Ultrathin Manganese Oxide Research Articles

Electrochemical determination of fenitrothion pesticide based on ultrathin manganese oxide nanowires/molybdenum titanium carbide MXene ionic nanocomposite and molecularly imprinting polymer

A novel molecularly imprinted electrochemical sensor is presented based on one-dimensional ultrathin manganese oxide nanowires/two-dimensional molybdenum titanium carbide MXene (MnO2NWs@Mo2TiC2 MXene) for fenitrothion (FEN) determination. After the synthesis of MnO2NWs@Mo2TiC2 MXene ionic nanocomposite was successfully completed with a facile hydrothermal and the pillaring methods, a new type molecular imprinted electrochemical sensor based on MnO2NWs@Mo2TiC2 MXene was constructed with cyclic voltammetry (CV) polymerization including pyrrole monomer and FEN target molecule. After the characterization studies including spectroscopic, electrochemical and microscopic methods, the analytical applications of the prepared sensor were performed. A linearity of 1.0×10−9–2.0×10−8 mol L−1 was obtained and the values of the quantification limit (LOQ) and the detection limit (LOD) were 1.0×10−9 mol L−1 and 3.0×10−10 mol L−1, respectively. The studies of selectivity, stability and reproducibility of the constructed sensor based on MnO2NWs@Mo2TiC2 nanocomposite and molecularly imprinting polymer (MIP) were carried out in detail. Finally, the developed sensor was applied to white flour samples with the values close to 100%.Graphical

Reticulation of 1D/2D Mo2TiC2 MXene for excellent supercapacitor performance

Heterostructures of MXene are promising for electrochemical energy storage devices (EESDs) because of their synergistic effect and interfacial-driven properties. However, the fabrication process of MXene heterostructures based on transition metal oxides (TMOs) is very challenging due to the poor compatibility of selected materials with MXene. Herein, we fabricate a novel reticulate heterostructure (MnO2 NWs@Mo2TiC2) composed of one-dimensional (1D) ultrathin manganese oxide (MnO2) nanowires (NWs) and two-dimensional (2D) double transition metal (DTM) carbides-based MXene (Mo2TiC2) via a facile liquid-phase pre-pillaring and pillaring method. This unique heterostructure was designed by mixing pre-pillared Mo2TiC2 MXene (cetyltrimethylammonium bromide (CTAB)) and MnO2 NWs in equal mass ratios under specific experimental conditions. The MnO2 NWs not only enhance the performance but also prevent the restacking of nanosheets, while 2D Mo2TiC2 facilitates ion diffusion and ultrafast electron transport. Due to the pillaring effect of MnO2 NWs between the layers of Mo2TiC2 and the synergistic effect between MnO2 NWs and Mo2TiC2 matrix, the heterostructure exhibits a superior gravimetric capacitance for both cyclic voltammetry (CV) 918.6 F/g at 2 mV/s (459.3 C/g) and galvanostatic charge-discharge (GCD) 399.2 F/g at 1 A/g (159.7 C/g) measurements, which is significantly higher than that of pristine MXene, and also show excellent cycling stability (83.3% capacitance retention after 10000 cycles at 10 A/g). These results may open the ways to extend the research more extensively to explore the properties of double transition metal based MXenes and their composites.

Boosting photoelectrochemical water splitting of bismuth vanadate photoanode via novel co-catalysts of amorphous manganese oxide with variable valence states

Bismuth vanadate (BVO) is a promising photoanode while suffers from sluggish oxygen evolution kinetics. Herein, an ultra-thin manganese oxide (MnOx) is selected as co-catalyst to modify the surface of BVO photoanode by a facile spray pyrolysis method. The photoelectrochemical measurements demonstrate that surface charge transport efficiency (ηsurface) of MnOx modified BVO photoanode (BVO/MnOx) is strikingly increased from 6.7 % to 22.3 % at 1.23 VRHE (reversible hydrogen electrode (VRHE)). Moreover, the ηsurface can be further boosted to 51.3 % at 1.23 VRHE after applying Ar plasma on the BVO/MnOx sample, which is around 7 times higher comparing with that of pristine BVO samples. Additional characterizations reveal that the remarkable PEC performance of the Ar-plasma treated BVO/MnOx photoanode (BVO/MnOx/Ar plasma) could be attributed to the increased charge carrier density, extended carrier lifetime and additional exposed Mn3+ active sites on the BVO surface. This investigation could provide a new understanding for the design of BVO photoanode with superior PEC performance based on the modification of MnOx and plasma surface treatment.

Cotton fabric decorated with manganese oxide nanorods as a supercapacitive flexible electrode for wearable electronics

We present the fabrication (using a hydrothermal process) and the properties of wearable fabrics decorated with ultrathin manganese oxide (MnO2) nanorods for supercapacitor applications. The superior mechanical durability of the supercapacitor was confirmed by cyclic voltammetry (CV) curves, which showed little change during 1000 bending cycles. The pseudocapacitive properties of the ultrathin MnO2 nanorods were confirmed by recording the CV curves at various scan rates. The galvanostatic charge–discharge curves at various specific currents confirmed the pseudocapacitance of MnO2. The ultrathin MnO2 nanorods exhibited a superior capacitance of 508 F·g−1 and an energy density of 35.3 Wh·kg−1. The MnO2 electrode with optimal properties demonstrated stable long-term cycling performance with 90% retention after 10,000 galvanostatic cycles.

On the Origin of the OER Activity of Ultrathin Manganese Oxide Films

There is an urgent need for cheap, stable, and abundant catalyst materials for photoelectrochemical water splitting. Manganese oxide is an interesting candidate as an oxygen evolution reaction (OER) catalyst, but the minimum thickness above which MnOx thin films become OER-active has not yet been established. In this work, ultrathin (<10 nm) manganese oxide films are grown on silicon by atomic layer deposition to study the origin of OER activity under alkaline conditions. We found that MnOx films thinner than 1.5 nm are not OER-active. X-ray photoelectron spectroscopy shows that this is due to electrostatic catalyst-support interactions that prevent the electrochemical oxidation of the manganese ions close to the interface with the support, while in thicker films, MnIII and MnIV oxide layers appear as OER-active catalysts after oxidation and electrochemical treatment. From our investigations, it can be concluded that one MnIII,IV-O monolayer is sufficient to establish oxygen evolution under alkaline conditions. The results of this study provide important new design criteria for ultrathin manganese oxide oxygen evolution catalysts.

Activation of CO over Ultrathin Manganese Oxide Layers Grown on Au(111)

Well-defined manganese oxide (MnOx) overlayers with a controlled chemical state and coverage were deposited on Au(111), and CO activation at the model MnOx/Au(111) surfaces was explored by combinin...

Synthesis of Ultrathin MnO2 Nanosheets/Bagasse Derived Porous Carbon Composite for Supercapacitor with High Performance

In this paper, activated porous carbon (AC) derived from bagasse was prepared by carbonization and activation using KOH. Then, a hydrothermal route was employed to fabricate ultrathin manganese oxide (MnO2) nanosheets/activated porous carbon (AC) composite (MnO2/AC). AC and MnO2/AC composite were employed as negative and positive electrode materials for a supercapacitor, respectively. An AC electrode delivers excellent electrochemical properties with a specific capacitance of 89 F g−1 at 1 A g−1 and super cycling stability of 89% capacitance retention after 5000 cycles. For a MnO2/AC composite, its specific capacitance can reach 492.5 F g−1 at 1 A g−1, but its cycle performance (78.4% capacitance retention after 5000 cycles) is lower than that of AC (89%). In view of the good electrochemical performance of AC and MnO2/AC composite, a MnO2/AC//AC all-solid-state asymmetric supercapacitor (ASC) was assembled. The constructed ASC exhibits high specific capacitance of 69.375 F g−1 at 1 A g−1 and delivers a high energy density of 24.67 Wh kg−1 at a power density of 814.8 W kg−1. Two ASCs in series can power one LED for more than 70 s. This work demonstrates that MnO2/AC//AC asymmetric supercapacitor shows good practical value.

Ultrathin manganese oxide nanosheets uniformly coating on carbon nanocoils as high-performance asymmetric supercapacitor electrodes

Two key limitations affecting supercapacitor application of manganese oxide (MO) are the poor electric conductivity and low accessible surface area. In this work, we reported an effective method to fabricate lamellar MO coating on carbon nanocoil (CNC) and investigated its supercapacitive properties. The elegant MO/CNC core shell structure enabled synergistic effects from both MO nanosheets and CNC by using nanosheets to provide a large interaction area for ion transport and CNC to improve the electric conductivity of composites. The investigation of electrochemistry showed that the specific capacitance of MO could reach 435 F g−1 at current density of 1 A g−1. Moreover, the composites presented an excellent rate capability and cycling performance with 92.7% capacitance retention at current density of 2 A g−1 after 5000 cycles. In addition, the asymmetric supercapacitor fabricated with MO/CNC as the positive electrode and CNC as the negative electrode demonstrated excellent energy density of 21.58 Wh kg−1 at a power density of 100 W kg−1. And the asymmetric supercapacitor exhibited an excellent electrochemical cycling stability with 96.3% initial capacitance remained after 1000 cycles.

Biocompatible caramelized carbonaceous nanospheres supported paramagnetic ultrathin manganese oxide nanosheets via self-sacrificing reduction as a MRI contrast agent for liver imaging

The elimination of nanoparticles remains the major roadblock to clinical translation. Caramelization reaction is a general type of non-enzymatic browning reactions to food caramels, the products of carbonaceous nanospheres can be considered safe for biological applications. Here, we report a biocompatible caramelized carbonaceous nanospheres supported paramagnetic ultrathin manganese oxide nanosheets via self-sacrificing reduction as a liver MRI contrast agent and for T1-weighted MR imaging, which are taken up by Kupffer cells resulting in a high relaxivity rate. Mn3O4-caramelized nanoparticles (Mn3O4-CNPs) were synthesized and their characteristics as MR contrast agents were investigated. The relaxation rate (r1) of Mn3O4-CNPs is calculated to 11.6 mM−1 s−1 by Mn concentrations and is nearly three times commercial GdIII-based complex agents at a 3.0 T clinical MR scanner, and the in vivo experiment shows that the signals of mouse liver increase by 50.1% under T1-weighted imaging in 4 h post-injection of Mn3O4-CNPs. The in vivo bio-distribution reveals that the concentrations of Mn are equal to the pre-injection after post-injection of Mn3O4-CNPs 48 h. Therefore, the Mn3O4-CNPs can be used as biocompatible liver MR contrast agents.

CO Oxidation Over Monolayer Manganese Oxide Films on Pt(111)

Ultrathin manganese oxide films grown on Pt(111) were examined in the low temperature CO oxidation reaction at near atmospheric pressures. Structural characterization was performed by X-ray photoelectron spectroscopy, Auger electron spectroscopy, high-resolution electron energy loss spectroscopy, and temperature programmed desorption. The results show that the reactivity of MnOx ultrathin films is governed by a weakly bonded oxygen species, which may even be formed at low oxygen pressures (~10−6 mbar). For stable catalytic performance at realistic conditions the films required highly oxidizing conditions (CO:O2 < 1:10), otherwise the films dewetted, ultimately resulting in the catalyst deactivation. Comparison with other thin films on Pt(111) shows, that the desorption temperature of weakly bonded oxygen species can be used as a benchmark for its activity in this reaction.

Growth and vibrational properties of MnOx thin films on Rh(111)

The growth, structures, and vibrational properties of ultrathin manganese oxide films on Rh(111) had been investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), low energy ion scattering spectroscopy (LEIS) and Auger electron spectroscopy (AES). MnOx grew in a layer-by-layer fashion on the Rh(111) surface. HREELS phonon features and XPS binding energies showed that an OMnO like tri-layer formed initially. Which was stable on the Rh(111) surface with MnOx coverage less than one monolayer. At above one monolayer, Mn3O4 was preferred as indicated from a four-phonon feature peaked at 13.3, 39, 68 and 83meV in HREELS. Higher temperature oxidation and annealing were found to improve the long-range order of the MnOx films.

Oxidation of an organic dye catalyzed by MnOx nanoparticles

We present a study on the catalytic oxidation of the organic dye morin by hydrogen peroxide in the presence of manganese oxide nanoparticles in aqueous solution. The ultrathin manganese oxide nanoparticles consist of c*-disordered potassium birnessite and are immobilized on spherical polyelectrolyte brushes. The catalytic activity of these composite particles was investigated using the oxidation of morin by hydrogen peroxide as a model reaction. The oxidative degradation of morin was followed by UV/vis spectroscopy leading to an apparent rate constant kapp. We propose a modeling of the results in terms of a Langmuir–Hinshelwood model. kapp can be related to the kinetic constant k and to the apparent adsorption constants of H2O2 and morin. Based on this model, the dependence of kapp on temperature can be traced back to the activation energy of the rate constant k and the adsorption enthalpies of both educts on the surface of the nanoparticles.

Large-Scale Synthesis of Ultrathin Manganese Oxide Nanoplates and Their Applications to T1 MRI Contrast Agents

Lamellar structured ultrathin manganese oxide nanoplates have been synthesized from thermal decomposition of manganese(II) acetylacetonate in the presence of 2,3-dihydroxynaphthalene, which promoted two-dimensional (2-D) growth by acting not only as a strongly binding surfactant but also as a structure-directing agent. Ultrathin manganese oxide nanoplates with a thickness of about 1 nm were assembled into a lamellar structure, and the width of the nanoplates could be controlled from 8 to 70 nm by using various coordinating solvents. X-ray absorption near-edge structure (XANES) spectra at the Mn K edge clearly showed that the nanoplates are mainly composed of Mn(II) species with octahedral symmetry. These hydrophobic manganese oxide nanoplates were ligand-exchanged with amine-terminated poly(ethyleneglycol) to generate water-dispersible nanoplates and applied to T1 contrast agents for magnetic resonance imaging (MRI). They exhibited a very high longitudinal relaxivity (r1) value of up to 5.5 mM–1s–1 derived from their high concentration of manganese ions exposed on the surface, and strong contrast enhancement of in vitro and in vivo MR images was observed with a very low dose.

Hybrid Supercapacitor Based on Coaxially Coated Manganese Oxide on Vertically Aligned Carbon Nanofiber Arrays

Hybrid supercapacitor electrodes with remarkable specific capacitance have been fabricated by coaxially coating manganese oxide thin films on a vertically aligned carbon nanofiber array. Ultrathin manganese oxide layers are uniformly coated around each carbon nanofiber via cathodic electrochemical deposition, likely based on water electrolysis initiated electrochemical oxidation. This results in a unique core-shell nanostructure which uses the three-dimensional brush-like vertical carbon nanofiber array as the highly conductive and robust core to support a large effective surface area and provide reliable electrical connection to a thin redox active manganese oxide shell. The pseudo-capacitance of 313 F/g in addition to the electrical double layer capacitance of 36 F/g is achieved by cyclic voltammetry at a scan rate of 50 mV/s and maintains at this level as the scan rate is increased up to 2000 mV/s. A maximum specific capacitance of 365 F/g has been achieved with chronopotentiometry in 0.10 M Na2SO4 aqueous solution with ∼7.5 nm thick manganese oxide. This hybrid core-shell nanostructure demonstrates high performance in maximum specific energy (32.5 Wh/kg), specific power (6.216 kW/kg), and cycle stability (∼11% drop after 500 cycles), which are derived from cyclic voltammetry and galvanostatic charge−discharge measurements. This new architecture can be potentially developed as multifunctional electrical energy storage devices.

Ultrathin transition-metal oxide films: Thickness dependence of the electronic structure and local geometry in MnO

Ultrathin manganese monoxide films on silver substrates are studied as a function of the thickness using x-ray absorption spectroscopy and x-ray photoemission spectroscopy. By combining these techniques, an improved understanding of both the local geometry and the electronic structure is achieved. It was found that both electronic and geometric properties in ultrathin films differ significantly from the bulk. A tetragonal distortion of the oxide films is revealed by polarization-dependent x-ray absorption measurements; the extent is decreasing gradually with increasing film thickness. A relaxation of an epitaxial oxide layer induced by heating also leads to a decrease of the tetragonal interface strain. The electronic structure of ultrathin manganese oxide films changes in the valence-band region with dependence on thickness.

Interface properties and electronic structure of ultrathin manganese oxide films on Ag(0 0 1)

Ultrathin manganese monoxide films on silver single crystal substrates are studied as a function of the thickness using X-ray absorption spectroscopy (XAS) and X-ray photoemission spectroscopy (XPS). It was found that electronic and geometric properties in ultrathin films differ from the bulk. A tetragonal distortion of the oxide films is revealed by polarisation-dependent X-ray absorption measurements: the extent decreases with increasing film thickness. A structural relaxation of epitaxial oxide layers induced by heating also leads to a decrease of the tetragonal interface strain. The electronic structure of ultrathin manganese oxide films in the valence band region is very similar to that in the bulk oxide.