Search

The extensive range of applications where synthetic nanomaterials are nowadays used is causing a huge commercial market. An incipient use of these nanomaterials arises from the need to generate alternative antimicrobial agents, anticipating the development of resistant micro- organisms. Here, we show a nanostructured ZnO with antimicrobial properties and low cytotoxicity based on a nanoparticle¿s arrangement by controlling the formation of sintering neck into nanoporous spheres. The antimicrobial effectiveness of ZnO spheres is tested in a broad spectrum of microorganisms such as fungi as well as Gram-negative and Gram-positive bacteria. The hierarchical structures show highly effective antimicrobial activity at low concentrations and in relatively short action times (24¿72 h). We demonstrate that the enhanced antimicrobial properties against microorganisms are ascribed to a combining of both physical and chemical interactions between microorganism and ZnO. The approximation mechanism between microorganism and ZnO is provided through electrostatic forces (physical interaction) which, thanks to the ZnO¿microorganism proximity, promote a rapid release of zinc cations and the reactive oxygen species penetration into microorganisms (chemical interaction). We believe that this work provides insights into the mechanisms underlying the interactions ZnO¿microorganism and possesses a combined action mechanism for which nanostructured ZnO is so effective to combat microorganisms., This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under the projects MAT2017-86450-C4-1-R, and the Spanish National Research Council (CSIC) under the project NANOMIND CSIC 201560E068. Dr. P. Leret is also indebted to MINECO for a “Torres Quevedo” contract (ref: PTQ-12-05470), which is cofinanced with European Social Fund. Dr. E. Enriquez is also indebted to MINECO for a ‘‘Torres Quevedo’’ contract (ref: PTQ-14-07289), which is co-financed with European Social Fund. Dr. F. R-M is also indebted to MINECO for a ‘Ramon y Cajal’ contract (ref: RyC-2015-18626), which is co-financed by the European Social. The authors acknowledge the ESRF The European Synchrotron and the SpLine CRG BM25 beamline staff for provision of synchrotron radiation and for assistance during X-ray diffraction measurements (ref: 25-01-966). Finally, authors are grateful to Aida Serrano and Rocío Estefanía Rojas-Hernandez for scientific and technical advice in XANES measurements, Mª José Velasco and Pilar Ortega for ICP-OES measurements, Alexandra Muñoz-Bonilla for scientific advice and Laura Pascual for scientific and technical advice

The synthesis of aluminum phosphates-based composites has been widely studied during the past decade because of the promising industrial application of these materials. Here we show a simple one-pot heterogeneous precipitation approach to fabricate a sepiolite-phosphate (SepP) composite with adequate control of the size and dispersion of the phosphate nanoparticles. This coupling between aluminum phosphate and sepiolite nanofibers results in the development of a novel three-dimensional rigid supported phosphate structure, which is generated during the thermal treatment. According to our results, this phenomenon can be explained by a migration-coalescence mechanism of phosphate nanoparticles over the sepiolite support, assisted by a liquid phase. It is worth pointing out that this stimulant behavior observed here could have potential technological applications such as halogen-free flame retardant materials.

[EN] The ultraviolet-visible, UV-vis, absorption edge behaviour of semiconductor oxides as TiO and ZnO promotes their use as inorganic UV filters for sunscreens. In cosmetics, the use of nanoparticles is favoured because of their higher yield and lower whiteness. However, the particle size effect in the UV absorption is unclear. For this reason, the performances of nano and microsized TiO and ZnO are evaluated in both the UV-vis spectroscopy and the Sun Protection Factor, SPF, value. In order to cover the UV range completely by using inorganic filters a new composite is attempted by dry nanodispersion methodology in which TiO nanoparticles are dispersed onto ZnO microparticles. The new composite shows superior UV absorbing properties and ca. 60% SPF value due to a synergism between components that resulted in extended UV coverage and reduction of the total amount of nanoparticles required in the sunscreens. In addition, nanoparticles are effectively anchored onto microparticles avoiding the presence of free nanoparticles., [ES] El comportamiento del borde de absorción ultravioleta-visible de óxidos semiconductorescomo el TiO2y el ZnO incentiva su uso como filtros inorgánicos para luz UV en cremassolares. En cosmética, el uso de nanopartículas está favorecido por el alto rendimiento quepresentan y la baja blancura que aportan a la crema en comparación con las micropartícu-las. Aun así, el efecto del tama˜no de partícula en la absorción de luz en el rango UV no estáclaro. Por esta razón, el comportamiento de nano y micropartículas de TiO2y ZnO se evalúamediante espectroscopia de luz UV-Visible y mediante el factor de protección solar en cre-mas. Con el fin de cubrir las necesidades de absorción de luz en todo el rango UV medianteel uso de filtros inorgánicos, se ha generado un nuevo composite mediante un proceso denanodispersión en seco en el que nanopartículas de TiO2se encuentran dispersas sobre micropartículas de ZnO. El nuevo composite presenta propiedades de absorción UV superiores al 60% en lo que al valor de protección solar se refiere. Este hecho es debido a la sinergia entre los componentes de forma que se cubre el rango UV de manera efectiva requiriendo una menor cantidad total de nanopartículas. Dichas nanopartículas se encuentran dispersas de manera efectiva sobre las micropartículas, evitando la presencia de nanopartículas libres., The authors express their thanks to the MINECO project MAT2013-48009-C4-1-P for their financial support. P. Leret is indebted to MINECO for a “Torres Quevedo” contract (ref: PTQ-12-05470) and C.M. Alvarez-Docio for a FPI grant, which areco-financed with FEDER funds.

ZnO presents favorable thermodynamics, equilibrium constant and stability for H2S chemisorption and sepiolite has excellent sorptive and rheological properties to be employed as a support. Four conformed ZnO/sepiolite composites are prepared, two by impregnation in zinc nitrate solution – one using activated carbon as a dispersing and pore generating agent – and two by dry mixing of the clay with dispersed or hierarchically assembled ZnO nanoparticles. The extrudates obtained with a mixture of sepiolite and nanodispersed ZnO particles are the most active for H2S chemisorption in temperature-programmed tests performed in an inert atmosphere, which can be correlated with the higher and homogeneous ZnO dispersion. ZnO sulfidation is reversible in the presence of O2. Thus, the activity can be regenerated, and these materials act as catalysts for H2S to SO2 oxidation in air., The authors would like to express their thanks for financial support to MINECO (Spain) for the projects MAT2013-48009-C4-1-P and CTQ2011-25517-PPQ and the Juan de la Cierva contract of Dr R. Portela (JCI-2010-08221). Dr F. Rubio-Marcos is also indebted to CSIC for a Junta de Ampliación de Estudios contract (JAEDOC071), which is co-financed with FEDER funds.

Electron Paramagnetic Resonance (EPR) is used to study the transport properties in CaCu3Ti4O12 (CCTO) and its mixtures with TiO2. The temperature dependence of the peak to peak linewidth of the EPR spectra in the temperature range 430 ≤ T ≤ 660 K, is studied for the powders of CCTO, 5% CCTO + 95% TiO2 and 1% CCTO + 99% TiO2. All the samples show a behavior predicted by the Small Polaron Hopping model. This behavior is studied as a function of the TiO2 content, finding an activation energy that decreases with increasing TiO2 concentration. We found that two mechanisms govern the conductivity in these system one, intrinsic to the CCTO, via oxygen vacancies and the other one, which improve the conductivity, related to the polarizability of the Ti-ions at the surface of the grains and mediated by the oxygen vacancies at the surface of the CCTO., Two of the authors, Leonardo Vivas and Pedro Silva, want to acknowledge to the Venezuelan Institute for Scientific Research for the support in the development of this research.

CaCu 3 (Ti 4− x Hf x )O 12 ceramics ( x = 0.04, 0.1 and 0.2) were prepared by conventional synthesis (CS) and through reactive sintering (RS), in which synthesis and sintering of the material take place in one single step. The microstructure and the dielectric properties of Hf-doped CCTO (CCTOHf) have been studied by XRD, FE-SEM, AFM, Raman and impedance spectroscopy (IS) in order to correlate the structure, microstructure and the electrical properties. Samples prepared by reactive sintering show slightly higher dielectric constant than those prepared by conventional synthesis in the same way than the pure CCTO. Dielectric constant and dielectric losses decrease slightly increasing Hf content. For CCTOHf ceramics with x > 0.04 for CS and x > 0.1 for RS, a secondary phase HfTiO 4 appears. As expected, the reactive sintering processing method allows a higher incorporation of Hf in the CCTO lattice than the conventional synthesis one.

In this work, the dielectric behaviour and capacitance–voltage ( C – V ) curves under an applied DC bias field of 1 wt% Nb-doped CaCu 3 Ti 4 O 12 ceramics have been studied. The dielectric properties reveal the existence of grain boundaries of different electrical nature. A new model is proposed to simultaneously explain the presence of insulating and conducting grain boundaries. At low frequency, the capacity curve of the material exhibits a double metal oxide semiconductor (MOS) capacitor-like behaviour and as the frequency is increased, the curve suffers an inversion showing a ferroelectric-like response. This behaviour does not correspond to ferroelectric domain movement phenomena but seems associated to charge accumulation on grain boundary regions.

In this work, two series of ceramic CaCu3Ti4O12 (CCTO) have been prepared by a solid-state reaction, studying the effect of an extra calcination and milling step of the raw materials in one of the products. The comparison of the green powder characteristics, microstructure, and electrical properties of the sintered materials is presented and discussed. The double calcination route diminishes the amount of unreacted CuO, and thus, a thinner secondary phase ≤10 nm is better distributed among the grain boundaries enhancing the giant dielectric response. Raman spectroscopy confirms the reduction of unreacted copper, indicating the relation of the Ag (1)/Ag (2) vibrational modes that the stoichiometry of the precursors approaches that of the ideal ceramic CCTO.

CaCu 3 Ti 4 O 12 (CCTO) ceramics have been processed by solid state reaction and sintered at 1100 °C for different times. A clear increase of the dielectric constant of the material up to values of 6 × 10 4 has been observed with the sintering time. This increase is accompanied by a limited grain growth and intergranular Cu-oxide phase thickness reduction. The disappearance of the Cu-oxide phase is caused by the incorporation of Cu cations into the grains, contributing to the increase of the dielectric constant. Raman spectroscopy shows the decrease of TiO 6 octahedral rotational modes with the sintering time due to the incorporation of Cu cations into the CCTO grains. XANES measurements show that the Cu main oxidation state is Cu 2+ and does not change with the sintering time. The fitting of the experimental dielectric constant to the Internal Barrier Layer Capacitance (IBLC) model reveals the change of the intergranular phase dielectric constant, caused by a compositional change due to the incorporation of Cu into the CCTO grains.

This work studies the effects of copper doping on the properties of the (K0.44Na0.52Li0.04)(Nb0.86Ta 0.10Sb0.04)O3 piezoelectric ceramic material. Cu2+ incorporation into the perovskite structure produces a transformation of the crystalline lattice from tetragonal to orthorhombic symmetry together with an increase of the secondary phase. The grain size of the ceramic samples is increased due to the formation of a liquid phase during sintering, which increases with the Cu2+ content. EDS analysis reveals that the secondary-phase regions present a Cu and Nb-rich composition, indicating that the Cu-excess accommodates through the formation of this secondary phase. Cu-doping induces a rapid increase of the orthorhombic- tetragonal phase transition temperature, while the tetragonal-cubic phase transition temperature is decreased, the latter becoming more diffuse with the increase of Cu content. The piezoelectric properties of the material are reduced with the copper concentration, whereas the mechanical quality factor increases by a factor of nearly four. © 2012 Elsevier Ltd and Techna Group S.r.l., The authors kindly acknowledge financial support from the MICINN project MAT 2010-21088-C03-01 and COST ActionMP0904 SIMUFER. We acknowledge the European Synchrotron Radiation Facility (ESRF) for provision of synchrotron radiation facilities (Project Reference: 25-01-784); beamline 25 (SPLINE). Dr. F. Rubio-Marcos is indebted to the “Conseil Regional du Limousin” for post-doctoral fellowship.

A simple method to precipitate nanoparticles of iron phosphate with acid character has been developed in which the control of pH allows to obtain amorphous nanoparticles. The acid aging of the precipitated amorphous nanoparticles favored the P–O bond strength that contributes to the surface reordering, the surface roughness and the increase of the phosphate acid character. The thermal behavior of the acid iron phosphate nanoparticles has been also studied and the phosphate polymerization at 400 °C produces strong compacts of amorphous nanoparticles with interconnected porosity.

Eutectic temperature and composition in the CuO–TiO2 pseudobinary system have been experimentally determined in air by means differential thermal analysis (DTA), thermogravimetry (TG) and hot-stage microscopy (HSM). Samples of the new eutectic composition treated at different temperatures have been characterized by X-ray diffraction (XRD) and X-ray absorption near-edge structural spectroscopy (XANES) to identify phases and to determine the Cu valence state, respectively. The results show that the eutectic temperature in air is higher by 100 °C (∼1000 °C) for a Ti-richer composition ( X TiO 2 = 25 mol % ) than the one calculated in the literature. The reduction of Cu2+ to Cu+ takes places at about 1030 °C. The existence of Cu2TiO3 and Cu3TiO4 has been confirmed by XRD in the temperature range between 1045 and 1200 °C.

CaCu3Ti4O12 (CCTO) was prepared by a conventional synthesis (CS) and through reaction sintering, in which synthesis and sintering of the material take place in one single step. The microstructure and the dielectric properties of CCTO have been studied by XRD, FE-SEM, EDS, AFM, and impedance spectroscopy to correlate structure, microstructure, and electrical properties. Samples prepared by reactive sintering show very similar dielectric behavior to those prepared by CS. Therefore, it is possible to prepare CCTO by means of a single-step processing method.

We describe a straightforward production pathway of polymer matrix composites with increased dielectric constant for dielectric elastomer actuators (DEAs). Up to date, the approach of using composites made of high dielectric constant ceramics and insulating polymers has not evidenced any improvement in the performance of DEA devices, mainly as a consequence of the ferroelectric nature of the employed ceramics. We propose here an unexplored alternative to these traditional fillers, introducing Calcium Copper Titanate (CCTO) CaCu3Ti4O12, which has a giant dielectric constant making it very suitable for capacitive applications. All CCTO/Polydimethylsiloxane (PDMS) composites developed display an improved electro-mechanical performance. The largest actuation improvement was achieved for the composite with 5.1 vol.% of CCTO, having an increment in the actuation strain of about 100% together with a reduction of 25% in the electric field compared to the raw PDMS matrix., LJR, MH, MALM and RV gratefully acknowledge the financial support of the Spanish Ministry of Science and Innovation (MICINN) through project MAT 2010-18749 and the 7th Framework Program of E.U. through HARCANA 55 (NMP3-LA-2008-213277). RV acknowledges the mobility grant PA1003132 from CSIC. PL, MAR and JFF kindly acknowledge financial support from the MICINN project MAT 2010-21088-C03-01.The authors are in debt to Manuel Rus, from ICTP-CSIC, for the technical support in the electro-mechanical experimental set-up.

In this work, ceramic CaCu3Ti4O12 has been prepared by a conventional solid-state route. The samples present rectifying properties. The study of the I–V curve with the sintering time shows an evolution of the nonlinear coefficient and the increase of barriers suitable to rectify. The dielectric constant increases with the sintering time, following the same trend observed for the number of rectifying barriers. This suggests the existence of a close relation between the barriers that produce electric rectification and the insulating barriers producing the high dielectric constant by the insulating barrier layer capacitor effect.

8 páginas, 2 tablas, 8 figuras., Fe3+- or Nb5+-doped CaCu3Ti4O12 (CCTO) ceramics show higher values of both room-temperature (RT) grain conductivity and dielectric constant than undoped ceramics. Microstructural and structural characterization combined with magnetic properties reveal the coexistence of two components that seem relevant for the dielectric behavior of the material. The grain possesses a nanostructure characterized by layered domains with thicknesses, This work was supported by the CSIC project PIF MAGIN and by CICYT project MAT2007-66845-C02-01.

In this work a comparative study of undoped CaCu3Ti4O12 (CCTO) and doped with Fe3+(CCTOF) and Nb5+(CCTON) ceramics, was aimed to modify the electronic transport.XRDpatterns, FE-SEM microstructural analysis, impedance spectroscopy and I–V response curves were afforded to correlate the microstructure with the nonlinear I–V behaviour. The appearance of nonlinear behaviour in doped CCTO samples has been correlated with the ceramic microstructure that consists in n-type semiconductor grains, surrounded by a grain boundary phase based on CuO. The presence of this secondary grain boundary phase is the responsible of the assisted liquid phase sintering in CCTO ceramics. Doped samples showed cleaner grain boundaries than CCTO and nonlinearity in the I–V response.