Applied macroinorganics. IV. Effect of the crosslinking agent on protonation,and metal ions complexing abilities,of ion exchange resins with poly(amido–amine) structure

Two classes of resins, having a poly(amido–amine) structure, have been synthesized. The basicity constants and the complexing abilities toward copper (II) and nickel (II) ions have been investigated by potentiometric techniques. The influence of the nature of the crosslinking agent on the basicities and the complexing abilities has been studied.     

Enhanced LSCF oxygen deficiency through hydrothermal synthesis

High-performance perovskites are promising materials for diverse renewable energy technologies. Besides design characteristics, the devices performance depends on the material synthesis, since the processes occurring during synthesis may produce different structures and properties. In this work, the perovskite La_0.1Sr_0.9Co_0.9Fe_0.1O_3-δ (LSCF1991) was synthesized by different methods, and the phase composition and oxygen deficiency were assessed and discussed. We show that it is possible to increase oxygen deficiency by promoting oxygen release during crystallization within hydrothermal synthesis, producing a remarkable improvement of ?δ ~0.2 in comparison with the citrate method. The single phase LSCF1991 powder was characterized, shaped by different routes and sintered to demonstrate the stability and suitability to manufacture electrochemical devices.     

A simple method for electroanalytical determination of ceftiofur in UHT milk samples using square-wave voltammetry technique

A simple electroanalytical method was developed to determine the antibiotic ceftiofur (CF) in milk. The method is based on the adsorptive accumulation of the drug on a hanging mercury-drop electrode (HMDE) and the accompanying initiation of a negative square wave, which yielded well-defined cathodic peaks at −0.60 V (1C) and −0.91 V (2C) vs. Ag/AgCl. Calibration graphs were constructed and statistical parameters were evaluated. At pH 2.5, the square-wave voltammetry method revealed linearity from 52.4 to 524 ng mL⁻¹ (r = 0.997), which is in accordance with the tolerance level of 100 ng mL⁻¹ for CF as a residue in bovine milk established by the Food and Drug Administration (FDA) and the European Union. The limits of detection and quantification were 1.86 and 6.20 ng mL⁻¹, respectively. The method was tested to determine CF in spiked milk samples using HPLC as reference method.     

Does Location or Sector Matters？ Analysis of Euro-Zone Energy Companies

This investigation is focused on answering if the location and sector of activity of energy companies located in the Euro-zone impact the performance of these companies. A database of eighteen largest energy companies in the Euro-zone between 2005 and 2009 was constructed. The method of linear regressions with panel data was applied. Results get possible to infer that oil and gas sector have the highest returns confirming the initial hypothesis. Location does not impact the economic and financial performance of energy companies refuting the initial hypothesis.     

Applied macroinorganics. II. Protonation and heavy metal ions complex-formation behavior of three crosslinked resins of poly(amido-amine) structure

Three resins having a poly(amido-amine) structure have been synthesized. The basicity and complexing ability towards copper(II) have been investigated by potentiometric techniques, and compared with those of the corresponding soluble polymers. The adsorbing capacities of the resins in columns were tested, and a sharp separation between different metal ions is achieved.     

Plastic dilution refrigerators

A new design for conventional,³He re-circulating, dilution refrigerators has been developed and tested. The units are made out of plastic and can be designed to have very small diameters (<15mm). These characteristics make them ideal to cool samples below 100 mK in high or time-varying magnetic fields. Furthermore, they are inexpensive, reliable and easily constructed. The best refrigerators reach continuous temperatures of around 10 mK at low circulation rates ( 100 mol/s). The cooling power at high temperatures is limited by the speed of the circulation pump and not by the refrigerator itself. The basic design and construction methods are discussed.     

Biomonitoring of methomyl pesticide by laccase inhibition on sensor containing platinum nanoparticles in ionic liquid phase supported in montmorillonite

This study focuses on the development and evaluation of a new biosensor for the determination of the pesticide methomyl, based on enzyme inhibition. Laccase (LAC) obtained from a genetically modified fungus (Aspergillus oryzae) was successfully immobilized in a new supported ionic liquid phase (SILP) based on platinum nanoparticles and the 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid (Pt-BMI·BF₄) supported in montmorillonite, and subsequently applied in the construction of the biosensor. The process of inhibition by methomyl carbamate was performed using dopamine as a phenolic substrate to obtain the base signal. All measurements for the optimization and application of the biosensor were performed by square-wave voltammetry, and the best experimental conditions were obtained in acetate buffer solution (0.1 mol L⁻¹, pH 5.5), with 0.5 units of enzyme and voltammetric parameters: 60 Hz of frequency, 100 mV of pulse amplitude and 8 mV of scan increment. The determination of methomyl in carrot and tomato samples using the proposed biosensor showed results consistent with those obtained by HPLC, verifying that the method developed can be used for the quantification of this pesticide.     

Determination of the steel fire protection material thickness by an analytical process—a simple derivation

Structural fire safety is assured if the design value of the effect of the actions (thermal and mechanical) is lower than the design value of each structural element fire resistance or, in other words, structural safety is assured when the steel temperature in a fire situation only reaches values less than the structure critical temperature. The critical temperature is the temperature that causes structural collapse in a fire situation. The temperature in the structural element can be determined either experimentally or analytically. In the case of a structure covered with thermally protective material, such methods serve, in practice, to determine the thickness of the protective material. In this work, a previously unpublished expression for the calculation of the temperature in thermally protected steel structural elements in fire is derived. Comparisons with international recommendations and with experimental and numerical analysis results are made. In view of its simple form and derivation, the use of such expression is recommended for the revision of the Brazilian Standard “Steel structures fire design”.     

The role of surfactant in the miniemulsion polymerization of biodegradable polyurethane nanoparticles

The influence of surfactant type and concentration on particle size, formulation yield and stability of the polyurethane (PUR) nanoparticles synthesized by miniemulsion polymerization was investigated. SDS, Tween 80 and Pluronic F68 were employed as surfactants in concentration ranging from 5 to 20% (vs monomer concentration). The surfactant SDS was found not efficient in our system, resulting in a low formulation yield (about 53%), two particle size distributions and zeta potential equal to − 52.3mV. On the other hand, the nonionic surfactants gave monomodal particle size distribution, good yields (> 85%) and zeta potential around to− 24mV. The particles synthesized with Tween 80 or Pluronic F68 were very similar to each other in terms of efficiency, particle size distribution and zeta potential. For instance, the particle diameter slightly decreases from 292nm to 261nm as the amount of Tween 80 surfactant increases from 5 to 20wt.% vs monomer. Moreover, we have observed that a concentration of at least 5wt. % of Tween 80 was necessary to favor particle stability and therefore to avoid aggregation.     

Polyurethane nanoparticles from a natural polyol via miniemulsion technique

Original natural triol (castor oil) was used as a monomer for the synthesis of monodisperse polyurethane nanoparticles (size ranging from 200 to 400 nm) by miniemulsion technique in water. Various parameters such as the concentration of the reactants, the nature of stabilizers and the shear were tuned to control the particle size and its distribution. The polyaddition between the natural triol and isophorone diisocyanate (IPDI) was conducted at 60 °C, in the absence of catalyst and monitored by infrared spectroscopy. The characterization of these polyurethane latexes was carried out using light scattering measurements and transmission electron microscopy (TEM).