Nm For Mn2 Research Articles

Physical properties of MnFeAl-based alloys affected by Mn content and annealing

The present study is devoted to the Mn2.4Fe0.8Al0.8 and Mn2FeAl alloys prepared by induction melting and studied in their original and subsequently annealed states. The annealing was carried out at 773 K/100 h and 1073 K/100 h in the argon atmosphere. The microstructure, phase composition, magnetic properties, and atom arrangement are followed with regard to Mn content and annealing conditions.The scanning electron microscopy completed by the energy dispersive X-ray spectroscopy and neutron activation analysis has detected single-phase alloys with compositions close to the nominal ones. Their structure, analyzed by X-ray diffraction, was found to be primitive cubic β-Mn with the lattice parameters of 0.6359(2) nm for Mn2.4Fe0.8Al0.8 and 0.6339(1) nm for Mn2FeAl. The coherent potential approximation calculations and positron annihilation spectroscopy have allowed obtaining an overview to the arrangement of Mn, Fe, and Al atoms in the β-Mn structure and formation of the open volume defects. It is shown that Mn atoms occupy predominantly 8c Wyckoff sites and remaining Mn, Fe and Al atoms occupy 12d sites in equal 1/3 proportion. The open volume defects, vacancies and vacancy clusters, occur in both alloys and both annealed states in a very low concentration. From the magnetic viewpoint, both alloys in the as-prepared state and after annealing at 773 K/100 h are paramagnetic at room temperature with transition to antiferromagnetic state at about 30-40 K. The ac susceptibility measurements have indicated spin glass nature of the Mn2FeAl alloys. The annealing at a higher temperature, 1073 K/100 h, has affected mainly Mn2.4Fe0.8Al0.8 alloy manifesting a weak ferro-/ferrimagnetic contribution at room temperature contributing to a strong magnetic ordering below 42 K.

Facile synthesis of M2(m‐dobdc) (M = Fe and Mn) metal‐organic frameworks for remarkable hydrogen storage

AbstractMetal‐organic frameworks (MOFs) are emerging as promising candidates for hydrogen storage material because of their porosity and adjustable hydrocarbon structures coordinated with the metal element. Present work explore the synthesis of M2(m‐dobdc) (M = Fe and Mn; m‐dobdc4− = 4,6‐dioxido‐1,3‐benzenedicarboxylate) metal‐organic frameworks via solvothermal method for the purpose of hydrogen storage application. The X‐ray diffraction, transmission electron microscope, scanning electron microscope, energy dispersive X‐ray analysis, and nuclear magnetic resonance spectroscopic studies have been done to ensure the synthesized material is M2(m‐dobdc) (M = Fe and Mn) MOFs. The Brunauer‐Emmett‐Teller (BET) analysis reveals the average pore size of 36.271 nm for Mn2(m‐dobdc) MOF whereas the average pore size for fe2(m‐dobdc) MOF was found to be 2.1992 nm. The as‐prepared MOF samples are in the mesoporous range based on pore size distribution (internal pore diameter greater than 2 nm) with spherical pore geometry. Hydrogen storage studies shows that Fe2(m‐dobdc) has a hydrogen storage capacity of 0.18 wt% at ambient temperature (30°C) under 100 atm H2 pressure, whereas the hydrogen storage capacity for Mn2(m‐dobdc) is 1.38 wt% under identical conditions of temperature and pressure. The hydrogen storage capacity at liquid nitrogen temperature (−196°C) under 100 atm H2 pressure for Fe2(m‐dobdc) and Mn2(m‐dobdc) is 4.31 and 8.21 wt%, respectively.

Rapid and green detection of manganese in electrolytes by ultraviolet-visible spectrometry to control pollutant discharge.

Controlling the manganese (Mn2+) concentration is important to product quality in the electrolytic manganese industry. Conventional methods for detecting Mn2+ are complex and reagent-consuming, which makes them slow and polluting. It is of great significance to develop a new fast and environmentally friendly method to quantify Mn2+ in electrolyte. The characteristic ultraviolet-visible (UV-vis) absorbance at 401 nm of Mn2+ will vary linearly with the Mn2+ concentration after data correction. Adjusting the pH, calibrating the spectral bandwidth (SBW) and optical path length (OPL), and subtracting the interference from coexisting substances by linear interpolation improve the measuring accuracy. Mn2+ concentration can be determined by direct fast UV-vis absorbance measurement at characteristic peaks without using harmful reagents which facilitates such measurement to be applicated as on-line detection method for electrolytic manganese industry. The method developed in this study will help achieve the goal of improving the detection speed while cutting back on pollutant discharge from concentration analysis process in electrolytic manganese industry.

The substitution of Mg2+ with Mn2+/4+ metal ions in chlorophyll structure isolated from Gliricidia sepium leaves

One of the critical issues of using chlorophyll (Mg-Chl) as a dye photosensitizer in DSSC is related to a rapid decay of this material. Changing the alkali metal using transition metal ions could theoretically increase the stability of chlorophyll. In this research, the substitution of Mg2+ with Mnn+ ions (n = 2 and 4) in chlorophyll structure isolated from Gliricidia sepium leaves had been carried out. The column chromatography technique was chosen to separate the chlorophyll followed by modifying the metal centre using two different compounds containing manganese, namely MnCl2 and MnO2. The results show that there are differences in Rf values after substitutions, [0.90 (Mg-Chl), 0.81 (Mn2+-Chl), and 0.96 (Mn4+-Chl)]. The Soret bands experience a redshift from 330 to 338 nm for Mn2+-Chl and a blue shift from 411 to 401 nm for Mn4+-Chl while the Q band has a redshift from 665 to 668 nm for Mn2+-Chl but a blue shift from 665 to 526 nm for Mn4+-Chl. The obtained products have similar IR absorption patterns to Mg-Chl but differ only in its transmittance with slightly higher wavenumbers shifts. Shifting of UV-Visible and Infra-red characteristics indicate different molecular electronic nature of the obtained compounds. This implies successful substitution for the metal centre without damaging the structure of the chlorophyll.

Solar light driven photocatalytic oxidative degradation of methyl viologen using Mn2+/Mn7+-TiO2 nanocomposites

Transition metal/metal ions are reported to impart very efficient co-catalytic activity to TiO2 for various photocatalytic reactions depending on the nature and oxidation state of metal ions. However, when certain metals (Mn+) having different oxidation states like Mn2+/Mn7+ or Cr3+/Cr6+ act as co-catalysts, the photocatalytic properties of Mn+-TiO2 nanocomposites may vary significantly. Different surface morphologies, electron transfer phenomena and adsorption efficacy provided by these co-catalysts will govern the Mn+-TiO2 photoactivity. In this context, this paper demonstrates the preparation and characterization of Mn2+/Mn7+-TiO2 nanocomposites for investigating the above physicochemical properties for the degradation of toxic herbicide Methyl viologen under sunlight irradiation. The optical spectra of these catalysts showed bathochromic shifts (from 355 to 572 nm) due to the presence of Mn2+ and Mn7+ ions. The higher co-catalyst stability, smaller Dmax (maximum average diameter) and mixed morphological characteristics have been illustrated by SAXS and TEM analysis with size range ∼ 25–30 and 20−35 nm for Mn2+-TiO2 and Mn7+-TiO2 nanocomposites, respectively. The adsorption-desorption studies using NH3 gas revealed that Mn7+ ions generate enhanced Lewis acidity on the co-catalyst surface compared to Mn2+ impregnations. The best fit for Freundlich adsorption isotherm (Kf = 23.44 μg/mg) was possessed by Mn7+-TiO2 than Mn2+-TiO2 and TiO2 photocatalyst confirming its higher substrate affinity and photodegradation efficiency. The Mn2+ and Mn7+ impregnations displayed 2.6 and 3.7 times higher photoactivity than bare TiO2 which has been correlated to different oxidation states and surface structural properties imparted by Mnn+ ions.

Novel luminescent paper based calix[4]arene chelation enhanced fluorescence- photoinduced electron transfer probe for Mn2+, Cr3+ and F-

A novel structurally simple calix[4]arene attached 1-aminoanthraquinone associated lower rim calix[4]arene conjugate was synthesized and has been used as turn on/off/on fluorescence probe for Mn2+, Cr3+ and F-. This chelation enhanced fluorescence - photoinduced electron transfer (CHEF-PET) based TAAC probe has been applied for its analytical application in real samples such as Mn2+ from blood serum, Cr3+ and F- from industrial effluent with 94–99% recovery. The limit of detection of this sensor is found to be 11 nM for Mn2+, 4 nM for Cr3+ and 19 nM for F- with the concentration range of 0–120 nM. Further, we report an easy-to-use, low cost and disposable paper-based sensing device for rapid chemical screening of Mn2+, Cr3+ and F-. The device comprises fluorescent sensing probes embedded into a nitrocellulose matrix where the resonance energy transfer phenomenon seems to be the sensing mechanism. It opens up new opportunities for simple and fast screening in remote settings where sophisticated instrumentation is not always available. The MOPAC-2016 software package has been used to optimize the TAAC using PM7 well established method and calculates the HOMO-LUMO energy band gap for structure TAAC and TAAC with Mn2+, Cr3+ and F- ion based structures.

Photoluminescence and cathodoluminescence of Mn doped zinc silicate nanophosphors for green and yellow field emissions displays

Mn2+-doped Zn2SiO4 (ZSM2+) was synthesized by a facile sol–gel technique. The obtained samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, photoluminescence (PL) and cathodoluminescence (CL) techniques. Under UV excitation, spectra showed that the α-ZSM2+ phosphor exhibited a strong green emission around 525 nm and reached the highest luminescence intensity with the Mn doping concentration of 5 at.%. However, for the β-ZSM2+ phase, an interesting yellow emission band centered at ~ 575 nm of Mn2+ at the Zn2+ tetrahedral sites was observed. In addition, an unusual red shift with increasing Mn2+ content was also found and attributed to an exchange interaction between Mn2+. Both PL and CL spectra exhibit an intense green and yellow emission centered at ~ 525 and ~ 573 nm, respectively, due to the 4T1 (4G)-6A1 (6S) transition of Mn2+. Furthermore, these results indicated that the Mn2+-doped zinc silicate phosphors may have potential applications in green and yellow emissions displays like field emission displays (FEDs).

Tunable Luminescence and Energy Transfer Investigation in Sr8La2[(PO4)4.5(SiO4)2(BO4)0.5](BO2): Ce3+/Mn2+ for White-Light-Emitting Diodes

Powder samples of Sr8La2[(PO4)4.5(SiO4)2(BO4)0.5](BO2) (SLP) doped with Mn2+ and Ce3+ were prepared by solid-state reaction method and their photoluminescence properties were studied for the first time. The crystalline structure of the samples was monitored by the X-ray powder diffraction (XRD) technique. The emission spectra of the phosphors show a blue broad band at about 420 nm of Ce3+ and an orange band at around 620 nm of Mn2+. Energy transfer mechanism from Ce3+ to Mn2+ in SLP host matrix was studied based on the decay lifetime data. In this work, the tunable emission colors from blue to orange have been achieved by tuning the relative ratio of the Ce3+ to Mn2+ based on the principle of energy transfer, and the developed phosphor could be promising as a single-component white-light-emitting phosphor for white light-emitting diodes (W-LEDs).

Improvement of Luminescence Properties of Blue‐to‐Red Emitting NaCaBO3: Ce3+, Mn2+ Phosphor Prepared by Sol–Gel Method

Color‐tunable phosphors NaCaBO3: Ce3+, Mn2+ were synthesized by sol–gel (SG) and solid state (SS) method. SEM observation indicated that the microstructure of phosphor (SG) consisted of regular fine grains with an average size of about 5 μm. NaCaBO3: Ce3+, Mn2+ showed two emission bands: one at 425 nm for Ce3+ and another at 610 nm for Mn2+. NaCaBO3: Ce3+, Mn2+ (SG) exhibit higher energy‐transfer efficiency (90%) and higher Mn2+ quantum efficiency (80%) than SS samples, due to smooth surface, narrow size distribution, and improved homogeneity of sensitizer/activator ions. NaCaBO3: Ce3+, Mn2+ exhibits blue‐to‐red tunable color by changing Ce3+/Mn2+ ratio.

Superposition-model analysis of zero-field splitting parameters for Mn2+ in NSHH and MSHH single crystals

The superposition-model suggested by Newman has been used to calculate the zero-field splitting parameters (ZFS) at room temperature that fit the experimental data taken from the literature. The satisfactory reproduction of experimental values of ZFS parameters indicates that Mn2+ substitute in place of Ni2+ and Mg2+ in the lattices and does not cause appreciable local distortion in the host crystals NSHH and MSHH. The calculations are made with the assumption that the total field experienced at an ion in a crystal is due to nearest neighbor ions, using power law exponent t2 = 7 ± 1 and t4 = 10 ± 1 the reference distance Rο = 0.22 nm for Mn2+ surrounded by oxygens. The superposition model analysis shows that for large values of ZFS parameters b20, b22, b40, b42 and b44, intrinsic parameters \( \bar{b}_{ 2} \) and \( \bar{b}_{ 4} \) can be estimated with suitable errors but for small values of these spin–Hamiltonian parameters it is very difficult to predict the correct sign and magnitude.

Quaternary Structure and Metal Ion Requirement of Family II Pyrophosphatases from Bacillus subtilis,Streptococcus gordonii, and Streptococcus mutans

Pyrophosphatase (PPase) from Bacillus subtilis has recently been found to be the first example of a family II soluble PPase with a unique requirement for Mn2+. In the present work, we cloned and overexpressed in Escherichia coli putative genes for two more family II PPases (from Streptococcus mutans and Streptococcus gordonii), isolated the recombinant proteins, and showed them to be highly specific and active PPases (catalytic constants of 1700-3300 s(-)1 at 25 degrees C in comparison with 200-400 s(-)1 for family I). All three family II PPases were found to be dimeric manganese metalloenzymes, dissociating into much less active monomers upon removal of Mn2+. The dimers were found to have one high affinity manganese-specific site (K(d) of 0.2-3 nm for Mn2+ and 10-80 microm for Mg2+) and two or three moderate affinity sites (K(d) approximately 1 mm for both cations) per subunit. Mn2+ binding to the high affinity site, which occurs with a half-time of less than 10 s at 1.5 mm Mn2+, dramatically shifts the monomer <--> dimer equilibrium in the direction of the dimer, further activates the dimer, and allows substantial activity (60-180 s(-)1) against calcium pyrophosphate, a potent inhibitor of family I PPases.

Purification and characterization of phosphoenolpyruvate phosphomutase from Pseudomonas gladioli B-1.

Phosphoenolpyruvate phosphomutase (PEPPM) catalyzes C-P bond formation by intramolecular rearrangement of phosphoenolpyruvate to phosphonopyruvate (PnPy). We purified PEPPM from a gram-negative bacterium, Pseudomonas gladioli B-1 isolated as a C-P compound producer. The equilibrium of this reaction favors the formation of the phosphate ester by cleaving the C-P bond of PnPy, but the C-P bond-forming reaction is physiologically significant. The C-P bond-forming activity of PEPPM was confirmed with a purified protein. The molecular mass of the native enzyme was estimated to be 263 and 220 kDa by gel filtration and polyacrylamide gel electrophoresis, respectively. A subunit molecular mass of 61 kDa was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, indicating that the native protein was a tetramer. The optimum pH and temperature were 7.5 to 8.0 and 40 degrees C, respectively. The Km value for PnPy was 19 +/- 3.5 microM, and the maximum initial velocity of the conversion of PnPy to phosphoenolpyruvate was 200 microM/s/mg. PEPPM was activated by the presence of the divalent metal ion, and the Km values were 3.5 +/- 1.4 microM for Mg2+, 16 +/- 5 nM for Mn2+, 3.0 +/- 1.5 microM for Zn2+, and 1.2 +/- 0.2 microM for Co2+.