MnO2 Particles Research Articles

Biogenic Mn2O3 via the redox of Shewanella oneidensis MR-1 for peroxymonosulfate advanced oxidation

The manganese Mn(II) oxidizing by Shewanella oneidensis MR-1 (MR-1) underlines a new pathway for Mn nanoparticle synthesis. However, the mechanism of Mn oxidizing and the compositions of biogenic products remain unknown. Here, the oxidation of Mn(II) to Mn2O3 nanoparticles was discovered, and was to be driven by cytochrome c reductase Complex III. According to the transcriptomic analysis, genes encoding Complex III were upregulated during the Mn(II) oxidizing process, corresponding to the inability of mutants ΔpetC and ΔpetA (Complex III subunits). The morphology and activity of Mn2O3 particles were further controlled by the extracellular electron transfer of MR-1, associated with the change of the shape from nanoparticle to nanosheet and with stronger electron transfer ability, and eventually led to a 1.5-fold higher methylparaben degradation rate by activating peroxymonosulfate radical oxidizing effectively. Our work provides insights into the Mn-oxidizing mechanism and modification of biogenic Mn for pollutant removal.

Copper nanoparticles incorporated manganese dioxide nanocomposites for electrochemical capacitance application

Chemically produced coppercontaining MnO2 nanoparticles were studied using FTIR, UV-Vis spectroscopy, XRD, AFM, cyclic voltammetric and charge/discharge behaviour. Mixed nanocomposites have a crystalline size of 50 nm was calculated through Debye Scherrer’s equation from XRD analysis. The FTIR spectra were recorded region 400- 4000 cm-1, of clean and doped Manganese dioxide nanoparticles. Mn–O can be ascribed to the stretching vibration band of MnO2 nanoparticles at 631 cm-1. The bending and stretching vibrations of the O-H group are ascribed to the fundamental absorption peaks at 1620 cm-1 and 3400 cm-1.AFM is used to characterize the impact of surface roughness on the fundamental properties of MnO2, copper induced nanocomposites of MnO2 particles. Electrochemical impedance and voltammetric experiments are used to investigate the behaviour of individual and mixed nanocomposites as supercapacitors.

The thermal activation of MnOx-Al2O3 catalysts: Effect of gallium doping

In this study, the effect produced by the gallium oxides intercalation into MnOx-Al2O3 catalysts on their catalytic properties and structural aspects of the active component formation was investigated. Three series of the catalysts, Mn–Al, Mn–Ga, and Mn–Al-Ga, having a similar Mn content but different Al/Ga ratio, were synthesized by coprecipitation and subsequent calcination at temperatures from 600 to 1200°С°. The catalysts were tested in CO oxidation. For the Mn–Al series of catalysts, a thermal activation effect is observed, defined as an increase in catalytic activity after high-temperature treatment at 900-1000°С. The increase in the activity after calcination is related to the formation of the Mn3-xAlxO4 solid solution at the synthesis temperature and its segregation upon cooling. Segregation of the solid solution leads to the formation of the Mn3O4+δ defect oxide and an amorphous aluminum-containing component. The addition of 5%Ga to the Mn–Al catalyst changes the phase transformation route during thermal activation. The in situ XRD data has showed that at 1000°С the high-temperature solid solution (MnGaAl)3O4 with the cubic spinel structure is formed; however, its further segregation upon cooling is hindered. The introduction of gallium stabilizes the structure of the (MnGaAl)3O4 mixed oxide, the parent oxide is partially decomposed after cooling with Mn3O4 nanoparticles formation. However the amount of produced active Mn3O4 particles and/or weakly bound oxygen is much lower, which in turn adversely affects the catalytic properties.

Preparation of NiAl LDH@Mn3O4@Co-MOF ternary composites using MOFs as a framework for high-performance asymmetric supercapacitors

In this work, we have successfully synthesized NiAl LDH@Mn3O4@Co-MOF ternary composites with good properties. Co-MOF sheets are first grown on NF (nickel foam) by the aqueous solvent method. Then Mn3O4 particles are grown on Co-MOF sheets by electrodeposition. Finally, ultrathin NiAl LDH nanosheet clusters were grown on Co-MOF sheets by hydrothermal method. The three-dimensional Co-MOF can offer a larger specific surface area and more active sites, and the combination of the three substances generates a synergistic effect, resulting in a ternary composite with superior performance, which has superior specific capacity characteristics of 1311 C g−1 at 1 A g−1 and can retain 74.6% of the original capacity after 5000 cycles. The asymmetric supercapacitor assembled with active carbon has a high energy density of 60.91 Wh kg−1 at a power density of 849.91 W kg−1 and retains 82.9% of the original performance after 5000 cycles. Therefore, the NiAl LDH@Mn3O4@Co-MOF can be applied as the positive material for supercapacitor, which has good research and application value.

X-ray Photoelectron Spectroscopy and Diffuse Reflectance Infrared Fourier Transform Spectroscopy Insight into the Pathways of Manganese Oxalate Thermal Decomposition to MnO and MnCO3.

X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were employed to study the isothermal decomposition of MnC2O4 under ultrahigh vacuum and N2 environmental conditions, respectively. High-resolution core-level XP spectra, X-ray-induced Auger spectra, and infrared spectra were obtained as a function of annealing time. In XPS studies, the time-dependent thermal decomposition characteristics were elucidated by analyzing surface composition, chemical shifts, satellites in the Mn 2p3/2 and Mn LMV bands, and Auger parameters for Mn and O. Functional groups developing during the ongoing reaction were identified by DRIFTS from characteristic vibrations. For the first time, the isothermal decomposition of manganese oxalate was shown to proceed via two pathways involving nucleation and accumulation of MnO and MnCO3. The kinetics of the decomposition in vacuum could be described by the Prout-Tompkins or/and by the Avrami-Erofeev models. The results obtained by XPS, DRIFTS, and ex situ XRD allowed concluding that the final product of oxalate decomposition was composed of MnO and MnCO3 or/and unidentate/polydentate carbonate structures populating the surface of the sample. A substantial formation of graphitic carbon was also observed and associated with interface chemical reactivities between the MnO particles and the supporting gold foil.

Effect of Mn-Based Slurries on Chemical Mechanical Polishing of SiC Substrates

High-efficiency and high-quality chemical mechanical polishing (CMP) of silicon carbide (SiC) substrates was achieved using slurries prepared with manganese oxide (MnO2, Mn2O3) particles. Experimental results showed that the oxidation-reduction potential (ORP) and zeta potential of these manganese (Mn)-based slurries decreased with increasing pH. For alkaline pH values (> 7), MnO2 particles were converted into strongly oxidizing MnO4 2− ions that promoted interfacial chemical reactions during CMP, thereby increasing the material removal rate. Observation and analysis of the SiC substrate surface showed that the surface roughness (Ra) reached 1 nm after polishing, but slight surface scratches remained. The binding energy of elemental oxygen (O) and Mn (O1s and Mn2p) indicated that the atoms on the substrate surface underwent an oxidation reaction, which weakened the Si-C molecular bond and thus increased the material removal rate.

Synthesis of flower-like MnO2 nanostructure with freshly prepared Cu particles and electrochemical performance in supercapacitors

Four types of flowerlike manganese dioxide in nano scale was synthesized via a liquid phase method in KMnO4-H2SO4 solution and Cu particles, wherein the effect of Cu particles was investigated in detail. The obtained manganese dioxide powder was characterized by XRD, SEM and TEM, and the supercapacity properties of MnO2 electrode materials were measured. The results showed that doping carbon black can benefit to better dispersion of copper particles, resulting in generated smaller size of Cu particles, and the morphology of MnO2 nanoparticles was dominated by that of Cu particles. The study of MnO2 synthesis by different sources of Cu particles showed that the size of MnO2 particles decreased significantly with freshly prepared fine copper powder compared with using commercial Cu powder, and the size of MnO2 particles can be further reduced to 120 nm by prepared Cu particles with smaller size. Therefore, it was suggested that the copper particles served as not only the reductant and but also the nuclei centre for the growth of MnO2 particles in synthesis process MnO2, and that is the reason how copper particles worked on the growth of flower-like MnO2 and electrochemical property. In the part of investigation for electrochemical property, the calculated results of b values indicated that the electrode materials have pseudo capacitance property, and the highest specific capacitance of 197.2 F g-1 at 2 mV s-1 and 148 F/g at 1 A/g were obtained for MCE electrode materials (MnO2 was synthesized with freshly prepared copper particles, where carbon black was used and dispersed in ethanol before preparation of Cu particles). The values of charge transfer resistance in all types of MnO2 materials electrodes were smaller than 0.08 Ω. The cycling retention of MCE material electrode is still kept as 93.8% after 1000 cycles.

CNT-Strung LiMn2 O4 for Lithium Extraction with High Selectivity and Stability.

LiMn2 O4 is of great potential for selectively extracting Li+ from brines and seawater, yet its application is hindered by its poor cycle stability and conductivity. Herein a two-step strategy to fabricate highly conductive and stable CNT-strung LiMn2 O4 (CNT-s-LMO) is reported, by first stringing Mn3 O4 particles with multiwalled carbon nanotube (CNT), then converting the hybrids into CNT-s-LMO through hydrothermal lithiation. The as-synthesized CNT-s-LMO materials have a net-like structure with CNTs threading through LMO particles. This unique structure has endowed the CNT-s-LMO electrode with excellent conductivity, high specific capacitance, and enhanced rate performance. Because of this, the CNT-s-LMO electrode in the hybrid capacitive deionization cell (HCDI) can deliver a high Li+ extraction percentage (≈84%) in brine and an outstanding lithium selectivity with a separation factor of ≈181 at the Mg2+ /Li+ molar ratio of 60. Significantly, the CNT-s-LMO-based HCDI cell has a high stability, evidenced by 90% capacity retention and negligible Mn loss in 100 cycles. This method has paved a new way to fabricate carbon-enabled LMO-based absorbents with tuned structure and superior capacity for electrochemical lithium extraction with high Li+ selectivity and exceptional cycling stability, which may help to tackle the shortage in supply of Li-ion batteries in industry in the future.

Synthesis of bimetallic Metal-Organic Frameworks composite for the removal of Copper(II), Chromium(VI), and Uranium(VI) from the aqueous solution using fixed-bed column adsorption

NiCo(BDC) bimetallic Metal-Organic Framework (MOF) is impregnated with MnO2 particles to synthesize a highly stable NiCo(BDC)@MnO2 composite. This MOF composite is applied for the removal of Copper (II), Chromium (VI), and Uranium (VI) heavy metal ions from aqueous solutions using batch adsorption and the fixed-bed column method. The physicochemical properties of the composite were analyzed by Fourier transform infrared spectrometry (FTIR), powder X-ray Diffraction (PXRD), Scanning Electron Microscope (SEM), and Brunauer−Emmett−Teller (BET) analysis. TG-DTA analysis shown the composite MOF is thermally stable up to 450°C. X-ray Photoelectron Spectroscopy (XPS) analysis confirms the presence of Nickel, Cobalt, and Mn. The fixed-bed column adsorption experiments on Cu(II), Cr(VI), and U(VI) were conducted to understand the effect of bed height, flow rate, and initial concentration on adsorption efficiency. NiCo(BDC)@MnO2 MOF composite showed a high adsorption capacity of 756.82 ​mg/g for Cu(II), 111.22 ​mg/g for Cr(VI), and 365.25 ​mg/g for U(VI) were examined by the Langmuir isotherm model. The equilibrium studies specified that Cu(II), Cr(VI), and U(VI) adsorption follows pseudo-second-order kinetics in the batch adsorption process and Thomas, Yoon-Nelson, Adam, and Bohart model in fixed-bed column adsorption, which indicates that chemisorption and surface complexation are maybe the primary mechanisms.

Extraction of silver ions from aqueous solutions by MnO(OH) particles

Extraction of silver ions from aqueous solutions by MnO(OH) particles

Ultra-light 3D MnO2-agar network with high and longevous performance for catalytic formaldehyde oxidation

Under the background of indoor air formaldehyde decontamination, a freestanding ultra-light assembly was fabricated via ice-templating approach starting from MnO2 nanoparticles and environmentally benign agar powder. The 3D composite of agar and MnO2 (AM-3D) was comparatively studied with powdered counterparts (including pure MnO2 and mixture of agar and MnO2) and the 3D-structured agar for formaldehyde oxidation, and their physicochemical properties were examined with XRD, ATR, SEM, XPS, isothermal N2 adsorption, ESR, Raman, CO-TPR and O2-TPD. For the single test of formaldehyde oxidation, the AM-3D catalyst exhibited 62.0%–67.0% removal percentage for ~400 mg/m3 formaldehyde, which did not demonstrate significant advantage over the control samples. However, thanks to the porous 3D agar scaffold with large spatial volume that could promote a rapid gas-phase formaldehyde concentration reduction, and the strong interaction between the dispersed MnO2 particles and agar substrate that could afford a large amount of reactive oxygen species to further oxidize the adsorbed formaldehyde, the AM-3D composite was a much better HCHO-to-CO2 converter and possessed much more advantageous stability for repeated cycles of formaldehyde oxidation: even after ten cycles, there was still 41.7% of formaldehyde removed. Furthermore, the viable sunlight irradiation could easily restore the activity of the used AM-3D catalyst back to the level approaching that of the fresh one. Finally, reaction pathways were put forward via the infrared spectroscopic and ion chromatographic investigations on the surface intermediates of the spent materials.

Alteration of birnessite reactivity in dynamic anoxic/oxic environments

Although the oxidative capacity of manganese oxides has been widely investigated, potential changes of the surface reactivity in dynamic anoxic/oxic environments have been often overlooked. In this study, we showed that the reactivity of layer structured manganese oxide (birnessite) was highly sensitive to variable redox conditions within environmentally relevant ranges of pH (4.0 – 8.0), ionic strength (0–100 mM NaCl) and Mn(II)/MnO2 molar ratio (0–0.58) using ofloxacine (OFL), a typical antibiotic, as a target contaminant. In oxic conditions, OFL removal was enhanced relative to anoxic environments under alkaline conditions. Surface-catalyzed oxidation of Mn(II) enabled the formation of more reactive Mn(III) sites for OFL oxidation. However, an increase in Mn(II)/MnO2 molar ratio suppressed MnO2 reactivity, probably because of competitive binding between Mn(II) and OFL and/or modification in MnO2 surface charge. Monovalent cations (e.g., Na+) may compensate the charge deficiency caused by the presence of Mn(III), and affect the aggregation of MnO2 particles, particularly under oxic conditions. An enhancement in the removal efficiency of OFL was then confirmed in the dynamic two-step anoxic/oxic process, which emulates oscillating redox conditions in environmental settings. These findings call for a thorough examination of the reactivity changes at environmental mineral surfaces (e.g., MnO2) in natural systems that may be subjected to alternation between anaerobic and oxygenated conditions.

Synthesis and electrochemical properties of crystalline K0.7MnO2 particles for K-ion batteries

Large-scale energy storage and depleting lithium resources spurred interest in efficient, abundant, low-cost potassium ion battery electrode materials. In this regard, the layered K0.7MnO2 cathode was prepared by the solution chemical method. The structural and morphological analyses were performed using XRD, SEM and TEM techniques. The electrochemical properties exhibited multiple redox peaks in CV, indicating the various phase transitions during the intercalation/ de-intercalation and ordering of K-ions in the interlayer. The prepared K-ion cell delivered a reversible specific capacity of 79 and 31 mAh/g at the current densities of 20 and 400 mA/g. The structural integrity accounted for better electrochemical performance from the initial discharge capacities at high current rates.

MnO2-MXene Composite as Electrode for Supercapacitor

A MnO2-MXene composite material is reported, in which MnO2 particles have been grown onto Ti3C2 MXene flakes. Thanks to its interconnected structure, it can not only boost the low electrical conductivity of MnO2, but also suppress the restacking of MXene flakes. As an electrode material in a three-electrode cell, the composite showed greater capacitance and improved stability performance than raw MnO2 in both KOH and Na2SO4 aqueous electrolytes. Equipped with MnO2–MXene composite material as positive and activated carbon as negative, an asymmetric device using Na2SO4 as electrolyte displayed an energy density of 20 Wh kg−1 at 500 W kg−1 power density. On the other hand, the device operated in KOH electrolyte showed an energy density of 17 Wh kg−1 at 400 W kg−1, and 11 Wh kg−1 at 8 kW kg−1.

In-situ formed amorphous manganese vanadate encapsulating MnO via salt-assisted ball milling toward 3D hierarchical porous electrodes for superior lithium storage

• KCl-assisted ball milling method was employed in this work. • Crosslinked 3D hierarchical porous electrodes were designed and synthesized. • MnO particles were embedded by amorphous manganese vanadate layer. Amorphous electrode has been witnessed for enhanced electrochemical performance as unique isotropic nature. Moreover, the fancy structures are beneficial to achieve superior electrochemical properties. However, it is a formidable challenge to acquire an electrode material which keeps both amorphous phase and organized morphology via a simple preparation method. In a departure of other sophisticated methods, ball milling could easily introduce amorphous phase with unique merits such as more interstitial sites for rapid diffusion of Li ions, and more void spaces for accommodation of volume change than the crystalline phase. In our work, 3D hierarchical porous electrodes were designed and synthesized via KCl-assisted ball milling method. Owing to the unique merits including crosslinked 3D porous network, amorphous manganese vanadate buffer layer and numerous oxygen defects introduced during the KCl-assisted milling, the as-prepared electrode showed boosted electrochemical performance. The as-prepared electrodes delivered a capacity as high as 540.55 mAh g −1 after 500 cycles at 2 A g −1 with 98.78% capacity retention and 85.39% after 900 cycles. In brief, KCl-assisted ball milling provided a feasible and efficient approach to achieve 3D hierarchical porous electrodes, casting light on new approach of developing advanced electrode materials with the organized morphologies and amorphous phase.

Colloidal Processing of Mn3O4-Carbon Nanotube Nanocomposite Electrodes for Supercapacitors.

This investigation addresses the challenges in the development of efficient nanostructured Mn3O4 cathodes for supercapacitors. A high areal capacitance and the ability to avoid a time-consuming activation procedure for electrodes with high active mass loading of 40 mg cm−2 are reported. This facilitates practical applications of Mn3O4 based electrodes. The highest capacitance of 6.11 F cm−2 (153 F g−1) is obtained from cyclic voltammetry at a scan rate of 2 mV s−1 and 6.07 F cm−2 (151.9 F g−1) from the chronopotentiometry at a current density of 3 mA cm−2 in a potential window of 0.9 V in a neutral Na2SO4 electrolyte. The new approach is based on the application of rhamnolipids (RL) as a capping agent for the synthesis of Mn3O4 particles and a co-dispersant for Mn3O4 and carbon nanotubes, which are used as conductive additives. The size and shape of the Mn3O4 particles are influenced by RL. The enhanced performance of the electrodes is linked to the chemical structure and properties of RL molecules, which exert influence on Mn3O4 particle size and shape during synthesis, reduce agglomeration, facilitate RL adsorption on Mn3O4 and carbon nanotubes, and influence their co-dispersion and mixing at the nanometric scale.

Synthesis of MnO2 Particles via One Step Localized Heating Method as Catalyst for Dye Degradation

This work demonstrated the synthesis of MnO2 particles via a rapid one-step localized heating method. The heat was transferred directly from the wire into the precursor solution, hence minimized the heat loss to the surrounding. As a result, the precursor solution was heated up rapidly and MnO2 particles with different morphologies were successfully synthesized in short duration within 10 to 15 min. These MnO2 particles were used as catalyst in the degradation of Rhodamine B (RhB) organic dye. Particularly, MnO2 particles synthesized at 10 min possessed outstanding catalytic activity with 99% degradation efficiency of RhB dye in 10 min of reaction time. This was greatly contributed by its 3D nanoflowers morphology that provided more active sites for catalytic activities to occur. The promising catalytic activity, synthesizing by a simple and affordable synthesis setup could provide an alternative in the development of MnO2 catalyst for organic pollutants removal.

Construction of K and Tb Co-doped MnO2 nanoparticles for enhanced oxidation and detoxication of organic dye waste

Developing low-cost and efficient materials for dye pollutant removal under mild condition remains a great challenge. Here K+ and Tb3+ co-doped porous MnO2 (K–Tb–MnO2) nanoparticles with tailored properties including crystal structure, surface area and catalytic activity have been synthesized. Experimental results reveal that K–Tb–MnO2 nanoparticle has higher specific surface area, Mn3+ content and surface oxygen vacancies than pristine MnO2 nanoparticle and single-doped MnO2 materials, showing the uniqueness of dual-doped metal ions. Using methyl blue (MB) as a model pollutant, its removal efficiency by K–Tb–MnO2 nanoparticles within 5 min is 93.6%, which is 18, 8.3, and 2.9 times higher than that of MnO2, K–MnO2, and Tb–MnO2 nanomaterials, respectively. Oxalic acid triggered MnO2 material dissolving assay and FT-IR spectrum suggested that remarkable performance of K–Tb–MnO2 nanoparticle toward MB removal can be attributed to a combined effect of adsorption (16% MB removal) and catalytic degradation (84% MB removal). Moreover, K–Tb–MnO2 nanoparticle mediated MB degradation is demonstrated to be a combination of non-radical oxidation by Mn3+ and radical-participated degradation, with 1O2 as the main species. And the intermediates and pathways of MB degradation were studied by liquid chromatography-mass spectrometry. Importantly, cell viability experiment suggests that the toxicity of MB dye could be efficiently alleviated after the treatment with K–Tb–MnO2 nanoparticle. These results demonstrate the great potential of the novel K–Tb–MnO2 particles to be used as a highly effective nanomaterials to reduce the risk of dye wastes toward the environment and human health.

One-pot synthesis of nanosized MnO incorporated into N-doped carbon nanosheets for high performance lithium storage

As potential anode materials for lithium-ion batteries, transition metal oxides have been extensively investigated due to their high theoretical capacity. Nevertheless, how to address rapid capacity degradation and improve rate capability is still a big challenge. Herein, nanosized MnO incorporated into N-doped carbon nanosheets (MnO/NCN) was rationally designed by a facile one-pot salt-templated synthesis method. The nanosized MnO particles (around 20 nm) were powerfully anchored on the ultrathin N-doped carbon nanosheets to build a high-efficiency electrons/ions hybrid conductive framework. In addition, based on the stable interfacial interaction between MnO and N-doped carbon nanosheets, the MnO/NCN hybrid exhibits great structural stability, thus delivering high reversible lithium storage capacity (719 mA h g−1 at 0.1 A g−1) and superior stability (497 mA h g−1 at 1 A g−1 over 1000 cycles). Besides, the assembled lithium-ion capacitor with MnO/NCN anode exhibits excellent energy-power characteristics (142 W h kg−1 at 412 W kg−1). Such impressive lithium storage performance demonstrates that the MnO/NCN electrode is promising for large-scale energy storage devices.

Improved titanium-manganese flow battery with high capacity and high stability

Manganese-based flow battery is desirable for electrochemical energy storage owing to its low cost, high safety, and high energy density. However, long-term stability is a major challenge for its application due to the generation of uncontrolled MnO2. To improve the cycle life, we propose a charge-induced MnO2-based slurry flow battery (CMSFB) for the first time, where nano-sized MnO2 is used as redox-active material. The reaction mechanism of MnO2 is discussed in detail. Benefiting from the electrostatic interaction, MnO2 particles are homogeneously dispersed in the electrolyte during the charge process and contact sufficiently with the reaction sites of the electrode during the discharge process. As a result, the novel CMSFB exhibits coulombic efficiency of over 99% and energy efficiency of over 85% at a current density of 40 mA cm−2 and can run stably over 1000 cycles without capacity decay. This work opens new opportunities for the development of manganese-based flow batteries and slurry flow batteries.