Synthesis and Characterization of Magnetic-Optical Co−Au Core−Shell Nanoparticles

Abstract

We report the successful synthesis of Co-Au core-shell nanoparticles by reducing an organo-gold compound onto cobalt seeds with a weak reducer in a nonpolar solvent. The core-shell morphology was unequivocally confirmed by complementary structural, magnetic, and optical property measurements. High-resolution transmission electron microscopy and Z-contrast imaging shows a gold shell composed of multiple grains. Electron-energy loss spectroscopy confirms the chemically distinct characteristics of the core (Co) and shell (Au). Temperature-dependent magnetic property measurements confirm that the particles are superparamagnetic with a blocking temperature, T B ∼ 55 K, consistent with a magnetic diameter ∼6 nm. The UV-visible absorption spectra of these nanoparticles show a red shift (relative to pure gold nanoparticles) in agreement with a Au-shell morphology.

Investigação <i>ab initio</i> dos mecanismos de formação de nanoligas <i>core-shell</i> com platina e metais de transição dos períodos 3<i>d</i>, 4<i>d</i> e 5<i>d</i>

“…Essas nanoligas vêm sendo exploradas nos últimos anos devido às potenciais aplicações tecnológicas, especialmente na área de catálise heterogênea, a qual será discutida adiante de forma particularizada. Além desta área, o estudo dessas nanoligas também são frequentes em óptica, 20 magnetismo 21, 22 e biomedicina 23 ; a título de exemplo, pode-se observar o estudo dirigido por Bao et al, 24 em que nanoligas de Co@Au mostraram propriedades opto-magnéticas bastante pronunciadas -dada a ressonância plasmônica do Au e do ferromagnetismo de Co em nanoescala -, tornando-se candidatas promissoras em aplicações biomédicas, em vistas de biosseparação e biossensoriamento.…”

Hollow, Branched and Multifunctional Nanoparticles: Synthesis, Properties and Applications

“…This reaction strategy can also be utilized to prepare core@shell Co@Au nanoparticles, where an organic modified Co nanoparticle is encapsulated in a Au shell through the reduction of gold atoms on the surface of the Co nanoparticle by oleylamine. 148 Another interesting approach to the preparation of core@shell nanoparticles is the development of redox-transmetalation chemistry on Co nanoparticles. 149 The development of transmetalation chemistry eliminates the need to nucleate a shell material on an existing nanoparticle or the "fusion" of two nanoparticle materials.…”

Structure and composition of Au/Co magneto-plasmonic nanoparticles

“…[16] There exist several studies on the synthesis and properties of Au-Ni and Au-Co NPs. [17][18][19][20][21][22][23] However, thiolate protected Au/Co NPs have not been reported so far. In general terms, segregation of Au toward the surface is predicted, considering only the metal-metal interaction, i.e., neglecting the effect of the surfactant molecules.…”