Valence State Of Manganese Research Articles

Efficient manganese ammonia oxidation (Mnammox) and its influencing factors at low temperature: Metal oxide-mediated denitrification process in water bodies

This study explores the metal oxide-mediated NH4+-N reduction process: manganese ammonia oxidation efficiency, influencing factors and its resistance to low-temperature environments in water bodies. After 177d of stabilized startup of an up-flow reactor, NH4+-N removal efficiency was 63.51 %, total nitrogen (TN) removal rate was 0.021 kg/(m3.d), and effluent Mn2+ concentration was 1.503 mg/L, which was in dynamic equilibrium. X-ray photoelectron spectroscopy exhibited manganese valence state 3.29, similar to biological manganese oxidation. High-throughput sequencing revealed that phyla’s denitrification function increased relative abundance, and manganese-reducing bacterial genera appeared. The batch test showed that 5 mg MnO2 had NH4+-N removal at 85.01 %. After 44 days, NH4+-N removal efficiency was 77.47 %, effluent Mn2+ concentration was 3.280 mg/L, TN removal rate was 0.063 kg/(m3.d). The long-term effect of the influent load change on the denitrification and Mnammox efficiency at 25 ∼ 15 °C was examined. Effluent Mn2+ concentration was 1.811 mg/L was relatively stable. Manganese valence decreased from 3.29 to 3.20, Mn4+ decreased by 9.58 %, while Mn3+ and Mn2+ increased by 10.94 % and 1.37 %, respectively. A new phylum Thermotogota and genus SBR1031 appeared in the microbial community.

Regulating the Manganese Valence State Improves the Kinetic Properties of Manganese‐Based Cathodes

AbstractManganese (Mn)‐based lithium (Li)‐ion batteries with high energy density and low cost have recently attracted considerable attention. One drawback of Mn‐based batteries is the severe capacity attenuation caused by the Jahn‐Teller effect, which distorts the crystal structure and reduces the kinetics of Li‐ion insertion/extraction in the cathodes. In this study, the Mn valence state is regulated on the surface of Mn‐based oxide particles and oxygen vacancies are introduced to facilitate rapid Li‐ion transport and charge storage by adding succinonitrile (SN) to Mn‐based cathodes. Because of the reaction between SN and Mn‐based cathode particles, the contents of Mn3+ ions and oxygen vacancies increase, leading to an improvement in the Li‐ion kinetic properties of the cathodes as well as a reduction in the dissolution of Mn from the cathodes. By regulating the Mn valence state, Li‐ion and Li metal batteries with LiMn2O4 or Li‐rich Mn‐based layered oxide cathodes show significantly enhanced discharge capacity and improved cyclic performance. This study demonstrates that regulating the valence state of Mn ions is an effective strategy for enhancing the electrochemical performance of Mn‐based Li batteries and that adding SN to the cathodes is a cost‐effective method for mass production.

Study on the influence of different manganese sources on the formation of P2/β Bi-phase cathode materials for sodium ion batteries

This work focuses on the effect of the of Mn3+/Mn4+ ratio in the reactants on the structure and electrochemical properties of NaMn0.9Cu0.1O2 cathode materials for sodium-ion batteries. By systematically varying the manganese valence states in the reactants, we observed a phase transition from the β-phase to the P2-phase with increasing Mn3+ concentrations in the reactants, contrary to the expected favorability of the β-phase at higher Mn3+ levels. This finding suggests a complex interplay between the valence states of the reactants and phase formation mechanisms, which needs further investigation. Additionally, electrochemical testing indicated that the phase composition significantly impacts the electrochemical performance of the material. Specifically, the M0 sample, possessing the optimal P2/β ratio, exhibited excellent electrochemical performances, achieving a high initial discharge capacity of 155.1 mA h g−1 and remains 88.1 % after 40 cycles. These results emphasize the importance of precursor selection and valence management in the development of high-performance cathode materials for sodium-ion batteries.

Mechanistic insights into δ-MnO2/biochar–activated persulfate-treated wastewater containing antibiotics and heavy metals: Nonradical pathway and pivotal role of Cu(Ⅱ) at low temperature

Herein, we present a high efficiency system based on biochar loaded with layered manganese dioxide to remove tetracycline and heavy metals from livestock wastewater. Under the optimal conditions, the degradation efficiencies of TC in the δ-MnO2/BC/PS system were 85.5% at 25 °C and 38.5% at 5 °C. Radical quenching experiments revealed that radical reactions in the δ-MnO2/BC/PS system were weak under 15 °C. Adsorption degradation experiments showed that the system maintained good adsorption performance at 5 °C. Galvanic cell experiments and cyclic voltammetry showed that the δ-MnO2/BC material had good electrochemical activity and high stability in response to temperature, indicating that TC was degraded by a nonradical pathway that was not limited by temperature, such as electron transfer. Copper ion was important coadsorbent and coactivator of the reaction system. Furthermore, FTIR, XPS, and X-ray diffraction (XRD) analyses showed that Cu(II) in the system was involved in changing the manganese valence state in the δ-MnO2/BC material and increasing the –OH content of BC. Comparison of the different products generated during metabolic testing revealed that the reaction pathway of the system at low temperature (5 °C) differed from that at normal temperature (25 °C). The δ-MnO2/BC material demonstrated good removal ability for antibiotics and heavy metals at normal and low temperatures in actual biogas slurry. The study provides insight for improving the efficiency of environmentally friendly treatments of aquaculture wastewater in cold regions, which is of great significance for resource utilization.

Significance of Engineering the MnO6 Octahedral Units to Promote the Oxygen Reduction Reaction of Perovskite Oxides.

The electronic structure and geometric configuration of catalysts play a crucial role to design novel perovskite-type catalysts for oxygen reduction reaction (ORR). Nowadays, many studies are more concerned with the influence of electronic structure and ignore the geometric effect, which plays a nonnegligible role in enhancing catalytic performances. Herein, this work regulates the MnO6 octahedral tilting degree of LaMnO3 by modulating the concentration of Y3+, excluding the electronic effect from the valence state of manganese. Plotting the MnO6 octahedral tilting degree as a function of concentration of Y3+ produces a volcano-shaped plot. The octahedral tilting can reduce the Mn-O covalency, generating more highly active Mn3+ and oxygen vacancies during ORR process. The specific activity has a positive correlation with octahedral tilting degree. Meanwhile, the octahedral tilting stabilizes Mn-O interactions during ORR process and promote stability. Based on experimental results and DFT calculations, octahedral tilting alters the rate-determining step (RDS) and decrease the energy barrier. Subsequent extended experiment confirms that octahedral tilting is the key factor to affect the catalytic performances.

MnF2 Surface Modulated Hollow Carbon Nanorods on Porous Carbon Nanofibers as Efficient Bi-Functional Oxygen Catalysis for Rechargeable Zinc-Air Batteries.

Developing highly efficient bi-functional noble-metal-free oxygen electrocatalysts with low-cost and scalable synthesis approach is challenging for zinc-air batteries (ZABs). Due to the flexible valence state of manganese, MnF2 is expected to provide efficient OER. However, its insulating properties may inhibit its OER process to a certain degree. Herein, during the process of converting the manganese source in the precursor of porous carbon nanofibers (PCNFs) to manganese fluoride, the manganese source is changed to manganese acetate, which allows PCNFs to grow a large number of hollow carbon nanorods (HCNRs). Meanwhile, manganese fluoride will transform from the aggregation state into uniformly dispersed MnF2 nanodots, thereby achieving highly efficient OER catalytic activity. Furthermore, the intrinsic ORR catalytic activity of the HCNRs/MnF2@PCNFs can be enhanced due to the charge modulation effect of MnF2 nanodots inside HCNR. In addition, the HCNRs stretched toward the liquid electrolyte can increase the capture capacity of dissolved oxygen and protect the inner MnF2, thereby enhancing the stability of HCNRs/MnF2@PCNFs for the oxygen electrocatalytic process. MnF2 surface-modulated HCNRs can strongly enhance ORR activity, and the uniformly dispersed MnF2 can also provide higher OER activity. Thus, the prepared HCNRs/MnF2@PCNFs obtain efficient bifunctional oxygen catalytic ability and high-performance rechargeable ZABs.

Multivalent manganese-based composite materials for sodium energy storage in ether electrolyte

The structural collapse of manganese-based materials during cycling greatly restricts its development in Sodium-ion batteries (SIBs). Hence, two-phase structures with different manganese valence states are designed based on an alternating voltage approach to mitigate volume expansion via two-phase coordination. Here distinct manganese valence states of precursor are driven via atmosphere. And in the following heat-induced phase transition, the elemental valence state is the decisive key for the structural and compositional evolution. In a batch of synthetic materials, MnO/MnS with bivalent states of manganese performs best as expected. Furthermore, NaPF6 in DEGDME is taken to replace the traditional carbonate electrolyte which is prone to produce unstable SEI film and leading to polarization. A series of characterization methods confirm that the energy barrier of charge transfer at the interface between electrolyte and electrode is the main factor determining the electrochemical characteristics of the interface and thus the energy storage performance. Ultimately, carbon dots (CDS) with rich functional groups are introduced in an effort to further promote the conductivity of MnO/MnS, and the in-situ generated C-S-Mn bond enhances electrochemical kinetic behaviors. This work provides an approach for designing manganese-based materials and the selection of electrolytes in sodium energy storage.

New Approach for Direct Determination of Manganese Valence State in Ferromanganese Nodules by X-ray Fluorescence Spectrometry

A new X-ray fluorescence technique is proposed as an alternative to the labor-consuming volumetric method for the estimation of manganese valence state in ferromanganese nodules. The approach is based on the measurement of the relative intensities of some X-ray fluorescence spectrum characteristic spectral lines and satellites (MnKβ5 and MnKβ′) preconditioned by electron transfer from the valence shell. Calibration curves were created using manganese oxide samples (MnO, Mn2O3, MnO2) and 12 certified reference materials of ferromanganese nodules, cobalt-bearing ferromanganese crusts, and manganese ores with certified (or determined by approved methods) total and tetravalent manganese content. The presence of high iron content was taken into account. A set of oceanic ferromanganese nodules samples collected in the Magellan Seamounts (Pacific Ocean) were analyzed. Differences between the results of the X-ray fluorescence method and volumetric techniques for tetravalent manganese content were 4.9 rel.%, which is comparable with the accuracy of the volumetric technique (3.6 rel.%).

New high temperature negative temperature coefficient thermistors in Mg0.5Mn0.5AlFeO4 ceramics

For high temperature thermistor applications, the MgAl2O4 exhibits poor conductivity and requires high sintering temperature for ceramic densification. In this study, we have reported on the preparation and characterization of spinel Mg0.5Mn0.5AlFeO4 ceramics by solid solution modification. The resultant ceramics exhibit a combination of high temperature stability and semi-conductivity, which are the characteristics of MgAl2O4 and MnFe2O4. The material has a moderate thermistor constant, which is in favor of application at high temperatures and a wide temperature range. The electrical conductivity is due to the small-polaron hopping in different valence states of manganese and iron ions. Our findings demonstrate a promising approach to extend the applicability of spinel ceramics for high temperature thermistors.

Hg0 removal performance of magnetic raffinate slag-based sorbents: Mechanism study on oxidation modification

The sulfur-containing carbon-based sorbent was regarded as potential sorbent for the removal of toxic elemental mercury (Hg0). However, due to its lower reaction temperature and the stronger Hg0 oxidation capacity of oxides at higher temperature, oxidation modification on sulfur-containing raffinate slag-based sorbents was proposed in the study. The effects of O2, H2O2 and KMnO4 oxidation modification on Hg0 removal performance and physicochemical properties of sorbents were investigated. The oxidation modification had little effect on pore structure of sorbents, but mainly affected the content and valence state of sulfur and oxygen elements. Compared with H2O2 oxidation, KMnO4 oxidation was more conducive to forming active lattice oxygen (Oα). The valence state of manganese bound with Oα influenced Hg0 capture a lot, and Oα in MnO2 showed strong oxidation capacity to Hg0. Active S22−and Oα in A850-0.1KMnO4-12h sorbent could both promote the Hg0 removal with HgS and HgO formed in used sorbent. The saturated magnetization of A850-0.1KMnO4-12h sorbent was 5.39 emu·g−1, making it possible to separate mercury-containing sorbents from fly ash. It showed good resistance to low concentration of SO2, and NO could promote its Hg0 removal ability. Meanwhile, KMnO4 oxidation successfully improved the Hg0 removal performance at higher reaction temperature and gas hourly space velocity.

Biomass-derived hierarchically porous carbon-supported MnOx enable fast ion/electron transport at high operating voltages

Metal oxide/carbon composite systems have been investigated extensively for fabrication of supercapacitors. To obtain high capacitance, a thick pseudocapacitive layer loaded on a conventional carbon support inevitably leads to high dead volume and poor rate/power characteristics. Herein, we propose a strategy with biomass-derived hierarchical porous carbon as supports to bridge two critical but mutually exclusive properties of supercapacitors: high capacitance and rapid ion/charge transport. Highly dispersed deposition of nanosized MnO2 and MnO on hierarchically porous carbon were achieved through slow redox reaction controlled by gradual hydrolysis of fibrous polymers remaining in the hydrothermal carbon. High surface area, ultrathin pseudocapacitance layer, and wide voltage window (1.6–2 V) improve the synergy between the high energy density of MnOx and the high power density of porous carbon. The maximum energy density of 40.95 Wh kg−1 (at 180 W kg−1) and power density of 9000 W kg−1 (at 23.85 Wh kg−1) was realized for the assembled asymmetric/symmetric supercapacitors in aqueous electrolytes. More importantly, a cycle life comparable to that of carbon-based double-layer capacitors (95.6% capacitance retention after 10,000 charge/discharge cycles) could be achieved. Furthermore, density functional theory (DFT) was also conducted to elaborate the differences between manganese valence states for in-depth understanding. The characteristics of low cost, environmental friendliness, and excellent performance highlight the great promise of biomass waste in designing carbon supports for electrochemical applications.

Manganese valence state regulated beta‑manganese dioxide porous nanoflowers as high-performance cathodes at large current densities for aqueous magnesium ions battery capacitor

Aqueous magnesium ion battery capacitor (AMIBC) is a promising sustainable clean and safe energy storage system to replace lithium-ion batteries, due to its similar electrochemical characteristics to lithium, low cost and safety. In this work, beta‑manganese dioxide (β-MnO2) porous nanoflowers with Mn valence modulation are demonstrated to be a promising cathode material for AMIBC. Due to the promotion of Faradic reaction by Mn3+ introduction and the high capacitive absorption from its high specific surface area, sample with 16 % Mn3+/Mn can exhibit a high specific capacity of 260 mAh g−1 at 0.2 A g−1 in 1 M MgSO4 electrolytes with greatly improved rate and cycle performance at large current densities. As assembled with active carbon (AC), β-MnO2//AC AMIBC shows a high energy density of 60.8 W h kg−1 at 180 W kg−1 with a cycling stability of 74.1 % after 3500 cycles at 2 A g−1.

Crystal growth of ReCa3Mn3O3(BO3)4 (Re = Gd, Y) gaudefroyite: Phase sequence and equilibrium study in multi-component fluxes

The work is aimed at studying the crystallization of ReCa3Mn3O3(BO3)4 (Re = Gd, Y) borates with the gaudefroyite structure in different flux systems. Gaudefroyites are promising materials in the field of spin ice and magnetocaloric effect. The study has been performed on systems based on the following solvents: Bi2Mo3O12-Na2B4O7-B2O3, Bi2O3-Na2B4O7-B2O3, Bi2O3-BaO-Na2B4O7-B2O3, Li2WO4-Li2O-B2O3. The influence of the solvent components on the sequence of high-temperature crystallizing phases has been studied. The feature of Mo- and W-containing fluxes consisting in the formation of stable chemical bonds of the M2+Mo(W)O4 (M = Ca, Mn) molybdate or tungstate types has been revealed which prevents the formation of gaudefroyite type bonds. An approach has been suggested for changing the sequence of the crystallizing phases which consists in the super saturation of molybdate (tungstate) bonds by Na+ or Li+ cations up to the formation of delafossite-type bonds (Li(Na)-Mn-O phase) with higher manganese valence states Mn3+ and Mn4+. The optimization of the growth conditions of ReCa3(MnO)3(BO3)4 (Re = Gd, Y) gaudefroyite crystals has allowed one to obtain single crystal samples with the size up to 0.8 × 0.8 × 5 mm3. The structural characterization and chemical composition of all the obtained phases are also presented.

Order-disorder transition mechanism for high-capacity amorphous anodes of lithium-ion batteries

As potential electrode materials with a high specific capacity, vanadium-based amorphous materials have attracted a great deal of attention in lithium-ion batteries (LIBs). Herein, different valence states of manganese, MnO2 and Mn2O3 are utilized to replace V in V2O5. The results reveal that the MnO2-substituted glass exhibits a high initial capacity of 1029.8 mAh g−1 and preserves a capacity of 210.3 mAh g−1 after 50 cycles at the current density of 10 mA g−1. After Mn substitution, the content of V4+ increases from 15.6% to 57.3% and 60.9%. Moreover, it is demonstrated that the increase in average valence state of Mn effectively suppresses the Jahn-Teller effect in the local structure. For instance, both VO and Li3MnO4 nano-crystals are identified after 50 charge/discharge cycles, whose synergistic effect with the amorphous matrix ameliorates the conductivity of the electrode and enhances the reaction kinetics. Furthermore, density functional theory calculations reveal that the substitution of Mn moves the Fermi level close to the conduction band to reduce the bond gap, corresponding to an increase in conductivity, and facilitates the charges transfer from Li to O contrarily, improving the cyclic stability of the anode material. The order-disorder transition mechanism presents a novel perspective for the selection of materials for LIBs.

Evidence for the oxidation of Earth\u2019s crust from the evolution of manganese minerals

Analysis of manganese mineral occurrences and valence states demonstrate oxidation of Earth’s crust through time. Changes in crustal redox state are critical to Earth’s evolution, but few methods exist for evaluating spatially averaged crustal redox state through time. Manganese (Mn) is a redox-sensitive metal whose variable oxidation states and abundance in crustal minerals make it a useful tracer of crustal oxidation. We find that the average oxidation state of crustal Mn occurrences has risen in the last 1 billion years in response to atmospheric oxygenation following a 66 ± 1 million-year time lag. We interpret this lag as the average time necessary to equilibrate the shallow crust to atmospheric oxygen fugacity. This study employs large mineralogical databases to evaluate geochemical conditions through Earth’s history, and we propose that this and other mineral data sets form an important class of proxies that constrain the evolving redox state of various Earth reservoirs.

Phase and microstructure control of electrodeposited Manganese Oxide with enhanced optical properties

Mn3O4 and Mn2O3 were synthesized by potentiostatic electrodeposition from a de-aerated manganese acetate and sodium sulfate electrolytic bath, followed by annealing. The electrodeposition parameters (including applied potential, precursor concentration, pH, temperature) and the thermal treatment conditions were investigated to obtain the best control over microstructure and stoichiometry of manganese oxides. We found that the applied voltage is the key parameter affecting the valence state of initial amorphous manganese while the thermal treatment leads to crystallization and tuning of optical properties without substantially changing the morphology. The as-electrodeposited manganese oxides are X-rays amorphous, while two different crystalline phases, Mn3O4 and Mn2O3, were obtained after the thermal treatment depending on the applied voltage. Through the analysis of TEM cross section images, a fiber-like growth was observed for Mn3O4, while Mn2O3 presented a less porous-more compact microstructure. The optical properties were investigated, resulting in an enhancement in the charge separation properties of the thermally treated manganese oxides, reflected by nearly a 40 % reduction in the photoluminescence peak intensity. We believe that these finding will be useful in the future development of environmental friendly manganese oxide-based photoelectrochemical systems.

Enhancing Electrochemical Performance of Layered Birnessite Materials with Metal Ions Intercalated Cation for Aqueous Zinc-Ion Batteries

Recently, rechargeable aqueous-based batteries become promising candidates owing to their cost-effectiveness, environmental friendliness, and high safety. Furthermore, aqueous electrolytes provide high ionic conductivity and also provide facile manufacturing processes. Among all rechargeable aqueous-based batteries, aqueous Zn-based batteries (AZBs) exhibit low redox potential (-0.76 V vs standard hydrogen electrode (SHE)) and high theoretical capacity of the Zn metal anode (840 mAh g-1), leading to superior energy density as compared to other low-cost batteries. However, there are many challenges remaining for AZBs including the cathode dissolution limiting their practical applications. Manganese-based oxides are promising cathode materials for AZBs due to their low cost and low toxicity. Moreover, there are various valence states of manganese (Mn2+, Mn3+, Mn4+, and Mn7+) and different crystallographic structures, including ɑ-, β-, γ-, δ-, and λ-MnO2. According to promising manganese-based oxides, δ-MnO2 is one of the most interesting materials because it exhibits a high theoretical capacity of about 616 mAh g-1. Also, the δ-MnO2 or layered structure provides a facile Zn2+ insertion, leading to high-rate capability. However, this structure is facing collapse issue during cycling, resulting in poor stability. In this work, we demonstrate the facile synthesis method of δ-MnO2 and investigate the effect of intercalated cations on its electrochemical performance towards AZBs. The as-fabricated Zn-MnO2 battery achieves 200 mAh g-1 at 0.1 A g-1 and high stability up to 68% after 200 cycles at 1 A g-1.

X-ray Microspectroscopy and Ptychography on Nanoscale Structures in Rock Varnish

X-ray microspectroscopy is a powerful analytical method in geoscientific and environmental research as it provides a unique combination of nanoscale imaging with high spectroscopic sensitivity at relatively low beam-related sample damage. In this study, “classical” scanning transmission soft X-ray microscopy (STXM) with X-ray absorption spectroscopy and the recently established soft X-ray ptychography are applied to the analysis of selected rock varnish samples from urban and arid desert environments. X-ray ptychography enhances the spatial resolution relative to STXM by up to 1 order of magnitude. With its high chemical sensitivity, it can resolve nanoscale differences in valence states of the key varnish elements manganese (Mn) and iron. Our results emphasize the complex nanoarchitecture of rock varnish as well as the diverse mineralogy of the Mn oxy–hydroxide matrix and its embedded dust grains. In contrast to the fast-growing urban varnish, the slow-growing arid desert varnish revealed a remarkable nanoscale stratification of alternating Mn valence states, providing hints on the layer-wise and still enigmatic growth process.

Multiple-Valence and Visible to Near-Infrared Photoluminescence of Manganese in ZnGa2O4: A First-Principles Study

The transition metal manganese is attractive for magnetism and luminescence engineering due to the nontrivial interplay of charge, spin, lattice, and orbital freedom degrees. Here, we report the manganese site occupancy and valence states by taking experimental synthesis conditions into consideration and the optical features of target intra-atomic Mn2+, Mn3+, and Mn4+ in the framework of density functional theory in a prototype spinel ZnGa2O4 host. The formation energy results show that Mn2+ dominates in tetrahedral ligands at the Zn2+ site and Mn3+ and Mn4+ dominate in octahedral ligands at the Ga3+ site under the corresponding different chemical potential conditions, and the distortion of the local coordination environment of Mn3+ in octahedral ligands due to the Jahn–Teller effect is studied in detail. The excited-state equilibrium geometries and energies are obtained via spin or orbital occupancy constraints, which are further complemented by the Tanabe–Sugano diagram to predict the energy spectra and to interpret the experimental results on Mn2+, Mn4+, and Mn3+. In particular, the competition of 5T2 and 1T2 excited states and the relaxation processes leading to near-infrared luminescence of rarely reported Mn3+ are analyzed. First-principles calculations complemented by the Tanabe–Sugano diagram analysis may serve as an effective and predictive tool for exploring valence states, energy structures, and luminescence of complexes containing 3dn transition-metal ions.

Fractal polymer islands on top of ferromagnetic La2Ni0.6Mn1.4O6 thin films

The formation of the crystalline organic polymer (OP) islands on top of double perovskite ferromagnetic La2Ni1–xMn1+xO6 (x = 0.4) thin films by RF sputtering is reported. The presence of randomly ramified organic polymer islands for film grown on top of SrTiO3 and LaAlO3 substrates suggest the fractal growth. The stability of fractal OP islands is tested by an in-situ oxygen annealing process as function of the annealing temperature. The evolution of the fractal structure of OP islands is followed in parallel with the evolution of structural and magnetic properties of LNMO thin films. The modification of the manganese valence state due to the presence of organic polymer fractals is studied by means of X-ray photoemission microscopy.