A simple and general route for the preparation of pure and high crystalline nanosized lanthanide silicates with the structure of apatite at low temperature

Rare earth silicates with the structure of apatite are attracting considerable interest since they show oxygen ion conductivities higher than that of yttria-stabilized zirconia (YSZ) at moderate temperature. Based on the hydrothermal synthesis we presented a simple one step process for the direct preparation of the pure and the high crystalline nanosized rare earth silicates with the structure of apatite under a mild condition (230 °C). Since the preparation of the high crystalline silicon based rare earth apatites is performed at high temperature previously and accompanied by subsequent process of grinding, results of this work provide a promising alternative of the existing methodology. Furthermore, due to the relatively low temperature of the preparation of these materials, high doping of monovalent cation can be done, which was not achieved before.     

Phase separation effects in charge-ordered Pr<Subscript>0.5</Subscript>Ca<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript> thin film

Compressed Pr_0.5Ca_0.5MnO₃ films (250 nm) deposited on LaAlO₃ have been studied by Electron Spin Resonance technique under high frequency and high magnetic field. We show evidences for the presence of a ferromagnetic phase (FM) embedded in the charge-order phase (CO), in form of thin layers which size depends on the strength and orientation of the magnetic field (parallel or perpendicular to the substrate plane). This FM phase presents an easy plane magnetic anisotropy with an anisotropy constant 100 times bigger than typical bulk values. When the magnetic field is applied perpendicular to the substrate plane, the FM phase is strongly coupled to the CO phase whereas for the parallel orientation it keeps an independent ferromagnetic resonance even when the CO phase becomes antiferromagnetic.     

One-dimensional WO3 and its hydrate: One-step synthesis,structural and spectroscopic characterization

We report on a one-step hydrothermal growth of one-dimensional (1D) WO₃ nanostructures, using urea as 1D growth-directing agent and a precursor free of metals other than tungsten. By decreasing the pH of the starting solution, the size of the nanostructures was reduced significantly, this development being accompanied by the realization of phase pure hexagonal WO₃ nanorods (elimination of monoclinic impurity phase) and a red shift in optical absorption edge. Surface analyses indicated the presence of reduced tungsten species in the WO₃ nanostructures, which increased two-fold in a hydrated WO₃ phase obtained with further decrease in pH. We suggest that oxygen vacancies are responsible for this defect state in WO₃, while protons are responsible or contribute significantly to the same in the hydrated phase.     

Aqueous mixtures of di-n-decyldimethylammonium chloride/polyoxyethylene alkyl ether: dramatic influence of tail/tail and head/head interactions on co-micellization and biocidal activity

Mixed aggregate formation and synergistic interactions of binary surfactant mixtures of di-n-decyldimethylammonium chloride, [DiC(10)][Cl], with polyoxyethylene alkyl ethers, C(i)E(j) (i=10, 12, j=4, 6, 8), have been investigated for various [DiC(10)][Cl]/C(i)E(j) ratios. The critical aggregation concentration of the binary mixtures has been determined by tensiometry, and the aggregate characteristics (i.e., size and composition, free ammonium concentration) have been estimated using the pulsed field gradient NMR spectroscopy and a [DiC(10)]-selective electrode. Diffusion coefficient measurements of micelles confirmed the synergistic interaction between the surfactants. It is thus shown that the formation of surface monolayers and mixed aggregates from [DiC(10)][Cl]/C(10)E(j) mixtures is driven by both tail/tail and head/head interactions, whereas [DiC(10)][Cl]/C(12)E(j) co-aggregation is mainly driven by tail/tail interactions. As a consequence, the co-aggregation phenomenon notably influences the biocidal activity of [DiC(10)][Cl] on the Candida albicans fungi. In the presence of C(12)E(j), the biocidal activity of the ammonium salt is inhibited due to the trapping of the cationic surfactants in the mixed aggregates, whereas in the presence of C(10)E(j), the biocidal activity of the surfactant mixture is maintained. The mode of action is also confirmed by a faster increase in the zeta potential of a C. albicans suspension in the presence of [DiC(10)][Cl]/C(10)E(8) than in the presence of [DiC(10)][Cl]/C(12)E(8). Therefore, a judicious adjustment of the alkyl (i) and polyoxyethylene (j) chain lengths of C(i)E(j) avoids its antagonistic effect on the biocidal activity of [DiC(10)][Cl].     

Redox reactivity at silver microparticle—glassy carbon contacts under a coating of polymer of intrinsic microporosity (PIM)

Silver microparticles (ca. 1 μm average size clustered into cage-like aggregates of 10–20 μm diameter) are shown to adhere to a glassy carbon electrode surface to give voltammetric current responses, which are considerably enhanced/stabilised when applying a coating with a molecularly rigid polymer of intrinsic microporosity (PIM-EA-TB). In preliminary voltammetric experiments characteristic Ag(0/I) surface oxidation and back-reduction processes are observed in aqueous phosphate buffer (associated with silver phosphate layer formation on the silver surface). In contrast to the oxidation, which is dominated by a nucleation process causing a sharp well-defined current signal, for the back-reduction stochastic current responses are observed possibly associated with density fluctuations in the surrounding liquid phase (“Brownian activation”) as an essential part of the mechanism of conversion of surface-oxidised silver back to silver metal.

Graphical abstract

     

Use of ring-disc electrodes and viologens for the titration of cytochrome C and oxygen and for the study of their reduction kinetics

The use of ring-disc electrodes enable the electrogeneration of viologen cation radicals V⁺ when the disc potential is controlled in the range ?0.3 to ?0.65 and ?0.2 to ?0.45 V/NHE respectively in MV²⁺ and BV²⁺ solutions. We confirmed the occurrence of very fast reactions between V^.+ and horse-heart cytochrome c or oxygen and of slow or no reaction between V^.+ and β-nicotinamide adenine dinucleotide with xanthine oxidase, riboflavine and ferricyanide. Ring current versus dise current curves enable the titration of cytochrome c and oxygen and the estimation of the reaction rate between cytochrome c and MV^.+ [(6.2±2)10⁵M^?1 s^?1].     

Detergency of stainless steel surface soiled with human brain homogenate: an XPS study

In the detergency field of re-usable medical devices, a special attention is focused on the non conventional transmissible agent called prions which is a proteinaceous infectious agent. Few cleaning procedures are effective against prions and few techniques are available to study cleaning effectiveness with respect to proteins in general. In our study, X-ray photoelectron spectroscopy (XPS) has been used to evaluate the effectiveness of detergent formulations to remove proteins from stainless steel surface soiled with a brain homogenate (BH) from human origin. Our results showed that XPS is a reliable surface analysis technique to study chemical species remaining on surface and substrate properties after cleaning procedures. A semi-quantitative evaluation of the detergency effectiveness could also be performed.     

A radical approach to promote multiferroic coupling in double perovskites

Double perovskites provide a unique opportunity to induce and control multiferroic behaviours in oxide systems. The appealing possibility to design materials with a strong coupling between the magnetization and the polarization fields may be achieved in this family since these magnetic insulators can present structural self-ordering in the appropriate growth conditions. We have studied the functional properties of La₂CoMnO₆ and Bi₂CoMnO₆ epitaxial thin films grown by pulsed laser deposition. Cation-ordered La₂CoMnO₆ films display a magnetic Curie temperature of 250 K while cation-disordered Bi₂CoMnO₆ films present ferromagnetism up to ∼800 K. Such high transition temperature for magnetic ordering can be further tuned by varying the strain in the films indicating an important contribution from the structural characteristics of the materials. Our approach might be generalized for other oxide systems. At this end, our results are compared with other multiferroic systems. The roles of various cations, their arrangements and structural effects are further discussed.