Nanostructured Manganese Oxide Research Articles

Engineering the Heterogeneous Interface of Sulphur Doped Nickel-Manganese Oxide for Efficient Overall Electrochemical Water Splitting

Electrochemical water splitting is the technique to utilize stochastic renewable sources for a continuous uninterrupted supply of energy through the production of hydrogen fuel. However, the performance of a water electrolyzer is limited due to the instability as well as larger overpotential associated with the current state of the electrocatalysts. Transition metal oxides show remarkable potential for catalyzing water electrolysis. Among transition metal oxides, binary transition metal compounds exhibit the forte to replace the expensive and scarce noble-metal electrocatalysts. The engineering of hetero-interfaces between sulphur doped nickel and manganese oxide nanostructures has been systematically presented in our study. The difference in morphology too affects the catalytic activity of the samples owing to variable electrolyte interaction. The strategic development of these hetero-interfaces wields the electrocatalyst its superior bifunctional activity for catalyzing oxygen evolution reaction at an overpotential as low as 300 mV at 20 mA cm-2 current density and hydrogen evolution reaction at 280 mV at 10 mA cm-2 current density. The catalyst also delivered a stable current density for a long-term durability study without any significant loss in the performance.

Citrate-promoted dissolution of nanostructured manganese oxides: Implications for nano-enabled sustainable agriculture

Nanostructured manganese oxides (nano-MnOx) have shown great promises as versatile agrochemicals in nano-enabled sustainable agriculture, owing to the coupled benefits of controlled release of dissolved Mn2+, an essential nutrient needed by plants, and oxidative destruction of environmental organic pollutants. Here, we show that three δ-MnO2 nanomaterials consisting of nanosheet-assembled flower-like nanospheres not only exhibit greater kinetics in citrate-promoted dissolution, but also are less prone to passivation, compared with three α-MnO2 nanowire materials. The better performance of the δ-MnO2 nanomaterials can be attributed to their higher abundance of surface unsaturated Mn atoms–particularly Mn(III)–that is originated from their specific exposed facets and higher abundance of surface defects sites. Our results underline the great potential of modulating nanomaterial surface atomic configuration to improve their performance in sustainable agricultural applications.

Tailored 3D Foams Decorated with Nanostructured Manganese Oxide for Asymmetric Electrochemical Capacitors

Tailored 3D (Ni and NiCo) metallic foam architectures were produced by electrodeposition and decorated via electrochemical routes with manganese oxide (MnOx) to serve as positive electrodes for supercapacitors. For comparative purposes, an electrode made of commercial Ni foam was also prepared. The foam-based electrodes were paired with a carbon cloth electrode and used to assemble asymmetric electrochemical cells. The electrochemical response of these cells was studied by applying different electrochemical techniques. In addition, two different protocols (cycling and floating) were applied to assess cells durability and fade. Despite the significant differences in the decorated foams morphology and structure their electrochemical responses revealed similar trends. The electrodes made of tailored foams showed higher specific capacitance, better capacitance retention at high current load and enhanced cycling stability compared to the electrodes made of commercial foam. The asymmetric cells made with the tailored foams revealed higher (maximum) specific energy (11–14 Wh kg−1) and specific power (1.3–1.4 × 104 W kg−1) compared to cells assembled with commercial foams (8.4 Wh kg−1 and 6.3 × 103 W kg−1). The durability tests evidenced that corrosion of the NiCo electrodeposited foams and electrochemical dissolution of MnOx are possible causes of cells degradation.

Engineering Effects on Efficacy and Toxicity of Manganese Oxide Nanostructures, as a Contrast Agent, in Magnetic Resonance Imaging: A Review

Magnetic resonance imaging (MRI) is a noninvasive, imaging technique of soft tissues, providing the possibility for three-dimensional, high temporal and spatial resolution imaging. Gadolinium complexes are the most frequently used [Formula: see text]-weighted contrast agents (CAs) to enhance the signal intensity of images. The toxicity of released Gd[Formula: see text] has shifted the attention of researchers to manganese (Mn) oxide nanoparticles (NPs) as a [Formula: see text]-weighted CA. Different phases and shapes of Mn oxide nanostructures with various coatings have been investigated to achieve the highest efficacy and lowest toxicity. In this review, engineering effects of Mn oxide nanostructures on image quality, toxicity and targeting have been studied. Switchable, multimodal imaging and theranostic systems, based on Mn oxide nanostructures, were also reviewed.

Degradation of Methylene Blue Using Hydrothermally Synthesized α‐Manganese Oxide Nanostructures as a Heterogeneous Fenton Catalyst

Lately, the upsurge in the liberation of synthetic dyes into the environment, primarily by the textile industries, is a threat to the natural habitat and existing ecosystem. Various methods such as adsorption and degradation with nanoparticles are currently being used to degrade those hazardous materials, but still, the yearning for novel methods continues. In this study, hydrothermal reactions were performed at 160°C to synthesize manganese dioxide nanostructures (MnNSs) under different incubation periods that facilitated the comparison of the size, morphology, and crystallinity of MnNSs. The study revealed the change in crystallinity over the incubation period; MnNSs prepared at 24 hrs were highly crystalline among others. Additionally, the size and morphology of MnNSs changed from the sea‐urchin or flower‐like structure, predominantly sheet/layer form, to nanorods as the reaction proceeded for 24 hrs. Characterization of MnNSs was followed by heterogeneous Fenton’s reaction, using α‐manganese dioxide nanostructures, for the degradation of methylene blue (MB). To further understand the catalytic activity of MnNSs, the synthesized nanostructures were subjected to degrade MB at varied time intervals, both with and without hydrogen peroxide (H2O2). Catalytically, MnNSs evinced good potential for degrading MB dye in the presence of H2O2; MnNSs prepared at 24 hrs degraded MB up to 73% within 110 minutes.

Nanostructured Manganese Oxides within a Ring-Shaped Polyoxometalate Exhibiting Unusual Oxidation Catalysis.

Nanosized manganese oxides have recently received considerable attention for their synthesis, structures, and potential applications. Although various synthetic methods have been developed, precise synthesis of novel nanostructured manganese oxides are still challenging. In this study, using a structurally defined nanosized cavity inside a ring-shaped polyoxometalate, we succeeded in synthesizing two types of discrete 18 and 20 nuclear nanostructured manganese oxides, Mn18 and Mn20, respectively. In particular, Mn18 showed much higher catalytic activity than other manganese oxides for the oxygenation of alkylarenes including electron-deficient ones, and the reaction proceeded through a unique reaction mechanism due to its unusual manganese oxide structure.

Progress in Development of Nanostructured Manganese Oxide as Catalyst for Oxygen Reduction and Evolution Reaction

The rise in energy consumption is largely driven by the growth of population. The supply of energy to meet that demand can be fulfilled by slowly introducing energy from renewable resources. The fluctuating nature of the renewable energy production (i.e., affected by weather such as wind, sun light, etc.), necessitates the increasing demand in developing electricity storage systems. Reliable energy storage system will also play immense roles to support activities related to the internet of things. In the past decades, metal-air batteries have attracted great attention and interest for their high theoretical capacity, environmental friendliness, and their low cost. However, one of the main challenges faced in metal-air batteries is the slow rate of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) that affects the charging and the discharging performance. Various types of nanostructure manganese oxide with high specific surface area and excellent catalytic properties have been synthesized and studied. This review provides a discussion of the recent developments of the nanostructure manganese oxide and their performance in oxygen reduction and oxygen evolution reactions in alkaline media. It includes the experimental work in the nanostructure of manganese oxide, but also the fundamental understanding of ORR and OER. A brief discussion on electrocatalyst kinetics including the measurement and criteria for the ORR and the OER is also included. Finally, recently reported nanostructure manganese oxide catalysts are also discussed.

Nanostructured manganese oxides as highly active catalysts for enhanced hydrolysis of bis(4-nitrophenyl)phosphate and catalytic decomposition of methanol

The nanostructured manganese oxides (MnOx) exhibited high catalytic activities for hydrolysis of phosphate diester-based substrate bis(4-nitrophenyl)phosphate and decomposition of methanol to carbon monoxide and hydrogen as a potential alternative fuel.

A polydopamine-gated biodegradable cascade nanoreactor for pH-triggered and photothermal-enhanced tumor-specific nanocatalytic therapy.

Despite the great potential of cascade catalytic reactions in tumor treatment, uncontrolled catalytic activities in vivo lead to inevitable off-target toxicity to normal tissues, which greatly hampers their clinical conversion. Herein, an intelligent cascade nanoreactor (hMnO2-Au@PDA, hMAP) was constructed by depositing glucose oxidase (GOx)-mimicking ultrasmall gold nanoparticles (Au NPs) into honeycomb-shaped manganese oxide (hMnO2) nanostructures and then coating them with polydopamine (PDA) to achieve pH-responsive and photothermal-enhanced nanocatalytic therapy. Upon exposure to the mild acidic tumor microenvironment (TME), the PDA gatekeeper would collapse, and the inner hMnO2 could simultaneously deplete glutathione (GSH) and generate Mn2+, while a considerable amount of H2O2 produced from the oxidation of glucose by GOx-mimicking Au NPs could accelerate the Mn2+-mediated Fenton-like reaction, yielding sufficient highly toxic ˙OH. More importantly, the pH-responsive cascade reaction between Au NPs and hMnO2 could be further enhanced by localized hyperthermia induced from PDA under near-infrared (NIR) laser irradiation, thereby inducing significant cell apoptosis in vitro and tumor inhibition in vivo. This work provided a promising paradigm by innovatively designing a TME-responsive and photothermal-enhanced cascade catalytic nanoreactor for safe and efficient cancer therapy.

Elaboration of Lamellar and Nanostructured Materials Based on Manganese: Efficient Adsorbents for Removing Heavy Metals

The lamellar and nanostructured manganese oxide materials were chemically synthesized by soft and non-toxic methods. The materials showed a monophasic character, symptomatic morphologies, as well as the predominance of a mesoporous structure. The removal of heavy metals Cd(II) and Pb(II) by the synthesized materials Na-MnO2, Urchin-MnO2 and Cocoon-MnO2 according to the mineral structure and nature of the sites were also studied. Kinetically, the lamellar manganese oxide material Na-MnO2 was the most efficient of the three materials which had more vacancies in the MnO6 layers as well as in the space between the layers. The nanomaterials Urchin-MnO2 and Cocoon-MnO2 could exchange with the metal cations in their tunnels and cavities, respectively. The maximum adsorbed quantities followed the order (Pb(II): Na-MnO2 (297 mg/g)>Urchin-MnO2 (264 mg/g)>Cocoon-MnO2 (209 mg/g), Cd(II): Na-MnO2 (199 mg/g)>Urchin-MnO2 (191 mg/g)>Cocoon-MnO2 (172 mg/g)). Na-MnO2 material exhibited the best stability among the different structures, Na-MnO2 presented a very low amount of the manganese released. The results obtained showed the potential of lamellar manganese oxides (Na-MnO2) and nanostructures (Urchin-MnO2 and Cocoon-MnO2) as selective, economical, and stable materials for the removal of toxic metals in an aqueous medium.

The Development of Antibiotics Based on Nanostructured Manganese Oxide; Understanding Mechanism from Fundamental Aspects to Application.

The emergence of bacterial resistance to currently available antibiotics emphasized the urgent need for new antibacterial agents. Nanotechnology-based approaches are substantially contributing to the development of effective and better-formulated antibiotics. Here, we report the synthesis of stable manganese oxide nanostructures (MnO NS) by a facile, one-step, microwave-assisted method. Asprepared MnO NS were thoroughly characterized by atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), dynamic light scattering (DLS), UV-Visible spectroscopy and X-ray powder diffraction (XRD). UV-Visible spectra give a sharp absorption peak at a maximum wavelength of 430 nm showed surface plasmon resonance (SPR). X-ray diffraction (XRD) profile demonstrated pure phase and crystalline nature of nanostructures. Morphological investigations by a scanning electron microscope showed good dispersity with spherical particles possessing a size range between 10-100 nm. Atomic force microscope data exhibited that the average size of MnO NS can be controlled between 25 nm to 150 nm by a three-fold increment in the amount of stabilizer (o-phenylenediamine). Antimicrobial activity of MnO NS on both gram-positive (Bacillus subtilis) and gram-negative (Escherichia coli) bacterial strains showed that prepared nanostructures were effective against microorganisms. Further, this antibacterial activity was found to be dependent on nanoparticles (NPs) size and bacterial species. These were more effective against Bacillus subtilis (B. subtilis) as compared to Escherichia coli (E. coli). Considering the results together, this study paves the way for the formulation of similar nanostructures as effective antibiotics to kill other pathogens by a more biocompatible platform. This is the first report to synthesize the MnO NS by green approach and its antibacterial application.

Nanostructured manganese oxide as an efficient eco-friendly catalyst for removing azo dye Calcon from water

Nanostructured manganese oxide was produced using a nontoxic reactive by a simple electrodeposition on solid substrates (SnO2). The structural and morphological characterizations of the electrodeposited material (Na-MnO2) confirmed the forming of homogeneous, adherent and well crystallized thin films. The highly efficient degradation of azo dye (Calcon) over electrodeposited material Na-MnO2 was studied by adjusting various parameters of the reaction. The degradation rate was facilitated by acidic pH (pH = 3). Kinetics and isotherm studies showed that the adsorption reaction is of the pseudo-second-order reaction model. The result was a monolayer that adsorbed a quantity of 294.12 mg/g. The adsorption data was consistent with Freundlich isotherm. The application of Na-MnO2/SnO2 material proved its ability to be used multiple times without prior processing, providing after 5 uses a discoloration efficiency superior to 86%. Low-cost efficient materials and methods are promising for the degradation of organic pollutants to maintain a clean environment.

Au–Manganese Oxide Nanostructures by a Plasma‐Assisted Process as Electrocatalysts for Oxygen Evolution: A Chemico‐Physical Investigation

AbstractEarth‐abundant and eco‐friendly manganese oxides are promising platforms for the oxygen evolution reaction (OER) in water electrolysis. Herein, a versatile and potentially scalable route to gold‐decorated manganese oxide‐based OER electrocatalysts is reported. In particular, MnxOy (MnO2, Mn2O3) host matrices are grown on conductive glasses by plasma assisted‐chemical vapor deposition (PA‐CVD), and subsequently functionalized with gold nanoparticles (guest) as OER activators by radio frequency (RF)‐sputtering. The final selective obtainment of MnO2‐ or Mn2O3‐based systems is then enabled by annealing under oxidizing or inert atmosphere, respectively. A detailed material characterization evidences the formation of high‐purity MnxOy dendritic nanostructures with an open morphology and an efficient guest dispersion into the host matrices. The tailoring of MnxOy phase composition and host–guest interactions has a remarkable influence on OER activity yielding, for the best performing Au/Mn2O3 system, a current density of ≈5 mA cm−2 at 1.65 V versus the reversible hydrogen electrode (RHE) and an overpotential close to 300 mV at 1 mA cm−2. Such results, comparing favorably with literature data on manganese oxide‐based materials, highlight the importance of compositional control, as well as of surface and interface engineering, to develop low‐cost and efficient anode nanocatalysts for water splitting applications.

Manganese oxides: promising electrode materials for Li-ion batteries and supercapacitors

Nanostructured transition metal oxides (NTMOs) have engrossed substantial research curiosity because of their broad diversity of applications in catalysis, solar cells, biosensors, energy storage devices, etc. Among the various NTMOs, manganese oxides and their composites were highlighted for the applications in Li-ion batteries and supercapacitors as electrode materials owing to their environmental friendly nature and various oxidation states. This review concerns the deposition, characterization, and applications of nanostructured manganese oxide thin films (NMOTFs) during the few decades. The deposition and characterization of NMOTFs are discussed. Characterization discussed here enlightens the structural and morphological studies. The focus of the application section includes Li-ion batteries and supercapacitors.

Effects of electrolyte doping on electrodeposited nanostructured manganese oxide and chromium oxide

Electrolyte additions are used to control the functionality of a nanostructured oxide. Dopant ions affect the size and shape of deposit crystallites and modify the host structure. Such ions can be incorporated into the deposit or form a separate oxide phase. The manganese dioxide family of polymorphs with ion-molecular sieve properties represents the additional possibilities of “template” effects of dopant ions on the phase composition, heterovalent substitution in the cationic sublattice, changes in morphology and alteration of nanocrystallite size during electrocrystallisation. The effects of electrolyte doping in electrodeposited, non-stoichiometric manganese dioxide (NH4+, Li+ and Co2+), chromium oxide-based films (Co2+, Li+) were investigated. The structural characteristics and morphology were studied for all the obtained nanocomposites and deposits were evaluated as highly crystalline cathode materials cathodes, having high cyclability, in Li batteries.The improved functionality of the electrodeposited nanomaterials was correlated to structural changes. Hollandite and pyrolusite electrodeposition pathways were proposed, based on symmetry principles of phase transitions.

Molten salt synthesis of α-MnO2/Mn2O3 nanocomposite as a high-performance cathode material for aqueous zinc-ion batteries

Abstract Thanks to low cost, high safety, and large energy density, aqueous zinc-ion batteries have attracted tremendous interest worldwide. However, it remains a challenge to develop high-performance cathode materials with an appropriate method that is easy to realize massive production. Herein, we use a molten salt method to synthesize nanostructured manganese oxides. The crystalline phases of the manganese oxides can be tuned by changing the amount of reduced graphene oxide added to the reactant mixture. It is found that the α-MnO2/Mn2O3 nanocomposite with the largest mass ratio of Mn2O3 delivers the best electrochemical performances among all the products. And its rate capability and cyclability can be significantly improved by modifying the Zn anode with carbon black coating and nanocellulose binder. In this situation, the nanocomposite can deliver high discharging capacities of 322.1 and 213.6 mAh g–1 at 0.2 and 3 A g–1, respectively. After 1000 cycles, it can retain 86.2% of the capacity at the 2nd cycle. Thus, this nanocomposite holds great promise for practical applications.

MnOx nanosheets anchored on a bio-derived porous carbon framework for high-performance asymmetric supercapacitors

MnO2 is regarded as one of the most promising electrode materials for supercapacitors due to its high theoretical capacitance and low cost; however, it suffers from poor electronic and ionic conductivity. Herein, nanostructured manganese oxides (MnOx) are anchored on a lotus seedpod-derived carbon framework (LSCF) in situ using a one-step hydrothermal-based redox synthesis strategy. The as-prepared MnOx@LSCF hybrid features a 3D conductive network and ultrathin MnOx nanosheets with oxygen vacancies, which can enhance both electrons and ions transfer intrinsically and facilitate sufficient surface Faradaic redox reactions. Benefitting from the synergistic effect of the nanostructured MnOx and the conductive LSCF, the optimized MnOx@LSCF hybrid exhibits a high specific capacitance (406 F g−1 at 0.5 A g−1) and a remarkable discharging rate capability (270 F g−1 at 10 A g−1). Moreover, an asymmetric supercapacitor fabricated by using MnOx@LSCF as the positive electrode and LSCF as the negative electrode achieves a high energy density of 48.1 Wh kg−1 at 500 W kg−1 (which still retains 22.2 Wh kg−1 at 10 kW kg−1), and a considerable cyclic stability of 90.1% after 5000 cycles. These properties demonstrate the MnOx@LSCF hybrid would have a valuable commercial application prospects in high-performance supercapacitors.

Nanostructured Manganese Oxides for Energy Storage: Synthetic Control Leading to Improved Electrochemistry

Manganese is desirable due to its high environmental abundance and low cost. Some manganese oxides (α-MnO2, Mn8O16) possess a tunneled structure comprised of one-dimensional 2 × 2 tunnels formed by corner and edge sharing manganese octahedral [MnO6] units which can be substituted in the central tunnel by a variety of cations of varying size, providing a robust framework for ion insertion and (de)insertion. Control of composition, crystallite size, and defect through scalable synthesis approaches will be described in this presentation. Impact of nanostructure and mesoscale electrode structure on capacity, rate capability, and capacity retention in lithium and beyond lithium batteries will be discussed. Specific improvements in capacity retention realized through targeted elemental substitution will be highlighted. Mechanistic differences in aqueous and non-aqueous battery systems will be described. The use of x-ray absorption spectroscopy to gain insight into mechanism and the evolution of local coordination environment in these systems will be reviewed.

A High-Rate Lithium Manganese Oxide-Hydrogen Battery.

Rechargeable hydrogen gas batteries show promises for the integration of renewable yet intermittent solar and wind electricity into the grid energy storage. Here, we describe a rechargeable, high-rate, and long-life hydrogen gas battery that exploits a nanostructured lithium manganese oxide cathode and a hydrogen gas anode in an aqueous electrolyte. The proposed lithium manganese oxide-hydrogen battery shows a discharge potential of ∼1.3 V, a remarkable rate of 50 C with Coulombic efficiency of ∼99.8%, and a robust cycle life. A systematic electrochemical study demonstrates the significance of the electrocatalytic hydrogen gas anode and reveals the charge storage mechanism of the lithium manganese oxide-hydrogen battery. This work provides opportunities for the development of new rechargeable hydrogen batteries for the future grid-scale energy storage.

Facile synthesis of manganese oxide nanostructures with different crystallographic phase and morphology for supercapacitors

The charge storage performances of manganese oxide (MnO2) nanostructures highly depend on their crystallographic phase and structure. In this work, MnO2 nanostructures (α-MnO2, β-MnO2 and δ-MnO2) with high crystallinity and different morphology are prepared through a simple, mild and controllable hydrothermal method at 120 °C. [Mn(C8H4O4) (H2O)2]n, a water insoluble metal-organic framework (Mn-MOF), can efficiently react with KMnO4 at different pH, which results in the generation of α-MnO2, β-MnO2 and δ-MnO2. The size of MnO2 nanostructures can be easily adjusted by controlling the ratio of Mn(II)/Mn(VII). The as-prepared MnO2 nanostructures with different structures and sizes are characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), X-ray photoelectron spectroscopy (XPS), and N2 adsorption/desorption. Among three samples, the layered δ-MnO2 nanostructures with Mn(II)/Mn(VII) = 2.0 show a specific surface area of 240 m2·g−1, specific capacitance of 416 F·g−1 at 0.5 A·g−1, which can be explained as both adsorption/desorption and intercalation/deintercalation process. The energy density of the asymmetric supercapacitor constructed by MnO2 and activated carbon (AC) is 23.2 W·h·kg−1 at a power density of 425 W·kg−1. The controllable synthesis of MnO2 nanostructures with different crystallographic phases based on Mn-MOF may give further insights into supercapacitors.