Structure Of Manganese Oxide Research Articles

Synergistic effects of prokaryotes and oxidants in rapid sand filters treatment of groundwater versus surface water: Purification efficacy, stability and associated mechanisms

Effective elimination of manganese (Mn) and ammonium (NH4+-N) from drinking water is still challenging. Utilizing oxidants to improve the simultaneous removals of Mn and NH4+-N from rapid sand filter (RSF) systems has been extensively studied. However, the prokaryotes containing in the water geochemical properties greatly affected the RSF performance. In this study, groundwater and micro-polluted surface water were used to compare with/without potassium permanganate (KMnO4) assistant on the contaminants removals and system stability. Results showed that KMnO4 reduced the start-up period of RSF for treating groundwater and surface water to 20 and 41 days, respectively, with excellent Mn removal rates (>97%). The relative abundance of efficient ammonia-oxidizing bacteria (Nitrospira) in RSF treated groundwater without KMnO4 was higher than that in RSFs treated micro-polluted surface water or with KMnO4, resulting in a higher NH4+-N removal rate of the former (∼57%). Notably, KMnO4 and prokaryotes synergistically contributed to the amorphous structure, mixed phases (buserite, MnO2 and birnessite) and mixed-valence Mn system of active manganese oxides (MnOx), whose abundant oxygen vacancies and highly reactive Mn(III) favored the autocatalytic oxidation of Mn, while NH4+-N removal relied more on bacteria actions. Additionally, prokaryotes enriched the bacterial community diversity, leading to a more stable RSF system when facing hydraulic loading shock. This paper provided new insight into the synergistic effect of KMnO4 and prokaryotes on Mn and NH4+-N eliminations in RSFs and was helpful for practical applications.

Nanostructured Manganese Oxides within a Ring-Shaped Polyoxometalate Exhibiting Unusual Oxidation Catalysis.

Nanosized manganese oxides have recently received considerable attention for their synthesis, structures, and potential applications. Although various synthetic methods have been developed, precise synthesis of novel nanostructured manganese oxides are still challenging. In this study, using a structurally defined nanosized cavity inside a ring-shaped polyoxometalate, we succeeded in synthesizing two types of discrete 18 and 20 nuclear nanostructured manganese oxides, Mn18 and Mn20, respectively. In particular, Mn18 showed much higher catalytic activity than other manganese oxides for the oxygenation of alkylarenes including electron-deficient ones, and the reaction proceeded through a unique reaction mechanism due to its unusual manganese oxide structure.

Raman Spectroscopy Investigation of a Manganese Oxide Layer Caused by Water Corrosion on an IrMn Thin Film

Abstract Raman spectroscopy was used to identify a manganese oxide layer established on iridium manganese (IrMn) thin films. A thin manganese oxide layer on the IrMn surface was created by dropping deionized (DI) water for 30 min. Field emission scanning electron microscope and Raman spectroscopy with a 532-nm laser wavelength were used to investigate the DI-water–exposed IrMn surface. The intensity of the Raman laser beam, varied from 0.05 to 50 mW, was carefully optimized to avoid laser-induced heat effects on the manganese oxide layer and IrMn thin film. The results showed that the laser-induced heat produced an α-Mn3O4 phase on the IrMn surface and a manganese oxide layer at 25 mW. Raman optimization was used to investigate the DI-water corrosion and manganese oxide structures on different areas of the IrMn surface.

Low-temperature degradation of toluene over Ag-MnOx-ACF composite catalyst

ABSTRACT Volatile organic compounds (VOCs) have caused a serious threat to the atmosphere and human health. Therefore, it is of great significance to exploit effective catalytic materials for the safe and effective catalytic elimination of VOCs. Herein, Ag-MnOx-ACF composite catalysts were constructed via a two-step impregnation strategy and used for catalytic toluene degradation. A remarkable low-temperature catalytic activity (T100 = 50℃), excellent stability, as well as CO2 selectivity (80%) were achieved over the Ag-MnOx-ACF catalyst. A series of characterizations indicated that the unique manganese defects structure of birnessite phase manganese oxide played an essential role for toluene oxidation, which was conducive to generating surface adsorbed oxygen. The higher ratio of Mn3+/Mn4+, abundant surface adsorbed oxygen and highly dispersed Ag species were determined to significantly facilitate toluene degradation. The mechanism of efficient degradation of toluene at low temperature was proposed. O3 and H2O molecules were activated via surface hydroxyl and Mn defects on Ag-MnOx-ACF to produce sufficient •OH, enhancing the degradation performance of toluene. We provide a new idea for the catalytic oxidation of benzene VOCs at low even room temperatures.

Photocatalytic Oxidation of Dissolved Mn2+ by TiO2 and the Formation of Tunnel Structured Manganese Oxides

Photocatalytic Oxidation of Dissolved Mn²⁺ by TiO₂ and the Formation of Tunnel Structured Manganese Oxides

Enhancing Electrocatalytic N2 Conversion to NH3 by MnO2 Ultralong Nanowires with Oxygen Vacancies

Background: At present, industrial synthesis of NH3 mainly relies on the Haber-Bosch process, which is characterized by harsh reaction conditions and high energy consumption. Electrochemical nitrogen reduction is considered to be a mild and sustainable alternative method for producing NH3, but efficient electrocatalyst under ambient conditions is the prerequisite for NH3 production. Objective: To demonstrate that CP@MnO2 ultralong nanowires are a highly-efficient electrocatalyst for N2 reduction reaction (NRR) under ambient conditions. Methods: The α-phase MnO2 synthesized by one-step hydrothermal method has an ultralong nanowires structure and oxygen vacancy defects. The catalysts were characterized by XRD, TEM, XPS, etc. The produced NH3 was estimated by indophenol blue method by UV-vis absorption spectra. Results: Such catalyst attains high Faradaic efficiency (FE) of 8.8% and a large NH3 yield of 1.13×10−10 mol cm−2 s−1 at −0.7 V versus reversible hydrogen electrode in 0.1 M Na2SO4. In addition, the catalyst also shows high electrochemical stability and selectivity for NH3 formation. Conclusion: MnO2 ultralong nanowires can expose higher density of active sites and the spontaneously formed oxygen vacancies can manipulate the electronic structure of manganese oxides and provide coordination unsaturation sites (CUS) to enhance the adsorption of N2, which is the main reason for the high activity of the catalyst.

Catalytic Evaluation of Nanoflower Structured Manganese Oxide Electrocatalyst for Oxygen Reduction in Alkaline Media

An electrochemical nanoflowers manganese oxide (MnO2) catalyst has gained much interest due to its high stability and high specific surface area. However, there are a lack of insightful studies of electrocatalyst performance in nanoflower MnO2. This study assesses the electrocatalytic performances of nanoflower structure MnO2 for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in a zinc–air battery as a bifunctional electrocatalyst. The prepared catalyst was characterized in term of morphology, crystallinity, and total surface area. Cyclic voltammetry and linear sweep voltammetry were used to evaluate the electrochemical behaviors of the as-prepared nanoflower-like MnO2. The discharge performance test for zinc–air battery with a MnO2 catalyst was also conducted. The results show that the MnO2 prepared at dwell times of 2, 4 and 6 h were nanoflowers, nanoflower mixed with nanowires, and nanowires with corresponding specific surface areas of 52.4, 34.9 and 32.4 g/cm2, respectively. The nanoflower-like MnO2 catalyst exhibits a better electrocatalytic performance towards both ORR and OER compared to the nanowires. The number of electrons transferred for the MnO2 with nanoflower, nanoflower mixed with nanowires, and nanowire structures is 3.68, 3.31 and 3.00, respectively. The as-prepared MnO2 nanoflower-like structure exhibits the best discharge performance of 31% higher than the nanowires and reaches up to 30% of the theoretical discharge capacity of the zinc–air battery.

Flexible Zn‐ion batteries based on manganese oxides: Progress and prospect

AbstractThe ever‐growing market of wearable electronic devices has greatly stimulated the rapid development of flexible Zn‐ion batteries (ZIBs). Manganese oxides are one of the most commonly used hosts for zinc ion accommodation and thus receive particular research interest for high‐performance flexible ZIB constructions. In this review, a comprehensive summary of the recent development of flexible ZIBs with manganese oxides as cathode materials is presented. Apart from the brief introduction of flexible electronic devices and ZIBs, the charge storage mechanisms and crystal structures of various manganese oxides are summarized. Modifications of the cathode materials in terms of morphology, conductivity, structures, and flexibilities are illustrated in detail, together with the demonstration of structure‐performance relationships and applications in flexible ZIBs. Finally, limitations to be overcome are indicated and the future work directions are proposed.

Temperature-dependent transport properties of micro and nano-sized zinc cobalt oxide (ZnCo2O4) and zinc manganese oxide (ZnMn2O4) particles synthesized by a hydrothermal route

In the present work, a hydrothermal method has been adopted to synthesize micro (~150 nm), and nano (~20 nm) particles of Zinc based, cobalt, and manganese oxide structures, i.e., ZnCo2O4 (ZCO) and ZnMn2O4 (ZMO). These structures have been examined by X-ray diffraction, Field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. The effect of different reducing agents and solvents have been ascertained on the morphological and the crystalline nature of the samples. The highly crystalline and micron-sized particle formation has been observed with the usage of NaBH4 as the reductant in the water solution, and a polycrystalline structure with nanosized particle formation has been found with NaOH as the reductant in the water and DMF solution. The electrical properties have been investigated between 100 Hz and 1 MHz by varying the temperature from 303 K to 513 K. The micro and nano sized particles of ZCO and ZMO have shown frequency dependence, thermally activated and relaxation-type dielectric behavior confirming the semiconducting nature. The variation of ac conductivity with frequency at different temperatures is according to Jonscher's power law for micro and nano sized particles of the ZCO and ZMO but supporting different conduction mechanisms. The conduction mechanism in microparticles and nano-particles is according to an overlapping-large polaron tunneling (OLPT) model, and the Non-overlapping small polaron tunneling (NSPT) model, respectively.

Unique amorphous manganese oxide/rGo anodes for lithium-ion batteries with high capacity and excellent stability

The utilization of manganese oxide anode materials in lithium-ion batteries is hindered by low conductivity, high stress/strain, volume expansion, and high over potential in the crystalline structure during cycling. Compared with crystal oxide, amorphous oxide has attracted attention for its weak chemical bond force and its low stress change during the phase change process, but few reported in lithium-ion batteries. This work combined both advantages of amorphous manganese oxide (AMO) and reduced graphene oxide (rGo) to produce a unique AMO/rGo composite electrode material through one-step chemical reduction the KMnO4 in graphene oxide containing solution. The rGo-supported porous amorphous structure of manganese oxide brought special character by reducing the stress/strain of the conversion reaction, thus ensuring a high capacity and high stability. The high electronic and lithium-ion conductivity of graphene also enhanced the rate capability. As a result, the as-synthesized AMO/rGo exhibited a large reversible specific capacity (784 mA hg−1 at the current density of 1 A g−1 over 500 cycles) and superior rate capability, making it a potential candidate as high-performance electrode material for long-term cycling in lithium-ion batteries.

Electronic structure of bulk manganese oxide and nickel oxide from coupled cluster theory

We describe the ground- and excited-state electronic structure of bulk MnO and NiO, two prototypical correlated electron materials, using coupled cluster theory with single and double excitations (CCSD). As a corollary, this work also reports an implementation of unrestricted periodic ab initio equation-of-motion CCSD. Starting from a Hartree-Fock reference, we find fundamental gaps of 3.46 and 4.83 eV for MnO and NiO, respectively, for the 16-unit supercell, slightly overestimated compared to experiment, although finite-size scaling suggests that the gap is more severely overestimated in the thermodynamic limit. From the character of the correlated electronic bands we find both MnO and NiO to lie in the intermediate Mott/charge-transfer insulator regime, although NiO appears as a charge transfer insulator when only the fundamental gap is considered. While the lowest quasiparticle excitations are of metal $3d$ and O $2p$ character in most of the Brillouin zone, near the $\mathrm{\ensuremath{\Gamma}}$ point, the lowest conduction band quasiparticles are of $s$ character. Our study supports the potential of coupled cluster theory to provide high-level many-body insights into correlated solids.

Accumulation charge mechanisms in electrochemical systems formed based on activated carbon and manganese oxide

In this work, the porous structure of the carbon material and the crystalline structure of manganese oxide α - modification (α - MnO2) have been investigated. The electrochemical performance of symmetric and asymmetric supercapacitors (α - MnO2 / Activated carbon) was investigated by cyclic voltammetry and galvanostatic cycling methods. The processes occur mainly at the electrode – electrolyte interface have been analyzed. It was determined that at discharge currents of 0.5 - 5 mA, the specific capacitance value for the α - MnO2 / Activated carbon hybrid capacitor exceeds the value of the symmetric capacitor by 45 - 55 % under the same conditions.

Nanoscale structure and compositional analysis of manganese oxide coatings on the Smithsonian Castle, Washington, DC

The Smithsonian Castle is a historic building in Washington, D.C. that was erected 165 years ago and served as the first home for the Smithsonian Institution. Currently, the building exhibits dark surface discoloration due to manganese-rich coatings that are growing in patches across its Seneca sandstone exterior. Bulk and microanalysis of this coating indicate that it is consistent with rock varnish, but the coating is difficult to analyze without contribution from the underlying minerals that comprise the sandstone. To address this limitation, SEM/FIB-prepared cross-sections of the coating were analyzed using HRTEM, STEM-EDX, and SAED analyses in order to study the nanoscale structure and composition of the Mn-rich coating in isolation, without convolution from the sandstone. Structurally, the coating is <1 μm thick, polycrystalline, and composed primarily of birnessite, a layered manganese oxide. High spatial resolution data reveal that the coating is Ca-bearing, with only minor quantities of Fe, Si, and Al, distinguishing it compositionally from typical manganese rock varnish and classifying it instead as a manganese skin. TEM revealed layers of aeolian detritus below and a thin silica glaze above the Mn-rich coating, providing a relative timeline of formation. Nanoscale particulates of barite found within the Mn-rich coating, along with the micro- and nanoscale detritus below the coating, indicate atmospheric deposition as the main source for both Mn and Ba. The compositional and structural information gathered from these analyses helps constrain mechanisms of formation towards a biological origin; however, no direct evidence for Mn oxide producing microorganisms was observed.

Amorphous manganese oxide as highly active catalyst for soot oxidation.

A series of highly active amorphous manganese oxide catalysts for soot combustion were synthesized using colloidal solution combustion synthesis (CSCS) method. The surface morphological and structural properties were systematically tested via various techniques: X-ray diffraction, N2 adsorption-desorption, temperature-programmed reduction, scanning electron microscopy, and X-ray photoelectron spectroscopy. Manganese precursors and calcination temperatures affect the crystal structure, redox properties, and surface properties of MnOx. With the calcination temperature increasing from 550 to 850°C, the crystalline structure of manganese oxides changed from amorphous phase to crystal phase. In general, the amorphous MnOx with a hierarchical porous structure showed better catalytic activity for soot oxidation than the crystal ones (T10 as indicator), which can be ascribed to the improved low-temperature reducibility, more surface active oxygen species, and abundant surface Mn4+ ions. The presence of NO in O2 also promoted soot oxidation which follows the NO2-assisted mechanism. Our work may provide a rational comparison between high-efficient amorphous and crystal MnOx catalysts for soot oxidation.

The Tremendous Catalytic Activities of the Cryptomelane-Type Manganese Oxide Octahedral Molecular Sieve Prepared Without Calcination Process for Degradation of Methylene Blue

The cryptomelane-type manganese oxides octahedral molecular sieve with different crystalline phases have been successfully synthesized and characterized. The oxides were synthesized using precipitation method through the redox reaction between KMnO4 and C6H8O7 with a mole ratio of 5:1 by the variation of flow rates (1, 2, and 3 mL/min). The prepared catalysts were characterized by XRD to determine their phase structures, purity, and crystallinity. The XRD results indicated that the samples without heat treatment (calcination) displayed the poor tunnel structures of cryptomelane-type manganese oxides with low intensities and broad peaks. Upon the thermal treatment at 600°C for 4 hours, the much more crystalline phases of similar cryptomelane structures were obtained. The high flow rate results in the more crystalline cryptomelane for calcined samples, whereas the flow rate has no substantial influence on the crystallinity of uncalcined samples. The catalytic activities of both oxides were evaluated for the degradation of methylene blue (MB) with H2O2 as an oxidant. The catalytic degradation of MB greatly enhanced using the uncalcined cryptomelane compared to calcined cryptomelane. The high flow rate has a positive impact on the degradation of MB for calcined samples, but the effect of flow rate results in the higher degradation of MB until a certain flow rate. The 98.4% degradation of MB was achieved by uncalcined samples under the optimum condition.

Synthesis and Catalytic Activities of Manganese Oxides Prepared by Precipitation Method: Effects of Mixing Modes of Reactants and Calcination Process

The two phases of manganese oxides are prepared by two different mixing modes using the same precipitation method from the solutions of KMnO4 dan maltose, resulting in marked different phase structures and catalytic activities. The oxides synthesized by adding dropwise of the maltose solution into KMnO4 solution (method A) resulted in the formation of layer manganese oxide birnessite, which turns into tunnel structured manganese oxide cryptomelane following the calcination at 600°C for 4 hours. The simultaneous addition of KMnO4 solution and maltose solution (method B) also produced birnessite before calcination, but remain unchanged as birnessite phase after calcination with cryptomelane as minor product. The samples without calcination obtained from method A posseses higher surface area and poor crystallinity compared to that with calcination. The catalytic test using Fenton-like Reaction for methylene blue (MB) degradation indicated the tremendeous difference in their catalytic activities for both samples without and with calcination. The birnessite catalysts (without calcination) prepared using method A show the highest activity and are able to degrade 93% methylene blue within 10 minute, much higher than other samples.

Exclusive T2 MRI contrast enhancement by mesoporous carbon framework encapsulated manganese oxide nanoparticles

Single mode (either T1 or T2) contrast agents employed during magnetic resonance imaging owe their advantage over their dual counterparts to the fact that they do not involve any quenching caused by interference between the two modes. The chemistry involving oxides of manganese is highly significant due to their applicability as MRI contrast agents. Manganese oxides are usually known to display a dominant T1 relaxation enhancement. But, in this work, an engineered structure of manganese oxide (Mn2O3) nanoparticles encapsulated within mesoporous carbon frameworks was developed which exhibited dominant T2 contrast enhancement, through regulation of contact between the magnetic ion and water. Microstructural characterization revealed that the mesoporous carbon frameworks were spherical in shape and the nanoparticles within them had an average size of 40–50 nm. Relaxivity measurement, MRI experiments and cell viability assay convincingly established the system as a new class of biocompatible T2 based magnetic resonance imaging agent.

Facile synthesis of hierarchically structured manganese oxides as anode for lithium-ion batteries

Developing high-performance lithium ion batteries (LIBs) using manganese oxides as anodes is attractive due to their high theoretical capacity and abundant resources. Herein, we report a facile synthesis of hierarchical spherical MnO2 containing coherent amorphous/crystalline domained by a simple yet effective redox precipitation reaction at room temperature. Further, flower-like CoMn2O4 constructed by single-crystalline spinel nanosheets has been fabricated using MnO2 as precursor. This mild methodology avoids undesired particle aggregation and loss of active surface area in conventional hydrothermal or solid-state processes. Moreover, both MnO2 and CoMn2O4 nanosheets manifest superior lithium-ion storage properties, rendering them promising applications in LIBs and other energy-related fields.

Surfactant selection as a strategy for tailoring the structure and properties of UCT manganese oxides

Mesoporous manganese oxides were synthesized using the UCT inverse micelle templating method with four different Pluronic surfactants to investigate the effects on the morphology, microstructure and desulfurization behavior of these materials. All of the as-synthesized samples exhibited similar hierarchical microstructures, but the size and shape of the primary nanoparticles for each sample was different. The primary nanoparticle sizes for these samples vary between 2.3 and 7.0 nm. Most of the samples are crystalline and are composed of a mixture of Mn3O4 and Mn5O8 phases. The adsorption behavior of these samples was tested using a fixed bed reactor at a temperature of 200 °C. Microstructural analysis of the samples after the desulfurization tests revealed a transformation of the mesoporous manganese oxide to a dense manganese sulfide phase; this involves a volumetric expansion of the crystal, leading to densification and a rapid decay in the sorption capacity after the breakthrough point. The variation in the structure and properties of these materials is related to ratio of the PEO and PPO chain segment lengths in the Pluronic surfactants used. This indicates that the ratio must dictate the volume, shape and assembly of the inverse micelles in the UCT synthesis.

Enhanced supercapacitive performance of MnOx through N2/H2 plasma treatment

This work relates to the research on the effect of plasma on the performance of manganese oxide. Manganese oxide nanoflakes were prepared through the reaction of KMnO4 and alcohol, and then treated by N2 and N2/H2 plasma. The crystal structure of manganese oxide can be destructed by plasma treatment and manganese oxide become more amorphous and aggregated than those of as-synthesized MnOx, both of which have been proven by XRD and TEM techniques. Results of XPS confirm that the ionic defects and oxygen vacancy are also formed in manganese oxide by plasma. The electrochemical behavior was studied using CV, GCD, and EIS method in 0.5 M Na2SO4 solution. The results show that N2/H2 plasma treatment can fascinate the coexistence of mixed valence of Mn and the formation of oxygen vacancies, reduce the charge-transfer resistance, and then enhance the capacitive performance efficiently.