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 (SBET), 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 (315 m2 g−1) was obtained when the smallest W (=20) and highest S (=0.20 mol L−1) were employed.

Stability of iron hydroxide nanoparticles prepared in microemulsions as a function of precipitating agent. NH3-precipitated nanoparticles (right) and TBAH-precipitated particles (left).Figure optionsDownload high-quality image (88 K)Download as PowerPoint slideResearch highlights
► Tetrabutylammonium hydroxide, promotes precipitation of nanoparticles out of the microemulsion.
► Tetrabutylammonium cations, block the pores of the powders which are removed by calcination.
► The droplet size and surfactant concentration have no direct effect on the dispersed nanoparticles.
► The droplet size and surfactant concentration have effects on the nanoparticle powders.
► High surfactant concentration and small droplets give the highest surface areas powders.