Calcium Manganese Oxide Research Articles

Spinel-type calcium manganese oxide adorned on g-CN composite: A highly proficient electrocatalyst for oxygen evolution reaction (OER)

A comprehensive study was performed on water electrolysis to address environmental challenges and energy issues. Eco-friendly and renewable energy systems are required to produce cost-effective electro-catalysts with long-term durability and higher electrocatalytic efficiency to enhance OER. Spinel oxide has recently been used as a promising substitute for transition metal catalysts. They can function as very effective electrocatalysts in water oxidation processes. In current study, the CaMn2O4/g-CN composite was prepared using the hydrothermal technique in 1.0 M KOH in primary media. Distinctive physical and electrochemical analyses evaluated the prepared material's morphology, structure and electrocatalytic components. The composite material showed enhanced electrocatalytic efficacy for OER having a reduced overpotential (η) of 220 mV than pure CaMn2O4 278 mV and possesses a minimal Tafel value (35 mV/dec) contrasted with pristine CaMn2O4 (57 mV/dec). In case of overpotential, the composite material revealed good performance than its pure material while the Tafel slope of CaMn2O4/g-CN exhibited lower value than its individual material (CaMn2O4). Additionally, cyclic stability and chronoamperometric studies measured the electrodes' durability over 30 h. Electrochemical impedance spectroscopy (EIS) investigations indicated that charge transformation at an electrode-electrolyte surface might be feasible with minimal Rct value (0.19 Ω) and it showed excellent improved performance (63 %) better than its pure material, leading it to boost OER properties, attributed to its remarkable electrical conductivity, greater surface area and outstanding stability. These outstanding electrochemical features of the CaMn2O4/g-CN differentiate as an attractive choice for future OER utilization.

Influence of carbon template and ultrasound irradiation on combustion design of nanostructured calcium manganese oxides used in biodiesel production

Biodiesel, derived from renewable biomass, serves as a sustainable alternative to diesel produced from fossil fuels. This study explores the use of nanostructured MgO/Ca2Mn3O8 catalysts for biodiesel production through transesterification. Ca2Mn3O8 was synthesized as a support catalyst via combustion synthesis, employing carbon templates to control pore size. MgO was impregnated as the active phase using ultrasonic irradiation to enhance particle dispersion. Various characterization techniques, including XRD, FESEM, AFM, TEM, EDX, BET-BJH, and TPD-CO2, were utilized to analyse morphology, porosity, basicity, and active phase dispersion. The use of carbon templates increased pore diameters compared to catalysts without templates, while ultrasonic irradiation improved MgO dispersion. The MgO/Ca2Mn3O8 catalyst with a 10 wt% carbon template and ultrasonic irradiation achieved a maximum conversion rate of 95.5%. Its mesoporous structure, resembling a sponge, facilitated triglyceride diffusion. Stability tests indicated a 90% conversion rate after five reuses. The nanostructured MgO/Ca2Mn3O8 catalyst, with its tailored porosity and structure, demonstrated excellent performance in biodiesel production. Systematically adjusting support porosity and active site dispersion provides a viable approach for designing effective heterogeneous catalysts.

Perfectly dense ceramics of highly pure calcium manganese oxide

Immensely thermally stable and perfectly dense ceramics of highly pure calcium manganese oxide (CaMnO3) powders is realized at optimized minimal processing temperature and time using cost-effective ball-milling and hot-press techniques. The effect of ball milling time on the calcination time to prepare highly pure CaMnO3 powder and sintering time on the temperature adequate enough to achieve perfectly dense CaMnO3 ceramics is studied thoroughly and systematically. The as-synthesized single phase CaMnO3 is attained by mixing precursors of calcium carbonate and manganese oxide, using high energy ball milling for longer time followed by calcination for shorter time duration and vice-versa. A decrease in particle size in as-synthesized CaMnO3 is noticed for powders prepared with longer ball milling and shorter calcination times. The minimal time required for achieving highly pure and fine-grained powders containing sub-micrometer particles of CaMnO3 is accomplished by ball milling the precursor mixture for 12 h and calcining at 1273 K for 2 h. Relative density of 99.03% is achieved for the as-synthesized CaMnO3 powders hot pressed at 1073 K for 30 min.

Crafting advanced supercapacitor electrodes with calcium manganese oxide in synergy with rGO and MWCNTs

Despite significant progress in developing metal oxide composite electrodes, methods to improve conductivity and integrate them with carbon nanocomposites remain scarce. Herein, we have synthesized carbon variants – metal oxide composite electrodes with reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs). This study outlines the process of synthesizing CaMn3O6 microbeads (∼0.4 μm), which are dispersed within reduced graphene oxide (rGO) sheets and carbon nanotubes (CNTs). The synthesis involves a hydrothermal reaction followed by a calcination process. The synthesized samples are fabricated as a pouch type asymmetric supercapacitor device. The electrodes labelled as CMO–G and CMO–M were tested in three electrode system wherein CMO–M delivered a capacitance of 483 F/g and CMO-G delivered a capacitance of 356 F/g. Low resistance, excellent cycling stability makes CMO–M a suitable electrode for practical applications. The device CMO–M||AC delivered capacitance of 140 F/g and showed a capacity retention up to 84 % even after 20,000 cycles. CMO–M||AC device delivered energy density of 43.81 Wh kg−1 at 750 W kg−1 power density. Our results distinctly demonstrate the significant potential achieved through the synergistic effect in CaMn3O6 and carbon variants. This understanding could prove valuable in the creation of advanced energy storage solutions.

Exploring Calcium Manganese Oxide as a Promising Cathode Material for Calcium-Ion Batteries.

The dependence on lithium for the energy needs of the world, coupled with its scarcity, has prompted the exploration of postlithium alternatives. Calcium-ion batteries are one such possible alternative owing to their high energy density, similar reduction potential, and naturally higher abundance. A critical gap in calcium-ion batteries is the lack of suitable cathodes for intercalating calcium at high voltages and capacities while also maintaining structural stability. Transition metal oxide postspinels have been identified as having crystal structures that can provide low migration barriers, high voltages, and facile transport pathways for calcium ions and thus can serve as cathodes for calcium-ion batteries. However, experimental validation of transition metal oxide postspinel compounds for calcium ion conduction remains unexplored. In this work, calcium manganese oxide (CaMn2O4) in the postspinel phase is explored as an intercalation cathode for calcium-ion batteries. CaMn2O4 is first synthesized via solid-state synthesis, and the phase is verified with X-ray diffraction (XRD). The redox activity of the cathode is investigated with cyclic voltammetry (CV) and galvanostatic (GS) cycling, identifying oxidation potentials at 0.2 and 0.5 V and a broad insertion potential at -1.5 V. CaMn2O4 can cycle at a capacity of 52 mAh/g at a rate of C/33, and calcium cycling is verified with energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) and modeled with density functional theory (DFT) simulations. The results from the investigation concluded that CaMn2O4 is a promising cathode for calcium-ion batteries.

Synthesis of Calcium Manganese Oxide Films Using a Sol–Gel Method and Evaluation of Color and Photocatalytic Properties

Herein, for developing colored photocatalysts, calcium manganese oxide (Ca–Mn–O) film and powder samples are synthesized by a sol–gel method using acetylacetone (acac) or citric acid as a chelating agent, and their color and photocatalytic properties are evaluated. Thin‐film X‐ray diffraction experiments clarify the precipitation of Ca–Mn–O phases, such as Ca3Mn2O7 (Ca/Mn = 1.5) and Ca2MnO4 (Ca/Mn = 2), in the film samples with drop‐cast coating. These films strongly absorb all visible light due to the interband transition between O 2p and Mn 3d orbitals, resulting in dark gray coloration. By testing photocatalytic activities using methylene blue dyes, it is revealed that the film sample (acac, 4‐drops) exhibits photocatalytic activities, which makes Ca–Mn–O films dual functional with photocatalytic functions and coloration.

A facile synthesis of calcium manganese oxide for supercapacitor application

A facile synthesis of calcium manganese oxide for supercapacitor application

Investigation of Transition Metal Oxide Post-Spinels for Calcium-Ion Batteries

The dependence on lithium for rising global energy demand coupled with the scarcity of lithium necessitates the exploration of post-lithium strategies. Calcium-ion batteries are one such post-lithium strategy that can mitigate rising costs owing to calcium’s natural abundancy. A critical gap in this field is the lack of cathodes capable of intercalating calcium at high voltages and capacities while also retaining structural stability. The handful of candidates evaluated thus far have been plagued by low capacities and poor cycling performance due to intercalation–induced phase changes and instability. Transition metal oxide post–spinel–type materials have been identified as potential candidates for reversible Ca–ion storage owing to their crystal structures and high theoretical energy densities. However, experimental validation of these theoretical predictions remains largely unaddressed. In this work, post-spinel Calcium Iron Oxide (CaFe2O4) and Calcium Manganese Oxide (CaMn2O4) are explored as cathodes for calcium-ion batteries. The redox activity of each cathode is investigated using galvanostatic (GS) cycling while their structural stabilities are evaluated with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The use of GS in tandem with XRD and SEM provides insights into the evolution of crystal structure with Ca–ion–transport within each cathode. Our results reveal that these post–spinel systems can cycle with a reversible capacity of 56 mAh/g, making them promising cathode candidates for Ca–ion batteries and warrant further investigation.

Enhancing the thermoelectric properties of CaMnO3-δ via optimal substituent selection

The interplay of crystal structure and thermoelectric properties of A- or B-site substituted high-density calcium manganese oxide ceramics, Ca1-zAzMn1-zMzO3-δ (A ​= ​Bi, Gd, Yb/Gd or M ​= ​W with 0 ≤ z ​≤ ​0.08) is investigated. For the same degree of substitution z, smaller sized substituents cause a unit cell volume contraction and higher electrical conductivity, whereas the Seebeck coefficients are not affected. Evaluation along with results from published reports shows that this is valid for both, A- and B-site substitutions. The mean tolerance factor is used to describe this dependency qualitatively. The high-density ceramics show large power factors (S2σ ​> ​400 ​μW/mK2) and moderate figures of merit zT ​≈ ​0.15 ​at 700 ​°C. The best thermoelectric performance is anticipated for calcium manganese oxide, substituted heterovalently as well as homovalently with small substituents, due to higher electrical conductivity and lower thermal conductivity.

Reversible Structural Isomerization of Nature's Water Oxidation Catalyst Prior to O-O Bond Formation.

Photosynthetic water oxidation is catalyzed by a manganese–calcium oxide cluster, which experiences five “S-states” during a light-driven reaction cycle. The unique “distorted chair”-like geometry of the Mn4CaO5(6) cluster shows structural flexibility that has been frequently proposed to involve “open” and “closed”-cubane forms from the S1 to S3 states. The isomers are interconvertible in the S1 and S2 states, while in the S3 state, the open-cubane structure is observed to dominate inThermosynechococcus elongatus (cyanobacteria) samples. In this work, using density functional theory calculations, we go beyond the S3+Yz state to the S3nYz• → S4+Yz step, and report for the first time that the reversible isomerism, which is suppressed in the S3+Yz state, is fully recovered in the ensuing S3nYz• state due to the proton release from a manganese-bound water ligand. The altered coordination strength of the manganese–ligand facilitates formation of the closed-cubane form, in a dynamic equilibrium with the open-cubane form. This tautomerism immediately preceding dioxygen formation may constitute the rate limiting step for O2 formation, and exert a significant influence on the water oxidation mechanism in photosystem II.

Synthesis of calcium manganese oxide with different constructions as potential materials for electrochemical hydrogen storage

The series of Ca-Mn-O based nanostructures were synthesized through leucine-assisted sol–gel procedure. In order to study the purity and components of samples, the effect of Ca:Mn ratio in the synthesis process was examined. The leucine as ideal fuel and capping agent is selected which led to the preparation of three types of manganate materials including Ca2Mn3O8, Ca2Mn3O8/CaMn3O6 and CaMn3O6 in the Ca:Mn ratio of 1:1, 1:2 and 1:3 respectively. The structural, chemical and physical properties of resulting samples compared with each other in terms of purity, surface area and magnetic attributes. The ability of Ca-Mn-O materials for electrochemical energy storage was investigated through CV and CP technique in three-electrode cell with 2 M KOH electrolyte. The results show Ca2Mn3O8/CaMn3O6 nanocomposites have the capacity of 604 mAh g−1. The hydrogen storage capacity for pristine CaMn3O6 and pristine Ca2Mn3O8 measured about 287 and 572 mAh g−1 after 15 cycles respectively. According to the obtained results, the Ca2Mn3O8/CaMn3O6 nanocomposites presents ideal electrochemical hydrogen storage capacity as promising active materials in storage systems.

Synthesis, characterization and thermoelectric properties of Ca substituted nanostructured SrMnO3 by sol-gel hydrothermal method

Perovskite manganites are pure and stable at elevated temperatures due to its thermal and chemical stability. Pure and Ca substituted SrMnO3 nanoparticles have been prepared by sol-gel hydrothermal method. Structural, micro structural, elemental, functional, optical, electrical and thermoelectric properties have been investigated by XRD, Raman, SEM with EDAX, FTIR, UV–Vis Spectroscopy and Physical properties respectively. Powder X-ray Diffraction studies reveals the formation of the single phase without secondary phases. Poly vinyl pyrrolidone as a capping agent decreases the grain size of the nanoparticles with different nanostructures. Electrical conductivity increases but thermal conductivity is strongly reduced due to grain size reduction. Thermoelectric properties are evaluated from ambient to 300 K. Ca2+ substituted at A-site of SrMnO3 nanoparticles leads to oxygen deficient calcium manganese oxide nanoparticles. The major charge carriers are an electron that reveals that pure and Ca substituted SrMnO3 nanoparticles are n-type promising thermoelectric oxides with high thermoelectric power.

Dual enzymes-mimic activity of nanolayered manganese-calcium oxide for fluorometric determination of metformin

There are different analytical methods available for the determination of metformin, as an oral hypoglycemic and antidiabetic drug, in biological samples. However, most of these methods suffer from some drawbacks, including high-priced materials and equipment, damaging chemical reagents, time-consuming nature, and tedious operation procedures. So, in this work a new, sensitive and simple method was reported for the detection of metformine. In this regard, nanolayered manganese-calcium oxide (NL-MnCaO2) were synthesized and characterized using scanning electron microscopy (SEM), fourier transform infrared (FTIR) spectroscopy, and X-ray powder diffraction (XRD) techniques. Also, we studied the enzyme-like activity of synthesized particles and reported a bifunctional nanozyme, which performs the dual roles for peroxidase and catalase-mimicking. The results demonstrated the hindering effect of metformin on the peroxidase-mimic activity of NL-MnCaO2 and this effect was increased by raising metformin concentration. So, a sensitive fluorometric detection system was designed for the analytical assay of metformin, based on the terephthalic acid (TA)-H2O2 reaction with NL-MnCaO2. An acceptable linearity was observed between the metformin concentration and fluorescence quenching of the system in the range of 0.07–0.77 mM. Limit of detection (LOD) and limit of quantification (LOQ) were 0.17 μM and 0.96 μM, respectively. The proposed system was applied for the estimation of metformin concentration in serum samples by recoveries of 86.68–106%. So, the proposed fluorometric method provides some main advantages such as wide linear range, low detection limit, rapid detections, high sensitivity, and good practicability for the determination of metformin in biological samples.

Thickness dependent electrical resistivity modulation in tensile-strained epitaxial thin films of calcium manganese oxide

We report our studies of the thickness dependence of electrical resistivity and lattice constants in strained epitaxial thin films of calcium manganese oxide. Our results indicate the potential of bi-axial lattice mismatch strain as a handle for modulating electrical resistivity. We observe thickness dependence of lattice constants consistent with what is expected for strain relaxation for films thicker than 400 Å. At lower thickness values, anomalies are observed suggestive of reduced oxygen stoichiometry. We observe a remarkable decrease in electrical resistivity with decreasing film thickness. The resistivity of our thinnest films (5–7 nm) is about three orders of magnitude lower than the resistivity of bulk CaMnO3. Resistivity increases as the film thickness increases, along with the progression of strain relaxation. It is noteworthy that the thickness dependence of resistivity we observe in CMO thin films is the opposite of what has been reported for their hole-doped rare earth manganite counterpart La0.67Ca0.33MnO3 (LCMO), where tensile lattice mismatch strain suppresses metallicity, leading to the increase in resistivity with film thickness. We believe that the enhanced conductivity in our thinnest films is related to the possible oxygen deficiency promoted by tensile strain. Recent x-ray absorption measurements have revealed reduced oxygen content and associated changes in Mn valence states in tensile-strained CMO thin films, as also predicted by density functional theory calculations. This report is the first observation of electrical transport behavior possibly indicative of strain–oxygen stoichiometry coupling.

Sol-gel synthesis and photocatalytic activity of biomimetic calcium manganese oxide catalysts

The water contaminations by dye residues are increasingly becoming serious concerns worldwide due to dye toxicity and persistent characteristics. Manganese oxide-based catalysts having similar structures with manganese compounds found in nature (biomimetic) have been considered as a very promising and effective photocatalyst for the degradation of organic pollutions in wastewater. This paper focuses on the synthesis of calcium manganese oxide catalysts from the octahedral layered birnessite-type manganese oxide and calcium carbonate via sol-gel method with citric acid as the complexing agent. The as-synthesized oxide was then tested as a photocatalyst for the degradation of methylene blue (MB) dye. The calcium manganese oxides prepared by the two different mole ratios of CaCO3/MnO2 resulted in the similar crystallinity and crystal phases but difference in the crystal sizes. The photocatalytic activities of the prepared calcium manganese oxides for the degradation of methylene blue are compared to that of the calcium manganese oxide prepared from tunnel cryptomelane-type manganese oxide. Both the calcium manganese oxides prepared from the different manganese oxide phases show the remarkable performance for the photocatalytic degradation of methylene blue after 10 minutes of reaction times. The birnessite-prepared calcium manganese oxide displays slightly higher photocatalytic performance than cryptomelane-prepared calcium manganese oxide.

Functions of MnOx in NaCl Aqueous Solution for Artificial Photosynthesis.

SummaryPhotoelectrochemical water splitting has been intensively investigated as artificial photosynthesis technology to convert solar energy into chemical energy. The use of seawater and salted water has advantages for minimum environmental burden; however, the oxidation of Cl− ion to hypochlorous acid (HClO), which has toxicity and heavy corrosiveness, should occur at the anode, along with the oxygen evolution. Here, O2 and HClO production in aqueous solution containing Cl− on photoanodes modified with various metal oxides was investigated. The modification of MnOx resulted in the promotion of the O2 evolution reaction (OER) specifically without HClO production over a wide range of conditions. The results will contribute not only to the practical application of artificial photosynthesis using salted water but also to the elucidation of substantial function of manganese as the element for OER center in natural photosynthesis.

A study of calcium ion intercalation in perovskite calcium manganese oxide

Abstract We report on the synthesis and characterization of perovskite calcium manganese oxide (CaMnO3) as an intercalation compound for calcium ion insertion and extraction. Cyclic voltammetry measurements indicate calcium ion insertion and de-insertion into and from the CaMnO3 host. Differential capacity analysis delineates the potentials at which the insertion and extraction redox processes occur (at −0.4 V and + 0.1 V vs. Ag/Ag+, respectively). The insertion and extraction of calcium ions is supported by post-mortem x-ray analysis, which indicates loss of Ca2+ ions from the native CaMnO3 phase as well as the presence of manganese oxide phases. This study shows that perovskite calcium manganese oxide is a promising intercalation host.

Optical and photocatalytic properties of biomimetic cauliflowered Ca2Mn3O8–CaO composite thin films

Inspired from the μ-oxido CaMn4 cluster unit present in the photosystem-II of plant cells, various manganese-based materials, particularly calcium-manganese oxides, have been investigated by the researchers as a new class of catalysts. Herein, we report the synthesis of single source heterobimetallic complex {[CaMn(OAc)(TFA)3(THF)(H2O)2].3THF}n (where OAc ​= ​acetate, TFA ​= ​trifluoroacetate and THF ​= ​tetrahydrofuran) for the deposition of thin films of Ca2Mn3O8–CaO composite on fluorine doped tin oxide (FTO) coated glass substrates at deposition temperatures of 450–550 ​°C via the aerosol assisted chemical vapour deposition (AACVD) method. The complex was characterized by melting point, microanalysis, proton nuclear magnetic resonance (1H NMR), Fourier transformed infra-red (FT-IR) spectroscopy, thermogravimetry (TGA) and single crystal X-ray diffraction. The deposited thin films were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, energy dispersive X-ray spectroscopy (EDX) and field emission scanning electron microscopy (FESEM) which confirmed the growth of Ca2Mn3O8–CaO composite with high purity and precise stoichiometry. The optical characterization gave direct band gap energies of 2.74, 2.68 and 2.77 ​eV for the Ca2Mn3O8–CaO thin films deposited at 450, 500 and 550 ​°C, respectively. Furthermore, photoelectrochemical studies revealed that the thin film deposited at 500 ​°C showed the photocurrent of 3.75 ​mA ​cm−2 at +0.8 ​V vs. SCE with 1.64% photo-conversion efficiency and 310 ​Ω Rct value, upon illumination with a 150 ​W (100 ​mW ​cm−2) halogen lamp. The improved photocatalytic activity of Ca2Mn3O8–CaO composite was due to the increased photo absorption ability, elevated surface area, and more efficient electron/hole transfer. In addition, this work provides an insight to design the growth of visible light active calcium-manganese based photocatalyst materials for solar energy utilization.

Microstructure Study of Calcium Manganese Oxide (CaMnO3) as Perovskite Materials

The use of metal oxide as an n-type semiconductor behavior is one of the important material in solar cells. Among the materials, these researches focus on perovskite structure of CaMnO3. The single phase of CaMnO3 synthesised by citrate method were studied for the microstructure of CaMnO3. The perovskite structure of CaMnO3 was characterized by using X-ray Diffraction (XRD), Fourier transform-infrared (FTIR) spectroscopy, Scanning Electron Microscope (SEM) and Thermogravimetric Analysis (TGA). Results indicated that the single phase of CaMnO3 was revealed by XRD analysis. The specific interactions in the metal oxide and hence about the complexation led by FTIR. The morphological structure of the samples was studied by SEM, which confirmed the XRD analysis. While TGA analysis affirmed the CaMnO3 was formed.

Solid state synthesis and photocatalytic activity of bio-inspired calcium manganese oxide catalysts

Calcium manganese oxides have structural similarities to the μ-oxo-Mn4Ca cluster in Photosystem-II protein that is responsible for water-splitting in natural photosynthesis. As such, calcium manganese oxides have attracted great interest in recent years as a new class of biomimetic redox catalysts in many energy-related applications. However, photo-induced catalytic activities of calcium manganese oxides have not been fully understood. This work reports the experimental investigation of the synthesis of different calcium manganese oxides nanoparticles (Ca2Mn3O8, CaMn2O4 and CaMnO3) by mechanochemical processing, a potentially green scalable method, and their photocatalytic activities on the decolourization of Rhodamine 6G aqueous solutions. Band gap energies of the three calcium manganese oxides showed their ability to absorb visible light. Valence bands of all the as-synthesized samples were more positive than the electrochemical potential required for the formation of hydroxyl free radicals from water. Without addition of any catalytic powder, 32% of the dye was decolorized within 3 ​h. The addition of Ca2Mn3O8 did not increase the dye decolourization upon 3 ​h of light irradiation. On the other hand, the presence of CaMn2O4 and CaMnO3 resulted in 61% and 62% degradation of the dye, respectively, within the same irradiation time. The photocatalytic activity of the prepared powders, per unit specific surface area, increased in the order Ca2Mn3O8 ​< ​CaMnO3 ​< ​CaMn2O4.