Eric M. Rivera-Muñoz

SBA-15 Mesoporous Silica as Catalytic Support for Hydrodesulfurization Catalysts—Review

SBA-15 is an interesting mesoporous silica material having highly ordered nanopores and a large surface area, which is widely employed as catalyst supports, absorbents, drug delivery materials, etc. Since it has a lack of functionality, heteroatoms and organic functional groups have been incorporated by direct or post-synthesis methods in order to modify their functionality. The aim of this article is to review the state-of-the-art related to the use of SBA-15-based mesoporous systems as supports for hydrodesulfurization (HDS) catalysts.

Sol Gel-Derived SBA-16 Mesoporous Material

The aim of this article is to review current knowledge related to the synthesis and characterization of sol gel-derived SBA-16 mesoporous silicas, as well as a review of the state of the art in this issue, to take stock of knowledge about current and future applications. The ease of the method of preparation, the orderly structure, size and shape of their pores and control, all these achievable through simple changes in the method of synthesis, makes SBA-16 a very versatile material, potentially applicable in many areas of science and molecular engineering of materials.

Growth of hydroxyapatite on silica gels in the presence of organic additives: kinetics and mechanism

Abstract Synthetic hydroxyapatite was grown on surfaces of silica gels by immersing silica monoliths in a simulated body fluid at 37 °C. The gels were prepared by the sol-gel method and the drying process was controlled by using different additives (mono- and di-ethylene glycol, formamide and glycerin) to obtain large monoliths. The additives affect the growth of the apatite by changing the kinetic constants of chemical reactions on the silica surface. Surface areas and pore size distributions were determined, energy dispersion and FTIR spectra obtained, and scanning electron microscopy performed. The formation of the hydroxyapatite competes with the formation of crystalline calcium carbonate, but the results allow optimization of conditions for the growth of the former as a function of the type and concentration of the additive. For these optimal conditions, the mechanism and the order of the reaction were determined.

Characterization of crystalline structures in Opuntia ficus-indica.

This research studies the crystalline compounds present in nopal (Opuntia ficus-indica) cladodes. The identification of the crystalline structures was performed using X-ray diffraction, scanning electron microscopy, mass spectrometry, and Fourier transform infrared spectroscopy. The crystalline structures identified were calcium carbonate (calcite) [CaCO3], calcium-magnesium bicarbonate [CaMg(CO3)2], magnesium oxide [MgO], calcium oxalate monohydrate [Ca(C2O4)•(H2O)], potassium peroxydiphosphate [K4P2O8] and potassium chloride [KCl]. The SEM images indicate that calcite crystals grow to dipyramidal, octahedral-like, prismatic, and flower-like structures; meanwhile, calcium-magnesium bicarbonate structures show rhombohedral exfoliation and calcium oxalate monohydrate is present in a drusenoid morphology. These calcium carbonate compounds have a great importance for humans because their bioavailability. This is the first report about the identification and structural analysis of calcium carbonate and calcium-magnesium bicarbonate in nopal cladodes, as well as the presence of magnesium oxide, potassium peroxydiphosphate and potassium chloride in these plants. The significance of the study of the inorganic components of these cactus plants is related with the increasing interest in the potential use of Opuntia as a raw material of products for the food, pharmaceutical, and cosmetic industries.

Rietveld refinement of Y2GeO5

Y2GeO5 (yttrium germanium pentaoxide) was synthesized by solid-state reaction at 1443 K. The arrangement, which has monoclinic symmetry, is isostructural with Dy2GeO5 and presents two independent sites for the Y atoms. Around these atoms there are distorted six-coordinated YO6 octahedra and seven-coordinated YO7 pentagonal bipyramids. The YO7 polyhedra are linked together, sharing their edges along a surface parallel to ab, forming a sheet. Each of these parallel sheets is interconnected by means of GeO4 tetrahedra, sharing an edge (or vertex) on one side and a vertex (or edge) on the other adjacent side. Parallel sheets of YO7 polyhedra are also interconnected by undulating chains of YO6 octahedra along the c axis. These octahedra are joined together, sharing a common edge, to form the chain and share edges with the YO7 polyhedra of the sheets.

Interconnected porosity analysis by 3D X-ray microtomography and mechanical behavior of biomimetic organic-inorganic composite materials

Hydroxyapatite-based materials have been used for dental and biomedical applications. They are commonly studied due to their favorable response presented when used for replacement of bone tissue. Those materials should be porous enough to allow cell penetration, internal tissue growth, vascular incursion and nutrient supply. Furthermore, their morphology should be designed to guide the growth of new bone tissue in anatomically applicable ways. In this work, the mechanical performance and 3D X-ray microtomography (X-ray μCT) study of a biomimetic, organic-inorganic composite material, based on hydroxyapatite, with physicochemical, structural, morphological and mechanical properties very similar to those of natural bone tissue is reported. Ceramic pieces in different shapes and several porous sizes were produced using a Modified Gel Casting Method. Pieces with a controlled and 3D hierarchical interconnected porous structure were molded by adding polymethylmethacrylate microspheres. Subsequently, they were subject to a thermal treatment to remove polymers and to promote a sinterization of the ceramic particles, obtaining a HAp scaffold with controlled porosity. Then, two different organic phases were used to generate an organic-inorganic composite material, so gelatin and collagen, which was extracted from bovine tail, were used. The biomimetic organic-inorganic composite material was characterized by Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray Diffraction, Fourier Transform Infrared Spectroscopy and 3D X-ray microtomography techniques. Mechanical properties were characterized in compression tests, obtaining a dramatic and synergic increment in the mechanical properties due to the chemical and physical interactions between the two phases and to the open-cell cellular behavior of the final composite material; the maximum compressive strength obtained corresponds to about 3 times higher than that reported for natural cancellous bone. The pore size distribution obtained could be capable to allow cell penetration, internal tissue in-growth, vascular incursion and nutrient supply and this material has tremendous potential for use as a replacement of bone tissue or in the manufacture and molding of prosthesis with desired shapes.

Characterization of Calcium Compounds in Opuntia ficus indica as a Source of Calcium for Human Diet

Analyses of calcium compounds in cladodes, soluble dietary fiber (SDF), and insoluble dietary fiber (IDF) of Opuntia ficus indica are reported. The characterization of calcium compounds was performed by using Scanning Electron Microscopy, Energy Dispersive Spectrometry, X-ray diffraction, and infrared spectroscopy. Atomic Absorption Spectroscopy and titrimetric methods were used for quantification of total calcium and calcium compounds. Whewellite (CaC2O4·H2O), weddellite (CaC2O4·(H2O)2.375), and calcite (CaCO3) were identified in all samples. Significant differences () in the total calcium contents were detected between samples. CaC2O4·H2O content in cladodes and IDF was significantly higher () in comparison to that observed in SDF, whereas minimum concentration of CaCO3 was detected in IDF with regard to CaCO3 contents observed in cladodes and SDF. Additionally, molar ratio oxalate : Ca2

Synthesis and Characterization of Hydroxyapatite-Based Nanostructures: Nanoparticles, Nanoplates, Nanofibers and Nanoribbons

Material science is taking an increasing important role in bioengineering and biomedical sciences, aiming to develop new systems and materials capable of adapting to the highly demanding environment of a living organism. One of those materials, Hydroxyapatite (HAp), is the principal calcium orthophosphate present in the mineral phase of bone.

Morphological Analysis of Hydroxyapatite Particels Obtained by Different Methods

Material science is playing an increasing role in bioengineering and biomedical sciences, aiming to develop new systems and materials capable of overcoming the highly demanding environment of a living organism. One of those materials, Hydroxyapatite (HAp), is the principal calcium phosphate present in the mineral phase of bone. Hydroxyapatite-based materials have been used for dental and biomedical applications, and the control of morphology and structure at micro and nanoscale levels in the synthesis processes, is crucial for several of those applications. Hydroxyapatite crystalline particles were obtained by the so-called sol-gel technique, in which silica gels induce the formation of apatite particles in a simulated body fluid at nearly 37°C, different chemical additives were used to control morphology and particle size, as previously reported by our group. Recently, the synthesis of HAp particles with similar morphologies obtained by different methods, have been reported by other groups. Differences and similarities in morphologies, as well as in the synthesis processes, are established in the present work, along with a discussion of possible crystal growth and assembly mechanisms, which lead to a better understanding of the particle growth processes, is included. This knowledge could be the basis for further synthesis methods aimed to obtain HAp nanostructures with a crystal preferential orientation.

Mechanical Characterization of Hydroxyapatite-Based, Organic-Inorganic Composites

Hydroxyapatite-based materials have been used for dental and biomedical applications. Newly developed synthesis techniques give cause to a broad field in the study of these materials and industry demands products with better properties day by day. The purpose of the present work was to evaluate the mechanical properties of hydroxyapatite-based (HAp-based), organic-inorganic composites. HAp-based, organic-inorganic composites were obtained by modified gel casting process and organic molecules in a gelatin solution. HAp samples of different sizes and shapes were obtained with controlled micro and macro porosity and then were immersed into several gelatin solutions with different concentrations. X-ray powder Diffraction (XRD), Infra Red (IR) Spectroscopy and Scanning Electron Microscopy (SEM) techniques were used to analyze samples before and after gel casting process in order to assure that chemical and physical properties remains the same after this process. IR Spectroscopy and SEM techniques were used to characterize samples after the introduction of organic phase in order to analyze the final morphology of samples. Mechanical characterization was made in compression mode to samples without and with different concentrations of organic phase in order to establish the optimum conditions in which the highest compressive strength and Young’s modulus is reached.