Growth kinetics evaluation of hydrothermally synthesized β-FeOOH nanorods

Abstract

Based on the proposition that a quantitative and qualitative relationship between alcohol surface tension and particle growth exists, the effect of four different organic solvents on the growth kinetics of β-FeOOH (akaganeite) nanorods have been evaluated in this study. Two-stage growth of akaganeite nanorods have been observed in the presence of butanol and propanol as solvents. The first growth stage follows a typical power law representing Ostwald Ripening (OR) kinetic. The second stage of growth was found to be asymptotic and was fitted by the Oriented Attachment (OA) kinetics. HRTEM images of the synthesized nanoparticles also showed crystallographically specific oriented attachment based growth of the nanocrystals. Signs of OA mechanism was not observed from the TEM images of the particles synthesized using ethanol and methanol as solvents. The rate constants for each kinetic was evaluated and the rate constant for OR kinetics, kOR, was found to be significantly higher than the rate constant for OA kinetics, kOA, under the reported conditions for the four different solvents used. The rate constants were related to the surface tension of alcohol. A factorial trial was used to evaluate the significance of interaction effects of process parameters. By correlating the surface tension of solvents with different process parameters a generalized correlation has been developed to predict β-FeOOH aspect ratios for the first time. This correlation was validated by an independent study. This correlation takes three different process parameters into consideration in conjunction with the solvent surface tension to predict particle aspect ratios with acceptable confidence.