Effect of Oleic Acid Concentration on the Physicochemical Properties of Cobalt Ferrite Nanoparticles

Abstract

We have investigated the effect of oleic acid concentration on the physicochemical properties of solvothermally derived cobalt ferrite nanoparticles (CFO NPs). Without the oleic acid, agglomerated nanoplatelets with a crystallite size of about 19 nm were obtained, according to X-ray diffraction (XRD) and transmission electron microscopy (TEM). However, the addition of oleic acid decreases the size of the CFO NPs and at critical concentration, which was determined to be 0.25 M, well-dispersed, nonagglomerated spherical particles of about 6 nm were obtained. A further increase in the oleic acid concentration affected the particle size only slightly, with a relatively constant surface coverage of the oleic acid ligand. The results of our study indicate that particle-size control was achieved by bridging bidentate interactions between the oleic acid molecules and the metal atoms on the surface of the NPs, as determined by Fourier transform infrared spectra. These interactions affected the surface strain of NPs considerably, but kept the initial cation redistribution according to the Raman spectra. The room temperature magnetic measurements revealed that oleic acid enables us to effectively control the magnetic behavior of the CFO, which changes from ferrimagnetic to superparamagnetic at a critical concentration. Interparticle interactions are further interpreted by using low-temperature magnetic measurements, which also showed decreased surface anisotropy for samples prepared with oleic acid concentration above the critical value. An investigation of the treatment time showed that the capping with oleic acid is already achieved after 1 h of synthesis, but in order to improve the crystallization and consequently achieve the desired magnetic response a synthesis time of at least 4 h is required.

LOW-TEMPERATURE SYNTHESIS OF SUPERPARAMAGNETIC Zn0.8Ni0.2Fe2O4 FERRITE NANOPARTICLES

“…Figure 3 shows the TEM images of samples heated at different temperatures for 6 h in autoclave. All of samples had the particles size arranged from 6 -8 nm, this is the same size as reported in other works [7,13].…”

“…This research had synthesized the cobalt ferrite using hydrothermal method heating only at 180 o C for 16 h. The study indicated that, for the oleic acid concentration up to 0.25 M the average crystallite size decreased with the oleic acid concentration, while further addition of oleic acid had only a small influence on the average crystallite size. At the oleic acid concentration of 0.25 M, obtained particles were spherical, of about 6 nm in diameter and they were well-dispersed and non-agglomerated [7].…”

“…[5][6][7]. The Zn-Ni ferrites have been synthesized by chemical co-precipitation method with high annealing temperature [8][9][10] and by hydrothermal method [11][12][13].…”

“…The Zn-Ni ferrites have been synthesized by chemical co-precipitation method with high annealing temperature [8][9][10] and by hydrothermal method [11][12][13]. A synthesis of cobalt ferrite assisted with the oleic acid is to avoid the agglomeration studied by Sonja Jovanović [7]. This research had synthesized the cobalt ferrite using hydrothermal method heating only at 180 o C for 16 h. The study indicated that, for the oleic acid concentration up to 0.25 M the average crystallite size decreased with the oleic acid concentration, while further addition of oleic acid had only a small influence on the average crystallite size.…”

“…In the present paper, nanoparticles of Zn 0,8 Ni 0,2 Fe 2 O 4 ferrite were first synthesized by chemical co-precipitation, then modified by 0.25 M oleic acid [7] and finally heated at different temperatures of 120, 140, 160 and 180 o C in 6 h (autoclave heating). This study aims to understand how the heating temperature influences on the crystallite size and magnetic properties of the ferrite.…”