Ethylenediamine Series as Additives to Control the Morphology of Magnetite Nanoparticles

Magnetite nanoparticles play a key role in the nano-industry, with crucial importance in the developing nanomedicine sector. Such particles must be homogeneous, with a consistent shape and size, due to the growing need to tailor particles to more defined faceted morphologies. Here an ethylenediamine series (H2N-(-CH2CH2N-)nH2, n = 2 (DETA), 3 (TETA), 4 (TEPA), and 5 (PEHA)), of additives have been successfully used to control the morphology of nanomagnetite produced via a green ambient co-precipitation method. Whilst DETA showed less control, TETA, TEPA and PEHA mediated the near universal synthesis of faceted particles (91-97%) suggesting a near pure octahedral population (compared to only 6% of control particles). The particle size was ≈ 22 nm for all the samples and was not affected by the addition of additives. Computational molecular dynamic modelling shows the binding to the octahedral [111] face to be preferred for all additives with binding to the [100] face unfavourable for TETA, TEPA and PEHA, showing a preference to bind and direct an octahedral morphology for these 3 additives. This is further explained by the increased numbers of interactions of the longer additives with the [111] surface through O and Fe in the magnetite surface bonding to H and N in the additive which is better able to lie flat on the [111] surface. An optimum concentration of a 1 : 125 additive : iron ion ratio was determined which shows that a relatively small quantity of a cheap, organic bioinspired amine-rich additive can have a massive impact on the morphological quality of the magnetite nanoparticles. This powerful, additive-directed, green synthesis approach could be universally applied to a vast range of nanomaterial syntheses to great impact.