Thermal stability and non-isothermal decomposition kinetics of a polynuclear coordination compound precursor of copper ferrite

Results are presented on the thermal behaviour of [Fe(III)₂Cu(C₂C₄)₂(OH)₄(H₂O)₂] precursor of copper ferrite. An investigation of the decomposition steps and intermediates was followed by a non-isothermal kinetic analysis of the processable steps.     

Thermal analysis of some polynuclear coordination compounds

The thermal behaviour of five polynuclear coordination compounds containing tartaric anion as ligand, namely (NH₄)₃[LnFe(C₄O₆H₄)₃(OH)₃] (Ln=La and Eu), (NH₄)₂[PrFe(C₄O₆H₄)₃(OH)₂] and (NH₄)[LnFe(C₄O₆H₄)₃(OH)]·3H₂O (Ln=Nd and Gd) was investigated. The reaction progress was studied by TG/DTA and FTIR measurements. Oxalates and oxocarbonates were identified as intermediates. In the case of Ln=La, Nd, Pr, Eu and Gd, pure LnFeO₃ was obtained as final decomposition product. The thermal decomposition of Eu-Fe compound, leads to a mixture of mixed (ortho-ferrite (EuFeO₃) and garnet (Eu₃Fe₅O₁₂)) and simple oxides (Eu₂O₃ and α-Fe₂O₃).     

Thermal analysis of some polynuclear coordination compounds as precursors of iron garnets (M3Fe5O12, M=Y3+ or Er3+)

The thermal behaviour of four coordination compounds (NH₄)₆[Y₃Fe₅(C₄O₅H₄)₆(C₄O₅H₃)₆]·12H₂O, (NH₄)₆[Y₃Fe₅(C₆O₇H₁₀)₆(C₆O₇H₉)₆]·8H₂O, (NH₄)₆[Er₃Fe₅(C₄O₅H₄)₆(C₄O₅H₃)₆]·10H₂O and (NH₄)₆[Er₃Fe₅(C₄O₆H₄)₆(C₄O₆H₃)₆]·22H₂O has been studied to evaluate their suitability for garnet synthesis. The thermal decomposition and the phase composition of the resulted decomposition compounds are influenced by the nature of metallic cations (yttrium-iron or erbium-iron) and ligand anions (malate or gluconate).     

Synthesis, characterisation and thermal behaviour of some thiosulfato-and sulfato copper(II) complexes

The investigation concerning the synthesis, spectrochemical and biological properties as well as thermal stability of some tiosulfato-and sulfato copper(II) complexes of type [Cuphen(S₂O₃)(H₂O)_n]·mH₂O (phen: 1,10-phenanthroline; (1): n=2, m=0; (2): n=2, m=0.5) and respectively [Cuphen(OSO₃)(H₂O)_n] ((3): n=0; (4): n=2) are presented in this paper. The bonding and stereochemistry of the complexes have been characterised by IR and electronic studies. The in vitro qualitative and quantitative assays of the antimicrobial activity of the tested compounds vs. planktonic and adherent Gram negative bacterial strains isolated from different surfaces in the hospital environment demonstrated that all compounds exhibited very good antimicrobial activity vs. Escherichia coli, Klebsiella sp. and Enterobacter sp. with very low M.I.C. values. The thermal analysis has evidenced the thermal intervals of stability and also the thermodynamics effects that accompany them both in synthetic air and argon. The thermal behaviour is complex according to DTG and DSC curves including dehydration as well as thiosulfate and phenanthroline decomposition.     

Synthesis of nanosized bismuth ferrite (BiFeO3) by a combustion method starting from Fe(NO3)3·9H2O-Bi(NO3)3·9H2O-glycine or urea systems

Two bismuth ferrite potential precursors systems, namely Fe(NO₃)₃·9H₂O-Bi(NO₃)₃·9H₂O-glycine/urea with different metal nitrate/organic compound molar ratios have been investigated in order to evaluate their suitability as BiFeO₃ precursors. The presence into the precursor of both reducing (glycine and urea) and oxidizing (NO₃⁻) components, modifies dramatically their thermal behaviour comparative with the raw materials, both from the decomposition stoichiometries and temperature occurrence intervals points of view. Also, the thermal behaviour is dependent on the fuel nature but practically independent with the fuel content. The fuel nature influences also some characteristics of the resulted oxides (phase composition, morphologies). In the case of the oxides prepared using urea as fuel, a faster evolution toward a single phase composition with the temperature rise is evidenced, the formation of the BiFeO₃ perovskite phase being completed in the temperature range of 500–550°C.     

Removal of reactive dye brilliant red HE-3B from aqueous solutions by hydrolyzed polyacrylonitrile fibres: equilibrium and kinetics modelling

A cheap and efficient fibrous hydrolyzed polyacrylonitrile (HPAN) sorbent was obtained by alkaline hydrolysis of Romanian polyacrylonitrile fibres. Scanning electronic microscopy and infrared spectroscopy were used to characterize the hydrolyzed product and to confirm its functionalization. The adsorptive potential of the proposed sorbent for reactive dye Brilliant Red HE-3B removal from aqueous solutions of pH=2 was examined by the batch technique as a function of dye concentration, temperature solution and contact time. The Freundlich, Langmuir and Dubinin-Radushkevich adsorption models were applied to describe equilibrium sorption data and to determine the corresponding isotherm constants. The thermodynamic parameters ΔG, ΔH and ΔS were also determined; the values obtained show that sorption of reactive dye on HPAN fibres is a spontaneous, endothermic and entropy-driven process. The kinetics of sorption of the reactive dye were analyzed using pseudo-first order and pseudo-second order kinetic models. The kinetic data fitted well to pseudo-second order kinetics, indicating the chemisorption of reactive dye onto the fibrous sorbent. The sorption mechanism of the dye onto hydrolyzed fibres was confirmed by FTIR spectroscopy. The dye-loaded HPAN sorbent can be regenerated by treatment with 0.1M NaOH and the regenerated sorbent may be reused in several adsorption-desorption cycles. The results of this study provided evidence that the HPAN fibres are effective for removing reactive dye Brilliant Red HE-3B from aqueous effluents.      

Homogenization of the Stokes Problem With Non-homogeneous Slip Boundary Conditions

We study the Stokes system with non-homogeneous Fourier boundary conditions depending on a parameter, in a domain with periodic inclusions of the size of the period. Following the values of this parameter, we obtain at the limit a Darcy's law, a Brinkmann type equation or a Stokes type equation. We also present a physical model to which the results apply. This model describes the flow of an incompressible viscous fluid through a porous medium under the action of an exterior electric field.     

Intense laser effects on the optical properties of asymmetric GaAs double quantum dots under applied electric field

We investigated the combined effects of a non-resonant intense laser field and a static electric field on the electronic structure and the nonlinear optical properties (absorption, optical rectification) of a GaAs asymmetric double quantum dot under a strong probe field excitation. The calculations were performed within the compact density-matrix formalism under steady state conditions using the effective mass approximation. Our results show that: (i) the electronic structure and optical properties are sensitive to the dressed potential; (ii) under applied electric fields, an increase of the laser intensity induces a redshift of the optical absorption and rectification spectra; (iii) the augment of the electric field strength leads to a blueshift of the spectra; (iv) for high electric fields the optical spectra show a shoulder-like feature, related with the occurrence of an anti-crossing between the two first excited levels.     

Magnetic nanoparticles and concentrated magnetic nanofluids： Synthesis, properties and some applications

This paper reviews some recent results concerning chemical synthesis of magnetic nanoparticles and preparation of various types of magnetic nanofluids. Structural properties and behaviour in external magnetic field of magnetic nanofluids will be emphasized with relation to their use in leakage-free rotating seals and in biomedical applications.