Influence of Reaction Solvent on Crystallinity and Magnetic Properties of MnFe₂O₄Nanoparticles Synthesized by Thermal Decomposition

Abstract

This study reports the synthesis of three kinds of manganese-doped magnetic ferrite nanoparticles (MnFe 2 O 4 ) in benzyl ether, octyl ether, and 1-octadecene by a simple and low cost thermal decomposition method. It was found that benzyl ether results in a dramatic improvement in nanoparticle crystallinity owing to its stronger reducibility compared to octyl ether and 1-octadecene, as demonstrated by X-ray diffraction and TEM measurements. Raman spectroscopy detection also indicated that the reducing solvent of benzyl ether was in favor of forming magnetite-like structure ferrite, while maghemite-like structured ferrite was obtained in octyl ether and 1-octadecene. The saturation magnetization (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mrow><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mi>S</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>) of MnFe 2 O 4 synthesized in benzyl ether was 85 emu/g [Fe], which was 3 and 5 times larger than MnFe 2 O 4 synthesized in octyl ether and 1-octadecene, respectively. The specific absorption rate (SAR) of MnFe 2 O 4 nanoparticles synthesized in benzyl ether was 574 W/g, while MnFe 2 O 4 nanoparticles synthesized in octyl ether and 1-octadecene have had much smaller SAR of 76 and 33 W/g, respectively. MnFe 2 O 4 nanoparticles synthesized in benzyl ether also exhibit higher relaxivity (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:msub><mml:mrow><mml:mi>r</mml:mi></mml:mrow><mml:mrow><mml:mn fontstyle="italic">2</mml:mn></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn fontstyle="italic">207</mml:mn></mml:math> mM −1 s −1 ) than those synthesized in octyl ether and 1-octadecene (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M3"><mml:msub><mml:mrow><mml:mi>r</mml:mi></mml:mrow><mml:mrow><mml:mn fontstyle="italic">2</mml:mn></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn fontstyle="italic">65</mml:mn></mml:math>and 22 mM −1 s −1 ). It was obvious that MnFe 2 O 4 nanoparticles synthesized in reducing benzyl ether have higher crystallinity and thus higher<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M4"><mml:mrow><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mi>S</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>, SAR, and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M5"><mml:mrow><mml:msub><mml:mrow><mml:mi>r</mml:mi></mml:mrow><mml:mrow><mml:mn fontstyle="italic">2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>values, which can serve as a better candidate for hyperthermia and magnetic resonance imaging.