Iron environment non-equivalence in both octahedral and tetrahedral sites in NiFe2O4 nanoparticles: study using Mössbauer spectroscopy with a high velocity resolution

Mössbauer spectrum of NiFe2O4 nanoparticles was measured at room temperature in 4096 channels. This spectrum was fitted using various models, consisting of different numbers of magnetic sextets from two to twelve. Non-equivalence of the 57Fe microenvironments due to various probabilities of different Ni2+ numbers surrounding the octahedral and tetrahedral sites was evaluated and at least 5 different microenvironments were shown for both sites. The fit of the Mössbauer spectrum of NiFe 2O4 nanoparticles using ten sextets showed some similarities in the histograms of relative areas of sextets and calculated probabilities of different Ni2+ numbers in local microenvironments. © 2012 American Institute of Physics

Nitrogen-doped Multi-walled Carbon Nanotubes-MnCo2O4 microsphere as electrocatalyst for efficient oxygen reduction reaction

Nitrogen-doped Multi-walled Carbon Nanotubes (N-doped MWCNT)/MnCo2O4 hybrid is synthesized by a facile hydrothermal method. The X-ray diffraction studies revealed the single phase formation of cubic spinel structured MnCo2O4 and their composites. The presence of D and G band of MWCNT is identified through Raman spectral analysis. The elemental oxidation state and nitrogen content is obtained using X-ray photoelectron spectroscopy, which elucidates that Co and Mn exists in multivalence state and the nitrogen functional groups are in pyrolytic and pyridinic-type. FE-SEM shows the microsphere formation of MnCo2O4 and size exhibits in the range of 6-9 μm. The N-doped MWCNT/MnCo2O4 hybrid catalyst exhibits an improved oxygen reduction electrocatalytic activity in an aqueous alkaline medium when compared with pristine MnCo2O4. © 2016 Hydrogen Energy Publications LLC.1

Suitability of Clustering Algorithms for Crime Hotspot Analysis

Abstract-Crime analysis is a field that needs immediate attention due to the drastic increase of number of crimes. Most of the crimes, from the past experiences of the police, are said to be concentrated in some areas, called hotspots and keep on recurring. Clustering algorithms are best applied to crime analysis, but suitability of broad spectrum of clustering algorithm for an application is an issue to be addressed. In this paper we evaluate three clustering algorithms i.e. hierarchical clustering, k-means clustering and DBSCAN clustering with the intent of finding the best one suitable for crime hotspot analysis. Each one of the clustering algorithm evaluated here need inputs such as number of clusters, neighbour distance, minimum number of points etc. are needed by a cluster. The cluster similarity measure is the Euclidean distance. The results suggest that DBSCAN is much more suitable to crime hotspot analysis due to its inherent nature of being density driven

Critical behavior of resistivity in the pressure-induced first to second order transition in Pr0.6Ca0.4Mn0.96B0.04O3(B = Co and Cr)

10.1016/j.jallcom.2014.08.112Journal of Alloys and Compounds618159-16

Synthesis of Bi2WO6 nanoparticles and its electrochemical properties in different electrolytes for pseudocapacitor electrodes

Nanosized Bi2WO6 particles were successfully synthesized by sonochemical method with an objective to develop an inexpensive and eco-friendly electrode material for supercapacitors. The prepared material was subjected to various thermal, structural, morphological, compositional, electrical and electrochemical studies. Bi2WO6 nanoparticle with homogeneous distribution was achieved through sonochemical process. The lattice parameter and atomic positions of Bi2WO6 structure were refined through Reitveld analysis. The electrochemical performance of Bi2WO6 nanoparticles was investigated in various aqueous electrolytes such as 1 M NaOH, 1 M LiOH, 1 M Na2SO4, 1 M KOH and 6 M KOH solutions. Among these, the material exhibited an enhanced electrochemical performance in KOH electrolyte due to its smaller hydration sphere radius, high ionic mobility and lower equivalent series resistance. The charge–discharge studies rendered a specific capacitance of 608 F/g in 1 M KOH at a current density of 0.5 mA/cm2. Bi2WO6 exhibited an excellent coulombic efficiency and specific capacitance of around 304 F/g at 3 mA/cm2 in the potential range from −0.9 to 0.1 V vs Hg/HgO in 1 M KOH electrolyte. The above results assured that Bi2WO6 could be utilized as suitable negative electrode material for supercapacitor applications and 1 M KOH could be its desirable electrolyt

Mossbauer spectroscopy of NiFe2O4 nanoparticles: The effect of Ni2+ in the Fe3+ local microenvironment in both tetrahedral and octahedral sites

Two samples of combustion synthesized nickel ferrite nanoparticles were characterized using X-ray diffraction, scanning and transmission electron microscopy, magnetization measurements and MOssbauer spectroscopy with a high velocity resolution. It was shown that MOssbauer spectra of nickel ferrite can be well fitted by using ten magnetic sextets related to the different numbers of Ni2+ cations in the Fe3+ local microenvironments in both tetrahedral and octahedral sites supported by calculations of such probabilities. it was shown that increase of the number of Ni2+ cations in the Fe-57 local microenvironment around both sites leads to decrease of the hyperfine field. (C) 2017 Elsevier B.V. All rights reserved

High Performance Solid-State Electric Double Layer Capacitor from Redox Mediated Gel Polymer Electrolyte and Renewable Tamarind Fruit Shell Derived Porous Carbon

The activated carbon was derived from tamarind fruit shell and utilized as electrodes in a solid state electrochemical double layer capacitor (SSEDLC). The fabricated SSEDLC with PVA (polyvinyl alcohol)/H₂SO₄ gel electrolyte delivered high specific capacitance and energy density of 412 F g^‑1 and 9.166 W h kg^‑1, respectively, at 1.56 A g^‑1. Subsequently, Na₂MoO₄ (sodium molybdate) added PVA/H₂SO₄ gel electrolyte was also prepared and applied for SSEDLC, to improve the performance. Surprisingly, 57.2% of specific capacitance (648 F g^‑1) and of energy density (14.4 Wh kg^‑1) was increased while introducing Na₂MoO₄ as the redox mediator in PVA/H₂SO₄ gel electrolyte. This improved performance is owed to the redox reaction between Mo­(VI)/Mo­(V) and Mo­(VI)/Mo­(IV) redox couples in Na₂MoO₄/PVA/H₂SO₄ gel electrolyte. Similarly, the fabricated device shows the excellent capacitance retention of 93% for over 3000 cycles. The present work suggests that the Na₂MoO₄ added PVA/H₂SO₄ gel is a potential electrolyte to improve the performance instead of pristine PVA/H₂SO₄ gel electrolyte. Based on the overall performance, it is strongly believed that the combination of tamarind fruit shell derived activated carbon and Na₂MoO₄/PVA/H₂SO₄ gel electrolyte is more attractive in the near future for high performance SSEDLCs

Facile synthesis of monodispersed 3D hierarchical Fe3O4 nanostructures decorated r-GO as the negative electrodes for Li-ion batteries

One-pot solvothermal process is adopted to develop, 3D hierarchical Fe3O4 nanoparticles supported 2D reduced graphene oxide sheets (Fe3O4/r-GO) as possible negative electrodes for lithium ion batteries. The synthesis parameters are optimized to prepare agglomeration-free Fe3O4 nanostructures with uniform size and shape on r- GO. The field emission scanning electron microscopic (FESEM) image reveals that the 3D hierarchical Fe3O4 nanostructures are uniformly decorated on r-GO. The physicochemical and functional properties of Fe3O4/r-GO are systematically investigated using various techniques. The fabricated Fe3O4/r-GO electrode delivers an initial discharge capacity of 1221 mAh g−1 at a current density of 100 mA g−1 and retains the specific capacity of 1560 mAh g−1 after 100 cycles. Fe3O4/r-GO significantly enhances cyclic performance, when compared with bare Fe3O4 nanoparticles due to the uniform distribution of Fe3O4 nanoparticles on the graphene sheet with the more number of electrochemically active sites.114Nsciescopu

High Performance Solid-State Electric Double Layer Capacitor from Redox Mediated Gel Polymer Electrolyte and Renewable Tamarind Fruit Shell Derived Porous Carbon

The activated carbon was derived from tamarind fruit shell and utilized as electrodes in a solid state electrochemical double layer capacitor (SSEDLC). The fabricated SSEDLC with PVA (polyvinyl alcohol)/H₂SO₄ gel electrolyte delivered high specific capacitance and energy density of 412 F g^‑1 and 9.166 W h kg^‑1, respectively, at 1.56 A g^‑1. Subsequently, Na₂MoO₄ (sodium molybdate) added PVA/H₂SO₄ gel electrolyte was also prepared and applied for SSEDLC, to improve the performance. Surprisingly, 57.2% of specific capacitance (648 F g^‑1) and of energy density (14.4 Wh kg^‑1) was increased while introducing Na₂MoO₄ as the redox mediator in PVA/H₂SO₄ gel electrolyte. This improved performance is owed to the redox reaction between Mo­(VI)/Mo­(V) and Mo­(VI)/Mo­(IV) redox couples in Na₂MoO₄/PVA/H₂SO₄ gel electrolyte. Similarly, the fabricated device shows the excellent capacitance retention of 93% for over 3000 cycles. The present work suggests that the Na₂MoO₄ added PVA/H₂SO₄ gel is a potential electrolyte to improve the performance instead of pristine PVA/H₂SO₄ gel electrolyte. Based on the overall performance, it is strongly believed that the combination of tamarind fruit shell derived activated carbon and Na₂MoO₄/PVA/H₂SO₄ gel electrolyte is more attractive in the near future for high performance SSEDLCs