage devices.

Controllable synthesis of monodisperse Mn 3O 4 and Mn 2O 3 nanostructures via a solvothermal route

A facile one-step solvothermal route was developed to synthesize monodisperse Mn 3O 4 and Mn 2O 3 nanostructures with the introduction of poly(vinyl-pyrrolidone)/stearic acid (PVP/SA) mixture. H 2O 2 played a key role in the determination of the products Mn 3O 4 and Mn 2O 3. The synthesis parameters for nanostructured MnO x such as surfactant and reaction time were investigated, along with their influences on morphology and composition. The morphology evolution of the Mn 3O 4 and Mn 2O 3 reveals that the nanostructures formed via two distinct mechanisms of nucleation and growth of nanocrystals.

PREPARATION OF NANOSTRUCTURE MnO$_{\bf 2}$ SINGLE CRYSTAL IN VARIOUS ACID SOLUTION

Nanostructure MnO_2 single crystal was prepared through redox reactions of potassium permanganate in different inorganic acid(hydrochloric acid,sulfuric acid and nitric acid)and organic acid(acetate).The products were characterized by TEM and XRD.It indicated that the crystal structure and morphology of the synthesized MnO_2 can be tailored by adjusting the pH value in solution and reaction temperature.It was also found that layer foldedδ-MnO_2 microspheres were obtained at low reaction temperature and low hydrochloric acid concentration,whereasα-MnO_2 single-crystal nanorods were fabricated with increased reaction temperature and hydrochloric acid concentration. The possible formation mechanism ofδ-MnO_2 microspheres andα-MnO_2 nanorods is also discussed.

Nano-structured manganese oxide as a cathodic catalyst for enhanced oxygen reduction in a microbial fuel cell fed with a synthetic wastewater

Microbial fuel cells (MFCs) provide new opportunities for the simultaneous wastewater treatment and electricity generation. Enhanced oxygen reduction capacity of cost-effective metal-based catalysts in an air cathode is essential for the scale-up and commercialization of MFCs in the field of wastewater treatment. We demonstrated that a nano-structured MnO x material, prepared by an electrochemically deposition method, could be an effective catalyst for oxygen reduction in an MFC to generate electricity with the maximum power density of 772.8 mW/m 3 and remove organics when the MFC was fed with an acetate-laden synthetic wastewater. The nano-structured MnO x with the controllable size and morphology could be readily obtained with the electrochemical deposition method. Both morphology and manganese oxidation state of the nano-scale catalyst were largely dependent on the electrochemical preparation process, and they governed its catalytic activity and the cathodic oxygen reduction performance of the MFC accordingly. Furthermore, cyclic voltammetry (CV) performed on each nano-structured material suggests that the MnO x nanorods had an electrochemical activity towards oxygen reduction reaction via a four-electron pathway in a neutral pH solution. This work provides useful information on the facile preparation of cost-effective cathodic catalysts in a controllable way for the single-chamber air-cathode MFC for wastewater treatment.

Preparation and electrochemistry of one-dimensional nanostructured MnO 2/PPy composite for electrochemical capacitor

One-dimensional nanostructured manganese dioxide/polypyrrole (MnO 2/PPy) composite was prepared by in situ chemical oxidation polymerization of pyrrole in the host of inorganic matrix of MnO 2, using complex of methyl orange (MO)/FeCl 3 as a reactive self-degraded soft-template. The morphology and structure of the composite were characterized by infrared spectroscopy (IR) X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the MnO 2/PPy composite consists of α-MnO 2 and PPy with nanotube-like structure. Electrochemical properties of the composite demonstrated the material showed good electrochemical reversibility after 500 charge–discharge cycles in the potential range of −0.4 to 0.6 V, the tube-like nanocomposite has the potential application in electrochemical capacitor.

Reactivity of Nanostructured MnO2 in Alkaline Medium Studied with a Micro-Cavity Electrode: Effect of Synthesizing Temperature

The influence of synthesizing temperature of manganese dioxide (MnO(2)) powders on their electrochemical reactivity in 1 M KOH was investigated. These powders were prepared chemically by the hydrothermal method by oxidation of Mn(2+) by ammonium peroxodisulphate. The observations by scanning electronic microscopy, energy-dispersive X-ray analyses, and transmission electron microscopy techniques on MnO(2) obtained at different temperatures show the formation of many nanometre scale sticks lumped together to form a spherical particle of several micrometers. The results obtained by BET and BJH methods reveal mesoporous texture, and the MnO(2) synthesized at 90 degrees C presents the largest expanded surface area. The electrochemical reactivity of these powders in 1 M KOH was characterized with microcavity electrode by cyclic voltammetry and electrochemical impedance spectroscopy. The results illustrate that the nanostructured MnO(2) powder synthesized at 90 degrees C shows the highest electrochemical reactivity in agreement with BET data. The X-ray powder diffraction identified the gamma-MnO(2), known as the most reactive species.

A novel method to prepare nanostructured manganese dioxide and its electrochemical properties as a supercapacitor electrode

Nanostructured MnO 2 was synthesized by co-precipitation in the presence of Pluronic P123 surfactant and characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscope (SEM) and transmission electron microscope (TEM). The sample without surfactant was spherical with particle size on the submicron scale, whereas P123-assisted samples were all loose clew shapes, consisting of MnO 2 nanowires, 8–20 nm in diameter and 200–400 nm in length. The electrochemical performances of the as-prepared MnO 2 as the electrode materials for supercapacitors were evaluated by cyclic voltammetry and galvanostatic charge–discharge measurements in a solution of 1 M Na 2SO 4. The sample without surfactant exhibited a relatively low specific capacitance of 77 F g −1, whereas the nanostructured MnO 2 prepared with 0.02% (wt%) P123 exhibited excellent pseudocapacitive behavior, with a maximum specific capacitance of 176 F g −1.

Preparation and characteristics of nanostructured MnO 2/MWCNTs using microwave irradiation method

Ball-nanostructured MnO 2/MWCNTs composite was successfully prepared by microwave irradiation. The surface morphology and structures of the composite were examined by scanning electron microscope and X-ray diffraction. Multi-walled carbon nanotubes play a role as sustainment to inhibit MnO 2 nanoplates from collapsing into nanorods. The electrochemical studies indicated that the composite had ideal capacitive performance and high specific capacitances of 298 F g − 1 , 213 F g − 1 and 198 F g − 1 at the current density of 2 mA·cm − 2 , 10 mA·cm − 2 and 20 mA·cm − 2 , respectively. The formation mechanism of nanostructured MnO 2/MWCNTs and the electrochemical behaviour of composites were discussed in detail.

Electrochemical capacitance of MnO x films

Cathodic electrosynthesis has been utilized for the fabrication of nanostructured MnO x films, containing chitosan additive as a binder. The films were studied by differential thermal analysis, thermogravimetric analysis, X-ray photoelectron spectroscopy, X-ray diffraction analysis and scanning electron microscopy. Cyclic voltammetry (CV) and chronopotentiometry data for the films tested in 0.1 M Na 2SO 4 solutions showed high specific capacitance (SC) in the voltage window of 0–0.9 V versus SCE. The capacitive properties of the films were enhanced within the first few cycles of testing. SEM investigations revealed changes in the film morphology during initial cycling. The highest SC of ∼400 F g −1 was obtained for a film of mass 50 μg cm −2 heat-treated at 300 °C at a CV scan rate of 5 mV s −1. The SC decreased with increasing film mass and scan rate. Ragone plots indicated that the obtained films possessed good power–energy density characteristics, with a highest power density of 45 kW kg −1 for the 50 μg cm −2 MnO x film. Excellent cycling behavior was observed for the films, with no loss in SC during 1000 cycles.

Capacitive behavior of nanostructured MnO 2 prepared by sonochemistry method

Nanostructured manganese dioxide has been successfully prepared by a sonochemical method from an aqueous solution of potassium bromate and manganese sulfate. Changing the proportions of reagents leads either to γ- or layered structures of MnO 2. The capacitive characteristics of the samples were systematically investigated in aqueous electrolytes through means of cyclic voltammetry and chronopotentiometry methods. The electrochemical properties of MnO 2 were strongly affected by the pH of electrolyte employed and this material exhibited ideally capacitive behavior in 0.5 M aqueous Na 2SO 4 solution. A maximum specific capacitance of 344 F g −1 was obtained for the layered structure determined via cyclic voltammetry at a scan rate of 5 mV s −1 in 0.5 M aqueous Na 2SO 4 solution at pH 3.3. Excellent electrochemical reversibility of the materials was also demonstrated. Layered structure MnO 2 showed higher energy density at high power density than the γ-structure material. Impedance spectroscopy studies revealed that charge transfer resistance of the γ-structure oxide has higher value than that of the layered structure.