Ciencias Exactas y Ciencias de la Salud

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Synthesis, characterization, and structural determination of ferrispinels
(Instituto Tecnológico y de Estudios Superiores de Monterrey, 2022-06-14) Murrieta Muñoz, Ana Cecilia; CONTRERAS TORRES, FLAVIO FERNANDO; 132171; Contreras Torres, Flavio Fernando; puelquio/mscuervo, emipsanchez; Medel Cobaxin, Héctor Javier; Rodríguez Macías, Fernando Jaime; Lozano García, Omar; School of Engineering and Sciences; Campus Monterrey
Spinel (AB2X4) crystalline system is typically characterized by a distribution of cations that can move from tetrahedral (A) to octahedral (B) sites. This movement also involves the X anions rearrangement into the cubic lattice. Accordingly, spinels can exhibit A-sites and B-sites distribution characterized by a partial to total cell inversion degree (x=1). We are interested in Zn-ferrites due to their chemical and thermal stability, ferrimagnetic properties, and earth abundance. ZnFe2O4 shows the unitary cell for a typical spinel structure; however, some previous reports suggested that this spinel can be inverted at the nanoscale regime. Hence, it is expected that ZnFe2O4 nanoparticles might show a ferrimagnetic behavior, which is an outstanding property for several applications, including high-density magnetic data storage and water splitting. The structural determination and microstructure properties are of great value in analyzing the cell inversion degree for particles synthesized following a proposed experimental design. In this Thesis, we synthesized nano and sub-micro, beam-like, and amorphous particles using a hydrothermal method varying the proportion of reactants, reaction time, and reagents. The morphology and size of the as-prepared particles were characterized by scanning electron microscopy. Atomic chemical composition and elemental stoichiometry were determined using energy-dispersive X-ray and inductively coupled plasma optical emission spectroscopy. Raman spectroscopy measurements indicate redshifts notably observed for the symmetric mode. Such wavenumber increments suggest that the frequency of phonons interacting with the incident photon is decreasing, probably due to the improved crystallinity during annealing treatments. The crystalline evolution was followed by X-ray diffraction. At the same time, lattice parameters were obtained from Rietveld refinements, and microstructure properties were assessed via Williamson-Hall type fittings. The cell parameter is estimated to be about 8.44 nm. The crystallite sizes range from 9 to 65 nm, and the microstrain is less than 0.2%. Finally, the degree of inversion of the crystalline system was evaluated using the Bertaut method. The cell inversion degree follows as 0.85 (400 °C), 0.67 (600 °C), and 0.38 (800 °C), suggesting that the annealing process helps to restore a standard spinel structure. Our simple synthesis method facilitates the tuning of the size and shape of particles, which appropriately leads to improved crystallinity as observed from structural parameters and cell inversion degrees. In this way, we assisted in evaluating and comparing the synthesis parameters to obtain ZnFe2O4 particles with different cell inversion degrees, sizes, and microstrain. We believe that this analysis could be replicated in other spinel structures and might help evaluate the relationship between their structure and magnetic properties.
Use of nanoparticles of copper with plant extracts as an alternative against multidrug-resistant bacteria causing urinary tract infections
(Instituto Tecnológico y de Estudios Superiores de Monterrey, 2021-08-29) De la Rosa Santana, Uriel; TORRES HUERTA, ANA LAURA; 207433; Torres Huerta, Ana Laura; emipsanchez; Hernández Cooper, Ernesto Manuel; Ordaz Cortés, Alberto; Tapia Ramírez, José Isabel; Escuela de Ingeniería y Ciencias; Campus Estado de México; António Pérez, Aurora
There is increasing concern due to the high incidence of multi-resistant bacteria. The importance of these microorganisms is in the economic and health impact that cause at global level in different countries. Many efforts have been made to improve drugs to attack these bacteria, however in the long term this only aggravates the situation. Due to this, alternatives that allow to reverse this situation are necessary. Thanks to the development of nanotechnology, the importance of nanoparticles has increased in the last years to fight infections. The green synthesis process is particularly appealing. It has been reported the use of plant extracts as reducing agents allows obtaining metallic nanoparticles with antibacterial activity. That is why in this project copper nanoparticles (CuNPs) with green synthesis were obtained. For this, extracts of Azadiractha Indica (Neem) and Eysenhardtia Polystachia (Palo Azul) were used given a previously reported medicinal properties in urinary tract infections and their high content of metabolites as reducing agents for the formation of nanoparticles (NPs). The extracts were characterized at different conditions of time and temperature, by IFTR (Fourier transform infrared) and UV-vis. Following this, mixtures of the selected extract with solutions of copper precursor salt at a specific concentration were heated under constant stirring for 20 h, taking samples at 4-hour intervals. The obtained nanoparticles were analyzed in terms of distribution, size, morphology, and concentration through dynamic light scattering (DLS) and scanning electron microscopy (SEM). Meanwhile, the characterization of its antimicrobial effect was determined thanks to absorbance analysis in liquid culture and plate reader. It was observed that as the synthesis time passes, the size of the nanoparticle tends to reduce. On the other hand, its morphology shows signs of being colloidal, although not uniformly. Meanwhile, when comparing the nanoparticles made with both extracts and different precursor salts, a different size trend was observed in nanoparticles. in terms of antibacterial activity, it was observed that the synthesis time at 20 h of the process shows an insight of bacteriostatic activity compared to a shorter stirring time. Meanwhile an indication of concentration-dependent inhibition was observed. On the other hand, it was observed that the combination of Neem extract with copper nitrate precursor salt is the best option for inhibition of bacteria. However, it is necessary to carry out more studies of antibacterial effects to guarantee its effectiveness to be an alternative to conventional antibiotic treatments.

Ciencias Exactas y Ciencias de la Salud

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