Acta Microscopica

SOL-GEL PREPARATION AND SINTERING OF AL, FE, SI MIXED OXIDES DOPED CERIA

M. Escalante — 2024-06-13

Undoped CeO₂, co-doped and tri-doped CeO₂ with Si, Si-Al and Si-Fe, were prepared by sol-gel method. Nanoparticles with an average crystal size of 2-10 nm, were obtained and structurally characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Powders were compacted by uniaxial pressure and sintered in air at 1250 °C to obtained sintered pellets. The different compositions maintained the cerianite crystal structure, implying that dopant elements enter in the structure forming a solid solution, although some segregation was observed by SEM and TEM analysis in pellets. The undoped CeO₂ material reached a relative density of 0.95 % at 1250°C while doped samples presented variations in this value and grain size and relative density, clearly attributed to doping. According to these results, these materials could have potential applications in solid oxide fuel cells, electrodes and sensors.

Effect of time on the Ag to AgO phase transformation in an aqueous/organic system

I. F. Caballero — 2024-06-13

The present work shows the synthesis of Ag nanoparticles in a two-phase system (organic/aqueous), in which the amphiphilic properties of naphthenic acid are used for the formation of reverse micelles that act as micro reactors. Therefore, the appropriate energy conditions are given for the precipitation of metallic Ag nanoparticles, using AgNO₃ as a precursor. Likewise, the effect of the synthesis reaction time was studied to know its relationship with the final morphology of the material. X-Ray Diffraction and Scanning Electron Microscopy, coupled with Energy Dispersive Spectroscopy, were used to characterize the solids. The results show that in the Ag+ -> Ag° reduction reaction carried out at t = 1.5 h and T = 200 °C, metallic silver nanoparticles precipitate of FCC structure, with homogeneous globular morphology and average diameter of 50 nm. By prolonging the residence time of the system at 200 °C (artificial aging), the material undergoes a series of transformations both in size and morphology, causing partial oxidation of the silver. At TEA of 0.5 h, the particles grow without evident structural change; by increasing TEA to 1 h, the transformation in solid state is observed, obtaining a mixture of phases, AgO, Ag3O₄ and Ag₂O, coming from the partial oxidation of silver, with monoclinic and hexagonal structures and the dimensions nano and micrometric. Finally, increasing the aging time to 1.5 h only causes an increase in particle size, without modification in the structures obtained at shorter times.

UNIQUE EXTRA-LONG CHEMICALLY-DERIVED GRAPHITIC PYRAMIDAL RIBBONS

Julio C. Chacón-Torres — 2024-06-14

In this letter, unique extra-long chemically derived pyramidal graphitic ribbons (PGR) were individualized and deposited onto a SiO₂ substrate via simple spin-coating. The length of the individualized PGRs was found to exceed the average length of graphene nanoribbons (GNRs) by hundreds of microns. The physicochemical individualization method resulted in the creation of a novel “graphene nanoribbon intercalation compound” (GNRIC), following a strict stoichiometric relation between the GNR powder and alkali metals. Our experiments were conducted with the use of Na and K as intercalants at NaC₈, KC₈, and KC₂₄ concentrations. Furthermore, we exposed them to THF and discovered that the nanoribbon bundles obtained from CVD bottom-up bulk synthesis of GNRs can be exfoliated. The exfoliated nanoribbons (ex-GNRs) were analyzed using SEM, Raman spectroscopy, optical microscopy, and AFM, revealing the existence of ribbon-like pyramidal nanostructures that are larger than 100 μm. The morphology of these graphitic ribbons, brings a new starting point and immense potential to the development of graphene-based devices for optoelectronics and solar cells.

SORPTION EFFICIENCY OF CO2 BY FUNCTIONALIZED CHITOSAN BIOFILMS AS A GREENHOUSE GAS EMISSION CONTROL SYSTEM

X. Galindo — 2024-06-14

The accumulation of greenhouse gases inevitably affects the temperature of both the atmosphere and the Earth's surface, standing as a primary driver of global climate change. The atmospheric concentration of CO₂, a greenhouse gas, has risen from a pre-industrial level (mid-18th century) of 280 ppmv to the current 421 ppmv, with an annual increase of approx. 1.8 ppmv. Using chitosan biofilms, a naturally occurring cationic polysaccharide, as a CO₂ sorbent presents an economically viable alternative. Chitosan can be sourced from waste in the fishing industry, and its low toxicity and biodegradability make it easy to handle and recycle. In this context, the main goal of this research is to assess the CO₂ sorption efficiency of amines-functionalized chitosan biofilms in batch injection systems, along with their characterization through Scanning Electronic Microscopy (SEM) and thermal stability analysis using DSC. The findings of this study reveal that chitosan films exhibit high thermal stability (215ºC) and a remarkable CO₂ sorption capacity (3.76 mmol CO₂/g film). Moreover, the immobilization of basic groups (tetraethylenepentamine – TEPA and polyethylenimine - PEI) through impregnation enhances the CO₂ fixation capacity, even at elevated temperatures, underscoring the significant potential of these materials for controlling CO₂ emissions.

Biosynthesis of Silver Nanoparticles using Moringa oleifera oil and their Antimicrobial Activity against Escherichia coli

Emily Gonzalez Tamayo — 2024-06-14

This work investigated the green synthesis of silver nanoparticles using Moringa oleifera oil as a capping agent and its antibacterial activity against Escherichia coli. The samples were characterized using Ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), and Raman spectroscopy. UV-vis spectroscopy showed a surface plasmon resonance band at 420 nm related to the formation of silver nanoparticles. Fourier transform infrared analysis shows the functionalization of the silver nanoparticles with M. oleifera oil. The bioactive compounds in M. oleifera oil play a dual role by reducing the silver ions and stabilizing the resulting nanoparticles, forming both 30 nm and of 5 nm nanoparticles. Raman spectroscopy reveals the interaction of the nanoparticles with the M. oleifera oil by a Surface-Enhanced Raman Scattering (SERS) effect. The agar diffusion method was used to study the antibacterial efficacy of the nanoparticles with M. oleifera, revealing an effective antibacterial activity against E. coli combined with an interesting SERS effect that could be applied in the biomedical field.

FIRST APPLICATION OF AN IMPROVED-RESOLUTION DARK-FIELD MICROSCOPY SETUP, COMBINED WITH A NOVEL DIRECT-STAINING LIVE IMMUNOFLUORESCENCE INVESTIGATION METHOD, VISUALISING THE MOTION OF BORRELIA BURGDORFERI SPIROCHETES

András P. Bózsik — 2024-06-14

Dark-field microscopy has been increasingly applied in diagnostics in recent years, for example in Lyme borreliosis, due to the growing concerns about the diagnostic utility of standard serological tests. Although the diagnostic value of microscopic methods is still debated due to the lack of proper clinical testing and the definition of the diagnostic cutoff levels, it is important that the spirochetes causing the disease can be visualized from body fluids via dark-field investigation. Additionally, a specific identification of Borrelia is still not routinely possible, visual observation is usually fortified with additional PCR investigations. We are publishing the pictures from the first-time application of an enhanced dark-field illumination technique that improves the resolution and picture quality of digital recordings. The same illumination setup, combined with a novel live staining of Borrelia burgdorferi with cleaned, FITC-labelled anti-Borrelia antibodies, has produced remarkable recordings of the same spirochetes, in natural motion. All experiments were performed on remnant samples of DualDur kit laboratory investigations.