Physicochemical Studies of Complex Silver–Magnetite Nanoheterodimers with Controlled Morphology

This work discusses the influence of synthesis conditions on self-assembly capability and morphology of obtained Ag–Fe₃O₄ nanoheterostructures. Samples were synthesized in two steps: first silver nanoparticles were synthesized and then used as seeds for the growth of iron oxide nanoparticles in a second step. The silver nanoparticle size was tuned, changing the oleylamine (OAm) and oleic acid (OA) ratio, which enables us to study the influence of chemical agents and seed size on the final magnetic nanoparticle morphology. The mechanism during the formation of these heterostructures has been discussed by several authors; however, it remains an open issue. In this paper we extend the discussion and advance on the understanding of synthesis conditions, related to silver sizes, chemical agents, and physical properties on the obtained nanoparticles. In our Ag–Fe₃O₄ system, two types of heterostructures were obtained: dimer, flower, or combination of the two. We have found that the final shape depends on silver seed size, as well as the polarity of the chemical agents used during the synthesis. We made an exhaustive study of the relationship between magnetic properties and structural features. The morphology and size distributions of the heterostructures were analyzed with transmission electron microscopy (TEM)

Red-Green Emitting and Superparamagnetic Nanomarkers Containing Fe₃O₄ Functionalized with Calixarene and Rare Earth Complexes

The design of bifunctional magnetic luminescent nanomaterials containing Fe₃O₄ functionalized with rare earth ion complexes of calixarene and β-diketonate ligands is reported. Their preparation is accessible through a facile one-pot method. These novel Fe₃O₄@calix-Eu­(TTA) (TTA = thenoyltrifluoroacetonate) and Fe₃O₄@calix-Tb­(ACAC) (ACAC = acetylacetonate) magnetic luminescent nanomaterials show interesting superparamagnetic and photonic properties. The magnetic properties (M-H and ZFC/FC measurements) at temperatures of 5 and 300 K were explored to investigate the extent of coating and the crystallinity effect on the saturation magnetization values and blocking temperatures. Even though magnetite is a strong luminescence quencher, the coating of the Fe₃O₄ nanoparticles with synthetically functionalized rare earth complexes has overcome this difficulty. The intramolecular energy transfer from the T₁ excited triplet states of TTA and ACAC ligands to the emitting levels of Eu³⁺ and Tb³⁺ in the nanomaterials and emission efficiencies are presented and discussed, as well as the structural conclusions from the values of the 4f–4f intensity parameters in the case of the Eu³⁺ ion. These novel nanomaterials may act as the emitting layer for the red and green light for magnetic light-converting molecular devices (MLCMDs)

Red-Green Emitting and Superparamagnetic Nanomarkers Containing Fe₃O₄ Functionalized with Calixarene and Rare Earth Complexes

The design of bifunctional magnetic luminescent nanomaterials containing Fe₃O₄ functionalized with rare earth ion complexes of calixarene and β-diketonate ligands is reported. Their preparation is accessible through a facile one-pot method. These novel Fe₃O₄@calix-Eu­(TTA) (TTA = thenoyltrifluoroacetonate) and Fe₃O₄@calix-Tb­(ACAC) (ACAC = acetylacetonate) magnetic luminescent nanomaterials show interesting superparamagnetic and photonic properties. The magnetic properties (M-H and ZFC/FC measurements) at temperatures of 5 and 300 K were explored to investigate the extent of coating and the crystallinity effect on the saturation magnetization values and blocking temperatures. Even though magnetite is a strong luminescence quencher, the coating of the Fe₃O₄ nanoparticles with synthetically functionalized rare earth complexes has overcome this difficulty. The intramolecular energy transfer from the T₁ excited triplet states of TTA and ACAC ligands to the emitting levels of Eu³⁺ and Tb³⁺ in the nanomaterials and emission efficiencies are presented and discussed, as well as the structural conclusions from the values of the 4f–4f intensity parameters in the case of the Eu³⁺ ion. These novel nanomaterials may act as the emitting layer for the red and green light for magnetic light-converting molecular devices (MLCMDs)

Stability and Relaxation Mechanisms of Citric Acid Coated Magnetite Nanoparticles for Magnetic Hyperthermia

Magnetite (Fe₃O₄) nanoparticles are proper materials for Magnetic Fluid Hyperthermia applications whenever these conjugate stability at physiological (neutral pH) medium and high specific dissipation power. Here, magnetite nanoparticles 9–12 nm in size, electrostatically stabilized by citric acid coating, with hydrodynamic sizes in the range 17–30 nm, and well dispersed in aqueous solution were prepared using a chemical route. The influence of media acidity during the adsorption of citric acid (CA) on the suspension’s long-term stability was systematically investigated. The highest content of nanoparticles in a stable suspension at neutral pH is obtained for coating performed at pH = 4.58, corresponding to the larger amount of CA molecules adsorbed by one carboxylate link. Specific absorption rates (SARs) of various magnetite colloids, determined calorimetrically at a radio frequency field of 265 kHz and field amplitude of 40.1 kA/m, are analyzed in terms of structural and magnetic colloid properties. Larger dipolar interactions lead to larger Néel relaxation times, in some cases larger than Brown relaxation times, which in the present case enhanced magnetic radio frequency heating. The improvement of suspension stability results in a decrease of SAR values, and this decrease is even large in comparison with uncoated magnetite nanoparticles. This fact is related to interactions between particles