Synthesis Of γ-Fe2O3 Nanoparticles Research Articles

The Solution Dependence of Cu Modification During the Synthesis of γ-Fe<sub>2</sub>O<sub>3</sub> Nanoparticles

During the synthesis of γ-Fe2O3 nanoparticles by a chemically-induced transition method in FeCl2 solution, Cu modification was attempted by adding CuCl/NaOH or CuCl2/NaOH to the solution. The as-prepared products were characterized using VSM, TEM, EDS, XRD, and XPS. When adding a NaOH solution with a certain concentration, the components of the as-prepared products changed in relation to the copper salt used. When CuCl 2.5 × 10-3 M was used, γ-Fe2O3/CuFeO2 composite nanoparticles coated by FeCl3·6H2O and with an average size of 11.47 nm were formed. When the CuCl concentration increased to 5 × 10-2 M, a mixture of γ-Fe2O3/CuFeO2 and Cu (OH)Cl nanoparticles was formed. When 5 × 10-2 M CuCl2 was used, the final product contained γ-Fe2O3 nanoparticles, coated with FeCl3·6H2O, and Cu (OH)Cl nanoparticles. The magnetization of the as-prepared products depends on the content of the γ-Fe2O3 and CuFeO2 ferrites.

Characterization of Co-Modified <i>γ</i>-Fe<sub>2</sub>O<sub>3 </sub>Based Composite Nanoparticles

During the synthesis of γ-Fe2O3 nanoparticles using a chemically-induced transition in a FeCl2 solution, Co-surface modification was attempted by adding Co (NO3)2 and NaOH to the solution. The magnetization behaviors, morphologies, crystal structure, and chemical compositions of the as-prepared samples were characterized using vibrating sample magnetometry, transmission electron microscopy, X-ray diffractometry, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The as-prepared particles consisted of γ-Fe2O3/CoFe2O4 composite crystallite and a CoCl2·6H2O coating. The molar, mass and volume ratios of the phases were estimated from the characterization results for each sample. The Co-modified γ-Fe2O3 nanoparticles’ anisotropic constant is approximately 1.48×10-1 J/cm3. Their coercivity depends on the size of composite crystallites, which is based on the γ-Fe2O3/CoFe2O4 content rather than the Co content.

Characterization and magnetism of Co-modified γ-Fe2O3 core–shell nanoparticles by enhancement using NaOH

During synthesis of γ-Fe2O3 nanoparticles by chemically-induced transition in FeCl2 solution, Co-modification of the particles has been attempted by adding Co(NO3)2 (sample (1)) or Co(NO3)2/NaOH (samples (2) and (3)). Using VSM, TEM, XRD, EDS, and XPS, the specific magnetization, morphology, crystal structure, and bulk and surface chemical compositions have been characterized. Particles in sample (1) are composed of γ-Fe2O3 and CoCl2·6H2O, and particles in samples (2) and (3) have CoFe2O4 in addition to γ-Fe2O3 and CoCl2·6H2O. Detailed analysis shows that the Co-modification can be enhanced by additional NaOH to form γ-Fe2O3/CoFe2O4 core–shell nanoparticles coated by CoCl2·6H2O. The molar, mass, and volume ratios of each phase have been estimated for each sample, and the average density and saturation magnetization are derived. Accordingly, it is revealed that for these nanoparticle systems, the magnetization and coercivity depend on the grain size of the spinel structure crystallites based on γ-Fe2O3 or γ-Fe2O3/CoFe2O4, but the anisotropy constant remains at 1.48×10−1J/cm3.

Synthesis and self-organization of γ-Fe2O3 nanoparticles by hydrothermal chemical vapor deposition

We report here the synthesis of γ-Fe2O3 nanoparticles in the presence of the water vapor, by thermally decomposing ferrocene at ∼1100 °C in a vacuum of 10−2 Torr. The γ-Fe2O3 nanoparticles synthesized, interestingly, self-organized into straight lines of several ten micrometers long and several ten nanometers wide, on planar substrates. This could bring arrays of aligned, nanometer-wide lines of γ-Fe2O3 nanoparticles in areas ∼ several hundred micrometers in diameter, thus providing an alternative idea to fabricate patterns of iron particles on the nanometer scale, i.e., by simply deoxidizing the γ-Fe2O3 nanoparticles. The structure and the magnetic properties of the γ-Fe2O3 particles were also investigated.

Higher crystallinity superparamagnetic ferrites: Controlled synthesis in lecithin gels and magnetic properties

The synthesis of γ-Fe2O3 nanoparticles in a novel organohydrogel medium is reported. The hydrogel consists of the phospholipid species, lecithin together with the anionic surfactant AOT, water and a hydrocarbon, isoocatane. Transmission electron microscopy observations indicate that the particles are spherical and range in size from 15 to 25 nm. Superconducting quantum interference device characterizations show that the particles exhibit superparamagnetic behavior with a blocking temperature of 24 K (at an applied field of 50 G) and a coercivity of 1600 G at 2 K. The results are compared to the magnetic properties of the γ-Fe2O3 particles of the same size and shape synthesized in water-in-oil microemulsions (reverse micelles). It was found that both blocking temperature and the coercivity of the ferrites synthesized in the lecithin gel media was higher than those synthesized in the reverse micelles. Similar results can be found for cobalt ferrites. These findings reveal the sizes of the domains are the same for these two kinds of particles, while the crystallinity may be higher for the particles synthesized in the lecithin gel media. It is proposed that slow ionic species diffusion through the channels of the gel may lead to such increases in crystallinity during particle growth.