M. Avalos-Borja

Biosynthesis and microscopic study of metallic nanoparticles

Nanobiotechnology, bionanotechnology, and nanobiology are terms that have emerged in reference to the combination of nanotechnology and biology. Through the convergence of these disciplines, the production of metallic nanoparticles (NPs) using biological material as reducing agents is rapidly progressing. In the near future, the application of clean, non-toxic, and eco-friendly nanostructured material will be possible in industry and/or biomedicine. Currently, there is a wide range of organisms that have been reported to be useful in producing NPs. However, the development of finer protocols and the applicability of biosynthesized nanostructures are presently under study. Silver and gold are among the most studied metals due to their potential use in medical treatment. In fact, silver NPs have been evaluated as antimicrobial agents, having been successfully used against several types of fungi and bacteria. However, the use of such material in our daily life must be carefully evaluated. This article summarizes some of the most significant results using organisms to produce metallic NPs as well as the microscopic analyses used to characterize the nanostructured material obtained, providing a valuable database for future research.

Influence of phosphorus on the structure and the hydrodesulphurization and hydrodenitrogenation activity of W/Al2O3 catalysts

Abstract A series of W/Al 2 O 3 catalysts containing various amounts of phosphorus (0–6 wt.-% P 2 O 5 ) were characterized, in the oxide state by X-ray diffraction and temperature-programmed reduction (TPR), and in the sulphide form by high-resolution transmission electron microscopy (HRTEM); their activities for simultaneous hydrodesulphurization (HDS) of gas oil and hydrodenitrogenation (HDN) were also evaluated. The TPR results indicated that phosphorus addition increased the amount of those tungsten species which are more easily reduced, such as octahedral polytungstates. Consistently, the HRTEM micrographs showed that when phosphorus content was increased the lateral dimension of the WS 2 structures did not significantly vary, while the number of stacks was clearly increased. Both HDS and HDN were notably enhanced by increasing the phosphorus content; the promotion being relatively larger for HDS than for HDN. Possible explanations for the phosphorus promotion on W/Al 2 O 3 catalysts are discussed.

Changes in poly-vinylidene fluoride produced by electron irradiation

Abstract A study was made of the effects of electron irradiation of poly-vinylidene fluoride, using the DSC, FTIR, and X-ray techniques, as well as determining the percent cross-linking. Changes in crystallinity and melting point of the sample as a function of dose were found, the latter due to competition between cross-linking and crystallinity. The cross-linking was observed to increase with radiation dose. Chemical changes observed include the formation of carbonyl groups and double bonding, associated with the loss of HF.

Synthesis and characterization of NiWO4 crystals

Nickel tungstate (NiWO4) catalyst has been synthesized by reacting ammonium metatungstate and nickel nitrate as a function of temperature from 673 to 1073 K and of 1-h reaction time. It was found that NiWO4 is formed from 823 to 1073 K. The yield of 99% was obtained from 903 K to higher temperatures. The average crystal sizes have been determined by the Scherrer analysis and the surface area was measured by the Brunauer–Emmett–Teller (BET) method. The former increase from 55 to 112 nm, while the second decrease from 16 to 3 m2 g−1 in both cases, as the reaction temperature increases from 823 to 1073 K. Elemental composition and morphological structure were studied by energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The structural characterization has been performed using X-ray diffraction (XRD).

Influence of pH of the impregnation solution on the phosphorus promotion in W/Al2O3 hydrotreating catalysts

Abstract W/Al 2 O 3 and WP/Al 2 O 3 catalysts, prepared by co-impregnation at different pH values (1.5, 7 and 9), were characterised by several techniques (XRD, TPR, Raman spectroscopy, SEM-EDX, XPS and HRTEM) and tested in the parallel hydrodesulfurization (HDS) of gas oil and hydrodenitrogenation (HDN) of pyridine. The results show that P addition, whichever the pH of the impregnation solution is, has a positive effect on HDS activity and, to a minor extent, on HDN activity. The promoter effect of P for gas oil HDS was clearly influenced by the impregnation pH, which increased substantially by decreasing the impregnation pH. This improvement in HDS activity is interpreted as a result of an increased homogeneous distribution of tungsten on alumina, formation of more polytungsten oxide species and incipient WO 3 crystallites, and slightly greater sulfidation of the oxo-tungsten species, as well as a slight increase in WS 2 -like stacking. By contrast, the P promotion for pyridine HDN was not significantly affected by the impregnation pH, indicating that HDN activity is less sensitive to the changes in the W distribution than the HDS activity. The possible role of P in the catalytic properties of W/Al 2 O 3 catalysts is discussed.

SERS properties of different sized and shaped gold nanoparticles biosynthesized under different environmental conditions by Neurospora crassa extract.

Surface-enhanced Raman scattering (SERS) is a surface-sensitive technique that enhances Raman scattering by molecules adsorbed on rough metal surfaces. It is known that metal nanoparticles, especially gold and silver nanoparticles, exhibit great SERS properties, which make them very attractive for the development of biosensors and biocatalysts. On the other hand, the development of ecofriendly methods for the synthesis of metallic nanostructures has become the focus of research in several countries, and many microorganisms and plants have already been used to biosynthesize metallic nanostructures. However, the majority of these are pathogenic to plants or humans. Here, we report gold nanoparticles with good SERS properties, biosynthesized by Neurospora crassa extract under different environmental conditions, increasing Raman signals up to 40 times using methylene blue as a target molecule. Incubation of tetrachloroauric acid solution with the fungal extract at 60°C and a pH value of a) 3, b) 5.5, and c) 10 resulted in the formation of gold nanoparticles of a) different shapes like triangles, hexagons, pentagons etc. in a broad size range of about 10-200 nm, b) mostly quasi-spheres with some different shapes in a main size range of 6-23 nm, and c) only quasi-spheres of 3-12 nm. Analyses included TEM, HRTEM, and EDS in order to corroborate the shape and the elemental character of the gold nanoparticles, respectively. The results presented here show that these ‘green’ synthesized gold nanoparticles might have potential applicability in the field of biological sensing.

Ultrastructural Analysis of Candida albicans When Exposed to Silver Nanoparticles

Candida albicans is the most common fungal pathogen in humans, and recently some studies have reported the antifungal activity of silver nanoparticles (AgNPs) against some Candida species. However, ultrastructural analyses on the interaction of AgNPs with these microorganisms have not been reported. In this work we evaluated the effect of AgNPs on C. albicans, and the minimum inhibitory concentration (MIC) was found to have a fungicidal effect. The IC50 was also determined, and the use of AgNPs with fluconazole (FLC), a fungistatic drug, reduced cell proliferation. In order to understand how AgNPs interact with living cells, the ultrastructural distribution of AgNPs in this fungus was determined. Transmission electron microscopy (TEM) analysis revealed a high accumulation of AgNPs outside the cells but also smaller nanoparticles (NPs) localized throughout the cytoplasm. Energy dispersive spectroscopy (EDS) analysis confirmed the presence of intracellular silver. From our results it is assumed that AgNPs used in this study do not penetrate the cell, but instead release silver ions that infiltrate into the cell leading to the formation of NPs through reduction by organic compounds present in the cell wall and cytoplasm.

Arsenic mobility controlled by solid calcium arsenates: A case study in Mexico showcasing a potentially widespread environmental problem

An As-contaminated perched aquifer under an urban area affected by mining was studied over a year to determine the contamination source species and the mechanism of As mobilization. Results show that the dissolution of calcium arsenates in residues disposed on an inactive smelter has caused high levels of As pollution in the adjoining downgradient 6-km perched aquifer, reaching up to 158 mg/L of dissolved As, and releasing a total of ca. 7.5 tons of As in a year. Furthermore, free calcium ion availability was found to control As mobility in the aquifer through the diagenetic precipitation of calcium arsenates (Ca5H2(AsO4)4·cH2O) preventing further mobilization of As. Results shown here represent a model for understanding a highly underreported mechanism of retention of arsenate species likely to dominate in calcium-rich environments, such as those in calcareous sediments and soils, where the commonly reported mechanism of adsorption to iron(III) oxyhydroxides is not the dominant process.

Crosslinking of recycled polyethylene by gamma and electron beam irradiation

Recycling of polymeric materials is usually accompanied by degradation and deleterious properties. Irradiation crosslinking of recycling low density polyethylene by electron beam and gamma rays could be the solution to improve their properties. This paper presents a comparison on the effects of gamma and electron irradiation on virgin and recycled polyethylene. Their mechanical, thermal and chemical properties were analyzed. VPE samples shown higher crosslinking percentages than RPE samples in all range of doses studied, unirradiated RPE samples had higher values on their tensile properties than VPE. Percentage crystallinity was similar in all range of doses studied.

Hydrodesulfurization activity of MoS2 catalysts modified by chemical exfoliation

The surface area of unsupported MoS2 catalysts prepared by thiosalt decomposition is found to increase after undergoing a treatment known as chemical exfoliation. Rate measurements of dibenzothiophene hydrodesulfurization in a batch reactor show that activity decreases for the chemically modified MoS2 catalysts, along with the hydrogenation/hydrodesulfurization ratios (HYD/HDS). These results indicate that both basal and edge planes of the layered sulfides are rearranged by the exfoliation treatment, but that other processes must also be involved. Reference crystalline MoS2 is also discussed in the work.