Magnetite nanoparticles play a key role in the nano-industry, with a key role in the developing nanomedical 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 – (- CH2CH¬2N-) nH2, n = 2 (DETA), 3 (TETA), 4 (TEPA) and 5 (PEHA)) of additives was successfully used to improve the morphology of nanomagnetite made via a green ambient coprecipitation method. While DETA showed less control, TETA, TEPA and PEHA mediated the synthesis of nearly universal (92-97%) faceted particles, suggesting a nearly pure octahedral population (compared to only 6% of the control particles). Particle size 22 nm for all samples and was not influenced by the addition of additive. Computer-aided molecular dynamic modeling shows the binding to the octahedra  Face to be preferred for all additives with bond to  unfavorable for TETA, TEPA and PEHA, indicating a preference for binding and directing an octahedral morphology for these 3 additives. This is further explained by the increased number of interactions of the longer additives with the  Surface due to O and Fe in the magnetite Surface binding to H and N in the additive, which can lie flat better  Surface. An optimal concentration of 1: 125 additive: iron ion ratio was determined, which shows that a relatively small amount of cheap, organically bio-inspired amine-rich additive can have a massive influence on the morphological quality of magnetite nanoparticles. This powerful green additive directed synthesis approach could be universally applied to a wide variety of nanomaterial syntheses with great impact.