O. Moscoso Londoño

Bio: O. Moscoso Londoño is an academic researcher from State University of Campinas. The author has contributed to research in topics: Magnetization & Superparamagnetism. The author has an hindex of 2, co-authored 3 publications receiving 29 citations.

Strategies to tailor the architecture of dual Ag/Fe-oxide nano-heterocrystals—interfacial and morphology effects on the magnetic behavior

Abstract: Bifunctional nanostructured architectures have shown appealing properties, since a single entity can combine the diverse properties of its individual constituents. Particularly, by growing Fe-oxide domains over Ag nanoparticles, the plasmonic and superparamagnetic properties can be combined in a single particle. Beyond the multifunctionality of this system, there are several properties that emerge from intrinsic factors, such as: interface and/or morphology. In this study, we present the synthesis protocols to obtain two sets of heterocrystals, each one with different morphology: dimer and flower-like. In addition, the magnetization behavior of these hybrid nano-heterocrystals is investigated and discussed. These nanomaterials were built by a seed assisted heterogeneous nucleation process, carried out in organic solvents of high boiling point, using the same batch of silver nanoparticles with a mean size of 6 nm as seeds, and tuning the electron-donor capacity of the reaction environment at the thermal decomposition of the iron precursor. Ag/Fe3O4 heterocrystals with dimer and flower-like morphologies were obtained. The synthesis protocols for generating these types of nanomaterials are discussed step-by-step. Structural and morphological properties were determined by transmission electron microscopy, x-ray diffraction and x-ray absorption fine structure. DC magnetization results suggest that the silver/magnetite coupling generates an increase of the blocking temperature in comparison to those obtained from pure magnetite. This behavior could be linked to a possible increase in the magnetic anisotropy produced by an additional disorder at the Ag–Fe3O4 interface. The higher interface area of the Ag/Fe3O4 heterocrystals with flower-like architecture leads to a higher blocking temperature and a stronger magnetic anisotropy. These results are supported by AC susceptibility data.

Enhancing arsenic adsorption via excellent dispersion of iron oxide nanoparticles inside poly(vinyl alcohol) nanofibers

Abstract: Superparamagnetic iron oxide nanoparticles (SPIONs) are great adsorbents of toxic arsenic in water. However, SPIONs efficiency is limited by a tendency towards agglomeration, and an extra filtering process is required in actual applications to avoid possible harmful effects of nanoparticles released to the environment. Here, we show a novel green method to confine and disperse SPIONs (10 nm) inside insoluble electrospun PVA nanofibers (final concentration 0.14 wt. %). We found that the resulting membrane has an enhanced arsenic adsorption capacity (> 52 mg/g) and presents a new adsorption mechanism, involving a high swelling of the superhydrophilic nanofibers before actual solution interchange can occur. A suitable heat treatment provided water insolubility to the membrane while maintaining hydrophilicity and active sites in the SPIONs. We show the excellent dispersion and homogeneous distribution of the SPIONs inside the nanofibers using electron microscopies and scale this analysis to an area of statistical significance via magnetic studies and novel Small and Wide Angle X-Ray Scattering SAXS/WAXS 2D scannings. The production process is environmentally friendly, given that only PVA was used as SPIONs dispersant and no chemicals were added for crosslinking. This work presents a novel material that expands the broad technological applications of both iron oxide nanoparticles and electrospinning, opening a route to new horizons in water purification.

Preparation and study of silica and APTES–silica-modified NiFe2O4 nanocomposites for removal of Cu2+ and Zn2+ ions from aqueous solutions

Abstract: Silica and (3-aminopropyl)triethoxysilane (APTES)–silica-modified NiFe2O4 samples were successfully synthesized by a two-/three-step process, depending on the sample, including the preparation of nickel ferrite sample by hydrothermal synthesis, the coating of its surface with silica, and the subsequent functionalization with APTES Samples were characterized by X-ray diffraction (XRD), Fourier transform-infrared (FTIR) analysis, transmission electron microscopy, and M–H curves XRD data of the NiFe2O4 sample shows diffraction maxima that can be indexed in a cubic symmetry of space group Fd-3m with Z = 8, compatible with an inverse spinel-type structure The estimated average crystalline size is 22 nm All FTIR spectra show absorption bands between 600 and 400 cm−1, characteristic of spinel-type structure Bands attributed to the vibration of O–Si–O and Si–O–Si bonds are found in the spectra of the silica-coated samples APTES–silica-modified NiFe2O4 nanocomposites show an increase in coating thickness as the reaction time with tetraethoxysilane increases A practically superparamagnetic behavior was found for the synthesized NiFe2O4 sample with a magnetization of 47 emu/g This value is slightly reduced with the thickness of the nonmagnetic coating The ultraviolet–visible spectroscopy measurements and titration curves clearly demonstrated that the APTES–silica-modified NiFe2O4 nanocomposites could be efficient materials for the removal of Cu2+ and Zn2+ ions from aqueous solutions The best adsorption is found in the NiFe2O4@SiO2(3)–APTES(6) sample, while the NiFe2O4@SiO2(6)–APTES(12) sample seems to be the most suitable for its application, considering its better adsorption capacity and its easy separation from the aqueous solution in the presence of an external magnetic field

Dipolar interactions among magnetite nanoparticles for magnetic hyperthermia: a rate-equation approach

Abstract: Rate equations are used to study the dynamic magnetic properties of interacting magnetite nanoparticles viewed as double well systems (DWS) subjected to a driving field in the radio-frequency range. Dipole–dipole interaction among particles is modeled by inserting an ad-hoc term in the energy barrier to simulate the dependence of the interaction on both the interparticle distance and degree of dipole collinearity. The effective magnetic power released by an assembly of interacting nanoparticles dispersed in a diamagnetic host is shown to be a complex function of nanoparticle diameter, mean particle interdistance and frequency. Dipolar interaction markedly modifies the way a host material is heated by an assembly of embedded nanoparticles in magnetic hyperthermia treatments. Nanoparticle fraction and strength of the interaction can dramatically influence the amplitude and shape of the heating curves of the host material; the heating ability of interacting nanoparticles is shown to be either improved or reduced by their concentration in the host material. A frequency-dependent cut-off length of dipolar interactions is determined and explained. Particle polydispersity entailing a distribution of particle sizes brings about non-trivial effects on the heating curves depending on the strength of dipolar interaction.