Commercial MnO2 Research Articles

MnO2 Nanosheet-Assembled Hollow Polyhedron Grown on Carbon Cloth for Flexible Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries (ZIBs) have been considered as prospective alternatives for lithium-ion batteries, which are able to serve as power sources for next-generation wearable and flexible devices, owing to the merits of abundant zinc resources and high safety of aqueous electrolyte. However, the lack of suitable cathode materials with flexibility for ZIBs hinders their further application. Herein, a novel cathode material [i.e., MnO2 nanosheet-assembled hollow polyhedron anchored on carbon cloth (MnO2 /CC)] was prepared through a rapid hydrothermal method by using ZIF-67 as self-sacrificing template. When tested in an aqueous ZIB, the MnO2 /CC delivered a high reversible capacity of 263.9 mAh g-1 at 1.0 A g-1 after 300 cycles, far exceeding those of the commercial MnO2 electrode. More importantly, benefiting from the unique structural advantages, a flexible ZIB assembled based on the MnO2 /CC displayed a stable output voltage of 1.53 V and a specific capacity of 91.7 mAh g-1 at 0.1 A g-1 after 30 cycles. It also successfully lit LED bulbs even under different bending angles, showing good flexibility. This research contributes to the development of MnO2 -based cathode materials for high-performance flexible ZIBs.

Facile fabrication of MnO2-embedded 3-D porous polyaniline composite hydrogel for supercapacitor electrode with high loading

To obtain the promising pseudocapacitance of MnO2, the composite hydrogel of MnO2 and polyaniline (PANI) was fabricated using in situ polymerization of aniline hydrochloride in the aqueous solution containing commercial MnO2 nanoparticles and additives. Both scanning electron microscopy and transmission electron microscopy results indicated that the composite hydrogel exhibited a 3-D porous structure, within which MnO2 nanoparticles were uniformly embedded. The investigations of cyclic voltammetry, galvanostatic charge−discharge, and electrochemical impedance spectroscopy demonstrated superior supercapacitor (SC) performance of the hydrogel electrode even with high loading. The electrode with loading of 1.5 mg cm–2 showed a favorable specific capacitance (293 F g–1, 10 mV s–1), which only decreased to 258 F g–1 when the loading of the electrode was seven times higher (10.8 mg cm–2). Furthermore, the hydrogel electrode displayed good cycle stability in the acidic solution (81% capacitance retention after 1000 charge/discharge cycles). The favorable electrochemical performance of the composite hydrogel should be attributed to the fast electron/ion transport and good protection for MnO2 in the 3-D porous structure. Due to the facile one-pot synthesis and optimized nanostructure, it could be expected that MnO2-embedded 3-D porous PANI composite hydrogels have great application in the field of high-performance electrode with high loading for SCs.

One Step Synthesis of One Dimensional Nano MnO2 and Their Application as Oxidizing Agent for Polysulfide Polymers

In this work, MnO2 nanowires and nanorods have been prepared via a simple hydrothermal reaction. The morphology of MnO2 can be easily controlled by the change of the mole ratio of Mn7+ to Mn2+. And the obtained products are well characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), the high-resolution TEM (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectrometer (XPS), etc. The obtained MnO2 samples are employed as the curing agent for polysulfide sealant. The maximum torque of the polysulfide polymer cured by MnO2 nanowires is the highest. The performances are verified by rheological tests of the curing profile, mechanical analysis, and tensile strength tests. The results demonstrate that both of the nanowires and nanorods have excellent vulcanization effects and reinforcing effects in comparison with commercial MnO2. The surface area, structure, and morphology of MnO2 are used to analyze the possible reasons for their promising application in vulcanizing agents for polysulfide rubber.

Pt/C@MnO2 composite hierarchical hollow microspheres for catalytic formaldehyde decomposition at room temperature

Hierarchical carbon@manganese oxide (MnO2) core-shell heterostructure was fabricated by a facile hydrothermal method with hollow carbon spheres as a sacrificial template, and then deposited with platinum (Pt) nanoparticles (NPs). The as-prepared Pt/C@MnO2 composite catalyst exhibited superb performance for removing formaldehyde (HCHO) at room temperature compared with the Pt loaded on MnO2 microspheres or commercial MnO2. The MnO2 nanosheet-assembled hierarchical architecture endowed Pt/C@MnO2 with larger specific surface area and open porous structure, which not only promotes the high dispersity of Pt NPs but also facilitates the diffusion and adsorption of HCHO onto the catalyst surface. The abundant surface active oxygen species resulted from the activation and dissociation of O2 adsorbed at oxygen vacancies adjacent to Pt NPs, and were identified as the primary active species for converting HCHO into intermediates such as dioxymethylene, formate and carbon monoxide. This work might provide enlightenment for designing morphology-dependent and highly active catalysts for HCHO elimination at ambient temperature.

Furfural Oxidation on Gold Supported on MnO2: Influence of the Support Structure on the Catalytic Performances

A series of catalysts consisting of gold nanoparticles supported on MnO2 presenting different morphologies were synthesized and tested in the base-free oxidation of furfural. Ultra-small Au particles (less than 3 nm) were deposited on low (commercial MnO2) and high (NF, nanoflowers and NW, nanowires MnO2) surface area supports. High activity was observed for Au/MnO2-NF material with very high selectivity to furoic acid. The X-ray photoelectron spectroscopy (XPS) study confirmed the presence of a significant amount of highly active Auδ+ species on the surface of the Au/MnO2-NF catalyst. These species seem to be responsible for the high activity in oxidation of furfural under mild conditions (air as oxidant, 110 °C).

Combining active phase and support optimization in MnO2-Au nanoflowers: Enabling high activities towards green oxidations

Among the several classes of chemical reactions, the green oxidation of organic compounds has emerged as an important topic in nanocatalysis. Nonetheless, examples of truly green oxidations remain scarce due to the low activity and selectivity of reported catalysts. In this paper, we present an approach based on the optimization of both the support material and the active phase to achieve superior catalytic performances towards green oxidations. Specifically, our catalysts consisted of ultrasmall Au NPs deposited onto MnO2 nanoflowers. They displayed hierarchical morphology, large specific surface areas, ultrasmall and uniform Au NPs sizes, no agglomeration, strong metal-support interactions, oxygen vacancies, and Auδ+ species at their surface. These features led to improved performances towards the green oxidations of CO, benzene, toluene, o-xylene, glucose, and fructose relative to the pristine MnO2 nanoflowers, commercial MnO2 decorated with Au NPs, and other reported catalysts. We believe that the catalytic activities, stabilities, and mild/green reaction conditions described herein for both gas and liquid phase oxidations due to the optimization of both the support and active phase may inspire the development of novel catalytic systems for a wealth of sustainable transformations.

TiO2/MnO2 composite electrode enabling photoelectric conversion and energy storage as photoelectrochemical capacitor

We prepared composite electrodes by using rutile TiO2 particles and γ-MnO2 particles, and evaluated their photoelectrochemical capacitor properties based on Na+ adsorption by light irradiation in aqueous electrolytes. By employing different synthesis method for TiO2 particles, we synthesized TiO2 particles with various particle sizes and crystallite sizes. An electrode of sol–gel-synthesized TiO2 showed higher photovoltages compared with an electrode of commercial TiO2. This probably originates from a larger contact area between electrode surface and electrolyte because of its smaller particle size than commercial TiO2's size. A further enhancement in photovoltage was attained for an electrode of a hydrothermally-synthesized TiO2 with good crystallinity. We consider that electron−hole recombination was suppressed because hydrothermal TiO2 has a lower density of lattice defect trapping the photoexcited carriers. As photoelectrochemical capacitor, a composite electrode consisting of hydrothermal TiO2 and MnO2 exhibited a 2.4 times larger discharge capacity compared with that of commercial TiO2 and MnO2. This result is attributed to an increased amount of Na+ adsorption induced by the enhanced photovoltage of TiO2.

Template free synthesize mesoporous manganese dioxides for water treatment

Mesoporous materials present infinite application prospect for their special pore structure and large specific surface area. However, the synthesis process of mesoporous transition metal oxides always needs a template such as mesoporous silica to create the porous structure, thus the synthesis technology became complicated and energy consumption. In this work, 3D mesoporous MnO2 microsphere have been successfully prepared by a facile and simple hydrothermal process through introducing a certain amount of Ni2+. A high specific surface area (426 m2/g) was realized due to the mesoporous and ultrathin nanosheets structure. Owing to the special pore structure and 3D morphology assembled with ultrathin nanosheets (∼4 nm). These 3D mesoporous MnO2 shows a high-efficiency catalytic activity contrast with commercial MnO2 and 1D MnO2 nanorods and displays admirable repeatability as well as structure stability in dye degradation.

Degradation of ciprofloxacin using α-MnO2 activated peroxymonosulfate process: Effect of water constituents, degradation intermediates and toxicity evaluation

Nanoscale α-MnO2 with different morphologies (nanoparticles, nanoflowers and nanorods) were synthesized via a facile hydrothermal method and tested in peroxymonosulfate (PMS) activation for ciprofloxacin (CIP) degradation. The catalytic activity of α-MnO2 mainly relied on the specific surface area and crystallinity, and followed the order of α-MnO2 nanoflowers>α-MnO2 nanorods>α-MnO2 nanoparticles>commercial MnO2. Acidic condition was more beneficial to CIP removal than neutral condition, and the degradation would be greatly accelerated in alkaline circumstance. The introduction of chloride and bicarbonate displayed concentration-dependent dual effect. The presence of natural organic matter (NOM) exerted the detrimental effect on CIP degradation. Eleven oxidation products were identified by UPLC–MS/MS and the changes of their concentrations were monitored, five products showed monotonous uptrend while four intermediates present monotonous downtrend once they were generated. Piperazine ring cleavage, hydroxylation and F/OH substitution were found to be the important oxidation pathways. The acute toxicity of resulted solution gradually decreased with the lapse of time, and higher PMS concentration favored the detoxification. The CIP removal in α-MnO2/PMS process was also efficient under the actual water background, which was testified by the results of fluorescence excitation-emission matrix (EEM).

Organic dye removal by MnO2 and Ag micromotors under various ambient conditions: The comparison between two abatement mechanisms

MnO2- and Ag- based micromotors were developed recently as new types of micromotors with the advantage of low costs and have been utilized to treat environmental pollutants. However, knowledge about the effects of ambient conditions on the performance of them is still lacking. In this article, the influences of pH, electrolytes and surfactant on the treatment of organic dye (with methylene blue as the representative) by the commercial MnO2 and Ag micromotors with H2O2 as the fuel were studied. In the motion visualization experiments, besides the routine types of trajectories, the circular motion of micromotors around the already formed bubbles was observed for the first time. In the pollutant removal experiments, two abatement mechanisms (catalytic degradation and adsorptive bubble separation) were studied. The decolorization efficiency for MnO2 due to catalytic degradation increased with the increasing pH, which disagreed with previous studies in which no H2O2 was added. The inhibitory effects of the tested electrolytes were in the order: CaCl2>NaNO3>NaCl. Surfactant can increase the decolorization efficiency only under highly alkaline conditions. For Ag, decolorization only occurs with the existence of surfactant at high pH values (pH = 11.4) indicating that the dominant mechanism is adsorptive bubble separation.

A Simple and Green Procedure to Prepare Efficient Manganese Oxide Nanopowder for the Low Temperature Removal of Formaldehyde

AbstractActivated reactive synthesis, as a top‐down synthesis approach, is proposed for the production of a nanocrystalline, high surface area, manganese (IV) oxide starting from commercial micrometric α‐MnO2. The developed approach consists of two‐steps: 1) high energy ball milling (HEBM) produces a nano‐sized material, 2) low energy ball milling (LEBM) improves textural properties. During the HEBM step, elementary crystals are observed to evolve from several hundred elongated cylindrical particles to short length cylinders and pseudo spherical particles. Despite fractioning of the elementary crystals, surface area remains low over the HEBM derived solid. The LEBM step, achieves crystal shape modification, giving rise to only pseudo‐spherical nanometric particles and significantly increasing the surface area to approximately 60–80 m2 g−1. Catalytic activity of α‐MnO2 powder is affected by the grinding process. Activity is similar to the fresh commercial MnO2 after HEBM, and increases upon LEBM reaching a maximum for LEBM time of 1 h. Thereafter, activity remains constant despite the further increase in surface area upon prolonged LEBM. The presence of an optimal activity after limited LEBM time is paralleled with the increase of the iron contamination occurring after prolonged LEBM time which impacts manganese reducibility and results in less reactive surface.

In-situ generation of gold nanoparticles on MnO2 nanosheets for the enhanced oxidative degradation of basic dye (Methylene Blue)

In this work, the gold nanoparticles (Au-NPs) were in-situ generated on the surface of MnO2 nanosheets to form MnO2/Au-NPs nanocomposite in a simple and cost-effective way. Multiple experiments were carried out to optimize the oxidation of basic dye (Methylene Blue (MB)), including the molar ratio of MnO2 to chloroauric acid (HAuCl4), the pH of the solution and the effect of initial material. Under the optimal condition, the highest degradation efficiency for MB achieved to 98.9% within 60 min, which was obviously better than commercial MnO2 powders (4.3%) and MnO2 nanosheets (74.2%). The enhanced oxidative degradation might attribute to the in-situ generation of ultra-small and highly-dispersed Au-NPs which enlarged the synergistic effect and/or interfacial effect between MnO2 nanosheets and Au-NPs and facilitated the uptake of electrons by MnO2 from MB during the oxidation, thus validating the application of MnO2/Au-NPs nanocomposite for direct removal of organic dyes from wastewater in a simple and convenient fashion.

α-MnO2 Nanowires/Graphene Composites with High Electrocatalytic Activity for Mg-Air Fuel Cell

This paper reports the preparation of α-MnO2 NWs/graphene composites as the cathode catalyst for magnesium-air fuel cell and its excellent electrochemistry performance. The composites are synthesized by self-assembly of α-MnO2 nan α-MnO2 NWs/graphene was synthesized and studied in Mg-air fuel cell. α-MnO2 NWs/graphene was synthesized and studied in Mg-air fuel cell. owires (NWs) on the surface of graphene via a simple hydrothermal method. The α-MnO2 NWs/graphene composites showed a higher electrochemical activity than the commercial MnO2. The oxygen reduction peak of the α-MnO2 NWs/graphene composites catalyst is tested in a 0.1M KOH solution at −0.252V, which is more positive than the commercial MnO2 (−0.287V). The ORR limit current density for 28% α-MnO2 NWs/graphene composite is approximately 2.74mA/cm2, which is similar to that of the 20% Pt/C(2.79mA/cm2) in the same conditions. Based on the Koutecky–Levich plot, the ORR mechanism of the composite involves a one-step, quasi-4-electron pathway. In addition, magnesium-air fuel cell with α-MnO2 NWs/graphene as catalyst possesses higher current density (140mA/cm2) and power density (96mW/cm2) compared to the commercial MnO2. This study proves that the cost-effective α-MnO2 NWs/graphene with higher power generation ability make it possible for the substitute of the noble metals catalyst in the Mg-air fuel cell.

Syntheses of Hierarchical MnO2via H2O2 Selectively Reducing KMnO4 for Catalytic Combustion of Toluene

AbstractMnO2 materials were facilely prepared via the rapid redox reactions of KMnO4 and H2O2 in acidic medium, which exhibit the significant improvement of catalytic activity in the degradation of gaseous toluene compared to commercial MnO2. It was found that the molar ratio of H2O2/KMnO4 has a great influence on the crystalline phase, morphology and average oxidation state of the as‐prepared MnO2. The 3‐MnO2 sample prepared by using three equivalents of stoichiometric H2O2 displays the best catalytic activity for the total combustion of toluene (concentration is up to 1000 ppm) at 300 oC. The mechanism of the influence of different H2O2 addition amount has also been discussed by catalytic performance and nature of materials.

Spin-Coated vs. Electrodeposited Mn Oxide Films as Water Oxidation Catalysts.

Manganese oxides (MnOx), being active, inexpensive and low-toxicity materials, are considered promising water oxidation catalysts (WOCs). This work reports the preparation and the physico-chemical and electrochemical characterization of spin-coated (SC) films of commercial Mn2O3, Mn3O4 and MnO2 powders. Spin coating consists of few preparation steps and employs green chemicals (i.e., ethanol, acetic acid, polyethylene oxide and water). To the best of our knowledge, this is the first time SC has been used for the preparation of stable powder-based WOCs electrodes. For comparison, MnOx films were also prepared by means of electrodeposition (ED) and tested under the same conditions, at neutral pH. Particular interest was given to α-Mn2O3-based films, since Mn (III) species play a crucial role in the electrocatalytic oxidation of water. To this end, MnO2-based SC and ED films were calcined at 500 °C, in order to obtain the desired α-Mn2O3 crystalline phase. Electrochemical impedance spectroscopy (EIS) measurements were performed to study both electrode charge transport properties and electrode–electrolyte charge transfer kinetics. Long-term stability tests and oxygen/hydrogen evolution measurements were also made on the highest-performing samples and their faradaic efficiencies were quantified, with results higher than 95% for the Mn2O3 SC film, finally showing that the SC technique proposed here is a simple and reliable method to study the electrocatalytic behavior of pre-synthesized WOCs powders.

Controlled synthesis of α-MnO2 nanowires and their catalytic performance for toluene combustion

α-MnO2 nanowires with a length about 6–10μm and an average diameter of 20nm were synthesized through a facile hydrothermal process without any templates or surfactants. The products were characterized by X-ray powder diffraction, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, hydrogen temperature-programmed reduction techniques, X-ray photoelectron spectroscopy and surface area analysis. The effects of the hydrothermal temperature and the concentration of CH3COOH on the crystal phase and morphology of the final products were studied in detail. The hydrothermal temperature and the concentration of CH3COOH play crucial roles in determining the crystal phase and morphology of the products. The possible formation mechanism of the α-MnO2 nanowires was investigated and discussed. Additionally, the as-prepared α-MnO2 nanowires showed higher catalytic activity for toluene combustion than the commercial MnO2, suggesting their potential applications in the elimination of volatile organic compounds.

One-pot synthesis of ultrathin manganese dioxide nanosheets and their efficient oxidative degradation of Rhodamine B

Ultrathin manganese dioxide (MnO2) nanosheets have been synthesized in aqueous solution by a facile one-step method. MnO2 nanosheets show a typical 2D lamellar morphology, possessing an average lateral dimension of 100–300nm, and a typical thickness of 3.1–7.5nm, corresponding to 4–10 layers of δ-MnO2. The resultant MnO2 nanosheets have been demonstrated to possess superior oxidative degradation ability to Rhodamine B (RhB) by investigating the decomposition rate and comparing the results with the commercial MnO2 powder. Typically, ultrathin MnO2 nanosheets have shown a high oxidation degradation performance of RhB solution (97.9% removed within 30min) in acid solution (pH 2.0), which can be attributed to special lamellar morphology and the large surface area of the layered MnO2 nanosheets. It is believed that such a convenient approach for the cost-effective and environmentally friendly synthesis of ultrathin MnO2 nanosheets holds great promise for the degradation of complex and various dye wastewater in practical application.

Effects of manganese dioxides on the ultrafiltration membrane fouling by algal extracellular organic matter

Abstract Membrane fouling caused by algal extracellular organic matter (EOM) is of great concern to the industrial implementation of ultrafiltration (UF) in algae-laden water treatment. Pre-oxidation with potassium permanganate (KMnO4) is thus widely utilized to tackle algae-related fouling issues. To verify the contribution of manganese dioxide (MnO2), which is the intermediate product in KMnO4 pre-oxidation, to fouling control, three types of manganese dioxides (commercial available, lab-prepared and in-situ formed MnO2) were adopted to treat EOM prior to filtration. The in-situ formed MnO2 exhibited a higher DOC removal rate (25% with 10 mg/L MnO2 used) than the commercial and lab-prepared MnO2 did. As far as adsorption selectivity was concerned, all MnO2 preferentially adsorbed the macromolecular and hydrophobic fractions of EOM, especially for protein-like substances. Filtration tests showed that the pretreatment with the in-situ formed MnO2 significantly alleviated the flux decline caused by EOM owing to the superb performance in removing macromolecular components. Other types of MnO2 brought about very minor improvements in membrane permeability. Moreover, reversibility analyses showed that the irreversible fouling was reduced to some extent by manganese dioxide adsorption, among which the in-situ formed MnO2 performed the best. However, the improvement in fouling reversibility was not prominent due to the minor removal in the hydrophilic fraction of EOM by manganese dioxides.

One-pot mass self-assembly of MnO2 sponge-like hierarchical nanostructures through a limited hydrothermal reaction and their environmental applications

We report an environmentally-responsible limited hydrothermal reaction to construct gram-scale MnO2 sponge-like hierarchical nanostructures composed of ultrathin nanosheets (∼5nm) in one pot. This template-free strategy simultaneously avoids the disposal of toxic materials and provides novel metal oxide nanostructures. As a typical application, the MnO2 hierarchical nanostructures prepared can easily remove positively-charged methylene blue in water with much more adsorption capacity than those of commercial carbon grain and MnO2 microparticles, TiO2 and Fe2O3 nanoparticles. Meanwhile, the solid–liquid separation is ready due to higher density resulted from their hierarchical nanostructures. Importantly adsorbed methylene blue can be reclaimed after elution with ethanol. Remarkably, the sponge-like hierarchical nanostructures can be recycled for many times with no obvious loss of adsorption capacity, qualifying them as a great potential application in environmental protection and resource reuse.

Selective catalytic oxidation of ammonia to nitrogen over MnO2 prepared by urea-assisted hydrothermal method

Selective catalytic oxidation of ammonia was studied over MnO2 catalysts synthesized by urea-assisted and tranditional hydrothermal method. A contrastive research was also made to a commercial MnO2 catalyst. The catalytic performance of MnO2 for NH3-SCO was found to be connected with the properties of the catalysts which were obviously determined by the preparation methods. The best catalytic activity was achieved at 170°C over the MnO2 synthesized by urea-assisted hydrothermal method. The properties of catalysts were characterized by BET, XRD, SEM, XPS, H2-TPR and NH3-TPD techniques. And it was found that MnO2 prepared by urea-assisted synthetic method showed larger surface area and lower reduction temperature. Abundant NH3 adsorption sites and oxygen vacancies were formed on its surface compared to the other catalysts, which evidently enhanced the catalytic performance for NH3 selective oxidation.