Oleic Acid Surface Modification in the Preparation of Magnetic Nanoparticles by a Chemically Induced Transition

Using a chemically induced transition method, magnetic nanoparticles of γ-Fe 2 O 3 coated by FeCl 3 · 6H 2 O (γ-Fe 2 O 3 /FeCl 3 · 6H 2 O nanoparticles) can be prepared. Surface modification is performed using oleic acid. By adding oleic acid during the synthesis, FeCl 3 · 6H 2 O can be replaced to produce nanoparticles of γ-Fe 2 O 3 coated by a monolayer of oleic acid (γ-Fe 2 O 3 /oleic acid nanoparticles). The amount of oleic acid added is sufficient, with the as-prepared sample single γ-Fe 2 O 3 /oleic acid nanoparticles, whereas the as-prepared sample is a mixture of both γ-Fe 2 O 3 /FeCl 3 · 6H 2 O and γ-Fe 2 O 3 /oleic acid nanoparticles. By chemical species analysis, the mass fraction of both the γ-Fe 2 O 3 phase and oleic acid adsorbed can be estimated. These magnetic nanoparticles coated by oleic acid can be considered as effective nanoparticles with an effective density ρ p.e . The ρ p.e reflects the amount of oleic acid chemisorbed on the nanoparticles. A kerosene-based suspension comprising the effective nanoparticles was synthesized. Results for the specific saturation magnetization σ f.s and density ρ f of the suspension confirm the effective particle structure, involving the mass fraction of oleic acid adsorbed and the effective density of the effective particles.