Electrochemical, Electrocatalytic, and Magnetic Properties of Vanadium-Containing Polyoxometalates

Mono-substituted vanadium-containing Dawson-type polyoxometalates having the general formula α1-[VIVW17X2O62]8− and α2-[VIVW17X2O62]8−, with X = As or P, were synthesised and subject to a comprehensive electrochemical study comprising the pH dependency. These POMs exhibit an electrocatalytic behaviour towards the oxidation of thiols (namely cysteine), rendering them interesting species for mimicking oxidative stress situations, at physiological pH values. The efficiency of the electro-oxidation was assessed with thiols of different nature, and the substrate that responded best was used to compare the electrocatalytic capabilities of the POM series. The magnetic behaviour of these POMs was also evaluated and compared to their analogues, α1- and α2-[VVW17X2O62]7− (X = As or P), at low temperatures and showed, as expected, a paramagnetic behaviour of VIV based compounds.

Influence of Drainage on Peat Organic Matter: Implications for Development, Stability, and Transformation

The agricultural use of peatlands, the stabilization of the substrate for building or road construction or for increasing the capacity of soil to support heavy machinery for industrial activities (peat and petroleum extraction), harvesting to provide peat for energy, and the growing media and initiation of chemical processes must be preceded by drainage. As a consequence of drainage, peat underwent an irreversible conversion into moorsh (secondary transformation of the peat). The object of the study was to investigate comparatively the organic matter composition and molecular structure of humic acids (HAs) in the raised bog, fen, and peat-moorsh soils developed in various compositions of botanical cover, peat-forming species, and oxic and anoxic conditions as a result of the oscillation of ground water during drainage as well as to evaluate the vulnerability of soil organic matter (SOM) to decomposition. Drainage was shown to be the principal factor causing the various chemical compositions and physicochemical properties of HAs. Large and significant differences in chemical composition of peat and the properties of HAs were found to be related to the degree of decomposition. The HAs from drained peatlands were less chemically mature. In contrast, the HAs from fen and raised bog were found to be more mature than that of the corresponding drained peatlands. The above findings showed the distinguishable structure of HAs within the soil profile created by the plant residue biodegradation and formed in both oxic and anoxic conditions. The analytical methods of thermal analysis together with the optical densities and paramagnetic behaviour are suitable and effective tools for studying structure–property relationships characterizing the origin and formation process of HAs in various environmental conditions.

Novel K/Mn phosphate hydrates, K2Mn3(H2O)2[P2O7]2 and KMn(H2O)2[Al2(PO4)3]: hydrothermal synthesis and crystal chemistry

Two novel K/Mn phosphate hydrates, namely, dipotassium trimanganese dipyrophosphate dihydrate, K2Mn3(H2O)2[P2O7]2, (I), and potassium manganese dialuminium triphosphate dihydrate, KMn(H2O)2[Al2(PO4)3], (II), were obtained in the form of single crystals during a single hydrothermal synthesis experiment. Their crystal structures were studied by X-ray diffraction. Both new compounds are members of the morphotropic series of phosphates with the following formulae: A 2 M 3(H2O)2[P2O7]2, where A = K, NH4, Rb or Na and M = Mn, Fe, Co or Ni, and AM 2+(H2O)2[M 3+ 2(PO4)3], where A = Cs, Rb, K, NH4 or (H3O); M 2+ = Mn, Fe, Co or Ni; and M 3+ = Al, Ga or Fe. A detailed crystal chemical analysis revealed correlations between the unit-cell parameters of the members of the series, their structural features and the sizes of the cations. It has been shown that a mixed type anionic framework is formed in (II) by aluminophosphate [(AlO2)2(PO4)2]∞ layers, with a cationic topology similar to the Si/Al-topology of the crystal structures of feldspars. A study of the magnetic susceptibility of (II) demonstrates a paramagnetic behaviour of the compound.

Fast Synthesis of Co3O4 by Microwave-Assisted Hydrothermal Treatment

This work describes a fast and simple procedure that combines the virtues of the microwave-assisted hydrothermal method with an oxidizing agent to produce Co3O4 nanocubes and nanoplates. We observed that particle morphology and size depend on the synthesis time and oxidizing agent (urea and hydrogen peroxide). The X-ray diffraction results showed that the samples are single phase, with crystallite sizes of approximately 30 nm. A similar crystalline domain is observed in the transmission electronic images. Magnetic measurements revealed the influence of the size and morphology of the particles on the magnetic curves. These measurements on the nanoplate samples revealed a paramagnetic behaviour at higher temperatures, and the presence of a cusp at that temperature was defined as TP. The TP decreases from 36 K to 21 K when the size of the plate particles decreases from ~70 nm to 10 nm. These samples also present weak ferromagnetism below TP, which is attributed to a superparamagnetic blockade state. The nanocube samples have a lower magnetic susceptibility magnitude and weak ferromagnetism behaviour at room temperature. Our results show that this synthesis produces Co3O4 nanoplates and nanocubes with interesting magnetic properties related to their shape and size.

Magnetic response of bovine spleen

Bovine spleen has been used as a sample for deep magnetochemical investigation. Temperature dependence of the magnetic susceptibility and field dependence of the magnetization reveal a paramagnetic behaviour that violates the Curie law. The zero-field cooled magnetization and field cooled magnetization experiments show the bifurcation point at ca TC = 20 K and the blocking temperature TB = 10 K confirming a dominating portion of ferritin along with the organic tissue. There is a remnant magnetization at temperature below 20 K and the search for the magnetic hysteresis was positive.

Structure and Magnetic Properties of (Cr,Ni)4-xCoxSi

The crystal structure of the (Cr,Ni)4Si phase with and without Co was refined from X-ray powder diffraction data. The compound crystallises with an Au4Al-type structure (Pearson symbol cP20, space group P213): unit-cell parameter a = 0.611959(6) nm for the composition (Cr0.312Ni0.688)4Si, a = 0.612094(6) nm for (Cr0.375Ni0.625)4Si, and a = 0.612316(6) nm for (Cr0.337Co0.063Ni0.600)4Si. The magnetic susceptibility was measured in external fields up to 7 T at temperatures between 1.8 and 400 K. The three investigated samples exhibited paramagnetic behaviour described by the modified Curie-Weiss law: χ0 = 146∙10-6 emu g-at.-1, μeff = 0.21 μB/atom, θP = -13 K for (Cr0.312Ni0.688)4Si; χ0 = 158∙10-6 emu g-at.-1, μeff = 0.20 μB/atom, θP = -15 K for (Cr0.375Ni0.625)4Si; χ0 = 169∙10-6 emu g-at.-1, μeff = 0.18 μB/atom, θP = -52 K for (Cr0.337Co0.063Ni0.600)4Si.

Investigations on Bi25FeO40 powders synthesized by hydrothermal and combustion-like processes

The syntheses of phase−pure and stoichiometric iron sillenite (Bi25FeO40) powdersby a hydrothermal (at ambient pressure) and a combustion−like process are described.Phase−pure samples were obtained in the hydrothermal reaction at 100 °C (1), whereas thecombustion−like process leads to pure Bi25FeO40 after calcination at 750 °C for 2 h (2a). Theactivation energy of the crystallite growth process of hydrothermally synthesized Bi25FeO40was calculated as 48(9) kJ mol−1. The peritectic point was determined as 797(1) °C. Theoptical band gaps of the samples are between 2.70(7) eV and 2.81(6) eV. Temperature andfield−depending magnetization measurements (5−300 K) show a paramagnetic behaviour with a Curie constant of 55.66·10−6 m3·K·mol−1 for sample 1 and C = 57.82·10−6 m3·K·mol−1for sample 2a resulting in magnetic moments of μmag = 5.95(8) μB·mol−1 and μmag = 6.07(4)μB·mol−1. The influence of amorphous iron−oxide as a result of non-stoichiometric Bi/Feratios in hydrothermal syntheses on the magnetic behaviour was additionally investigated.

Slow magnetic relaxation in Cu(ii)–Eu(iii) and Cu(ii)–La(iii) complexes

A dinuclear [(H2O)Cu(HLN2O2)Eu(NO3)3] complex exhibits paramagnetic behaviour with S = 1/2 ground state. At low temperature it displays slow magnetic relaxation that is supported by a small external magnetic field.

A CuII complex with an carbamoylcyanonitrosomethanide ligand formed in situ by the nucleophilic addition of water to dicyanonitrosomethanide: structure, spectral and magnetic properties

The complex (2,2′-biquinoline-κ2 N,N′)(carbamoylcyanonitrosomethanide-κ2 N,O)chloridocopper(II) acetonitrile monosolvate, [Cu(C3H2N3O2)Cl(C18H12N2)]·CH3CN or [Cu(ccnm)Cl(biq)]·acn (acn is acetonitrile, biq is 2,2′-biquinoline and ccnm is carbamoylcyanonitrosomethanide), (I), was prepared as a result of nucleophilic addition of water to the dicyanonitrosomethanide ion in the presence of CuII and biq. IR spectroscopy confirmed the presence of ccnm, biq and acn in (I). The solid-state structure consists of the neutral complex containing ccnm and biq ligands, coordinated to the CuII atom in a bidendate chelating manner, and a chloride ligand, resulting in a distorted tetragonal pyramidal coordination of CuII. The asymmetric unit is supplemented by one molecule of solvated acn which, along with the nitrile group of ccnm, serves as an acceptor in intermolecular hydrogen bonding, creating infinite chains along the b axis. Magnetic measurements revealed a paramagnetic behaviour with a very small Weiss temperature Θ = −0.32 K and high anisotropy of the g tensor (g x = 2.036, g y = 2.120 and g z = 2.205).

Formation of nanocrystalline B2-structured (Fe,Ni)Al in mechanically alloyed Fe50Al30Ni20 (wt.%) powder

B2-structured (Fe,Ni)Al was synthesised by an abrupt reaction during mechanical alloying (MA) of the elemental powders of Fe, Al and Ni. The structural, microstructural, morphological and magnetic changes occurring in the studied material during MA were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Two crystalline phases were found, a majority one corresponding to (Fe,Ni)Al bcc phase with a crystallite size less than 10 nm, a lattice strain up to 1.6% and a dislocation density of about 2.3 x1016 m-2. The other phase was in a low proportion corresponding to Fe (Al,Ni) solid solution. SEM images showed an irregular morphology of powder particles. Mossbauer spectra of the milled powders, recorded at room temperature, reveal the paramagnetic behaviour of the obtained powder. Keywords: Mechanical alloying, ternary composition, dislocation density, structural properties, paramagnetic behaviour.