Dialkylamide as Both Capping Agent and Surfactant in a Direct Solvothermal Synthesis of Magnetite and Titania Nanoparticles

Abstract

An ecofriendly, low-cost, one-pot solvothermal approach has been developed to prepare spherical magnetite nanoparticles with sizes in the 7–12 nm range capped with a dialkylamine. Iron isopropoxide, water vapor, absolute ethanol, oleic acid, and oleylamine were used as iron oxide precursor, hydrolysis agent, solvent and surfactants, respectively. The surfactants’ role was investigated and an accurate correlation among the synthetic parameters, the crystallographic phases, and both crystallite and particle size was found. The amounts of oleylamine and oleic acid and the temperature have been revealed to be the key parameters in order to tune particle size and their polydispersity. An in-depth study on the role of each surfactant has pointed out the fundamental role of the amine as a reduction promoter as demonstrated by using different amines and confirmed by Mössbauer measurements. A dual 1H NMR-Fourier transform infrared spectroscopy approach on selected experiments for the investigation of the capping agents (in the presence of a magnetic phase (Magnetite) or a diamagnetic one (Anatase) prepared in the same synthetic conditions) has been found to be fundamental to clarify the actual nature of the capping agent of the nanoparticles and the reactions involved between the surfactants. New insights on the reaction mechanism confirm the formation of an amide that represents a new cosurfactant for the size and shape regulation and a biocompatible molecular coating of magnetite and anatase nanoparticles.