Dissolution Of Manganese Oxides Research Articles

Simultaneous Oxidation of Bromide and Dissolution of Manganese Oxide Induced by Freezing.

This study demonstrates that the oxidation of bromide by birnessite (δ-MnO2) results in the concurrent production of soluble manganese (Mn(II)) and reactive bromine (RBr) species in frozen solutions, a process not observed in aqueous solutions. This enhanced oxidation in ice is attributed to the concentration of protons, birnessite, or bromide in the ice grain boundary region. Furthermore, different types of commercial manganese oxides can also oxidize bromide to RBr and release Mn(II) in ice. The presence of fulvic acid (FA) further increases the simultaneous production of RBr and Mn(II) in ice, accompanying the formation of organobromine compounds (OBCs). In frozen δ-MnO2/Br-/FA system, a significant increase in OBCs, mainly highly unsaturated and phenolic compounds, was detected using Fourier transform ion cyclotron resonance mass spectrometry. A marked contrast was observed in the number of OBCs formed in frozen solutions (853 and 415 OBCs at initial pH 3.0 and 5.8, respectively) compared to their aqueous counterparts (11 and 23 OBCs). These findings introduce a new pathway for the formation of RBr, Mn(II), and OBCs in ice, highlighting the need for further research on the environmental fate of bromide and manganese.

Ultralong Bistable, Electrolytic MnO2-Based, Electrochromic Battery Enabled by Porous, Low-Barrier, Hydroxylated TiO2 Interface.

Electrochromic (EC)battery technology shows great potential in future "zero-energy building" by controlling outdoor solar transmission to tune heat gain as well as storing the consumed energy to reuse across other building systems. However, challenges still exist in exploring an electrochemical system to satisfy requirements on both ultra-long optical memory (also called bistability) without continuous power supply and high energy density. Herein, an ECbattery is proposed to demonstrate ultra-long bistability (>760h) based on the reversible deposition and dissolution of manganese oxide (MnO2) without the addition of any mediators. A porous low-barrier hydroxylated titanium dioxide (TiO2) interface is incorporated to synergistically enrich Mn2+-affinity active sites for deposition and effectively reduce the electron transport barrier of MnO2 for dissolution, thereby significantly improving the reversibility, high optical modulation (60.2% at 400nm), and energy density (352mAhm-2). The modification strategy is also verified on the cathode-less button cells with a much higher average coulombic efficiency (99.9%) compared to the batteries without the porous hydroxylated TiO2 interface (74.6%). These achievements lay a foundation for advancements in both electrochromism and Zn-Mn aqueous batteries.

Ultrathin ZnO coating layer to boost the electrochemical reaction kinetics of MnO cathode for advanced aqueous zinc-ion batteries

Although conventional carbon-based materials and metallic oxide coating on manganese oxides (MnO) cathodes have been extensively researched, there are still some issues, including low electron conductivity, sluggish ions diffusion kinetics and inferior cycling stability, that need to be addressed through material modification. In this work, a simple atomic layer deposition strategy is proposed to fabricate ZnO-coated MnO (MnO@ZnO) as cathode for aqueous zinc-ion batteries. Benefiting from the heterogenous interface between ZnO and MnO, a strong built-in electric fields generated, which accelerates the electron transport and promotes a fast reaction kinetics. Additionally, the ZnO coating layer effectively alleviate the dissolution of MnO and also boost its electrical conductivity. In contrast to the pristine MnO, MnO@ZnO exhibits enhanced specific capacity of 350 mA h g−1 at 0.1 A g−1 and excellent longterm stability. In addition, the reaction mechanism is further comprehensively verified through various ex-situ characterization analyses. This work offers a simple coating method to boost electrochemical energy storage of MnO, which is of great significance for the design of cathodes with excellent performance.

Sustainable porous biochar coated MnO2 composites as the cathode in aqueous Zn/Mn batteries

Sustainable development is the theme of the current era, and the reutilization of resources and clean energy are the keys to achieve it. Zn/Mn batteries had become a research hotspot due to its advantages of safety and efficiency, but the poor conductivity and the dissolution of manganese oxides restrict the further development of the batteries. Herein, we put forward a strategy to form a uniform graphitized carbon layer with porous structure on the MnO2 by a simple hydrothermal reaction from pistachio shell, which immobilizes MnO2 and effectively inhibits its dissolution into the electrolyte. The electrochemical results shows that the specific capacity of biochar composites cathode reaches 292.9 mA h g−1 after 50 stable cycles at a current density of 100 mA g−1, which is three times higher than that of the non-coated MnO2 cathode (92.5 mA h g−1). This unique porous material with high conductivity provides some new ideas for the modification of Mn-based zinc ion batteries and the sustainable reuse of biological resources.

The effect of Fe3+ ions on the electrochemical behaviour of ocean manganese nodule reduction leaching in sulphuric acid solution.

The effect of Fe3+ ions on the ocean manganese nodule reductive leaching in imitated sulphuric acid solutions was investigated. This work is presented in two courses, including the influence of Fe3+ ions on valuable metal extraction and the electrochemical reductive dissolution of manganese nodules. The results show that the beneficial effects of Fe3+ ion can be interpreted based on two aspects: the first is the acceleration caused by the active transformation of Fe3+/Fe2+ pair, and the second is the hydrogen ion buffer action generated by Fe3+ ion hydrolysis on the surface. On one side, Fe3+ ion could lessen the hydrogen consumption happening at the interface layer of the nodule supported by the leaching test and cyclic voltammetry results. On the other side, Fe3+ ions could be converted into Fe2+ ions and then preferentially reduce manganese oxide leading to an acceleration of the charge transfer reaction of the manganese nodule based on cyclic voltammetry, polarization, and impedance analysis results. The reduction leaching of manganese nodules in sulphuric acid solution is mainly controlled by the electrochemical interface reduction corresponding to manganese oxide dissolution, and the active conversion of the Fe3+/Fe2+ couple affects the dissolution of high valence manganese oxide.

In-situ electrochemical induced artificial solid electrolyte interphase for MnO@C nanocomposite enabling long-lived aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (AZIBs) have attracted widespread attention as a sustainable energy storage system owing to the safe aqueous electrolyte. Manganese-based materials are potential cathodes for AZIBs, whereas, the dissolution of manganese would result in the significantly decline of capacity and unsatisfied lives. Herein, an in-situ electrochemical induced artificial solid electrolyte interphase (SEI), (Zn(OH)2)3(ZnSO4)(H2O)5 nanoflakes, is discovered to generate and coat on the surface of MnO@C in the initial charging process which could prevent the direct contact between the electrolyte and electrode with the result of inhibiting the excessive dissolution of manganese oxides. Benefiting from the artificial SEI, MnO@C exhibits an extremely excellent cycle performance with 0.003% capacity decay per cycle over 10,000 cycles without Mn2+ additive in electrolyte. Moreover, MnO@C is proved to demonstrate a (de)intercalation reaction mechanism after the electrochemical activation process in initial charging process. The strategy proposed in this study provides a new proposal to develop high stable manganes oxide cathodes for AZIBs.

Manganese Oxide Nanoparticle Synthesis by Thermal Decomposition of Manganese(II) Acetylacetonate.

For biomedical applications, metal oxide nanoparticles such as iron oxide and manganese oxide (MnO), have been used as biosensors and contrast agents in magnetic resonance imaging (MRI). While iron oxide nanoparticles provide constant negative contrast on MRI over typical experimental timeframes, MnO generates switchable positive contrast on MRI through dissolution of MnO to Mn2+ at low pH within cell endosomes to 'turn ON' MRI contrast. This protocol describes a one-pot synthesis of MnO nanoparticles formed by thermal decomposition of manganese(II) acetylacetonate in oleylamine and dibenzyl ether. Although running the synthesis of MnO nanoparticles is simple, the initial experimental setup can be difficult to reproduce if detailed instructions are not provided. Thus, the glassware and tubing assembly is first thoroughly described to allow other investigators to easily reproduce the setup. The synthesis method incorporates a temperature controller to achieve automated and precise manipulation of the desired temperature profile, which will impact resulting nanoparticle size and chemistry. The thermal decomposition protocol can be readily adapted to generate other metal oxide nanoparticles (e.g., iron oxide) and to include alternative organic solvents and stabilizers (e.g., oleic acid). In addition, the ratio of organic solvent to stabilizer can be changed to further impact nanoparticle properties, which is shown herein. Synthesized MnO nanoparticles are characterized for morphology, size, bulk composition, and surface composition through transmission electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy, respectively. The MnO nanoparticles synthesized by this method will be hydrophobic and must be further manipulated through ligand exchange, polymeric encapsulation, or lipid capping to incorporate hydrophilic groups for interaction with biological fluids and tissues.

Water chemistry and estimation of background levels of elements in surface water bodies from a protected area in the vicinity of Fe deposits, Southeastern Amazon

This paper aimed to provide the knowledge of water chemistry and quality and background values of the elements in surface waters around the Fe-ore deposits of N3 and N4WSul of Serra dos Carajás, Brazil. Water samples were collected from 17 monitoring points monthly/quarterly between 2013 and 2016 and the elemental analyses were carried out using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The waters are slightly acidic to slightly alkaline in nature and are classified into “good” and “optimum” water quality category. Seasonal variation impacted water quality, with significantly higher content of metals (such as Fed, Fet, and Ald) during the rainy period that is due to more intense surface-runoff and leaching. Comparing with CONAMA 357/05/WHO limits, nonconformities were mainly observed for pH, Fe and Mn, and in some cases for Ald, Znt, Cud, Cdt and Znt, and were significantly higher in the N4WSul area than in the N3. Although, Fe and Mn mostly enter the water bodies from catchment weathering, the poor correlation between Fe and Mn indicated that their source and transport processes are different. In fact, elevated Mnd concentrations associated with low DO content in the dry period are explained by a reductive dissolution of manganese oxides via bacterial decomposition of OM. The background threshold values (BTVs) of elements were estimated by the upper 95% simultaneous limit (USL95; using ProUCL software) and the median ± 2 Median Absolute Deviation (mMAD) method, while the former was considered as the most suitable method for defining BTVs. The BTVs for Al(d), Fe (d), Mn and Zn are mostly exceeding the maximum limits stipulated by the legislation. However, since these areas are located in a protected region, these values are seen as representative of the natural conditions of the study area and reflect geogenic influence.

Laboratory spectral induced polarisation signatures associated with iron and manganese oxide dissolution because of anaerobic degradation

Degradation of organic chemicals in natural soils depends on oxidation-reduction conditions. To protect our groundwater resources we need to understand the degradation processes under anaerobic conditions. Available iron and manganese oxides are used as electron acceptors for anaerobic degradation and are reduced to the dissolved form of metallic cations in pore water. To monitor this process is a challenge, because anaerobic conditions are difficult to sample directly without introducing oxygen. A few studies have shown an impact of iron reduction on spectral induced polarisation (SIP) signature, often associated with bacterial growth. Our objective is to study the impact of iron and manganese oxide dissolution, caused by degradation of an organic compound, with spectral induced polarisation signatures.Twenty-six vertical columns (30 cm high, inner diameter 4.6 cm) were filled with a sand rich in oxides (manganese and iron) with a static water table in the middle. In half of the columns, a 2 cm high contaminated layer was installed just above the water table. As the contaminant degrades, the initial oxygen is consumed and anaerobic conditions form Every three days over a period of one month, spectral induced polarisation (twenty frequencies between 5mHz and 10 kHz) data were collected on six columns: three contaminated replicates and three control replicates. Chemical analysis was done on twenty columns assigned for destructive water sampling, ten contaminated columns and ten control.The results show an increase of the real conductivity associated with the degradation processes, independent of frequency. Compared with the pore water electrical conductivity in the saturated zone, the real conductivity measurement revealed the formation of surface conductivity before iron was released in the pore water. In parallel, we also observed an evolution of the imaginary conductivity in both saturated and unsaturated zones at frequencies below 1 Hz. Overall, the anaerobic reduction of iron and manganese oxide during the organic degradation increased both the conductive and polarisation component of the complex conductivity.

Facile electrochemical phosphatization of Mn3O4 nanosheet arrays for supercapacitor with enhanced performance

Phosphating manganese oxide (PMn) nanosheet arrays were synthesized via a facile and fast cathodic electrodeposition and following cyclic voltammetry phosphating as binder-free electrode materials for supercapacitors application. The morphology, chemical composite and structure characteristic of PMn nanosheets confirm that phosphate ions have been introduced to the surface of Mn3O4 nanosheets successfully. The as-prepared PMn electrode shows excellent electrochemical properties in 0.1 M Na2SO4 aqueous solution with a three-electrode system. The optimal specific capacitance of the PMn nanosheet arrays electrode at 5 mV s−1 (6.7 mF cm−2) is superior to that of the Mn3O4 nanosheets electrode (2.7 mF cm−2). Furthermore, the specific capacitance of obtained PMn nanosheets electrode reaches a retention of 87.6% after 5000 charge–discharge cycles at 0.08 mA cm−2, indicating great cycling stability. Therefore, modification of phosphate ions can effectively suppress the dissolution of manganese oxide and achieve a significant improvement in electrochemical property for supercapacitors with a manganese oxide electrode.

An Electrochemical Quartz Crystal Microbalance Investigation of Manganese Oxide Deposition and Dissolution in Sulfuric Acid Relevant for Zinc Electrowinning

The deposition and dissolution of manganese oxide from a sulfuric acid solution were investigated by conventional electrochemical techniques and EQCM on gold and platinum electrodes. The product of the oxidation was found by EQCM to be MnO2 at a higher potential (1.55 V), whereas a mixture between MnOOH and MnO2 was produced at a lower potential (1.45 V). An ECE mechanism involving the formation of MnOOH was proposed as the oxidation mechanism. A higher deposit porosity was obtained at the higher deposition potentials. The reduction mechanism was proposed to involve an electrochemical reduction of MnO2 to MnOOH, followed by a chemical reaction yielding Mn2+ and MnO2.

Effect of Ethanedioic Acid Additives on the Dissolution of Manganese Oxides in Sulfuric Acid Solution

The effect of ethanedioic acid additives on the rate of manganese(IV) oxide dissolution in sulfuric acid solutions was studied by kinetic and electrochemical methods. Interaction modes were established, and some details of the studied process mechanism were elucidated. Interaction schemes corresponding to the observed kinetic dependences were proposed.

Dissolution of Manganese Oxides of Various Compositions in Sulfuric Acid Solutions Studied by Kinetic Methods

The dissolution of manganese oxides in sulfuric acid solutions of various concentrations has been studied by kinetic methods. We have investigated the dissolution of manganese oxides of various compositions in sulfuric acid solutions of various concentrations. The composition of the manganese oxides and the sulfuric acid concentration have been shown to influence the dissolution rate. We have calculated kinetic parameters of the dissolution of manganese oxides in sulfuric acid solutions (dissolution rate, activation energy for dissolution, and reaction orders) and proposed a model for the dissolution of manganese oxides in sulfuric acid solutions.

Interaction mechanism and kinetics of ferrous sulfide and manganese oxides in aqueous system

The oxidation of ferrous sulfide (FeS) causes soil acidification and the release of toxic heavy metal ions. Manganese oxides usually participate in the oxidation of FeS and affect the geochemical cycling of elemental Fe and S. Here, we studied the mechanism and influencing factors of FeS oxidation by oxygen and manganese oxides including birnessite, todorokite, and manganite. Metallic cavity electrode was used to study the kinetics of the electron transfer between FeS and manganese oxides. Manganese oxide minerals, including birnessite, todorokite, and manganite, were synthesized and used for the oxidation of FeS. The oxidation products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, spectroscopy, high-performance liquid chromatography, and ion chromatography. The effects of pH and Fe(II) concentration on the oxidation rate of FeS were investigated. Metallic cavity electrodes filled with manganese oxides and FeS were respectively used as cathode and anode electrodes to study their reaction kinetics and the influence of crystal structure on the oxidation activity of manganese oxides. Elemental sulfur, SO4 2−, and lepidocrocite were formed as the intermediates during the oxidation of FeS by todorokite and oxygen in air. Low pH facilitated the dissolution of manganese oxides and the oxidation of FeS. When FeS suspension was oxidized by oxygen in air, the participation of todorokite decreased the degree of crystallinity of the newly formed ferric (hydr)oxides and accelerated the oxidation of polysulfide to S0 and S0 to SO4 2− via rapid adsorption and oxidation of Fe(II). The formation of Fe(II)/Fe(III) redox couple promoted electron transfer and resulted in increased oxidation rate of FeS. Fe(III) worked as the dominant oxidant under acidic conditions (pH 4.0) in ambient atmosphere. Todorokite accelerates FeS oxidation via adsorption and oxidation of Fe(II). Electrons are mainly transported by Fe(II)/Fe(III) shuttle at lower pH, and oxygen accepts electrons when pH is higher than 4.0. The oxidation activity follows the order of birnessite>todorokite>manganite. This work expands the understanding of the interactions and geochemical processes of FeS and manganese oxides, and provides a new technique to study the redox kinetics between soil mineral particles.

Enhanced Dissolution of Manganese Oxide in Ice Compared to Aqueous Phase under Illuminated and Dark Conditions

Manganese is one of the common elements in the Earth's crust and an essential micronutrient for all living things. The reductive dissolution of particulate manganese oxide is a dominant process to enhance mobility and bioavailability of manganese for the use of living organisms. In this work, we investigated the reductive dissolution of manganese oxides trapped in ice (at -20 °C) under dark and light irradiation (visible: λ > 400 nm and UV: λ > 300 nm) in comparison with their counterparts in aqueous solution (at 25 °C). The reductive dissolution of synthetic MnO₂, which took place slowly in aqueous solution, was significantly accelerated in ice phase both in the presence and absence of light: about 5 times more dissolution in ice phase than in liquid water after 6 h UV irradiation in the presence of formic acid. The enhanced dissolution in ice was observed under both UV and visible irradiation although the rate was much slower in the latter condition. The reductive dissolution rate of Mn(II)(aq) (under both irradiation and dark conditions) gradually increased with decreasing pH below 6 in both aqueous and ice phases, and the dissolution rates were consistently faster in ice under all tested conditions. The enhanced generation of Mn(II)(aq) in ice can be mainly explained in terms of freeze concentration of electron donors, protons, and MnO₂ in liquid-like ice grain boundaries. The outdoor solar experiment conducted in Arctic region (Ny-Ålesund, Svalbard, 78°55'N) also showed that the photoreductive dissolution of manganese oxide is enhanced in ice. The present results imply that the dissolution of natural minerals like manganese oxides can be enhanced in icy environments such as polar region, upper atmosphere, and frozen soil.

Influence of oxalic acid on the dissolution kinetics of manganese oxide

The kinetics and electrochemical processes of the dissolution of manganese oxides with various oxidation states in sulfuric acid solutions containing oxalate ion additives is studied under variable conditions (concentration, pH, temperature). The parameters favoring a higher degree of the dissolution of manganese oxides in acidic media are determined. The optimal conditions are found for the dissolution of manganese oxides in acidic media in the presence of oxalate ions. The mechanism proposed for the dissolution of manganese oxides in sulfuric acid solutions containing oxalic acid is based on the results of kinetic and electrochemical studies. The steps of the dissolution mechanism are discussed.

Applicability of selective dissolution of manganese oxide by acidified 0.1 M NH 2OH–HCl in Japanese soils

We investigated the extraction of manganese (Mn) oxides and iron (Fe) oxides from samples of three Andisols and seven other major Japanese soils with acidified 0.1 M NH 2OH–HCl in order to evaluate this method's applicability to selective dissolution of Mn oxide. The temporal changes in the amounts of Mn and Fe extracted revealed the following: 1. Mn oxides in non-volcanic-ash soil (low Alo + 1/2Feo) could be dissolved semi-completely upon extraction for 30 min, which is the customary extraction time. 2. Mn oxides in volcanic ash-containing soils (moderate or high Alo + 1/2Feo) continued to dissolve substantially after 30 min of extraction; 3. Fe oxides in all soils gradually dissolved throughout 4 h of extraction, although dissolution rates in volcanic ash-containing soils were much lower than in other soils. These results indicated that the solubility of Mn and Fe oxides in volcanic ash-containing soils were low, suggesting characteristic state of the oxides in these soils, and that the method is therefore unsuitable.

Synthesis of mesoporous polythiophene/MnO 2 nanocomposite and its enhanced pseudocapacitive properties

Mesoporous nanocomposite of polythiophene and MnO 2 has been synthesized by a modified interfacial method, aiming to develop electrode materials for supercapactitors with an enhanced cycle performance and high-rate capability. The N 2 adsorption/desorption isotherm test of the prepared hybrid indicates a high surface area and a typical mesoporous feature. A uniform hierarchical microstructure with submicron-spheres assembled from ultrathin nanosheet with diameters less than 10 nm has been confirmed by field-emission scanning electron microscopy and transmission electron microscopy. The employed interfacial synthesis is found to be advantageous to retard the overgrowth of nuclei. The retention of 97.3% of its initial capacitance after 1000 cycles at a charge/discharge rate of 2 A g −1 indicates excellent cycle performance of the nanocomposite electrode. At a high-rate charge/discharge process of 10 A g −1, the nanocomposite electrode retained 76.6% of its capacitance at 1 A g −1, suggesting good high-power capability. The important roles of polythiophene in the as-prepared nanocomposite are highlighted in terms of their functions on enhancing the electrical conductivity and constraining the dissolution of manganese oxides during charge–discharge cycles.

Synergistic Dissolution of Manganese Oxides as Promoted by Siderophores and Small Organic Acids

Recent studies have revealed that siderophores, biogenic chelating agents that strongly complex Fe(III) and other hard metals, may function in concert with low‐molecular‐mass organic acids (LMMOAs) to facilitate Fe (hydr)oxide dissolution via synergistic reactions. The siderophore desferrioxamine B (DFOB) may also participate in a number of chemical reactions at Mn (hydr)oxide surfaces. The goal of this study was to determine the rates and products of δ‐MnO2, a layer type Mn(IV) oxide, dissolution as promoted by LMMOA–DFOB mixtures. As with Fe (hydr)oxides, the rate of DFOB‐promoted dissolution of δ‐MnO2 is strongly influenced by the presence of the LMMOAs citrate and oxalate. In the presence of DFOB, citrate increases the dissolution rate relative to the sum of dissolution rates from corresponding single‐ligand systems by promoting both Mn(III)HDFOB+ complex formation and Mn(II) production in a pH‐dependent mechanism. In contrast, oxalate–DFOB mixtures produce predominantly Mn(II), with rates enhanced up to threefold from the sum of dissolution rates in single‐ligand systems at acidic pH values. We investigated possible mechanisms to describe this synergistic dissolution processes by building on observations of single‐ligand systems. These results suggest that biological exudation of LMMOAs in conjunction with siderophores may allow the selection of dissolution products, including regulation of the formation of potentially reactive aqueous Mn(III) complexes.

黄鉄鉱とのガルバニック反応によるコバルト・リッチ・クラストの浸出について

Cobalt-rich ferromanganese crusts (cobalt crust) contain strategic metals such as copper, nickel and cobalt. In order to recover cobalt, the reduction and dissolution of manganese oxide in crusts is required because cobalt is interlocked in manganese oxide. It is known that galvanic interactions between metal sulfide minerals and manganese nodule cause oxidation-reduction reactions on them. In this study, galvanic leaching of chemical analytical MnO2 and cobalt crust has been examined in the presence of pyrite.The measurement of rest potential indicated that MnO2 was nobler than pyrite. The dissolution of the MnO2 was accelerated in the presence of pyrite because MnO2 could act as cathode to be reduced in the galvanic couple MnO2/FeS2 .The dissolution of manganese and cobalt from the cobalt crust was enhanced in the presence of pyrite, and 84% of cobalt was extracted in three days while about 1% in the absence of pyrite in sulfuric acid solution of pH0.8. The leaching of the cobalt crust has been studied under various experimental parameters such as pH, amount of pyrite and particle size.