MnO2 Microspheres Research Articles

Hollow-porous carbon microspheres with hierarchically micromesoporous shells and superhydrophilic surfaces for high-performance aqueous supercapacitors

Hollow-porous carbon microspheres (SPC-MnO2) are synthesized using sucrose as a carbon source and MnO2 microspheres with a porous and rough surface as a template, followed by activation with KHCO3. The activation process involves anchoring carbon onto the MnO2 template while simultaneously creating pores in the carbon shell. The SPC-MnCO3 sample, which utilizes well-defined MnCO3 microspheres as a template, exhibits disintegrated grains with irregular shapes owing to the substantial decomposition of MnCO3 during activation. The SPC-MnO2 sample demonstrates a large surface area of 1589 m² g⁻¹ and a pore volume of 2.52 cm³ g⁻¹, featuring substantial amounts of mesopores ranging from 3 to 30 nm in size. The micromesoporous structure of SPC-MnO2 provides a hydrophilic surface, thereby enhancing wettability in aqueous KOH electrolytes and improving charge-storage capabilities. The SPC-MnO2 electrode exhibits superior specific capacitance (317 F g⁻¹ at 1 A g⁻¹) and high-rate performance (202 F g⁻¹ at 50 A g⁻¹) in 6 M KOH compared with microporous carbon produced without a template. The notable enhancement in supercapacitor performance can be attributed to the hollow structural integrity of the microspheres, the superhydrophilic surface, high electrical conductivity, and the hierarchical micromesoporous nature. These features facilitate efficient ion/electron transport and surface-controlled redox kinetics.

Morphology evolution of bacterial cellulose carbon and loaded with MnO2 microspheres for high performance supercapacitors

The rapid development of economy and technology caused numerous irreversible effects on the environment, and the rational use and storage of existing resources have became an indispensable process in modern development. Energy storage through supercapacitors can effectively alleviate part of the energy crisis. Here, the effects of heating rates on the morphology of carbonized bacterial cellulose (CBC) carbon and its electrochemical properties were studied and CBC-5 (heating rate of 5 ℃/min) with porous structure was confirmed to be supporting material for loading MnO2. The specific capacitance of CBC-5@MnO2 composites was high up to 190 F g−1 at 1 A g−1, and its capacitance retention rate was up to 96.6% after 8000 cycles. The superior electrochemical performance cannot be achieved without the cooperative effect among the metal oxides and carbon materials, which also benefits from the fast transport of ions and electrons in solution. The assembled CBC-5//CBC-5@MnO2-6 h hybrid supercapacitors exhibited largest energy density and power density values of 44.5 Wh kg−1 (at 0.2 A g−1) and 11111.1 W kg−1 (at 10 A g−1), respectively. The assembled button cells can light up small LED bulbs for at least 10 min. The porous bacterial cellulose carbon can provided possibilities for high electrode design.

Conformal poly 3,4-ethylene dioxythiophene skin stabilized ε-type manganese dioxide microspheres for zinc ion batteries with high volumetric energy density

Manganese dioxide (MnO2) is an important active material for energy storage. Constructing microsphere-structured MnO2 is key for practical application due to the high tapping density for high volumetric energy density. However, the unstable structure and poor electrical conductivity hinder the development of MnO2 microspheres. Herein, Poly 3,4-ethylene dioxythiophene (PEDOT) is painted conformally on ε-MnO2 microspheres to stabilize the structure and enhance the electrical conductivity via in-situ chemical polymerization. When used for Zinc ion batteries (ZIBs), the obtained material (named MOP-5) with high tapping density (1.04 g cm−3) delivers a superior volumetric energy density (342.9 mWh cm−3) and excellent cyclic stability (84.5% after 3500 cycles). Moreover, we find the structure transformation of ε-MnO2 to ZnMn3O7 during the initial few cycles of charge and discharge, and the ZnMn3O7 provides more reaction sites for Zinc ions from analysis of the energy storage mechanism. The material design and theoretical analysis of MnO2 in this work may provide a new idea for future commercial applications of aqueous ZIBs.

Honeycomb-like MnO2/Biochar Catalyst Fabricated by High-Energy Electron Beam Irradiation for Degradation of Antibiotics in Swine Urine.

The modification of biochar is essential for the development of multifunctional biochar materials with enhanced remediation effects on contaminated water. In this work, a biochar-based microcatalyst with sunlight sensitivity was synthesized by a creative modification method that involved the rapid fabrication of MnO2 microspheres by high-energy electron beam (HEEB) irradiation, and loading them into corn straw-derived honeycomb-like KOH-modified biochar (MBC) to obtain a sunlight-sensitive microcatalyst (SSM). The honeycomb-like structure of MBC facilitated the improvement in MnO2 dispersion and photocatalytic property through confinement effect. The effects of photocatalyst dosage, initial chlortetracycline (CTC) concentration, solution pH, temperature and coexisting ions on the photocatalytic performance of SSM were systemically investigated. The results indicated that SSM could efficiently degrade CTC in water and swine urine under sunlight, and exhibited high stability against coexistence of urea, Cl- and SO42-. Moreover, SSM showed good reusability in regeneration studies. This work provides a novel method for degrading CTC with potential application prospect.

Modifying acidic oxygen production properties of PbO2 by porous Mn2O3 microspheres for boosting stability

Designing active and durable cost-effective electrocatalysts for catalyzing the oxygen evolution reaction (OER) under a strongly acidic environment is a highly promising approach for OER-associated sustainable energy supplies. Herein, a Pb-Sn-Ca/α-PbO2/β-PbO2-Mn2O3 (PSC/PbO2-Mn2O3) composite electrode is fabricated via a simple two-step process. First, porous Mn2O3 microspheres are synthesized by the solvothermal method. Then, a PSC/PbO2-Mn2O3 composite electrode with a special embedded structure is prepared through the introduction of Mn2O3 by composite electrodeposition. The low OER overpotential (621 mV) of the PSC/PbO2-Mn2O3 (12 g L−1) composite electrode is reduced by 445 mV compared with that of the industrial Pb-(0.76 wt%) Ag electrode at a current density of 50 mA cm−2. In addition, it shows a service life of up to 91 h at a high operation current density of 1.5 A cm−2 in acidic media (3.06 g L−1H+), which indicates its excellent stability. Therefore, this work not only demonstrates a design for a durable and high-efficiency electrocatalyst for acidic water oxidation but also provides strategies for the synthesis of advanced electrocatalytic electrodes.

Temperature-controlled fabrication of hydrophilic manganese oxide microspheres as high-performance electrode materials for supercapacitors

The supercapacitive properties of manganese oxides (MnOx) are strongly affected by their crystal structure. Nevertheless, the relationship between the crystal structure and supercapacitive performance of MnOx is elusive. Herein, a temperature-controlled fabrication method was developed to achieve MnO2, Mn3O4, MnO and Mn2O3 microspheres with various crystal structure as electrode materials tunable for supercapacitors. The detailed material and electrochemical characterizations revealed the structure-activity relationship of MnOx microspheres by systematically investigating the effect of valence state, specific surface area, conductivity and morphology on supercapacitive performance. Among these MnOx materials, nanoneedle-like MnO2 delivered a relatively high specific capacitance of 274.1 F/g at 1 A/g due to a high Mn valence state of +4, a large specific surface area of 113.4 m2/g and a desirable electronic conductivity of 1.73 × 10–5 S/cm. Furthermore, MnO2 presented a remarkable cycle stability with 115% capacitance retention after 10,000 cycles owing to the enhancement of wettability. This work not only provides a facile strategy to modulate MnOx crystal structure, but also offers a deep understanding of structure-dependent supercapacitive performance of MnOx.

Emulsion-templated construction of enzyme-nanozyme integrated hierarchically porous hydrogels for smartphone-assisted pesticide biosensing

Due to their great threat to human health and the environment, it is always of significance to develop efficient tools to monitor pesticide residues. Although the enzyme inhibition-based strategy is considered as a potential method and has been intensively explored for pesticide analysis, both vulnerable enzymatic activity and tedious operation greatly hinder its practical applications. Developing robust, easy-to-use and efficient devices for pesticide sensing is still challenging. Herein, we recommend an enzyme-nanozyme integrated hierarchically porous hydrogel (AChE-MnO2@HPH) for the convenient detection of pesticides. MnO2 microspheres were first employed as an emulsion stabilizer to fabricate MnO2@HPH by thermal polymerization, and AChE was then immobilized into the MnO2@HPH via a fast self-absorption process. With the unique porous structure and hydrophilic microenvironment, the constructed AChE-MnO2@HPH exhibited excellent enzymatic activity and stability as well as rapid response toward pesticides through inhibiting the activity of AChE. By applying a smartphone to read the color information originating from the chromogenic reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) catalyzed by oxidase-mimicking MnO2, highly sensitive and convenient determination of fenthion, an organophosphorus pesticide model, was achieved with a detection limit down to 0.63 ng mL−1. Excellent performance robustness over 30 storage days and reliable detection of the target in real food samples were also demonstrated. With the advantages of easy operability, free of equipment, and good detection performance and long-term stability, the integrated AChE-MnO2@HPH will find promising use for pesticide residue in-field analysis.

Can Manganese Dioxide Microspheres be Used as Intermediaries to Alleviate Intervertebral Disc Degeneration With Strengthening Drugs?

Degenerative disc disease (DDD) is a pathological condition associated with intervertebral discs (IVDs) that causes chronic back pain. IVD degeneration has become a significant issue in contemporary society. To date, numerous biological therapies have been applied to alleviate the progression of DDD, among which therapeutic protein injection is the most direct and convenient. However, there are some limitations to applying direct protein injection therapy, the most significant being that the efficacy of this method has a short duration, which is a major factor in its effectiveness and the resulting patient satisfaction. How do we solve this problem? Or how can the effectiveness of the treatment be enhanced? It has been proved that manganese dioxide (MnO2) microspheres, widely used in environmental science, not only regulate the expression of cell genes and cytokines in the microenvironment, but also have the ability to release drugs slowly. We propose that direct injection of protein encapsulated in hollow MnO2 (h-MnO2) microspheres could solve the problem of rapid drug release. In addition, the use of a MnO2 and protein injection in the treatment of DDD may have a synergistic effect, which would be highly significant for the degradation of pro-inflammatory factors in the DDD microenvironment. Therefore, the combination of MnO2 and protein may provide a new therapeutic approach to alleviate the progression of DDD.

Nanoarchitectured MnO2 Confined to Mesoporous Carbon Microspheres as Bifunctional Electrodes for High-Performance Supercapacitors and Lithium-Ion Capacitors

Manganese dioxide (MnO2) is an outstanding electrode material to obtain high pseudocapacitance and specific capacity, but the structure pulverization and poor conductivity during the charge/discharge process are the inevitable problems. Restricting nanoscaled MnO2 in stable pore channels of mesoporous carbon spheres can effectively inhibit its pulverization and obtain an excellent conductive network. Herein, nanoarchitectured MnO2/mesoporous carbon microspheres (MCMs) as bifunctional electrodes for supercapacitors and lithium-ion capacitors (LICs) were prepared through a charily designed facile stratagem containing spray drying and the subsequent redox reaction. The MnO2/MCMs electrode delivers a gravimetric capacitance of 188 F g–1 and a volumetric capacitance of 347 F cm–3 with an outstanding cyclic performance of 90% capacitance retention after 1000 cycles at 1 A g–1, which is ideal for supercapacitors. Moreover, the assembled MnO2/MCMs//activated carbon (AC) lithium-ion capacitors exhibit a long cyclic life of 1300 times with 7.7% capacity loss at 1 A g–1 and a superior energy density of 147 Wh kg–1, as well as a power density of 4952 W kg–1, demonstrating its feasibility on LIC anodes. The excellent electrochemical performance is ascribed to the synergistic effect between MnO2 and mesoporous carbon microspheres, which improves the electrochemical capacities and cyclic stability of both systems. This work provides the possibility for applying bifunctional MnO2/MCMs as electrode materials for high-efficiency hybrid systems.

N-doped carbon coated porous hierarchical MnO microspheres as superior additive-free anode materials for lithium-ion batteries

Novel N-doped carbon coated porous hierarchical MnO microspheres have been successfully synthesized via the simultaneous pyrolysis of MnCO3 and polyacrylonitrile (PAN) at low calcination temperature. The micro/nano structure with uniform N-doped carbon coating, suitable interior pores and tiny primary MnO nanocrystals can significantly increase the electronic conductivity of the composite, reduce the amount of irreversible solid-electrolyte interphase (SEI) layer, accommodate the huge volume change of MnO during cycling and facilitate easier redox reaction of Mn2+/Mnx+ (x>2) to generate extra capacity. By using partially pyrolytic PAN as the conductive agent and binder, the obtained additive-free MnO-based electrode (MnO@NC-S) demonstrates a high reversible capacity of 998 mAh g−1 after 100 cycles at 0.1 A g−1 and remarkable long-term cycling stability with the capacity of 629 mAh g−1 after 500 cycles at 0.5 A g−1.

Modifying Acidic Oxygen Production Properties of Pbo2 by Porous Mn2o3 Microspheres for Boosting Stability

Modifying Acidic Oxygen Production Properties of Pbo2 by Porous Mn2o3 Microspheres for Boosting Stability

Ni-doped Mn2O3 microspheres as highly efficient electrocatalyst for oxygen reduction reaction and Zn-air battery

Herein, Ni-doped Mn2O3 microspheres are successfully synthesized via the facile coprecipitation of metal ions and ammonium bicarbonates, followed by a heat treatment process. Ni-doped Mn2O3 exhibits outstanding catalytic performance toward the oxygen reduction reaction (ORR) in alkaline media with a half-wave potential of 0.801 V, limiting current density of 6.02 mA cm−2 at 0.6 V vs. RHE, outstanding long-term durability, and strong tolerance to methanol. Furthermore, a Zn–air primary battery using Ni-doped Mn2O3 as an air cathode shows high open-circuit voltage of 1.52 V and high power density of 88.2 mW cm−2, outperforming the commercial Pt/C cathode. The exceptional performance of the Ni-doped Mn2O3 microspheres is ascribed to the hierarchical structure, optimized particle size, and Ni incorporation into Mn2O3. The proposed synthesis strategy provides a new methodology for the design and fabrication of electrochemically active transition metal-doped materials as efficient electrocatalysts for a variety of energy storage and conversion reactions.

Introducing hierarchical hollow MnO2 microspheres as nanozymes for colorimetric determination of captopril.

A simple sensor was developed for the colorimetric determination of captopril (CPT). Herein, hierarchical hollow MnO2 microspheres (HH-MnO2) were applied as nanozymes with peroxidase-mimetic activity. Free cation radicals with a strong absorption signal (λmax at 653nm) were generated via a redox reaction between 3, 3', 5, 5'-tetramethylbenzidine (TMB) and HH-MnO2. Captopril could successfully prevent the generation of blue-colored free cation radicals. The influence of CPT concentration on the absorption of the generated radicals was monitored by UV-Vis spectroscopy. The corresponding linear concentration range was from 1.0 to 30.0μgmL-1 (4.6-138.1μmolL-1), and the detection limit was found to be 0.26μgmL-1 (1.2μmolL-1). As a practical usage, the developed sensor was effectively utilized to measure the content of CPT in pharmaceutical formulations.

3D Wearable Fabric‐Based Micro‐Supercapacitors with Ultra‐High Areal Capacitance

AbstractMiniaturized electronics require integrated unit configuration in very limited space, where energy storage per unit area is thus extremely critical. Micro‐supercapacitors (MSCs), mainly established on planar substrates, are superior but still suffer from limited areal capacitance. Herein, a novel strategy is introduced to construct high cross‐section MSCs using 3D fabrics as the porous skeleton. Interdigitated poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) is patterned on 3D fabrics to achieve continuous conductive networks, while MnO2 microspheres epitaxially grown on PEDOT:PSS are fully exposed to electrolyte with the support of fabric fibers. The unique architecture can utilize more active sites of thick electrodes and the high conductivity of interpenetrating fiber networks. The resulting fabric‐based MSCs demonstrate ultra‐high areal capacitance of 135.4 mF cm−2, which is 3.5 times that of devices on polyethylene terephthalate substrates and is among the highest values for planar‐based MSCs using the same interdigital geometry. Moreover, the flexible fabrics endow MSCs with extremely high bending stability with 94% capacitance retention even after 3000 cycles. These figures‐of‐merit enable fabric‐based MSCs promising to be used in the next‐generation of wearable electronics.

Reduced graphene oxide encapsulated MnO microspheres as an anode for high-rate lithium ion capacitors

Reduced graphene oxide encapsulated MnO microspheres as an anode for high-rate lithium ion capacitors

Preparation of enhanced AgI@MnO2 heterojunction photocatalysts for rapid sterilization under visible light

Aimed at solving food poisoning and food-borne diseases caused by drug-resistant pathogens bacteria, the optimum utilization of abundant, green, and sustainable sunlight through photocatalytic technology is definitely an appealing task. Herein, a new series of AgI@MnO2X:1 (X = 5, 10, 15) heterostructure photocatalysts were synthesized by in-situ growth of AgI nanoparticles on the surface of MnO2 microspheres using the deposition method. Compared with MnO2 or AgI alone, the AgI@MnO2 heterostructure system exhibited enhanced photocatalytic performance due to the improved rapid separation efficiency of photogenerated electron-hole pairs. Moreover, AgI@MnO210:1 had higher photocurrent density and more ROS production, indicating the accelerated charge transfer and increased photocatalytic efficiency. Based on this, the photocatalytic mechanism was proposed. The antibacterial experiment verified the excellent broad-spectrum bactericidal performance of AgI@MnO210:1 against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus), which was because AgI@MnO210:1 with high catalytic activity under visible light would generate more ROS by consuming glutathione (GSH) to improve antibacterial efficiency. This study provides new insight into the development of superior general photocatalyst for environmental disinfection, healing wounds from bacterial infections, and other fields that quickly kill bacteria.

Reduced graphene oxide encapsulated MnO microspheres as an anode for high-rate lithium ion capacitors

Developing an anode material with high-rate Li+ intercalation and stable charge/discharge platform is important for achieving high performance lithium ion capacitors (LICs). Reduced graphene oxide (rGO)-encapsulated MnO microspheres (∼2 μm) are obtained by a simple process including solvothermal and calcination techniques. The material contains a large number of mesopores (∼2.8 nm diameter). The MnO/rGO has a favorable cycling stability (846 mAh g−1 at 0.1 A g−1 after 110 cycles) and an outstanding rate performance (207 mAh g−1 at 6.4 A g−1). Kinetic analysis reveals that a pseudocapacitive contribution plays a dominant role for the energy storage. The improvement in the pseudocapacitive behavior is ascribed to the fact that the uniform rGO coating on the MnO provides continuous pathways for electron transport, and the mesoporous structure provides numerous migration paths for Li-ions. Furthermore, MnO/rGO//activated carbon (AC) LICs have a high energy density of 98 Wh kg−1 at a relatively high power density of 10,350 W kg−1, and have a capacity retention of 71% after 5000 cycles at 1.6 A g−1. These outstanding results indicate that the enhanced Li+ intercalation of the anode offsets the kinetic imbalance between the two electrodes.

Morphology-controlled self-assembly synthesis and excellent microwave absorption performance of MnO2 microspheres of fibrous flocculation

Pure dielectric absorbers with a tunable wide-band response and strong attenuation capability for electromagnetic wave (EMW) absorption are challenging to synthesize. Herein, a series of hierarchical MnO2 microspheres composed of MnO2 nanofibers are synthesized via a simple one-step hydrothermal method. By varying the hydrothermal synthesis conditions, the surface architectures of the MnO2 microspheres could be adjusted, thereby tuning their EMW absorption performance. In addition, nickel doping causes defects in the MnO2 nanofibers, which further boosts microwave absorption performance. Compared to 2D MnO2 nanorods, the hierarchical microspheres formed by the self-assembly of MnO2 nanofibers offer tunable microwave absorption in the X and Ku bands. The Ni-doped microspheres with the optimized morphology show a maximum reflection loss of −40 dB is observed at 8.31 GHz, and an effective absorption bandwidth of 6.1 GHz at 2 mm thickness.

Nanostructure Fe2O3 surface-coating on MnO2 microspheres as high rate performance anode materials for lithium-ion batteries

Manganese dioxide (MnO2) anode materials with high energy and power density have attracted wide attention in lithium-ion batteries (LIBs). However, the poor rate capability and inferior cycling stability hindered their commercial applications. To address the issues, we designed and synthesized MnO2 @Fe2O3 composite microspheres by a solvothermal treatment and subsequent annealing process, on which Fe2O3 nanoparticles are coated on the surface of MnO2 microspheres with a diameter of about 2 µm. The Fe2O3 thin protective film on the surface of MnO2 alleviates the volume change of MnO2 and the dissolution of Mn element during cycling, and improves the Li+ diffusion coefficient of the electrode materials through the kinetics analysis. The MnO2 @Fe2O3 microspheres deliver excellent rate capacity of 296.2 mA h g −1 at a high current density of 6.4 A g −1, and superior reversible capacity of 675.4 mA h g −1 and 784.6 mA h g −1 after 150 cycles at 100 mA g −1 and after 1000 cycles at 500 mA g −1, respectively. The enhanced electrochemical performance is attributed to the synergistic effect of different components. The results indicate that MnO2@Fe2O3 composite microspheres will be a promising anode materials for superior performance in LIBs.

MnO2@V2O5 microspheres as cathode materials for high performance aqueous rechargeable Zn-ion battery

The development of manganese dioxide (MnO2) as cathode materials in rechargeable aqueous zinc-ion batteries (ZIBs) is tremendously restricted by the dissolution of MnO2 during charge/discharge process. Herein, vanadium pentoxide (V2O5)-coated MnO2 as cathode is proposed via a facile thermal decomposition method. The V2O5 nanoparticles are coated on the MnO2 microsphere with an average diameter of 1 μ m, enhancing ion insertion/extraction kinetics and suppressing the dissolution of the cathode material during cycling. The MnO2@V2O5 microspheres exhibit a high specific capacity of 381.4 mA h g−1 at 100 mA g−1, excellent rate capability of 160.7 mAh g−1 at 1600 mA g−1 and good long-term cycling stability with 73% capacity retention after 3000 cycles at 2000 mA g−1. This study highlights the potential of Zn-ion conductor oxide coating as a strategy of improving the electrochemical performance of MnO2 in aqueous ZIBs.