Characterization of iron hydroxide/oxide nanoparticles prepared in microemulsions stabilized with cationic/non-ionic surfactant mixtures

Iron oxide-hydroxide (α-Fe₂O₃; Fe(OH)₃) nanoparticles have been prepared by a microemulsion route using ammonia (NH₃) solution or tetrabutylammonium hydroxide (TBAH) as precipitants. The iron oxide-hydroxide nanoparticles obtained were characterized by TGA, N₂ sorptiometry, XRD, IR, SEM, HR-TEM, and DLS techniques. Properties such as specific surface area (S_BET), pore sizes and shapes, average particle size and distribution, crystallite structure, and thermal stability were determined. The properties of nanoparticles prepared using NH₃ and TBAH were compared after drying at 100°C and after being calcined in the temperature range 250-1100°C. It was found that the suspensions prepared using TBAH suffered immediate separation while those prepared using NH₃ resulted in very stable suspensions. Also, it was found that TBAH did not offer any advantage over NH₃ either in terms of specific surface area or in particle size of the prepared nanoparticles. Hence, the later part of the study was concentrated on the NH₃-precipitated nanoparticles with particular emphasis on finding the most favorable, W (water-to-surfactant ratio) and/or surfactant concentration, S, to obtain the best conditions in terms of higher surface areas and narrower particle size distribution. It was found that the prepared suspension consisted of monodisperse nanoparticles (standard deviations <10%) and after separation and drying, high surface area powders were obtained. The highest surface area (315m²g^-1) was obtained when the smallest W (=20) and highest S (=0.20molL^-1) were employed.