Efecto de la temperatura de calcinación sobre la concentración de grupos silanoles en superficies de SiO2 (SBA–15)

The preparation of SBA-15 materials involves both, calcination and activation processes. The effects of the temperatures of these stages on the silanol superficial concentration are studied experimentally. The characterization techniques employed were: nitrogen adsorption, infrared spectroscopy, nuclear magnetic resonance, and X-ray diffraction. To improve the concentration of silanols groups on the solid surface, the obtained results indicate that the best temperatures of calcination and activation are 623K and 373K, respectively

DETECCIÓN DE ESCHERICHIA COLI O157:H7 EN CARNE FRESCA DE RES MEDIANTE PCR MÚLTIPLEX

Para la detección de E. coli O157:H7 en carne fresca de res, se comparó el método microbiológico tradicional y dos ensayos de PCR Múltiplex. En ensayos con muestras inoculadas se obtuvo una diferencia significativa entre PCR Múltiplex y aislamiento microbiológico. PCR Múltiplex mostró porcentaje mayor de sensibilidad, precisión relativa e índice kappa en el enriquecimiento con el caldo Ecm+n en comparación al CST+ccv. En 40 muestras de res corte tipo americano se detectaron 2 positivas (5%) por PCR múltiplex, mientras que por el método microbiológico no se logró su aislamiento en ninguna muestra. AbstractIn the present study were compared the traditional microbiological method and two tests of multiplex PCR for the detection of E. coli O157:H7 in fresh beef meat. A significant difference was obtained between PCR multiplex and microbiological isolation in inoculated samples; in addition, in multiplex PCR was obtained a higher percentage of sensitivity, precision relative and Kappa index using the Ecm+n broth in comparison to the CST+ccv in the enrichment. In 40 samples of meat cuts American type were detected two positive samples (5%) by Multiplex PCR, whereas by the microbiological method was not obtained the isolation in any sample. Palabras clave: PCR Múltiplex, E. coli O157:H7, Carne,  Beef

Nuevos escenarios para la docencia universitaria : entornos híbridos y pedagogías emergentes.

Memorias del IX Simposio Internacional de Docencia Universitaria (SIDU)Los trabajos reunidos en esta Memoria representan una contribución importante al campo de la educación y de la docencia universitaria, en tanto muestran distintas maneras de responder a las problemáticas educativas cotidianas y presentan propuestas para afrontar los retos emergentes en el campo de la educación superior. Invitamos a los lectores a realizar una lectura atenta y crítica de los trabajos compilados en esta publicación. Estamos seguros de que este acercamiento propiciará la reflexión y el análisis riguroso de los objetos de estudio abordados por los autores, y estimulará la generación de nuevos proyectos de investigación, intervención e innovación educativa que incidan en el desarrollo de mejores prácticas de docencia en educación media superior y superior.Pimera edición digitaldoi.org/10.56019/EDU-CETYS.2024.182

Improve in CO2 and CH4 Adsorption Capacity on Carbon Microfibers Synthesized by Electrospinning of PAN

Carbon microfibers (CMF) has been used as an adsorbent material for CO2 and CH4 capture. The gas adsorption capacity depends on the chemical and morphological structure of CMF. The CMF physicochemical properties change according to the applied stabilization and carbonization temperatures. With the aim of studying the effect of stabilization temperature on the structural properties of the carbon microfibers and their CO2 and CH4 adsorption capacity, four different stabilization temperatures (250, 270, 280, and 300 °C) were explored, maintaining a constant carbonization temperature (900 °C). In materials stabilized at 250 and 270 °C, the cyclization was incomplete, in that, the nitrile groups (triple-bond structure, e.g., C≡N) were not converted to a double-bond structure (e.g., C=N), to form a six-membered cyclic pyridine ring, as a consequence the material stabilized at 300 °C resulting in fragile microfibers; therefore, the most appropriate stabilization temperature was 280 °C. Finally, to corroborate that the specific surface area (microporosity) is not the determining factor that influences the adsorption capacity of the materials, carbonization of polyacrylonitrile microfibers (PANMFs) at five different temperatures (600, 700, 800, 900, and 1000 °C) is carried, maintaining a constant temperature of 280 °C for the stabilization process. As a result, the CMF chemical composition directly affects the CO2 and CH4 adsorption capacity, even more directly than the specific surface area. Thus, the chemical variety can be useful to develop carbon microfibers with a high adsorption capacity and selectivity in materials with a low specific surface area. The amount adsorbed at 25 °C and 1.0 bar oscillate between 2.0 and 2.9 mmol/g adsorbent for CO2 and between 0.8 and 2.0 mmol/g adsorbent for CH4, depending on the calcination treatment applicated; these values are comparable with other material adsorbents of greenhouse gases

Effect of Calcination Temperature and Chemical Composition of PAN-Derived Carbon Microfibers on N2, CO2, and CH4 Adsorption

This work investigates the interplay of carbonization temperature and the chemical composition of carbon microfibers (CMFs), and their impact on the equilibration time and adsorption of three molecules (N2, CO2, and CH4). PAN derived CMFs were synthesized by electrospinning and calcined at three distinct temperatures (600, 700 and 800 °C), which led to samples with different textural and chemical properties assessed by FTIR, TGA/DTA, XRD, Raman, TEM, XPS, and N2 adsorption. We examine why samples calcined at low/moderate temperatures (600 and 700 °C) show an open hysteresis loop in nitrogen adsorption/desorption isotherms at −196.15 °C. The equilibrium time in adsorption measurements is nearly the same for these samples, despite their distinct chemical compositions. Increasing the equilibrium time did not allow for the closure of the hysteresis loop, but by rising the analysis temperature this was achieved. By means of the isosteric enthalpy of adsorption measurements and ab initio calculations, adsorbent/adsorbate interactions for CO2, CH4 and N2 were found to be inversely proportional to the temperature of carbonization of the samples (CMF-600 > CMF-700 > CMF-800). The enhancement of adsorbent/adsorbate interaction at lower carbonization temperatures is directly related to the presence of nitrogen and oxygen functional groups on the surface of CMFs. Nonetheless, a higher concentration of heteroatoms also causes: (i) a reduction in the adsorption capacity of CO2 and CH4 and (ii) open hysteresis loops in N2 adsorption at cryogenic temperatures. Therefore, the calcination of PAN derived microfibers at temperatures above 800 °C is recommended, which results in materials with suitable micropore volume and a low content of surface heteroatoms, leading to high CO2 uptake while keeping acceptable selectivity with regards to CH4 and moderate adsorption enthalpies

Isosteric Enthalpy Behavior of CO2 Adsorption on Micro-Mesoporous Materials: Carbon Microfibers (CMFs), SBA-15, and Amine-Functionalized SBA-15

The isosteric enthalpy of adsorption (Δadsh˙) of CO2 in three different micro and mesoporous materials was evaluated in this work. These materials were a microporous material with functional groups of nitrogen and oxygen (CMFs, carbon microfibers), a mesoporous material with silanol groups (SBA-15, Santa Barbara Amorphous), and a mesoporous material with amine groups (SBA-15_APTES, SBA-15 amine-functionalized with (3-Aminopropyl)-triethoxysilane). The temperature interval explored was between 263 K and 303 K, with a separation of 5 K between each one, so a total of nine CO2 isotherms were obtained. Using the nine isotherms and the Clausius–Clapeyron equation, the reference value for Δadsh˙ was found. The reference value was compared with those Δadsh˙ obtained, considering some arrangement of three or five CO2 isotherms. Finally, it was found that at 298 K and 1 bar, the total amount of CO2 adsorbed is 2.32, 0.53, and 1.37 mmol g−1 for CMF, SBA-15, and SBA-15_APTES, respectively. However, at a coverage of 0.38 mmol g−1, Δadsh˙ is worth 38, 30, and 29 KJ mol−1 for SBA-15_APTES, CMFs, and SBA-15, respectively. So, physisorption predominates in the case of CMF and SBA-15 materials, and the Δadsh˙ values significantly coincide regardless of whether the isotherms arrangement used was three or five. Meanwhile, in SBA-15_APTES, chemisorption predominates as a consequence of the arrangements used to obtain Δadsh˙. This happens in such a way that the use of low temperatures (263–283 K) tends to produce higher Δadsh˙ values, while the use of high temperatures (283–303 K) decreases the Δadsh˙ values

Correlation of Rh Particle Size with CO Chemisorption: Effect on the Catalytic Oxidation of MTBE

This study was conducted to identify the correlation between the CO chemisorption (linear interaction and gem dicarbonyl) and the specific size of rhodium particles, and further to determine the influence of this relationship on the catalytic oxidation reaction of methyl tert-butyl ether (MTBE). During the synthesis, first, TiO2 was developed by the sol-gel method under acidic conditions. Second, Rh was deposited (1 wt %) by the incipient wetness impregnation method. Later, with the aim of controlling the particle size, the Rh/TiO2 materials were crystallized at different reduction conditions during 3 h heat treatment. The results obtained by TEM micrographs indicated that the average particle size varies between 1.0 and 8.1 nm, depending on the conditions of heat treatment. From the histogram analysis of each TEM micrograph, two correlations were made: (i) the gem-dicarbonyl interaction was typical of Rh particles ≤ 1.5 nm, and (ii) a linear interaction, bridged interaction and dentate interaction were observed in particles ≥ 1.6 nm. The gem-dicarbonyl interaction (particle size ≤ 1.5 nm) was the most active in the oxidation reaction of MTBE

Synthesis of Supported Metal Nanoparticles (Au/TiO2) by the Suspension Impregnation Method

This work reports a new technique called “Suspension Impregnation Method” (SiM) as an alternative to the “Incipient Impregnation Method” (IiM) for the synthesis of noble metal (Au) nanoparticles. The SiM was used to synthesize gold nanoparticles supported by titanium oxide and compared with those of IiM. The reactor for the SiM technique was based on the principles of mixing, heat, and mass transfer of the suspension reactors and the metal particle synthesis was processed in situ under the oxidation reduction potentials. Three different conditions were established to observe the effect of pH on the size of the metal particles: acid (HCl), neutral (water) and alkaline (urea). The samples were characterized by nitrogen adsorption, X-Ray Diffraction (XRD), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), Thermogravimetric Analysis (TGA)/Differential Thermal Analysis (DTA), Transmission Electron Microscopy (TEM) and CO2 adsorption. The surface area was slightly modified, and the average pore diameter was reduced in all materials. The structure of the titanium oxide was not altered. A deposit of organic material was detected in samples synthesized in alkaline medium for both methods. The pH influenced the formation of conglomerates in IiM and resulted in large particle sizes (3–9 nm). In contrast, an in situ reduction in the species in SiM resulted in smaller particle sizes than IiM (2–3 nm)

Prevalence of Dysexecutive Symptoms in High School Students during the COVID-19 Pandemic

This is an observational cross-sectional study designed to ascertain the prevalence and severity of dysexecutive symptoms in high school students during the COVID-19 pandemic. The validated Spanish version of the Dysexecutive Questionnaire (DEX) was used. A total of 2396 participants aged 14–22 years were included. Our sample yielded a mean DEX scale score of 28.14 ± 17.42. By the DEX classification, 889 (37.1%) students achieved optimal scores, 384 (16%) reported mild dysexecutive symptoms, 316 (13.2%) reported moderate dysexecutive symptoms, and 807 (33.7%) reported strong dysexecutive symptoms. We found a significant difference between those with and those without employed mothers, with the former scoring higher (p = 0.004), the same as those with both parents employed (p = 0.004). Adolescents face emotional susceptibility and changes in their family, social, and educational environment related to isolation, resulting in altered emotional responses and social interaction

Espacios de la Ciudad de México. 75-76 Nueva Época (2004) julio-diciembre. Antropología. Boletín Oficial del Instituto Nacional de Antropología e Historia

- Los lugares de una megaciudad, una introducción por Abilio Vergara Figueroa. - Etnografía de un barrio obrero: La Fama, Tlalpan por María Ana Portal. - Entre la tradición y el anonimato. Etnografía de la identidad urbana en un barrio de la colonia Roma por Daniel Hernández Rosete. - Habitar en el Centro Histórico, detrás de los monumentos por Reyna Sánchez Estévez. - Vecindad, condominio y modernidad: etnografía de un proceso por Anja Clara Novell y Hugo Sánchez Arteaga. - Pequeñas iluminaciones sobre la ciudad: el parque Los Coyotes por Abilio Vergara Figueroa. - La Alameda y la plaza de la Solidaridad. Exploraciones desde el margen por Sara Makowski. - La Ciudadela: de la tragedia histórica al disfrute de la ciudad por Amparo Sevilla. - La plaza de las Vizcaínas: socialidad y conflicto por Isaura C. García López. - El zapatista por Lucio Ernesto Maldonado Ojeda. - Razón y proporción del Gran Teatro Nacional de Santa Anna por Hugo Arciniega. - Etnografía de urgencia: el hospital Xoco por Alí Ruiz Coronel. - La pulquería como lugar de encuentro: el caso de La Pirata por Ernesto Licona Valencia. - Para una mañana fría o una noche lluviosa, una taza de chocolate en El Moro por Judith Katia Perdigón Castañeda. - La línea tres del metro de la Ciudad de México: espacios y usuarios por Olivia Domínguez Prieto. - El Sistema de Transporte Colectivo metro de la Ciudad de México: un espacio diverso por Melissa García Meraz. - La Ciudad de México como supermercado para transeúntes por Mauricio García. - Etnografía de la manifestación pública: la megamarcha por la Soberanía Nacional por Xóchitl Cruz-Guzmán y Sergio Tamayo. - De la marcha por la Dignidad a la marcha de la Paz por Aída Analco Martínez. - La órbita de la capital mexicana y la crisis de la nación en 1848 por Esteban Sánchez de Tagle. - El “esto es” de una vida por Graciela de Garay