Antonio Esteban-Cubillo

The antibacterial and antifungal activity of a soda-lime glass containing silver nanoparticles

The antibacterial and antifungal activity of a low melting point soda-lime glass powder containing silver nanoparticles has been studied. Nano-Ag sepiolite fibres containing monodispersed silver nanoparticles (d(50) approximately 11 +/- 9 nm) were used as the source of silver. This powder presents a high antibacterial (against gram-positive and gram-negative bacteria) as well as antifungal (against I. orientalis) activity. The observed high activity against yeast has been explained by considering the inhibitory effect of the Ca(2+) lixiviated from the glass on the growth of the yeast colonies.

Surface Modification of Sepiolite in Aqueous Gels by Using Methoxysilanes and Its Impact on the Nanofiber Dispersion Ability

Surface modification reactions on needle-like sepiolite using alkyl and functional silanes have been carried out in the form of aqueous gels. In contrast with modifications in organic solvents, reactions in water make it possible to modify the surface of almost-individual sepiolite fibers and produce either a continuous coating or a nanotexturization of the sepiolite fiber surface, depending on the reaction conditions. This clean procedure substitutes advantageously organic solvent surface modifications and allows the tuning of surface properties such as specific surface area, wetting behavior, and chemical functionalization. A consequence of such tuning is, for example, the excellent dispersion of modified sepiolite nanofibers in a great variety of polymers by routine compounding and processing techniques.

Current Industrial Applications of Palygorskite and Sepiolite

Abstract Sepiolite and palygorskite are very versatile materials due their properties. This chapter gives an overview of the applications and markets of the products that are currently manufactured with sepiolite and, to a lesser extent, palygorskite. An special emphasis is given to new applications and those that are being developed and are expected to become a reality in the near future. The shape of the particles and the large and active surface area are a source of physico-chemical and rheological characteristics useful in a wide variety of systems. The particular surface of this silicate influenced by six generations of processing methods opens new windows for applications that provide new solutions for industrial problems. New materials based on palygorskite and sepiolite, such as nanoclays, hybrids, bio-hybrids, biomimetic and functional materials, are being developed and studied for different uses that require new and better performance advanced materials.

Chapter 17 - Advanced Materials and New Applications of Sepiolite and Palygorskite

Abstract Sepiolite and palygorskite are versatile clay minerals deserving many diverse applications due to their unique textural and structural characteristics compared to layered clay minerals. Currently, these microfibrous silicates are regarded as nanomaterials, whose use appears as very promising for advanced applications as, for instance, nanofillers in polymer–clay nanocomposites. Bio-nanocomposites based on sepiolite and palygorskite assembled to different types of biopolymers, such as polysaccharides or proteins, are biohybrid materials useful as bioplastics (green nanocomposites) or macroporous materials showing cellular structure (foams). These biohybrids can be of interest to build clay-biological interfaces for tissue engineering, as new adjuvants for vaccines, as support of enzymes or as bioreactor devices. Combination at the nanometric scale of both microfibrous silicates with carbonaceous materials, such as graphene-like compounds and carbon nanotubes (CNTs), offers the possibility to develop conductive materials of interest for diverse electrochemical applications. Sepiolite and palygorskite are also excellent candidates to develop other nanostructured materials for a broad range of potential applications, including support of metal and metal oxide nanoparticles for applications as sensor devices, as high-performing catalysts, as biocide additives or as magnetic adsorbents.

Multiscale gold and silver plasmonic plastics by melt compounding

This work presents a strategy to obtain plasmonic plastics by conventional large scale polymer processing methods using metal nanoparticles (Au and Ag) supported on sepiolite fibers acting as carriers. Two conventional polymers, polyethylene and polystyrene, have been used as matrices, and composites were prepared up to high inorganic contents. The resulting composites exhibited at all loadings the corresponding optical absorption plasmon bands ascribed to the metal nanoparticles. In addition the sepiolite fibers acting as carriers remarkably improved the thermal stability and produced mechanical reinforcement of the polymer matrices as well as they appear invisible due to the index matching with the matrix. Therefore, highly transparent and robust plasmonic plastics can be easily prepared by industrially scalable processing techniques.

Micro/nano composites : a simple and safe way to fabricate nanomaterials

In this paper we detail how the use of nanoparticles supported or embedded in microparticles (nanostructured powders) may overcome many of the problems of nanoparticle manipulation as well as allowing bulk compacts in which nanoparticles appear monodisperse to be obtained. The main advantage of this procedure is that the possibility to use the well developed knowledge about compounding of microparticles to obtain dense composites instead of developing new methods to handling nanoparticles. The obtained nanostructured powders or dense composites can be used for different applications, such as medical implants, cutting tools, optical devices, magnetic powders, etc. Examples of alumina/nano-zirconia, alumina/nano-YAG, zirconia/nano-nickel, alumina/nano-Ag and sepiolite/nano-(Cu, Au, Ag, Ni and Fe) are also reported.

Faraday activity in flexible maghemite/polymer matrix composites

Homogeneous 10-30 nm γ-Fe2O3 (maghemite) nanoparticles have been synthesized on magnesium silicate fibers and further incorporated into a polymeric matrix (polystyrene). The similarity in the refractive indices of both materials (nSep = 1.53 and nPS = 1.59) and the optimal dispersion allowed obtaining highly transparent composites from near IR to the visible range. Therefore, particles of γ-Fe2O3 appear perfectly dispersed inside a heterogeneous but transparent matrix, and consequently, it is possible to measure their Faraday rotation. These composites present a ferromagnetic behavior, yet close to superparmagnetism due to the size of the γ-Fe2O3 particles. High real in-line transmittance in the visible range together with a Faraday activity over 0.4° are obtained in 60 µm films, which is over twice larger than that reported for commercially available devices based on single crystal terbium gallium garnets.