Controlled synthesis of Mn3O4nanoparticles in ionic liquids

Abstract

This work describes a simple one-step synthesis of Mn₃O₄ nanoparticles by thermal decomposition of [Mn(acac)₂] (acac = acetylacetonate) using imidazolium ionic liquids (ILs) and a conventional solvent, oleylamine, for comparison. The Mn₃O₄ nanoparticles were characterized by XRD, ATR-FTIR, TEM, Raman, UV/VIS and magnetometry techniques. The addition of 1-n-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide IL (BMI·NTf₂) yielded a smaller particle size (9.9 ± 1.8 nm) with better dispersion and more regular sizes than synthesis using oleylamine as the solvent (12.1 ± 3.0 nm). The complete conversion of the precursor to Mn₃O₄ nanoparticles occurred after 96 h at 180 °C for the reaction performed in BMI·NTf₂. However, under these reaction conditions in oleylamine, no precursor was detected, but two different phases were observed: a major phase corresponding to Mn₃O₄ and a minor phase corresponding to MnO₂. Magnetometry revealed that Mn₃O₄ nanoparticles synthesized in either oleylamine or BMI·NTf₂ exhibited ferrimagnetic behavior at low temperatures, whereas they were paramagnetic at room temperature. As expected, the blocking temperature and the coercivity decreased with the size of nanoparticles. Our results demonstrate that reaction conditions such as time, and the nature of the ionic liquid play important roles in determining the size of Mn₃O₄ nanoparticles.