RESUMEN
This work focuses on a systematic method to produce Ag, Cu, and Ag/Cu metallic nanoparticles (MNPs) in situ assisted with ultrasound on cellulose paper. By tuning the concentration of AgNO3 and CuSO4 salt precursors and ultrasound time, combined with a fixed concentration of ascorbic acid (AA) as a reducing agent, it was possible to control the size, morphology, and polydispersity of the resulting MNPs on cellulose papers. Notably, high yield and low polydispersity of MNPs and bimetallic nanoparticles are achieved by increasing the sonication time on paper samples pre-treated with salt precursors before reduction with AA. Moreover, mechanical analysis on paper samples presenting well-dispersed and distributed MNPs showed slightly decreasing values of Young's modulus compared to neat papers. The strain at break is substantially improved in papers containing solely Ag or Cu MNPs. The latter suggests that the elastic/plastic transition and deformation of papers are tuned by cellulose and MNPs interfacial interaction, as indicated by mechanical analysis. The proposed method provides insights into each factor affecting the sonochemistry in situ synthesis of MNPs on cellulose papers. In addition, it offers a straightforward alternative to scale up the production of MNPs on paper, ensuring an eco-friendly method.
RESUMEN
The influence of electrodeposition potential, pH, composition and temperature of the electrolytic bath on the structure of cobalt nanowires arrays electrodeposited into anodic aluminum oxide (AAO) porous membranes is reported. XRD, SEM, and TEM analysis were employed to characterize structural (crystal phase, crystallographic texture, and grain size), and morphological nanowire properties. It was confirmed that at pH 2 the electrodeposition potential has not influence on the preferred crystallographic orientation of the electrochemically grown Co nanowires. At pH 4 the electrodeposition potential controls the growth of cobalt nanowires along some preferential crystallographic planes. The electrolytic pH bath modulates the fcc or hcp phase exhibited by the cobalt nanowires. Single crystalline nanowires with a hcp phase strongly oriented along the (2021) crystallographic plane were obtained at pH 4 and at -1.1 V (vs. Ag/AgCl), a result not previously reported. High electrolytic bath temperatures contributed to improve the single crystalline character of the cobalt nanowires. The presence of chloride anion in the electrolytic bath also influenced on the structural properties of the resulting cobalt nanowires, improving their crystallinity. The optical reflectance of the samples shows a structure in the UV-blue region that can be assigned to the two-dimensional morphology arising in the shape of the almost parallel nanowires. Magnetic measurements showed that different electrodeposition potentials and electrolytic bath pH lead to different magnetic anisotropies on the nanowire array samples.
RESUMEN
Este artículo pretende un breve análisis de la biopiratería experimentada y resistida por parte de los pueblos mayas de Chiapas. Para ello se da cuenta de acuerdos y normas internacionales para la protección de los recursos y conocimientos de los pueblos indígenas; las bases económicas y características, en los ámbitos mundial y nacional, que dan la pauta para la nueva ola de proyectos de bioprospección de los recursos vegetales de la medicina indígena tradicional, dirigida por los países del norte hacia los del sur; algunas experiencias de su implantación en Sudamérica y otros países subdesarrollados; se explican los elementos más importantes del proyecto de bioprospección denominado «Investigación farmacéutica y uso sustentable del conocimiento etnobotánico y biodiversidad en la Región Maya de Los Altos de Chiapas, México¼, que fue operado por parte de El Colegio de la Frontera Sur, Ecosur, la Universidad de Georgia con apoyo económico del gobierno de Estados Unidos y la compañía biotecnológica molecular Nature Limited de Gales, Reino Unido; por último, se describe la lucha que llevó a cabo el Consejo de Médicos y Parteras Indígenas Tradicionales de Chiapas, Compitch, para que fuera cancelado el mencionado proyecto, así como algunas propuestas alternativas de Compitch a este proyecto de biopiratería.
