Formation of highly crystalline maghemite nanoparticles from ferrihydrite in the liquid phase

• Published in: Chinese science bulletin 2014-10, Vol.59 (29), p.3904-3911
• Main Authors: Gong, Xiaomin, Li, Jian, Lin, Yueqiang, Liu, Xiaodong, Chen, Longlong, Li, Junming, Li, Decai
• Format: Article
• Language: English
• Subjects: Chemistry/Food Science; Earth Sciences; Engineering; Humanities and Social Sciences; Life Sciences; multidisciplinary; NaOH溶液; Physics; Science; Science (multidisciplinary); X射线光电子能谱法; 氯化亚铁; 水晶; 磁性纳米颗粒; 磁赤铁矿; 结晶; 透射电子显微镜
• ISSN: 1001-6538; 1861-9541
• DOI: 10.1007/s11434-014-0520-2

Fe5O7（OH）·4H2O ferrihydrite is a low-crystal- linity antiferromagnetic material, γ-Fe2O3 （maghemite） magnetic nanoparticles were prepared from a ferrihydrite precursor, by chemically induced transformation in FeCl2/ NaOH solution. The magnetization, morphology, crystal structure and chemical composition of the products were determined by vibrating sample magnetometry, transmission electron microscopy, X-ray diffraction （XRD）, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy （XPS）. Ferrihydrite underwent aggregation growth and transformed into α-FeO（OH） （goethite） particles, which subsequently transformed into γ-Fe2O3 nanoparticles, that became coated with NaCI. The γ-Fe2O3 particles had a flake-like morphology, when prepared from 0.01 mol/L FeCl2 and a FeCl2：NaOH molar ratio of 0.4. The γ-Fe2O3 particles were more spherical, when prepared from a FeCl2：NaOH molar ratio of 0.6. The Fe content of the flake-like particles was lower than that of the spherical particles. Their magnetizations were similar, and the coercivity of the flake-like particles was larger. The differences in morphology and magnetization were attributed to the surface effect, and the difference in coercivity to the shape effect.