Hydrophobic SPM Fe3O4 NPs having mean particle size as large as 20 nm

In summary, colloidal Fe3O4 NPs have been successfully prepared in large quantities using novel or improved methods based on controlled coprecipitation and hydrothermal synthesis. Physical property measurements reveal that our strategy for increasing the size of the particles toward 20 nm through synthesis under elevated temperatures has worked effectively, offering functional SPM Fe3O4 NPs with the desired exceptionally high Ms. In this paper, we outline new and improved large-scale routes to highly crystalline hydrophilic and hydrophobic SPM Fe3O4 NPs having mean particle sizes as large as 20 nm and exhibiting room temperature Ms as high as 84 emu/g. We analyze the structure and phase composition of synthesized SPM Fe3O4 NPs by several complementary bulk- and surface-sensitive techniques. We observe that the synthesized NPs have a single-phase magnetite structure with an overoxidized surface, although no distinct core−shell nanostructure appears. Furthermore, we show that hydrothermally prepared NPs can exhibit dimer-like or twinned internal structures formed by oriented attachment crystal growth. Finally, we demonstrate that the synthesized colloidal NPs show superparamagnetic behavior with notably high saturation magnetization and excellent performance in magnetic hyperthermia. Fe3O4 NPs were collected by a NdFeB magnet and redispersed in water using a propeller VOS 14 stirrer (VWR) and ultrasonic treatment in an S-250D signifier (Branson). To remove any unbound poly(acrylic acid) (PAA), the water-dispersed NPs were centrifuged at 20 000 rpm for 15 min with an Allegra 64R centrifuge (Beckman Coulter) and washed. This purification procedure was repeated twice, and the resultant NPs were redispersed in water. Unbound oleate (OL) ligands, ethanol was added to precipitate the NPs, followed by centrifugation at 6 000 rpm for 10 min and further redispersion in cyclohexane. After repeating this procedure twice, the NPs were stored in cyclohexane. The surface of as-prepared OL-coated NPs is hydrophobic due to the long alkyl chains from the fatty OL ligands. This enables the NPs to be readily dispersed in nonpolar solvents, generating colloidally stable samples for months. The yield of colloidal OL-coated Fe3O4 NPs synthesized by the hydrothermal method (OL-HT) was calculated to be 68% (≈0.9 g). If you are looking for high quality, high purity and cost-effective Fe3O4, or if you require the latest price of Fe3O4, please feel free to email contact mis-asia.