Jesús Arenas-Alatorre

Determination of the size distribution of metallic nanoparticles by optical extinction spectroscopy

A method is proposed to estimate the size distribution of nearly spherical metallic nanoparticles (NPs) from optical extinction spectroscopy (OES) measurements based on Mies theory and an optimization algorithm. The described method is compared against two of the most widely used techniques for the task: transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS). The size distribution of Au and Cu NPs, obtained by ion implantation in silica and a subsequent thermal annealing in air, was determined by TEM, grazing-incidence SAXS (GISAXS) geometry, and our method, and the average radius obtained by all the three techniques was almost the same for the two studied metals. Concerning the radius dispersion (RD), OES and GISAXS give very similar results, while TEM considerably underestimates the RD of the distribution.

Berthierine and chamosite hydrothermal : genetic guides in the Peña Colorada magnetite-bearing ore deposit, Mexico

We report the first finding of berthierine and chamosite in Mexico. They occur in the iron-ore deposit of Peña Colorada, Colima. Their genetic characteristics show two different mineralization events associated mainly to the magnetite ore. Berthierine is an Fe-rich and Mg-low 1:1 layer phyllosilicate of hydrothermal sedimentary origin. Its structure is 7 Å, dhkl [10 0] basal spacing and low degree structural ordering. The phyllosilicate has been identified by a lack of 14 Å basal reflection on X-ray diffraction (XRD) patterns. These data were supported by High Resolution Transmision Electron Microscopy (HRTEM) images that show thick packets of berthierine in well defined parallel plates. From the analysis of Fast Fourier Transform (FFT), we found around [1 0 0] reflections of berhierine 7.12 Å and corresponding angles of hexagonal crystalline structure. Berthierine has a microcrystalline structure, dark green color, and high refraction index (1.64 to 1.65). Birefringence is low, near 0.007 to null and it is associated to nanoparticles (<15 nm) and microparticles of magnetite (<25 μm), fine grain siderite, and organic matter. Its texture is intergranular-interstratified with colloform banding. The chamosite Mg-rich is of hydrothermal epigenetic origin affected by low-degree metamorphism. It is an Fe-rich 2:1 layer silicate, with basal space of 14 Å, dhkl [0 0 1]. The chamosite occurs as lamellar in sizes ranging from 50 to 150 μm. It has intense green color and refraction index from 1.64 to 1.65. The birefringence is near 0.008, with biaxial (-) orientation and a 2V small. It is associated mainly to sericite, epidote, clay, feldspar, and magnetite. Chamosite is emplaced in open spaces filling and linings. Mössbauer spectra of berthierine and chamosite are similar. They show the typical spectra of paramagnetic substances, with two well defined unfoldings corresponding to the oxidation state of Fe+2 and Fe+3. Chemical composition of both minerals was obtained by an electron probe X-ray micro-analyzer (EPMA). The radio Fe+Mg+Mn vs Si and Al show similar chemical compositions and different XRD patterns in the crystalline structure provoked by the environmental conditions of emplacement. A hydrothermal environment was predominant, occurring before, during, and after the magnetite mineralization. The identification of magnetite nanoparticles supports the hypothesis of a marine environment, specifically exhalative sedimentary (SEDEX) for the berthierine.

Optical Absorption and Visible Photoluminescence from Thin Films of Silicon Phthalocyanine Derivatives

The interest of microelectronics industry in new organic compounds for the manufacture of luminescent devices has increased substantially in the last decade. In this paper, we carried out a study of the usage feasibility of three organic bidentate ligands (2,6-dihydroxyanthraquinone, anthraflavic acid and potassium derivative salt of anthraflavic acid) for the synthesis of an organic semiconductor based in silicon phthalocyanines (SiPcs). We report the visible photoluminescence (PL) at room temperature obtained from thermal-evaporated thin films of these new materials. The surface morphology of these films was analyzed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM indicated that the thermal evaporation technique is an excellent resource in order to obtain low thin film roughness when depositing these kinds of compounds. Fourier transform infrared spectroscopy (FTIR) spectroscopy was employed to investigate possible changes in the intra-molecular bonds and to identify any evidence of crystallinity in the powder compounds and in the thin films after their deposition. FTIR showed that there was not any important change in the samples after the thermal deposition. The absorption coefficient (α) in the absorption region reveals non-direct transitions. Furthermore, the PL of all the investigated samples were observed with the naked eye in a bright background and also measured by a spectrofluorometer. The normalized PL spectra showed a Stokes shift ≈ 0.6 eV in two of our three samples, and no PL emission in the last one. Those results indicate that the Vis PL comes from a recombination of charge carriers between conduction band and valence band preceded by a non-radiative relaxation in the conduction band tails.

Biosynthesis of silver nanoparticles using chenopodium ambrosioides

Biosynthesis of silver nanoparticles (AgNPs) was achieved using extract of Chenopodium ambrosioides as a reducer and coating agent at room temperature (25°C). Two molar solutions of AgNO3 (1mM and 10mM) and five extract volumes (0.5, 1, 2, 3, and 5 mL) were used to assess quantity, shape, and size of the particles. The UV-Vis spectra gave surface plasmon resonance at 434- 436 nm of the NPs synthesized with AgNO3 10 mM and all extract volumes tested, showing a direct relationship between extract volumes and quantity of particles formed. In contrast, the concentration of silver ions was related negatively to particle size. The smallest (4.9 ± 3.4 nm) particles were obtained with 1 mL of extract in AgNO3 10 mM and the larger amount of particles were obtained with 2 mL and 5 mL of extract. TEM study indicated that the particles were polycrystalline and randomly oriented with a silver structure face centered cubic (fcc) and fourier transform infrared spectroscopy (FTIR) indicated that disappearance of the -OH group band after bioreduction evidences its role in reducing silver ions.

Facile Solventless Synthesis of a Nylon-6,6/Silver Nanoparticles Composite and Its XPS Study

Silver nanoparticles were synthesized and supported on thin nylon membranes by means of a simple method of impregnation and chemical reduction of Ag ions at ambient conditions. Particles of less than 10 nm were obtained using this methodology, in which the nylon fibers behave as constrained nanoreactors. Pores on nylon fibres along with oxygen and nitrogen from amide moieties in nylon provide effective sites for in situ reduction of silver ions and for the formation and stabilization of Ag nanoparticles. Transmission electron microscopy (TEM) analysis showed that silver nanoparticles are well dispersed throughout the nylon fibers. Furthermore, an interaction between nitrogen of amides moieties of nylon-6,6 and silver nanoparticles has been found by X-ray photoelectron spectroscopy (XPS).

Photoluminescence enhancement from silicon quantum dots located in the vicinity of a monolayer of gold nanoparticles

In this paper we show that it is possible to carry out a functional coupling between a thin film of silicon quantum dots embedded in a silicon nitride matrix (SiQDs) and a monolayer of gold nanoparticles by using dry and low temperature techniques, such as those used in microelectronics industry, i.e., Remote Plasma Enhanced Chemical Vapor Deposition (RPECVD) and Sputtering. The coupled structure showed 105% of photoluminescence (PL) enhancement, compared with PL observed from the SiQDs without the gold monolayer. The SiQDs used as light emitters have an average diameter of 3.1 nm, a particle density of 6.04 × 1012 particles per cm2 and a maximum PL peak at 505 ± 5 nm. Additionally, the gold nanoparticles were designed with the following characteristics: the particles are embedded in a silicon nitride matrix, show quasi-spherical shapes, an average diameter of 2.9 nm, a particle density of 2.52 × 1012 particles per cm2 and their surface plasmon resonance is located at 540 ± 3 nm. We found that there is an optimum separation distance between SiQDs and the gold monolayer to achieve the maximum photoluminescence enhancement. For our structure, such optimal distance was 10 ± 1 nm. We consider that there could be two combined physical effects responsible of the enhancement: (a) a plasmonic diffraction-limited coupling and (b) a change of the scattering mechanisms of the primary laser light.

Temperature and amino acid-assisted size- and morphology-controlled photochemical synthesis of silver decahedral nanoparticles

Stable silver decahedron nanoparticles were produced under the blue light irradiation (light-emitting diodes) of a modified precursor solution that has been previously reported. To improve the formation of the nano-decahedrons under blue light, we proposed the use of amino acids with electrically charged side chains (L-arginine, L-lysine and L-histidine). Our results show that L-arginine and L-lysine are best suited to improve the yield of the decahedrons. We also followed the kinetics of the photochemical synthesis under different irradiance conditions of 80, 50 and 15 mW/cm2. The maximum irradiance, 80 mW/cm2, resulted in a synthesis that was twice as fast as those associated with lower irradiances, and the corresponding decahedron yield was higher. The optimal temperature of the precursor solution for the improvement of the photochemical synthesis of silver decahedrons with Triton X-100 as a surfactant was also determined.

Structural Effect of Different EDC Crosslinker Concentration in Gelatin- Hyaluronic Acid Scaffolds

Introduction: Gelatin and hyaluronic acid are two biopolymers with different applications in tissue engineering. They may be employed to construct diverse scaffolds that allow cells to differentiate and proliferate on them. In order to obtain the best functional and mechanical conditions in scaffolds, they must be crosslinked to form covalent links between gelatin and hyaluronic acid. The crosslinker 1-ethy-3-(3-dymethylaminopropyl) carbodiimide hydrochloride (EDC) is a compound widely used due to its low cytotoxicity. Besides, the concentration of the crosslinker may modify the physical properties and morphological characteristics of scaffolds when it forms covalent links between biopolymers, helping to construct different kinds of scaffolds used for developing soft tissues. However, the development of scaffolds made of gelatin and hyaluronic acid crosslinked with EDC has been poorly studied. In addition, the concentrations used for crosslinking gelatin and hyaluronic acid are contradictory. Therefore, the aim of this study was to analyze the structure of gelatin/hyaluronic acid scaffolds crosslinked with EDC. Methods: Gelatin-hyaluronic acid scaffolds were prepared by direct freeze-drying. Afterwards, They were crosslinked with different concentrations of EDC (6, 30, 50 and 60 mM) for 12 h. Results: This research has demonstrated that the gelatin/hyaluronic acid scaffolds crosslinked with the highest concentrations of the crosslinker had fewer water concentration absorbed, pore size diminished and pore number increased in comparison with control groups. Despite scaffolds composition has not changed in any of the concentrations, the bone marrow mesenchymal cells mortality percentage increased when cells were placed on the scaffolds of concentration 60 mM, perhaps for the residual 1-ethy-3-(3-dymethylaminopropyl) carbodiimide hydrochloride found in the scaffolds. Conclusion: Our results revealed that different EDC concentrations may modify the physical and biological characteristics of gelatin/hyaluronic acid scaffolds; as a result, the scaffolds obtained may be used for the manufacture of different tissues in regenerative medicine.

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.

Microstructure and Adhesive Properties of Copal Composite in Dental Incrustations

There are evidences that in ancient cultures in Mexico, copal was probably used for gluing precious stones in teeth cavities and for dental restorations as well. This is an important reason for making experiments using copal and copal-based composites in order to have more information for the potential applications of this material in modern dentistry. In our experiments concerning with dental incrustations of turquoise, we have practiced round cavities (about 1 mm depth) in the middle of incisive teeth by using a low-speed air turbine. Turquoise was cut in such a way that fits exactly on the tooth cavity. Copal and powdered apatite were used to glue the stone into the cavity. With Scanning electron microscopy we have observed that the composite copal-powdered apatite, penetrates the dentin tubules in the tooth tissue (depth of penetration from 5.6 to 41 micrometers), suggesting the existence of a micromechanical adherence. Concerning to the characterization of the adhesive properties, we have applied the ASTM D2095-72 test considering the adhesion of two cylinders of bone, and the copal composite as the adhesive. A maximum cohesive tensile strength around 0.1 MPa for elastic response was measured for hydroxyapatite compositions of 0, 25 and 75 wt%. We will discuss these results considering the reports of dental incrustations in ancient Mexico.