The Dissociation Rate of Acetylacetonate Ligands Governs the Size of Ferrimagnetic Zinc Ferrite Nanocubes

Abstract

Magnetic nanoparticles are critical to a broad range of applications, from medical diagnostics and therapeutics to biotechnological processes and single molecule manipulation. To advance these applications, facile and robust routes to synthesize highly magnetic nanoparticles over a wide size range are needed. Here, we demonstrate that changing the degassing temperature of thermal decomposition of metal acetylacetonate precursors from 90 to 25°C tunes the size of ferrimagnetic Zn<sub>x</sub>Fe<sub>3-x</sub>O<sub>4</sub> nanocubes from 25 to 100 nm, respectively. We show that degassing at 90°C nearly entirely removes acetylacetone ligands from the reaction, which results in an early formation of monomers and a reaction-controlled growth following LaMer's model towards small nanocubes. In contrast, degassing at 25°C only partially dissociates acetylacetone ligands from the metal center and triggers a delayed formation of monomers, which leads to intermediate assembled structures made of tiny irregular crystallites and an eventual formation of large nanocubes via a diffusion-controlled growth mechanism. Using complementary techniques, we determine the substitution fraction x of Zn<sup>2+</sup> to be in the range of 0.35-0.37. Our method reduces the complexity of the thermal decomposition method by narrowing the synthesis parameter space to a single physical parameter and enables fabrication of highly magnetic and uniform zinc ferrite nanocubes over a broad size range. The resulting particles are promising for a range of applications, from magnetic fluid hyperthermia to actuation of macromolecules.

Embracing Defects and Disorder in Magnetic Nanoparticles

“…The effect of competition between short and long ligands on the particle structure has recently been shown in zinc ferrite nanoparticles. Increasing the ratio of acetylacetone to oleic acid ligands results in assembly of small magnetic zinc ferrite subdomains into 100 nm cubic-particles, due to less bulkiness and higher mobility of acetylacetone ligands as compared to oleic acid [143] .…”

Decoupling the Characteristics of Magnetic Nanoparticles for Ultrahigh Sensitivity

“…As Zn doping increases the particle size dramatically, 22 we use 0.25 mol equiv of Zn for 1.0 mol equiv of Fe. This produced about 8.1 ± 0.6 nm NCs.…”

“…The particle design is based on our previous expertise and results, where we have demonstrated the impact of synthesis conditions on size and shape of the particles. 22 Other studies have shown that the choice of surfactant types also plays a crucial role in the size, shape, and growth of the particles. 13,16,23,24 Here, we have optimized four crucial synthesis parameters: feed ratio of dopants, choice of solvents to stabilize growth temperature, choice of surfactants to Figure 2.…”