Gas Sensing and Half-Metallic Materials Design Using Metal Embedded into S Vacancies in WS2 Monolayers: Adsorption of NO, CO, and O2 Molecules.

The adsorption of CO, NO, and O2 molecules onto Cu, Ag, and Au atoms placed in the S vacancies of a WS2 monolayer was elucidated within dispersion-corrected density functional theory. The binding energies computed for embedded defects into S vacancies were 2.99 (AuS), 2.44 (AgS), 3.32 eV (CuS), 3.23 (Au2S2), 2.55 (Ag2S2), and 3.48 eV/atom (Cu2S2), respectively. The calculated diffusion energy barriers from an S vacancy to a nearby site for Cu, Ag, and Au were 2.29, 2.18, and 2.16 eV, respectively. Thus, the substitutional atoms remained firmly fixed at temperatures above 700 K. Similarly, the adsorption energies showed that nitric oxide and carbon oxide molecules exhibited stronger chemisorption than O2 molecules on any of the metal atoms (Au, Cu, or Ag) placed in the S vacancies of the WS2 monolayer. Therefore, the adsorption of O2 did not compete with NO or CO adsorption and did not displace them. The density of states showed that a WS2 monolayer modified with a Cu, Au, or Ag atom could be used to design sensing devices, based on electronic or magnetic properties, for atmospheric pollutants. More interestingly, the adsorption of CO changed only the electronic properties of the MoS2-AuS monolayer, which could be used for sensing applications. In contrast, the O2 molecule was chemisorbed more strongly than CO or NO on Au2S2, Cu2S2, or Ag2S2 placed into di-S vacancies. Thus, if the experimental system is exposed to air, the low quantities of O2 molecules present should result in the oxidation of the metallic atoms. Furthermore, the O2 molecules adsorbed on WS2-Au2S2 and WS2-CuS introduced a half-metallic behavior, making the system suitable for applications in spintronics.

Substitutional Coinage Metals as Promising Defects for Adsorption and Detection of Gases on MoS2 Monolayers: A Computational Approach.

Defective molybdenum disulfide (MoS2) monolayers (MLs) modified with coinage metal atoms (Cu, Ag and Au) embedded in sulfur vacancies are studied at a dispersion-corrected density functional level. Atmospheric constituents (H2, O2 and N2) and air pollutants (CO and NO), known as secondary greenhouse gases, are adsorbed on up to two atoms embedded into sulfur vacancies in MoS2 MLs. The adsorption energies suggest that the NO (1.44 eV) and CO (1.24 eV) are chemisorbed more strongly than O2 (1.07 eV) and N2 (0.66 eV) on the ML with a cooper atom substituting for a sulfur atom. Therefore, the adsorption of N2 and O2 does not compete with NO or CO adsorption. Besides, NO adsorbed on embedded Cu creates a new level in the band gap. In addition, it was found that the CO molecule could directly react with the pre-adsorbed O2 molecule on a Cu atom, forming the complex OOCO, via the Eley-Rideal reaction mechanism. The adsorption energies of CO, NO and O2 on Au2S2, Cu2S2 and Ag2S2 embedded into two sulfur vacancies were competitive. Charge transference occurs from the defective MoS2 ML to the adsorbed molecules, oxidizing the later ones (NO, CO and O2) since they act as acceptors. The total and projected density of states reveal that a MoS2 ML modified with copper, gold and silver dimers could be used to design electronic or magnetic devices for sensing applications in the adsorption of NO, CO and O2 molecules. Moreover, NO and O2 molecules adsorbed on MoS2-Au2s2 and MoS2-Cu2s2 introduce a transition from metallic to half-metallic behavior for applications in spintronics. These modified monolayers are expected to exhibit chemiresistive behavior, meaning their electrical resistance changes in response to the presence of NO molecules. This property makes them suitable for detecting and measuring NO concentrations. Also, modified materials with half-metal behavior could be beneficial for spintronic devices, particularly those that require spin-polarized currents.

Temperature Effect on the Corrosion Inhibition of Carbon Steel by Polymeric Ionic Liquids in Acid Medium.

In the present research work, the temperature effect on the corrosion inhibition process of API 5L X60 steel in 1 M H2SO4 by employing three vinylimidazolium poly(ionic liquid)s (PILs) was studied by means of electrochemical techniques, surface analysis and computational simulation. The results revealed that the maximal inhibition efficiency (75%) was achieved by Poly[VIMC4][Im] at 308 K and 175 ppm. The PILs showed Ecorr displacements with respect to the blank from -14 mV to -31 mV, which revealed the behavior of mixed-type corrosion inhibitors (CIs). The steel micrographs, in the presence and absence of PILs, showed less surface damage in the presence of PILs, thus confirming their inhibiting effect. The computational studies of the molecular orbitals and molecular electrostatic potential of the monomers suggested that the formation of a protecting film could be mainly due to the nitrogen and oxygen heteroatoms present in each structure.

Ingesta alimentaria y composición corporal asociadas a síndrome metabólico en estudiantes universitarios / Dietary intake and body composition associated with metabolic syndrome in university students

Resumen El objetivo de este estudio fue conocer la relación de la ingesta alimentaria (IA) y la composición corporal (CMC) con el síndrome metabólico (SM) entre estudiantes universitarios. Participaron 50 alumnos (56% mujeres) de entre 19 y 25 años de edad (M = 20.58, DE = 1.86), quienes completaron un cuestionario dirigido a evaluar IA, además se recabaron parámetros bioquímicos y de CMC. De acuerdo con el porcentaje de grasa corporal (PG), se identificó una alta ocurrencia de sobrepeso (22%) y obesidad (38%). Además, la grasa visceral incrementó conforme aumentó el PG. En ambos sexos existió un consumo bajo de hidratos de carbono y alto en lípidos, mayormente de origen animal, así como alto consumo de grasas saturadas, pero bajo de omegas 3 y 6. El SM fue identificado en 20% de la muestra, principalmente mujeres. El criterio de riesgo más frecuente fue los bajos niveles séricos de colesterol HDL, seguido de la obesidad abdominal; en tanto que la dislipidemia más frecuente fue la hipertrigliceridemia. En este estudio, aunque no se encontró relación directa entre IA y SM, si de éste con indicadores de CMC. Resulta inminente la necesidad de implementar estrategias que permitan a los estudiantes universitarios adquirir hábitos alimentarios y de actividad física saludables.

Abstract The objective of this study was to know the relationship between dietary intake (DI) and body composition (BC) with the metabolic syndrome (MS) among university students. A total of 50 students (56% female) among 19 and 25 years of age (M = 20.58, SD = 1.86), completed a questionnaire aimed at assessing DI, in addition biochemical and BC parameters were collected. According to the percentage of body fat (BF), a high prevalence of overweight (22%) and obesity (38%) was identified. In addition, visceral fat increased as the BF increased. In both sexes, there was a low consumption of carbohydrates and high in lipids, mostly of animal fat as well as high consumption of saturated fats, but low omegas 3 y 6. The MS was identified in 20% of the sample, mainly in women. The most frequently risk criteria were low levels of HDL cholesterol, followed by abdominal obesity; whereas the most frequent dyslipidemia was hypertriglyceridemia. In this study, although no direct relationship was found between DI and MS, it was found between MS and BC indicators. It is imminent the need to implement strategies that allow university students to acquire healthy eating and physical activity habits.