Continuous hydrothermal synthesis of polymer-coated Fe2O3 and CoFe2O4 nanoparticles

Metal oxide nanoparticles are of practical interest in a variety of applications including high-density information storage [1], magnetic resonance imaging [2] and targeted drug delivery [3]. Many of these applications require particles of predetermined size and narrow size distribution. Processes that lead to particles with these characteristics are therefore of considerable interest. Cobalt ferrite, CoFe2O4, is a wellknown hard magnetic material with very high cubic magnetocrystalline anisotropy, high coercivity, and moderate saturation magnetization [4], which makes it a promising material for high-density magnetic recording. We have previously [5-7] reported on the continuous hydrothermal synthesis of α-Fe2O3, Co3O4, and CoFe2O4 particles and shown that speciation and solubility play a key role in the production of these oxides. Particle agglomeration, however, was a key limitation in these studies. Aggregation and growth of such particles can be avoided (1) by coating the nanoparticles with a protective layer; (2) by fixing the particles to a substrate; or (3) by precipitating the particles in a confined space [8, 9]. In the present work, we have employed a continuous hydrothermal technique for the synthesis of PVA-coated Fe2O3 and CoFe2O4 nanoparticles. The continuous process allows effective control of particle size because nucleation and growth stages of particle formation are essentially separated. Iron and cobalt ferrite nanoparticles were synthesized in the presence of poly(vinyl alcohol) (PVA) and the results are reported in this work. The effect of experimental conditions on particle size, size distribution, particle morphology, and crystallinity were studied. The particles were characterized by powder x-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques.