Gas phase condensation of superparamagnetic iron oxide–silica nanoparticles – control of the intraparticle phase distribution

Abstract

Spherical, softly agglomerated and superparamagnetic nanoparticles (NPs) consisting of maghemite (γ-Fe2O3) and amorphous silica (SiO2) were prepared by CO2 laser co-vaporization (CoLAVA) of hematite powder (α-Fe2O3) and quartz sand (SiO2). The α-Fe2O3 portion of the homogeneous starting mixtures was gradually increased (15 mass%-95 mass%). It was found that (i) with increasing iron oxide content the NPs' morphology changes from a nanoscale SiO2 matrix with multiple γ-Fe2O3 inclusions to Janus NPs consisting of a γ-Fe2O3 and a SiO2 hemisphere to γ-Fe2O3 NPs each carrying one small SiO2 lens on its surface, (ii) the multiple γ-Fe2O3 inclusions accumulate at the NPs' inner surfaces, and (iii) all composite NPs are covered by a thin layer of amorphous SiO2. These morphological characteristics are attributed to (i) the phase segregation of iron oxide and silica within the condensed Fe2O3-SiO2 droplets, (ii) the temperature gradient within these droplets which arises during rapid cooling in the CoLAVA process, and (iii) the significantly lower surface energy of silica when compared to iron oxide. The proposed growth mechanism of these Fe2O3-SiO2 composite NPs during gas phase condensation can be transferred to other systems comprising a glass-network former and another component that is insoluble in the regarding glass. Thus, our model will facilitate the development of novel functional composite NPs for applications in biomedicine, optics, electronics, or catalysis.

Temperature-dependent dynamic correlations in suspensions of magnetic nanoparticles in a broad range of concentrations: a combined experimental and theoretical study

“…Secondly, one can modify the internal structure of the particles varya Ural Federal University, Lenin av. 51 34,35 or creating core-shell particles with various types of agglomerates serving as a core, thus providing particle internal anisotropy [36][37][38][39][40][41] . High demand for specific magnetic building blocks stems from the potential for diagnostics, therapy and in-vitro analysis 2,42-45 .…”

Risk and life cycle assessment of nanoparticles for medical applications prepared using safe- and benign-by-design gas-phase syntheses

“…1) were prepared by using the CoLAVA method. 23 For the synthesis, 70 mass% hematite powder (α-Fe 2 O 3 ; Sigma-Aldrich Chemie GmbH, Steinheim, Germany, product no. 310050, purity ≥99%, grain size ≤5 µm) and 30 mass% silica powder (SiO 2 ; Sigma-Aldrich Chemie GmbH, Steinheim, Germany, product no.…”

“…24,25 CoLAVA synthesis and formation of these SiliFe nanoparticles were described in detail previously. 23 The ferromagnetic maghemite nanoparticles in this study were prepared by using the LAVA method starting from the same hematite raw powder and applying the same process conditions already used for the synthesis of the SiliFe nano- particles. LAVA synthesis and formation of the maghemite nanoparticles were described in detail previously.…”

Europium(III)‐Doped MgAl2O4 Spinel Nanophosphor Prepared by CO2 Laser Co‐Vaporization

“…The CO 2 laser vaporization technique has proven its versatility to prepare a broad range of functional, single or multiphase ceramic NPs with excellent properties . Briefly, a CO 2 laser beam is focused onto the surface of a coarse‐grained raw powder.…”

“…The CO 2 laser vaporization technique has proven its versatility to prepare a broad range of functional, single or multiphase ceramic NPs with excellent properties. [15][16][17][18] Briefly, a CO 2 laser beam is focused onto the surface of a coarsegrained raw powder. By absorbing the high-intensity laser radiation, the raw powder heats up, vaporizes, and forms a plasma.…”