Isabel Gonzalo-Juan

Transferable graphene oxide films with tunable microstructures.

This report describes methods to produce large-area films of graphene oxide from aqueous suspensions using electrophoretic deposition. By selecting the appropriate suspension pH and deposition voltage, films of the negatively charged graphene oxide sheets can be produced with either a smooth rug microstructure on the anode or a porous brick microstructure on the cathode. Cathodic deposition occurs in the low pH suspension with the application of a relatively high voltage, which facilitates a gradual change in the colloids charge from negative to positive as they adsorb protons released by the electrolysis of water. The shift in the colloids charge also gives rise to the brick microstructure, as the concurrent decrease in electrostatic repulsion between graphene oxide sheets results in the formation of multilayered aggregates (the bricks). Measurements of water contact angle revealed the brick films (79°) to be more hydrophobic than the rug films (41°), a difference we attribute primarily to the distinct microstructures. Finally, we describe a sacrificial layer technique to make these graphene oxide films free-standing, which would enable them to be placed on arbitrary substrates.

Evolution of Ordering in Iron Oxide Nanoparticle Monolayers Using Electrophoretic Deposition

Iron-oxide nanoparticle monolayers and multilayers were assembled using dc electrophoretic deposition. The rate of deposition and the total particle deposition were controlled by varying the concentration of nanoparticles and the deposition time, respectively. Using scanning electron microscopy, we performed a time-resolved study that demonstrated the growth of the monolayer from a single isolated nanoparticle to a nearly complete layer. We observed tight, hexagonal packing of the nanoparticles indicating strong particle-particle interaction. Multilayer growth was assessed using scanning electron microscopy and atomic force microscopy, revealing a monolayer-by-monolayer growth process.

Using Voronoi tessellations to assess nanoparticle-nanoparticle interactions and ordering in monolayer films formed through electrophoretic deposition.

Monolayers of iron oxide nanoparticles of two different sizes, 9.6 nm and 16.5 nm, were fabricated through electrophoretic deposition. The arrangements of nanoparticles within the films were analyzed using the technique of Voronoi tessellations. These analyses indicated that the films possessed equivalent degrees of ordering, and that the films were uniform over centimeter length scales. Precise measurements of the interparticle spacing were obtained, and the magnitudes of magnetic dipole interactions were calculated. The dipole-dipole interaction among the larger nanoparticles was 14 times larger than that of the smaller nanoparticles, indicating that magnetic coupling interactions could not have been the lone source of ordering in the system.

Synthesis and In Vitro Activity Assessment of Novel Silicon Oxycarbide-Based Bioactive Glasses

Novel bioactive glasses based on a Ca- and Mg-modified silicon oxycarbide (SiCaMgOC) were prepared from a polymeric single-source precursor, and their in vitro activity towards hydroxyapatite mineralization was investigated upon incubating the samples in simulated body fluid (SBF) at 37 °C. The as-prepared materials exhibit an outstanding resistance against devitrification processes and maintain their amorphous nature even after exposure to 1300 °C. The X-ray diffraction (XRD) analysis of the SiCaMgOC samples after the SBF test showed characteristic reflections of apatite after only three days, indicating a promising bioactivity. The release kinetics of the Ca2+ and Mg2+ and the adsorption of H+ after immersion of SiCaMgOC in simulated body fluid for different soaking times were analyzed via optical emission spectroscopy. The results show that the mechanism of formation of apatite on the surface of the SiCaMgOC powders is similar to that observed for standard (silicate) bioactive glasses. A preliminary cytotoxicity investigation of the SiOC-based bioactive glasses was performed in the presence of mouse embryonic fibroblasts (MEF) as well as human embryonic kidney cells (HEK-293). Due to their excellent high-temperature crystallization resistance in addition to bioactivity, the Ca- and Mg-modified SiOC glasses presented here might have high potential in applications related to bone repair and regeneration.

Ceramic synthesis from condensed phases

Advanced ceramics have progressed significantly in the last few years. This progress is closely related to the development of new synthetic routes providing not only the preparation of known materials with improved properties, but also the discovery of novel compounds. This chapter gives an overview of established synthetic methods to prepare oxide- and non-oxide-based ceramics from precursors in condensed phases. Typical synthetic strategies performed either in liquid or solid phases are summarized. In addition, innovative synthesis methods such as sol–gel and polymer-derived pyrolysis technique to develop advanced ceramics with exceptional properties are considered.

Finely Tuned SnO2 Nanoparticles for Efficient Detection of Reducing and Oxidizing Gases: The Influence of Alkali Metal Cation on Gas-Sensing Properties

Tin dioxide (SnO2) nanoparticles were straightforwardly synthesized using an easily scaled-up liquid route that involves the hydrothermal treatment, either under acidic or basic conditions, of a commercial tin dioxide particle suspension including potassium counterions. After further thermal post-treatment, the nanomaterials have been thoroughly characterized by Fourier transform infrared and Raman spectroscopy, powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and nitrogen sorption porosimetry. Varying pH conditions and temperature of the thermal treatment provided cassiterite SnO2 nanoparticles with crystallite sizes ranging from 7.3 to 9.7 nm and Brunauer-Emmett-Teller surface areas ranging from 61 to 106 m2·g-1, acidic conditions favoring potassium cation removal. Upon exposure to a reducing gas (H2, CO, and volatile organic compounds such as ethanol and acetone) or oxidizing gas (NO2), layers of these SnO2 nanoparticles led to highly sensitive, reversible, and reproducible responses. The sensing results were discussed in regard to the crystallite size, specific area, valence band energy, Debye length, and chemical composition. Results highlight the impact of the counterion residuals, which affect the gas-sensing performance to an extent much higher than that of size and surface area effects. Tin dioxide nanoparticles prepared under acidic conditions and calcined in air showed the best sensing performances because of lower amount of potassium cations and higher crystallinity, despite the lower surface area.