Improving the magnetic heating by disaggregating nanoparticles

• Co-precipitation synthesis of homogeneous MnFe2O4 and CoFe2O4 nanoparticles.
• Control of the particle size by varying the synthesis time.
• Reduction of the aggregation degree by exchanging TMAOH by oleic acid surfactant.
• Huge improvement of the nanoparticle heating efficiency by reduction of the hydrodynamic size.
• Benefits of the hydrodynamic size distribution.

Recently, potential applications of the magnetic heating for heterogeneous catalysis or organic synthesis have been reported. As these new applications are not limited by biocompatibility requirements, a wide range of possibilities for non-aqueous colloidal nanoparticles with enhanced magnetic properties is open. In this work, manganese and cobalt ferrite nanoparticles are synthesized by co-precipitation method with average particle size around 12 nm. The particles are either coated with tetramethylammonium hydroxide (TMAOH) and dispersed in water or with oleic acid (OA) and dispersed in hexane to produce aggregated or disaggregated nanoparticles, respectively. It is observed that the particle disaggregation improves significantly the heating efficiency from 12 to 96 W/g in the case of cobalt ferrite, and from 120 to 413 W/g for the manganese ferrite. The main responsible for this improvement is the reduction of hydrodynamic volume that allows a faster Brownian relaxation. This work also discusses the relevance of the size distribution.

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