Francisco Márquez

Preparation of hollow magnetite microspheres and their applications as drugs carriers

AbstractHollow magnetite microspheres have been synthesized by a simple process through a template-free hydrothermal approach. Hollow microspheres were surface modified by coating with a silica nanolayer. Pristine and modified hollow microparticles were characterized by field-emission electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, FT-IR and Raman spectroscopy, and VSM magnetometry. The potential application of the modified hollow magnetite microspheres as a drug carrier was evaluated by using Rhodamine B and methotrexate as model drugs. The loading and release kinetics of both molecules showed a clear pH and temperature dependent profile.Graphical abstractHollow magnetite microspheres have been synthesized. Load-release experiments with Rhodamine-B as a model drug and with Methotrexate (chemotherapy drug used in treating certain types of cancer) demonstrated the potential applications of these nanostructures in biomedical applications.

An alternative route for the synthesis of silicon nanowires via porous anodic alumina masks

Amorphous Si nanowires have been directly synthesized by a thermal processing of Si substrates. This method involves the deposition of an anodic aluminum oxide mask on a crystalline Si (100) substrate. Fe, Au, and Pt thin films with thicknesses of ca. 30 nm deposited on the anodic aluminum oxide-Si substrates have been used as catalysts. During the thermal treatment of the samples, thin films of the metal catalysts are transformed in small nanoparticles incorporated within the pore structure of the anodic aluminum oxide mask, directly in contact with the Si substrate. These homogeneously distributed metal nanoparticles are responsible for the growth of Si nanowires with regular diameter by a simple heating process at 800°C in an Ar-H2 atmosphere and without an additional Si source. The synthesized Si nanowires have been characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman.

Synthesis and Characterization of Zeolite Based Porous Ceramic Membranes

Abstract New porous zeolite based membranes were synthesized using a ceramic methodology and characterized by means of XRD, SEM, EDAX and permeation tests. The membranes were produced by thermal transformation of natural clinoptilolite. The XRD study showed clinoptilolite amorphization at 600–900°C. A posterior recrystallization to a siliceous phase and a compact aluminosilicate phase at 900–1150°C was also produced. The Permeability [B] and Permeance [Π] of H2 and CO2 were measured using the Darcy Law correlation. It was also applied for gaseous laminar flow using the Carman‐Kozeny equation. With the help of this equation the membrane pores sizes were measured. It was shown that the membrane porosity can be controlled by the grain size of the original natural zeolite powder. The membranes were further transformed by hydrothermal synthesis to obtain materials covered with an AlPO4‐5 molecular sieve. In conclusion, novel, inexpensive, strong, high permeation rate, and high temperature membranes were produced with natural clinoptilolite, a low cost and available material.

Microspheres for the growth of silicon nanowires via vapor-liquid-solid mechanism

Silicon nanowires have been synthesized by a simple process using a suitable support containing silica and carbon microspheres. Nanowires were grown by thermal chemical vapor deposition via a vapor-liquid-solidmechanism with only the substrate as silicon source. The curved surface of the microsized spheres allows arranging the gold catalyst as nanoparticles with appropriate dimensions to catalyze the growth of nanowires. The resulting material is composed of the microspheres with the silicon nanowires attached on their surface.

Structure and characterization of vertically aligned single-walled carbon nanotube bundles

Arrays of vertically aligned single-walled carbon nanotube bundles, SWCNTs, have been synthesized by simple alcohol catalytic chemical vapor deposition process, carried out at 800°C. The formed SWCNTs are organized in small groups perpendicularly aligned and attached to the substrate. These small bundles show a constant diameter of ca. 30nm and are formed by the adhesion of no more than twenty individual SWCNTs perfectly aligned along their length.

Synthesis and characterization of amorphous SiO2 nanowires directly grown on Cu substrates

A novel procedure for the growth of Silica nanowires directly from Cu substrates is reported. The single-step synthesis procedure consists of a thermal treatment at 900 °C in Ar-H2 atmosphere, without the need for additional catalysts. Nanowires grow from Cu protrusions generated on the surface during annealing via Vapor–Liquid–Solid method, giving rise to a branched structure. These SiO2 nanostructures present an amorphous structure as evidenced by transmission electron microscopy. Silica nanowires grown on Cu and Si substrates have been characterized by XPS. Additionally, room-temperature photoluminescence measurements show a blue-green emission peak at ca. 509 nm (2.44 eV) attributed to oxygen deficiencies in the structure. The success of this procedure allows for future possible incorporation of these nanowires in optoelectronic devices.Graphical AbstractNew procedure for the growth of silica nanowires (SiO2NWs) directly on Cu substrates, via a single-step thermal treatment process without the need for additional catalysts. The process follows a VLS mechanism where SiO acts as the gaseous precursor of both: the SiO2NWs grown on the top Si fragment and those grown on the Cu substrate, roots-like nanowires (SiO2NRs). This synthesis permits to preserve the PL properties of the SiO2NWs on conductive Cu substrates, which could be of paramount importance in the design and implementation of integrated electronics and devices.

Nanosensors: From near field to far field applications

The DoD Center for Chemical Sensors Development at the University of Puerto Rico-Mayagüez has worked in developing sensors for threat agents for over 8 years. Work has continued under the ALERT DHS Center of Excellence. The approaches for sensing have covered many types of threat chemicals and some types of biological simulants, including high energetic materials, homemade explosives, mixtures and formulations, chemical agents simulants, toxic industrial chemicals and spore forming microorganisms. Sensing in the far field has been based in vibrational spectroscopy: Raman and infrared. Near field detection has been mainly based on nanotechnology enabled sensing platforms for Surface Enhanced Raman Scattering. Initial use of colloidal suspensions of silver and gold nanospheres eventually evolved to metallic and metal oxide nanorods and to particle immobilization, including sample smearing on substrates and drop-on-demand thermal inkjet printing of nanoparticles. Chemical reduction of metal ions has been substituted by clean photonic physical reduction that leaves the nanoactive surface highly exposed and overcomes the physico-chemical problem of double electrical layers posed by colloidal suspensions of nanoparticles. New avenues have open wide research endeavors by using laser techniques to form nanoprisms and interference based metallic nano-images and micro-images. UV based metal reduction on top of metal oxides nanostructures promises to provide the selectivity and sensitivity expected for the last 30-40 years. Various applications and experimental setups will be discussed.