Manganese Fluoride Research Articles

Variable one-dimensional Manganese(III) chains with bridging fluoride: Synthesis, structures, and magnetic properties

Three new manganese(III) fluorides—Na2Ba3Mn4F20 (I), NaBa2Mn3F14(II), and NaBaMnF6(III)—were hydrothermally prepared. The crystal structures of these compounds contain variable one-dimensional (1D) manganese(III) chains with bridging fluoride. I features 1D cis chains composed of corner-sharing, alternating [MnF6]3- octahedra, while III contains trans chains, comprised by corner-sharing uniform [MnF6]3- octahedra. II, however, features 1D diamond-shaped chains, where two octahedra are linked to a single octahedron by trans-vertices. The successful preparation of single-crystal and powdered samples of the pure phase allows us to investigate into the relationship between their low-dimensional structures and magnetic properties. Magnetic measurements revealed a variety of magnetic properties at low temperatures, although predominant antiferromagnetic interactions were observed in the titled compounds at high temperatures. I possess canted antiferromagnetic (AFM) ordering, II shows ferrimagnetic-type long-range ordering, and III displays robust antiferromagnetic behaviour. Additionally, the strength of the magnetic coupling in I and III was analyzed based on the local geometry induced by the Jahn−Teller (JT) effect.

Designing a MnF2/MnO2 heterostructure for enhanced electrocatalysis in the oxygen reduction reaction

Studying noble-metal-free oxygen reduction reaction (ORR) catalysts is crucial for advancing fuel cells. Manganese dioxide (MnO2) has garnered widespread attention due to its convenient synthesis, low cost, high electrochemical activity, and diverse structures. However, it still faces challenges, such as poor conductivity and relatively lower inherent catalytic activity. In this study, a novel ORR electrocatalyst is introduced by constructing a heterostructure of manganese fluoride (MnF2) and MnO2, referred to as MnF2/MnO2. In a 0.1 M KOH solution, the ORR half-wave potential (E1/2) of MnF2/MnO2 is measured at 0.804 V, surpassing that of the original MnO2 catalyst (0.69 V). Compared to the MnO2 electrocatalyst, the MnF2/MnO2 heterostructure exhibits faster ORR reaction kinetics and a larger electrochemically active surface area. Density functional theory (DFT) calculations confirm that the MnF2/MnO2 heterostructure possesses enhanced intrinsic conductivity, facilitating the rapid transfer of ions of and electrons. Therefore, this study provides a promising pathway for enhancing the ORR catalytic activity of noble-metal-free electrocatalysts through rational heterostructure design.

Crystal structure of KMnPO4F with short- and long-range order inside the layered magnetic system.

Potassium manganese fluoride phosphate, KMnPO4F, has been obtained through mild hydrothermal synthesis and characterized by scanning electron microscopy, microprobe analysis and X-ray diffraction. The compound possesses an orthorhombic symmetry and chiral space group P212121 with a = 4.7884(2), b = 9.0172(4), c = 9.5801(4) Å, and Z = 4. Its crystal structure is composed of Mn3+O4F square pyramids sharing vertices with PO4 tetrahedra. This anionic framework is neutralized by K+ cations. As the temperature decreases, a short-range correlation state (Tmax ∼ 35 K) of KMnPO4F is formed, followed by the establishment of antiferromagnetic (AFM) long-range order at TN = 25 K. The latter is marked by sharp λ-type anomalies in both Fisher's specific heat d(χ‖T)/dT and heat capacity Cp. Pulsed magnetic field measurements on the single crystals identify the a axis as the easy magnetic axis and reveal a spin-flop transition at μ0Hspin-flop = 19 T. Density functional theory indicates that in variance with the three-dimensional network of KMnPO4F, it is a two-dimensional Ising magnetic system represented by buckled layers of integer spins S = 2 of Mn3+ ions. The strongest AFM exchange interaction, J1 ∼ -13 K, couples Mn3+ ions into linear chains running along the a axis. The chains themselves are ferromagnetically connected (J3 ∼ -4 K) within the ab plane. The interplane AFM exchange interaction (J2 ∼ -1 K) is weak and frustrated.

Insights into the conversion mechanism of the restriction strategy and self-activation enabled high-performance manganese fluoride anodes

A growth-limited and self-polymerizing carbon layer-coated fluoride electrode creates refined nanodomains during cycling that cooperate with amorphous phases to promote Li+ conduction, providing excellent cycling life and specific capacity.

Valorization of acid mine drainage into potable water and valuable minerals through membrane distillation crystallization

Owing to the rise in population growth and demands for the current living standards, mineral and water resources are depleting at the alarming rate. Also, the mineral–water-energy nexus raises a concern of high-quality water and mineral production at low costs. Membrane distillation crystallization (MDC) has emerged as a promising technology capable of simultaneous water and mineral recovery from wastewater or industrially discharged brines. Herein, the MDC was evaluated for recovery of water and precious minerals from acid mine drainage discharged from the mine tailings. High quality fresh water with 99.9 % salt rejection and permeate flux of 2.32 kg·m−2·h−1 was recovered at 52 °C feed inlet temperature. Also, feed temperatures were varied to determine their impact on mineral crystal morphology, size distribution and growth rate. Predominantly recovered minerals were gypsum, manganese fluoride, potassium iron oxide, nickel oxide hydroxide, sodium sulphate and dihydrogen sulphate. Orthorhombic crystal structure of mineral salts was attained at low feed inlet temperature (34 °C). Higher feed inlet temperatures (i.e. 41° C and 52° C) promoted co-crystallization giving rise to orthorhombic polymorph structures. Narrow crystal size distribution was reported at low water recovery factor (initial growth) for all temperatures. However, the particle size distribution broadened as the recovery factor increased. The crystal sizes ranged from 3.91 ± 0.97 µm to 14.04 ± 3.31. Remarkably, crystal growth rate increased with an increase in feed inlet temperature. These findings open a research direction towards economic recovery of mineral and water to supplement the existing shortages. With a myriad of crystals obtained from the MDC process, an additional operational unit is required to selectively recover high economic minerals.

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.

Electrolyte effect on electrochemical behaviors of manganese fluoride material for aqueous asymmetric and symmetric supercapacitors

Electrolyte effect on electrochemical behaviors of manganese fluoride material for aqueous asymmetric and symmetric supercapacitors

A Novel Procedure for Comprehensive Recovery of Zinc Fluoride, Manganese Fluorides, Manganese Dioxide, and Carbon Powder from the Electrode Powder of Spent Alkaline Batteries

A Novel Procedure for Comprehensive Recovery of Zinc Fluoride, Manganese Fluorides, Manganese Dioxide, and Carbon Powder from the Electrode Powder of Spent Alkaline Batteries

The Crucial Role of Sb2F10 in the Chemical Synthesis of F2.

The purely chemical synthesis of fluorine is a spectacular reaction which for more than a century had been believed to be impossible. In 1986, it was finally experimentally achieved, but since then this important reaction has not been further studied and its detailed mechanism had been a mystery. The known thermal stability of MnF4 casts serious doubts on the originally proposed hypothesis that MnF4 is thermodynamically unstable and decomposes spontaneously to a lower manganese fluoride and F2. This apparent discrepancy has now been resolved experimentally and by electronic structure calculations. It is shown that the reductive elimination of F2 requires a large excess of SbF5 and occurs in the last reaction step when in the intermediate [SbF6][MnF2][Sb2F11] the addition of one more SbF5 molecule to the [SbF6]- anion generates a second tridentate [Sb2F11]- anion. The two tridentate [Sb2F11]- anions then provide six fluorine bridges to the Mn(II) cation thereby facilitating the reductive elimination of the two fluorine ligands as F2.

Die entscheidende Rolle von Sb2F10 bei der chemischen Synthese von F2

AbstractDie Synthese von elementarem Fluor auf rein chemischem Weg ist spektakulär und galt länger als ein Jahrhundert als unmöglich. Im Jahr 1986 war man schließlich erfolgreich. Seitdem wurde diese wichtige Reaktion nicht weiter untersucht und ihr detaillierter Mechanismus blieb ein Rätsel. Die ursprüngliche Hypothese eines thermodynamisch instabilen MnF4, welches sich spontan zu einem Manganfluorid niedrigerer Oxidationsstufe und elementarem Fluor zersetzt, wird durch die bekannte thermische Stabilität von MnF4 in Frage gestellt. Diese scheinbare Diskrepanz konnte nun experimentell und durch quantenchemische Rechnungen aufgeklärt werden. Die reduktive Eliminierung von F2 aus MnF4 erfordert einen großen Überschuss an SbF5. Sie findet im letzten Reaktionsschritt statt, wenn sich an das Zwischenprodukt [SbF6][MnF2][Sb2F11] ein weiteres SbF5‐Molekül unter Bildung eines weiteren tridentaten [Sb2F11]−‐Anions anlagert. Die beiden [Sb2F11]−‐Anionen stellen dem Mn‐Atom so sechs verbrückende F‐Atome zur Verfügung und ermöglichen damit die reduktive Eliminierung der beiden terminalen Fluoridoliganden als F2.

Aggregation of Magnetic Nanoparticles in Biological Solvents Evaluated by HTS-SQUID Magnetic Immunoassay System

Magnetic nanoparticles (MNPs) have been studied for various medical applications by taking advantage of their unique magnetic properties. Magnetic immunoassay (MIA) is a technique for the rapid detection of target biomarkers by antigen-antibody reaction between antibody-modified MNPs and the target biomarker. In this study, we aim to improve the accuracy of the MIA, we evaluated the AC magnetic properties of MNPs in the biological solvents. To measure the magnetic signal of MNPs, we used the developed HTS-SQUID magnetic immunoassay system. First, we evaluated the instability of the HTS-SQUID magnetic immunoassay system using pellets of manganese (II) fluoride. The results show that the device instability due to operating time does not affect the measurement of magnetic signal changes in MNPs due to biological solvents. Since the magnetic properties of MNPs depend on particle size and viscosity, we measured the time evolution of the magnetic signal of Resovist in glycerin, human serum, sheep whole blood, and NaCl. It was found that the magnetic signal of Resovist decreased exponentially with ions contained in the solvent. The results are fitted as the exponential double function, suggesting that the magnetic signal of MNPs in biological solvents is affected by the aggregation of MNPs in the blood and that there are at least two steps in the mechanism of the aggregation.

Interfacial Engineering of Defect‐Rich and Multi‐Heteroatom‐Doped Metal–Organic Framework‐Derived Manganese Fluoride Anodes to Boost Lithium Storage

Manganese fluoride (MnF2) is a high‐performance lithium‐ion battery anode material with an excellent structural stability, low synthesis cost, and better manufacturing convenience. However, its low theoretical capacity (577 mAh g−1), weak conductivity of fluoride, and poor recyclability limit its practical application. Fortunately, oxygen vacancies (Ov) and heteroatomic doping are among the most promising strategies to modulate the inherent reduced electronic conductivity and kinetic response of electrode materials in order to boost their lithium storage capacity. Herein, self‐templating, self‐optimizing, and self‐supporting metal–organic framework template approach with the introduction of oxygen vacancies by substitution of exogenous heteroatoms is proposed, where triple heteroatom‐doped (N, O, and F) carbon‐encapsulated MOF‐derived manganese fluoride (Ov‐ZMF@NOFs) microstructures are designed. Interestingly, the exogenously introduced triple heteroatomic carbon matrix forms a fluffy three‐dimensional mechanical structure, interlaced conducting networks, efficient conducting pathways, and intense electrochemical dynamics at the periphery of the manganese fluoride nanoparticles. Benefiting from the above‐mentioned features, the Ov‐ZMF@NOFs exhibit expected electrochemical properties with ultra‐long recyclability (high reversible capacity of 419 mAh g−1 at 6 A g−1) and good rate performance (capacity of 232 mAh g−1 at a current density of 16 A g−1). Theoretical calculations underline the essential contribution of multiple heteroatoms doping in boosting the electrode conductivity and reducing the lithium‐ion migration energy barrier. Combining controllable vacancy engineering and heteroatom doping technology at the nanoscale provides a new philosophy and concept for the design and fabrication of next‐generation high‐energy lithium‐ion battery materials.

Formation of fringed carnation-like cobalt manganese fluoride hydroxide assisted by ammonium fluoride for supercapacitor applications

The binary transition metal oxides or hydroxides have received significant attention as potential materials in supercapacitor applications owing to their unique characteristics. In this study, a binary cobalt-manganese fluoride hydroxide-CoMn(OH)F is assembled successfully through the crucial assistance of an ammonium fluoride agent in an alkali source of hexamethylenetetramine (HMTA). At a rational design, the CoMn(OH)F with fringed carnation-like morphology obtains a specific capacitance of 541 F g −1 (at a current density of 1 A g −1 ) in a three-electrode system and cycling stability of 84% after 15,000 cycles. Furthermore, an asymmetric device CoMn(OH)F//activated carbon in a two-electrode system not only exhibits a remarkable specific capacitance of 135 F g −1 (at 0.4 A g −1 ), a high energy density of 39 Wh kg −1 , and a power density of 3.65 kW kg −1 but also maintains 91% of the initial capacitance after 10,000 cycling tests. These electrochemical performances demonstrate the considerable potential of the fluoride hydroxide CoMn(OH)F for supercapacitor applications. • CoMn(OH)F was formed via the key role of NH 4 F and the optimal precursor ratio. • CoMn(OH)F had a fringed carnation-like morphology. • Sample obtained synergistic effects of diffusion and capacitive-controlled process. • CoMn(OH)F//AC exhibited energy density 39 Wh kg −1 and power density 3.65 kW kg −1 .

Manganese fluoride as non-battery type anode for high performance Li-ion capacitors

Lithium-ion hybrid capacitors (LIHCs) are considered as promising next-generation energy storage devices with high energy density, large power density, and ultra-long cycle life. Anode material is an important factor affecting LIHCs. Here, we prepared hexagonal MnF2 with good morphology by solvothermal method. MnF2 was used as the anode to deliver a high specific capacity of 330 mAh g−1 after 1050 cycles at 0.1 A g−1. The specific capacity of MnF2 electrode, after 5000 cycles at 2 A g−1, can also reach 65 mAh g−1. LIHCs of MnF2 as anode and AC as cathode offer an excellent energy density of 81 Wh kg−1 at 95 W kg−1 and power density of 6840 W kg−1 at 26 Wh kg−1. Also, the capacity retention rate is 72% after 3000 cycles at 1 A g−1. The implementation of MnF2//AC, an energy storage device, extends the practical application of MnF2 in energy storage.

Efficient vapor-solid fluorination synthesis of MOF-derived MnF2/C for superior lithium storage with boosted kinetics

Transition metal fluorides have attracted widespread interest in recent years on account of their high energy density. However, their low conductivity and poor cyclability limit their development in next-generation power batteries. Herein, two methods (vapor-solid method and traditional calcination fluorination method) were used to successfully synthesize the manganese fluoride nanoparticle anode material attached on in-situ multi-vacancy carbon. Experimental data shows that vapor-solid method can provide more additional active sites, better electrical conductivity and more space to relieve volume expansion when compared to calcined fluorination. Pseudocapacitance analysis show their exceeding theoretical capacity phenomenon. By comparison, it is found that the spherical hollow manganese fluoride nanoparticles embedded carbon anode material obtained by the vapor-solid method exhibits excellent long cycle performance (450 loops at 1 A g−1, and a capacity of up to 864 mAh g−1, at a current density of 2 A g−1 1700 cycles with a capacity of up to 519 mAh g−1).

Hierarchical nanostructured MnF2 fabricated using rapid microwave synthesis as abnormal high-capacity of anode materials for Li-ion batteries

Tailoring various architectures of electrode material has been deemed a feasible route for improving the surface reactivity, the contact area between electrode and electrolyte, and enabling shortened electronic pathways to realize higher performance lithium-ion batteries. Here, we rapidly synthesized the manganese fluoride (MnF2) with various morphologies by microwave irradiation using ionic liquid as the fluoride source, soft template, and microwave absorber solvent. The hierarchical nanostructured MnF2 were optimized by controlling the purity of ionic liquid, microwave heating rate, and precursor concentration. The dominant factors influencing the morphologies of MnF2 were systematically investigated and relevant descriptions for the formation mechanism were suggested. Also, we demonstrated the abnormal high-capacity lithium-ion battery anode using the hierarchical nanostructured MnF2 anode based on the conversion mechanism. The prepared MnF2 anode yielded a maximum reversible specific capacity of 986 mAhg−1 at 0.1C after 30 cycles. This study provides a comprehensive understanding of the morphological control of the hierarchical structured MnF2 using the microwave-ionic liquid combination method for high-capacity lithium-ion battery anode.

Syntheses and Characterization of the Mixed-Valent Manganese(II/III) Fluorides Mn2F5 and Mn3F8

We obtained single crystals of the binary mixed-valent fluorides Mn2F5 and Mn3F8 using a high-pressure/high-temperature approach. Mn2F5 crystallizes isotypic to CaCrF5 in the monoclinic space group C2/c (No. 15), with a = 8.7078(8) Å, b = 6.1473(6) Å, c = 7.7817(7) Å, β = 117.41(1)°, V = 369.80(6) Å3, Z = 4, and mC28 at T = 173 K. Mn3F8 crystallizes in the monoclinic space group P21 (No. 4) with a = 5.5253(2) Å, b = 4.8786(2) Å, c = 9.9124(4) Å, β = 92.608(2)°, V = 266.92(2) Å3, Z = 2, and mP22 at T = 183 K and presents a new structure type. Crystal-chemical reasoning, CHARDI calculations, and quantum-chemical calculations allowed for the assignment of the oxidation states of the Mn atoms. In both bulk compounds, MnF2 was present as an impurity, as evidenced by powder X-ray diffraction and IR and Raman spectroscopy.

Variable Structures and One-Dimensional-Canting Antiferromagetism Found in Fluoride Selenates, A2Mn(SeO4)F3 (A = K, Rb, Cs).

Three new alkali-metal manganese fluoride selenates, A2Mn(SeO4)F3 (A = K, Rb, Cs), were prepared through hydrothermal redox reactions. The products consisted of one-dimensional polymeric anionic ∞[Mn(SeO4)F3]2- chains, where the A+ cations are connected by O and/or F atoms to form blocks with two-dimensional layers. A2Mn(SeO4)F3 (A= Rb, Cs) is isostructural with the monoclinic space group P21/c, while K2Mn(SeO4)F3 crystallizes in the orthorhombic space group Pbcn. A2Mn(SeO4)F3 (A = K, Rb, Cs) forms spin chains of Mn3+ with different Mn-F-Mn bridges, which showed canting antiferromagnetic behaviors. Single-crystal magnetic measurements revealed that the magnetic moments of the Mn ions were more canted for larger alkali-metal compounds in an antiferromagnetically ordered state.

An integrated analysis of sinkholes in Kadapa region, Andra Pradesh, India: Implication to pedology

Sinkholes are one of the common karst features of geographical formations, which come into existence due to the dissolution of underneath lime-rich formations and subsequent collapse of the ceiling of the holes. Since sinkholes are formed in agricultural lands, this study aimed to understand the impact of sinkhole formation on heavy metals and minerals by collecting samples from sinkholes from various localities of Kadapa District of the state of Andhra Pradesh in India. The heavy metals were determined by ICP-AES analysis and characterization of soils in sinkholes was carried out. The FTIR spectroscopic technique was utilized to identify the minerals present in sinkholes. The XRD and SEM techniques were used to assess clay mineral composition and particle size and morphology of soil samples, respectively. Following the available literature, the minerals were identified from the location or band position of peaks from the Infra Spectrum. The minerals found were Quartz, Cesium di alumino tri silicate hydrate, Natrolite (Cs), Sodium Rhodium Oxide, Cobalt Uranium, Cesium Manganese Fluoride Hydrate, Quartz alpha, alpha-Si O2, Di copper (I) oxide, Erbium Indium Silver. Subsequently, we assessed the consequence of heavy metal pollution on soil microorganisms in sinkholes. The total population of microorganisms (bacteria, fungi, actinomycetes) was found to be decreased with increasing concentration of heavy metals.Additional analysis identified the bacteria resistant to Zinc, Manganese, lead (2 mM), copper (5 mM) metals. In sum, the findings from our integrated analysis of sinkholes provide an understanding of local pedology of the Kadapa region in India with implications for safety measures, agriculture land management and productivity.

Manganese Fluoride Nanoparticles Synthesized by Microwave Irradiation Using Ionic Liquid–Ethylene Glycol Mixtures: Room-Temperature Photoluminescence, Crystalline Phase, and Morphology

The facile and rapid microwave-assisted method has been demonstrated to be effective in synthesizing manganese fluoride (MnF2) nanoparticles in binary mixtures of ethylene glycol and imidazolium-based ionic liquid containing fluorine, within a minute, without any surfactant and stabilizer. The effect of volume ratio of an ionic liquid in the binary mixtures with ethylene glycol and the length of the alkyl chain of imidazolium on the morphologies and crystalline structures of MnF2 was investigated. Two types of crystalline phases MnF2, P42/mnm rutile and P4̅2m space group, were synthesized depending on the volume ratio of EMIM BF4. The morphologies of rutile MnF2 clearly varied depending on what kind of ionic liquid was used in the synthesis. MnF2 nanoparticles and spherical nanoclusters assembled by nanospheres were synthesized when the used ionic liquid was OMIM BF4 and EMIM BF4, respectively. Clear room temperature photoluminescence (PL) spectra of MnF2 nanoparticles were observed at ambient pressure. The change of PL spectra depending on the crystalline phase was also observed. In this study, we report that the microwave-assisted method using ethylene glycol–ionic liquid binary mixtures is proper for synthesizing high-quality MnF2 nanoparticles with controllable crystalline phase and morphology.