Enhancing the magnetic response on polycrystalline nanoframes through mechanical deformation.

The mechanical and magnetic properties of polycrystalline nanoframes were investigated using atomistic molecular dynamics and micromagnetic simulations. The magneto-mechanical response of Fe hollow-like nanocubes was addressed by uniaxial compression carried out by nanoindentation. Our results show that the deformation of a nanoframe is dominated at lower strains by the compression of the nanostructure due to filament bending. This leads to the nanoframe twisting perpendicular to the indentation direction for larger indentation depths. Bending and twisting reduce stress concentration and, at the same time, increase coercivity. This unexpected increase of the coercivity occurs because the mechanical deformation changes the cubic shape of the nanoframe, which in turn drives the system to more stable magnetic states. A coercivity increase of almost 100 mT is found for strains close to 0.03, which are within the elastic regime of the Fe nanoframe. Coercivity then decreases at larger strains. However, in all cases, the coercivity is higher than for the undeformed nanoframe. These results can help in the design of new magnetic devices where mechanical deformation can be used as a primary tool to tailor the magnetic response on nanoscale solids.

Nanoparticle Shape Influence over Poly(lactic acid) Barrier Properties by Molecular Dynamics Simulations.

Climate change is leading us to search for new materials that allow a more sustainable environmental situation in the long term. Poly(lactic acid) (PLA) has been proposed as a substitute for traditional plastics due to its high biodegradability. Various components have been added to improve their mechanical, thermal, and barrier properties. The modification of the PLA barrier properties by introducing nanoparticles with different shapes is an important aspect to control the molecular diffusion of oxygen and other gas compounds. In this work, we have described changes in oxygen diffusion by introducing nanoparticles of different shapes through molecular dynamics simulations. Our model illustrates that the existence of curved surfaces and the deposition of PLA around them by short chains generate small holes where oxygen accumulates, forming clusters and reducing their mobility. From the several considered shapes, the sphere is the most suitable structure to improve the barrier properties of the PLA.

As(V) removal capacity of FeCu bimetallic nanoparticles in aqueous solutions: The influence of Cu content and morphologic changes in bimetallic nanoparticles.

In this study, bimetallic nanoparticles (BMNPs) with different mass ratios of Cu and Fe were evaluated. The influence of the morphology on the removal of pollutants was explored through theoretical and experimental studies, which revealed the best structure for removing arsenate (As(V)) in aqueous systems. To evidence the surface characteristics and differences among BMNPs with different mass proportions of Fe and Cu, several characterization techniques were used. Microscopy techniques and molecular dynamics simulations were applied to determine the differences in morphology and structure. In addition, X-ray diffraction (XRD) was used to determine the presence of various oxides. Finally, the magnetization response was evaluated, revealing differences among the materials. Our cumulative data show that BMNPs with low amounts of Cu (Fe0.9Cu0.1) had a non-uniform core-shell structure with agglomerate-type chains of magnetite, whereas a Janus-like structure was observed in BMNPs with high amounts of Cu (Fe0.5Cu0.5). However, a non-uniform core-shell structure (Fe0.9Cu0.1) facilitated electron transfer among Fe, Cu and As, which increased the adsorption rate (k), capacity (qe) and intensity (n). The mechanism of As removal was also explored in a comparative study of the phase and morphology of BMNPs pre- and post-sorption.

Nanoscale zero valent supported by Zeolite and Montmorillonite: Template effect of the removal of lead ion from an aqueous solution.

In this work, we have studied the Pb(2+) sorption capacity of Zeolite (Z) and Montmorillonite (Mt) functionalized with nanoscale zero-valent iron (nZVI), at 50% w/w, obtained by means of an impregnating process with a solvent excess. The composites were characterized by several techniques including X-ray diffraction; scanning electron microscopy (SEM); BET area; isoelectric point (IEP); and, finally a magnetic response. Comparatively significant differences in terms of electrophoretic and magnetic characteristics were found between the pristine materials and the composites. Both structures show a high efficiency and velocity in the removal of Pb(2+) up to 99.0% (200.0 ppm) after 40 min of reaction time. The removal kinetics of Pb(2+) is adequately described by the pseudo second-order kinetic model, and the maximum adsorbed amounts (q(e)) of this analyte are in close accordance with the experimental results. The intraparticle diffusion model shows that this is not the only rate-limiting step, this being the Langmuir model which was well adjusted to our experimental data. Therefore, maximum sorption capacities were found to be 115.1±11.0, 105.5±9.0, 68.3±1.3, 54.2±1.3, and 50.3±4.2 mg g(-1), for Mt-nZVI, Z-nZVI, Zeolite, Mt, and nZVI, respectively. The higher sorption capacities can be attributed to the synergetic behavior between the clay and iron nanoparticles, as a consequence of the clay coating process with nZVI. These results suggest that both composites could be used as an efficient adsorbent for the removal of lead from contaminated water sources.

Surface rearrangement of nanoscale zerovalent iron: the role of pH and its implications in the kinetics of arsenate sorption.

We consider the use of metallic iron nanoparticles for cleaning contaminated water, focusing our study in the sorption of arsenic compounds. In particular, we discuss the results of their sorption process on the surface of zerovalent iron nanoparticles (nZVI) by performing a complete characterization of the surface modifications. Using scanning electron microscopy, X-ray diffraction analysis and high-resolution transmission electron microscopy, spectroscopy diffraction measurements and elemental mapping, we typify the surface reconstruction during the sorption process of As(V) from aqueous solutions using nZVI when it goes into a crystalline parasymplesite structure. The experimental results were correlated to the Freundlich isotherm sorption where the sorption capacity is depleted by the increase in the pH from 4 to 7 and associated with the surface passivation of nZVI. These techniques confirm the dependence of the sorption of arsenic as a function of pH and describe the specific details on the modification of the surface area of the nanoparticles.