A novel magnetic composite made of Peruvian pyroclastic dust material decorated with maghemite nanoparticles was synthesized and characterized using a variety of analytic techniques. The 13 nm maghemite nanoparticles were grown on the pyroclastic dust using the conventional coprecipitation chemical route. A short-term acute assay was developed to study the ecotoxicological behavior of the water flea, Daphnia magna. A 24 h-lethal concentration (LC₅₀) value equal to 123.6 mg L⁻¹ was determined only for the magnetic composite. While the pyroclastic dust material did not exhibit a lethal concentration, it caused morphologically significant changes (p < 0.05) for heart and tail parameters at high concentrations. Morphologies exposed to the magnetic composite above the 24 h-LC₅₀ revealed less tolerance and significant changes in the body, heart, antenna, and eye. Hence, it affects biomarker growth and swimming. The reproduction rate was not affected by the raw pyroclastic dust material. However, the number of individuals showed a decrease with increasing composite concentrations. The present study indicates the LC₅₀ value, which can be used as a reference concentration for in-situ water cleaning with this material without damaging or changing the Daphnia magna ecosystem.

The use of natural organic extracts in nanoparticle synthesis can reduce environmental impacts and reagent costs. With that purpose in mind, a novel biosynthesis procedure for the formation of magnetic iron-oxide nanoparticles (IONPs) using Eucalyptus globulus extract in an aqueous medium has been systematically carried out. First, the biosynthesis was optimized for various extract concentrations, prepared by decoction and infusion methods, and yielded IONPs with sizes from 4 to 9 nm. The optimum concentration was found at 5% w/v, where the biosynthesis reaction time and ammonium hydroxide amount were the lowest of all samples. This extract concentration was tested, including in replicated samples, for a scale-up process, yielded a total mass of 70 g. It was found by Rietveld and electron microscopy analyses that the structural and morphological properties, such as crystalline and particle sizes (9 nm), are equivalent when scaling the synthesis process. ⁵⁷Fe Mössbauer spectroscopy results indicated that Fe ions are atomically ordered and in a trivalent state in all samples, corroborating with structural results found by X-ray diffraction. Magnetic analysis showed that the scale-up sample exhibited ferrimagnetic-like behavior suitable for magnetic remediation performance (55 emu g⁻¹). The eucalyptus functionalization was demonstrated by thermogravimetric measurements, whereas the colloidal analysis supported the stability of the magnetic suspensions at pH = 7 (zeta potential > −20 mV). The kinetic adsorption performance indicated a fast kinetic adsorption time of 40 min and remarkable removal efficiency of 96% for lubricant removal from water (emulsion systems). The infrared analysis confirmed the presence of the eucalyptus chemical groups even after the removal experiments. These results suggest that the scale-up sample can be recovered for future and sustainable magnetic remediation processes.

In search of efficient solutions for the treatment of contaminated soils and in favor of the sustainable development of agriculture, this work aimed at developing an efficient method that helps to directly overcome the contamination by nickel in soils and Theobroma cacao L. seedlings. In this study, the genotypes ICS-39, CCN-51, and TSH-1188, which are high-yielding varieties in South America, were studied. The compound used as an adsorbent was commercial zeolite 5A. The zeolite 5A and soil samples were analyzed by X-ray diffraction, Raman microscopy, chemical analysis, electron microscopy techniques, and atomic absorption spectroscopy. This last technique was used for quantitative determination of Ni concentrations in seedlings. Zeolite 5A presented a high adsorption efficiency (95%) among the studied cacao genotypes, making this material a viable adsorbent and inhibitor agent of Ni. In addition, zeolite 5A was found to be not chemically harmful to the plant morphology (root and height), as demonstrated using statistical analysis. Finally, the Ni mechanism was described based on zeolite 5A physicochemical properties, suggesting that this material has remarkable soil remediation application.

The purpose of this research is to have a quantitative analysis on the temperature dependence magnetization of ferromagnetic nanoparticles (NPs), i.e., the Curie temperature (Tc), was systematically studied. The atomistic simulations were carried out using the VAMPIRE 5.0 software based on the Landau-Lifshitz-Gilbert-Heun method. The variable parameters of the simulations were damping, time step, particle geometry (spherical, cubic, and cylindrical) and particle size. We have calculated λ for Fe and Ni, in addition we have found different Tc values for each nanogeometry studied following a finite-size effect. We have found ν values for cubic NPs close to the reported values. In particular, it was observed that the Tc values for the studied geometries in the case of Fe and Ni decreases from their theoretical bulk values, for a critical particle size diameter less than 5 nm. Hence, the presented results (optimized atomistic parameters such as simulation time step, damping, and critical exponents) are the basis for advanced simulations of hybrid and complex nanostructures with perspective in biomedical and environmental applications.