My research interests have always been very broad. However, my primary interest has been the structure and properties of nanoparticles including metals, semiconductors, and magnetic materials. I have done research on: synthesis and characterization of new materials most of them nanoparticles, surfaces and interfaces, defects in solids, electron diffraction and imagining theory, quasicrystals, archaeological materials, and catalysis.

Research in Nanotechnology

At the present my main interest is related to nanotechnology research. The field of nanotechnology and its applications is an emerging field in which the science is rapidly developing. A particular aspect which is my main interest is the research in nanoparticles capped with an organic molecule. This are also called in the literature monolayer protected clusters (MPC) or single Nanocrystals (NC´s) and show many exciting applications in the materials science such as; nanoscale electronics, electroptics, electronic inks, molecular machines, optical filters and switches among others. They also appear very interesting as chemical platforms in; catalysis, chemical reactions, nano-sensors, polymer additives and also for some biological applications such as; sio-sensing and drug-delivery[i],[ii],[iii]. Research into the properties of capped nanocrystals or MPCS has recently matured into a field that is both fundamental and wide-ranging. A mayor source of motivation for research in those areas arises from technological questions concerning ultimate limits of the miniaturization of solid state devices.

• Properties and structure of nanoparticles capped with an organic ligand molecule.

• Synthesis and properties of nanoparticle (NC´s) superlattices.

• Synthesis and growth of nanorods of different materials and the fabrication of ordered arrays of nanorods.

• The preparation of a new generation of catalysts using new methods to prepare particles monodisperse in size, shape, internal structure, surface chemistry on a porous support.

• The structure and potential role of atmospheric nanoparticles in photocatalytic and thermal production of atmospheric pollutants.

• The synthesis and properties of fullerene-like structures of layered materials, such as: MoS2, ReS2, WS2, etc. and their applications to catalysis and lubrication at the nanolevel.

Nanoparticles: Synthesis and Properties

The topic of the shape and structure of nanoparticles has been extensively studied over the last 40 years for the case of “bare” clusters. It is well known that nanoparticles tend to assume structures which are unlike the bulk state. For instance, they form structures such as icosahedral, decahedral, star decahedral, truncated decahedral, star decahedral, and truncated icosahedral. In other cases, they follow the bulk structure and form, for instance, a truncated octahedron or a cubo-octahedron.

However as mentioned before, the most exciting applications of nanoparticles will be for the case when they are capped with an organic ligand molecule. In this case of such nanoparticles much less information exists on the shape and crystal structure. In the proposed research program we intend to grow NC´s and study in a systematic way the dependence of the crystal structure and shape with the type of ligand and conditions of growth. We will use three different methods to grow ligand capped particles:

1. Gas-vapor deposition at high pressures

2. Two phase reduction methods

3. Bioreduction methods
    

Nanorods; Synthesis and Characterization.

Nanoroads of metals gold have been recently synthesized using electrochemical methods and in our group by bioreduction methods. The nanorods appear to have very surprising properties. El Sayed et. al. has recently reported that while NC´s of 35nm did not emit light, nanorods are found to have a fluorescence of quantum efficiency which is 6-7 orders of magnitude higher than that of the metal. Furthermore its wavelength maximum and quantum efficiency are found to increase linearly with increasing the nanorod length. Also nanorods will find many applications on the buiding of mechanical and electronic nanodevices.

The methods of high pressure gas evaporation and bioreduction can be used to synthesize nanorods. This represents a very interesting system for practical application of nanorods for the production of Au, Pt, Rh, Fe, and Mn. We will also try to produce nanorods of some oxides such as MnO2 and Mn2O3. The nanorods will be ligand capped and, therefore, it will be possible to produce ordered structures of them.

Nanotechnology and Catalysis.

One of the goals of modern catalysis is to synthesize well-defined monodispersed nanoparticles. This might represent a very exciting breakthrough in the catalysis fields. In order to achieve this goal, it is also important to control the shape and the structure at the nanolevel. We propose to grow nanoparticles by either of the three methods described before, including the stabilization of the clusters on an organic solvent. Then adsorption of the nanoparticles on a high surface area support. Finally the process includes removal of the support particles from the solvent and then oxidation/reduction treatment to eliminate residual solvent and surfactant.

Previous work has demonstrated that the size and shape of the particle is determined by the first step[xi] which gives the possibility of producing catalysts which are monodisperse in shape, crystal structure, composition and surface chemistry. We intend to produce Pt/Si02, Rh/Si02, Pt/Rh/Si02, Pt/Al2O3 / Rh/Al2O, Pt/Rh/Al2O3. We will test the catalytic properties at the catalysis laboratory in Ensenada (UNAM), some well known reactions will be used to compare their activity and selectivity with that of catalyst prepared by standard reduction methods.
 

Selected Papers