Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

La contribución del microscopio electrónico a las nanociencias ha sido excepcional por ser el equipo que permite estudiar y analizar materiales nanométricos. En este trabajo se presenta una breve reseña histórica sobre el descubrimiento y evolución del microscopio electrónico de transmisión (TEM, por sus siglas en inglés) y el electrónico de barrido (SEM, por sus siglas en inglés), así como la instalación de estos microscopios electrónicos en México. El escrito se presenta de tal manera que el texto y las ilustraciones se complementen.

On December 2019 a new virus appears in China, the SARS-CoV-2, which is the cause of a severe acute respiratory syndrome known as COVID-19. This virus is extremely contagious and thus a pandemic has been declared just after four months for the first reported case. To face this challenge, the development of efficient diagnosis methods, at least one alternative of treatment and to get a vaccine are the highest priorities for scientists. This review article explores the efforts that have been made from nanoscience and nanotechnology to improve the diagnosis methods, enhancing the sensitivity, selectivity and trueness of the currently available analytical techniques, but also pursuing the miniaturization of the devices. Some strategies to achieve this involve the surface plasmon resonance effect. Lastly, it is shown the most recent advances in a vaccine based on nanoparticles and messenger RNA; the synthesis methods, the formulation and the immunization mechanisms of this potential vaccine are explained. It is highly possible that the nanoparticle based vaccine will be able to efficiently immunize people, which would be one of the biggest milestones achieved by nanosciences and nonotechnology so far.

El descubrimiento de catalizadores sólidos generalmente se realiza a través de una metodología que incorpora elementos de prueba y error. En el mejor de los casos, esta estrategia se apoya en información obtenida de técnicas de caracterización. Sin embargo, como la estructura de los catalizadores sólidos es generalmente complicada, dicha información es insuficiente para tener una descripción precisa y rigurosa del modo en que funcionan los catalizadores. Además, la estrategia tampoco permite establecer si los catalizadores encontrados serán los mejores posibles. Como contraparte de la prueba y error está el diseño de catalizadores, con el cual se pretende desarrollar materiales a partir de su comprensión a nivel fundamental (i.e., detalles específicos y rigurosos de la naturaleza del sitio activo). En principio, el diseño permitiría predecir la estructura necesaria en un material para que este sea catalíticamente activo. En este trabajo se contrastan las estrategias que típicamente se emplean para estudiar catalizadores sólidos, poniendo énfasis especial en la posibilidad de diseñar materiales. Se discute qué significa comprender el funcionamiento de los catalizadores a nivel fundamental y se hace un análisis crítico de posibles oportunidades que ofrece el diseño para abordar algunos problemas relevantes en el estudio de catalizadores en la actualidad.

Scanning transmission electron microscopy (STEM) offers techniques which may give structural and chemical information down to 0.1 nm of spatial resolution, which sub-angstrom resolution is achieved with a spherical aberration corrector. In the STEM, the electron probe is focused and scanned over the sample and the image is formed by measuring the electron signal arising after the electrons-specimen interactions. The scattered electron signals can be employed to obtain bright and dark field images. The STEM is a powerful instrument to understand the physical properties of nanostructures which requires the local structure and local chemistry to be determined at the atomic scale. Therefore STEM is a technique able to identify the position of atoms and atomic columns. In this work, the basic instrumental parameters before applications were evaluated. And also, experimental high angle annular dark field (HAADF)-STEM and annular bright field (ABF)-STEM images of LaAlO3 sample were obtained at low voltages and compared with simulated images obtained with the multislice method. Images simulated were found to agree well with experimental images.

The methods to obtain nanostructures have been a fundamental area of ​​study since the beginning of the nanotechnology. The biosynthesis of nanostructures is inspired by the behavior that some microorganisms and plants have for subsisting in environments with chemical stress. This paper presents novel results achieved by our research group to generate Au and Ag nanostructures with tunable morphology, assisted by Camellia sinensis and Anemopsis californica extracts as reducing agents of Au+3 and Ag+1 ions; as well as magnetite nanoparticles (Fe2O3) biosynthesis with size homogeneity and better phase control than other biogenic methods reported in the literature. Additionally, the effective use of biotemplates to design nanostructured materials with green synthesis methods is demonstrated. Finally, the evidence of the nanomaterials obtained by biosynthesis was shown via characterization with Transmission Electron Microscopy, Scanning Electron Microscopy and X-ray Energy Dispersion Spectroscopy.

TiO2 is used in a wide variety of applications, including photocatalysis in the environmental area for surface self-cleaning as well as air and water purification. In order to develop new materials with better photocatalytic response using sunlight, it has been proposed the TiO2 modification following various strategies. In this work, the basics of photocatalysis are summarized discussing the advantages of using photocatalysts in thin film form. The case of zinc-modified TiO2 thin films prepared using a novel synthesis approach that allows good control over the composition and structure of the materials obtained is presented. The obtained results using the photocatalysts obtained in the degradation of the Malachite's green dye are shown.

Catalytic deactivation is a serious problem in different sections of the oil refining process, causing loss of catalytic activity with respect to operating time. This review is focused on the deactivation catalyst mechanisms, such as poisoning, fouling, thermal degradation and sintering, chemical degradation and mechanical failures like attrition and crushing, in fluid catalytic cracking (FCC), hydrodesulfurization (HDS), and catalytic reforming. The causes of these deactivation catalyst mechanisms are chemical, thermal and mechanical. The key features and considerations for each of these deactivation mechanisms types are reviewed. Additionally, the total cost for catalyst deactivation is increasing gradually each year because of the replacement of spent catalyst, generating thousands of tons of industrial waste.

This article discusses the importance of kinetic analyses. The mathematical function of the chemical reaction rate expression (-RA) is introduced, including the expression used in the presence of a catalyst and the functionality of (-RA) with temperature and concentration. Several rate expressions such as power law expressions, theoretical expressions, and LHHW equations are described. It also revises typical reactors used in the laboratory and describes the criteria that can be used to disdain the mass and energy transfer problems commonly presented in catalytic assessments.

This article shows the importance of chemical kinetic analyses and the issues needed to obtain reliable kinetic parameters which are addressed to provide information on the kinetic modeling of catalysts. The article focuses on how to make the fit of kinetic coefficients and present the most common least squares algorithms to perform this fitting. Statistical criteria are also presented to decide whether the fit is appropriate or not. Finally, different cases of how the scientific literature presents data on catalytic activity are described.

Introducción: la sepsis continúa siendo un problema sanitario global que nos involucra a todos.Objetivo: determinar los factores pronósticos de muerte por sepsis al ingreso en la UTIP Bayamo (2011-2017).Método: se realizó un estudio analítico ambispectivo. La variable marcadora del pronóstico fue la muerte por sepsis al ingreso y las covariables: edad, sexo, albuminemia, estado nutricional, comorbilidad, nivel de atención de procedencia, foco de la infección, estadio de sepsis al ingreso, necesidad de procedimientos invasivos y estadía en el servicio.Resultados: al concluir los estudios univariado y multivariado, quedó conformado el modelo predictivo de mortalidad por sepsis por la estadía prolongada, estadio avanzado al ingreso, hipoalbuminemia y desnutrición por defecto, en orden de significación y su asociación determinó un riesgo 18 veces superior y una probabilidad del 95,2 % de fallecer por esta causa. Conclusiones: La asociación de: estadía prolongada, estadio avanzado, hipoalbuminemia y desnutrición, determinó el mayor pronóstico de fallecer por sepsis y conformó el modelo predictivo de mortalidad por sepsis al ingreso.