Jorge Sánchez-Marcos

One-pot electrochemical synthesis of polydopamine coated magnetite nanoparticles

Herein a facile and versatile one step synthesis of magnetite nanoparticles coated with polydopamine is described. Magnetite nanoparticles are synthesized electrochemically by electrooxidation of iron in an aqueous medium in the presence of dopamine. The oxidative conditions and alkaline pH involved in the synthesis favor the self-polymerization of dopamine that adheres at the surface of the magnetic nanoparticles in a simultaneous process. It is shown that the size of the magnetite nanoparticles as well as the polydopamine coating can be controlled by varying the synthetic approach that is, adding dopamine at the beginning of the electrosynthesis, in the middle or at the end of the process. The particle size of the core varies between a few nanometers and 25 nm while the shell can reach thicknesses of up to ∼5 nm. The obtained hybrid nanoparticles were characterized by thermogravimetric analysis (TGA), infrared spectroscopy (FTIR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). In addition, the magnetic measurements of the different obtained materials were carried out showing a variety of magnetic behaviors depending on the synthetic procedure.

Magnetic Nanoparticles-Based Conducting Polymer Nanocomposites

This chapter reviews the state of art of nanocomposites based on conducting polymers and magnetic nanoparticles. The preparation of hybrid nanocomposites with both magnetic and electrical properties has emerging as attractive alternative in a wide number of applications especially as microwave absorbing material and electromagnetic shielding. An overview of the different synthetic routes of the hybrid nanocomposites is presented, which outlines the most development techniques to prepare homogenous matrix, core–shell nanoparticles, and thin films. This chapter also covers the discussion of both the magnetic and electrical properties of the nanocomposites that significantly vary from the individual components. Finally varies of the most relevant applications of the magnetic nanoparticles-based conducting polymer nanocomposites are highlighted.

Synthesis and structural characterization of ZnxFe3−xO4 ferrite nanoparticles obtained by an electrochemical method

A series of zinc ferrite nanoparticles were synthesized following a single-step electrochemical method in aqueous medium. This strategy allowed the control of both the size and chemical composition of the nanoparticles in an easy and reproducible manner by simply varying the intensity of the applied current. The obtained nanoparticles were morphologically and structurally characterized as a function of the particle size and the Zn content in the sample by X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma emission spectroscopy (ICP) and Raman microscopy. The formation of ZnxFe(3−x)O4 (x = 0.18–0.93) ferrite nanoparticles with crystal sizes in the range of 9 to 18 nm and with a homogeneous distribution of the Zn2+ cation in the crystalline structure was observed. However, following a thermal treatment, a migration of zinc cations was detected that led to the formation of two different crystalline phases, stoichiometric zinc ferrite and hematite. Raman microscopy revealed the formation of segregated micro-domains enriched within these crystalline phases. The study of the magnetic properties of the electro-synthesized ferrite nanoparticles with a homogeneous incorporation of Zn in the structure shows that the saturation magnetization and the coercively values are highly dependent on the chemical composition and crystal size.

Huge photoresistance in transparent and conductive indium titanium oxide films prepared by electron beam-physical vapor deposition.

Transparent and conductive indium titanium oxide (ITiO) films have been obtained by electron beam physical vapour deposition with Ti content from 5 at % up to 28 at %. X-ray absorption spectroscopy techniques have been used to identify the local environment of Ti ions. Even at the lowest concentrations Ti is not incorporated into the In2O3 structure but forms clusters of a Ti-In mixed oxide that present a distorted rutile TiO2 short-range order. The optical transmittance of the annealed samples reaches 95 % and no significant variation of the gap energy (around 3.7 eV) is observed with Ti content. The electronic conductivity under light irradiation is studied evidencing a huge photo-resistance in the samples with Ti content above 22 at % reaching more than two orders of magnitude for the 26 at % Ti under illumination with few μW/cm(2) at 365 nm. Hall and conductivity results are analyzed using a model that takes into account both electron and hole carriers as well as the conductivity enhancement by carrier photogeneration. The electron carrier density decreases with Ti content while its mobility increases up to values of 1000 cm(2)/(V s). Oxygen annealed ITiO films obtained by this technique with Ti content below 10 at % have properties adequate as transparent semiconductors and those with Ti content higher than 22 at % have exceptional photoresistive properties relevant for numerous applications.