The Stage Dependent Effect of Capping Agent Introduction in the Synthesis of Magnetite Nanoparticles

In this paper, three techniques to obtain capped magnetite nanoparticles were compared. In the formation of magnetite nanoparticles via the co-precipitation route, capping agents were introduced pre-, simultaneously with, or post-addition of the precipitating agent, ammonia. The amino acids L-glutamine and L-glutamic acid were used as the capping agents. Characterization via TEM, pXRD, EDX, and magnetic analysis displayed that the stage of introduction affected the properties of the nanoparticles obtained. Confirmation of capping was performed by FTIR and X-ray photoelectron spectroscopy. TEM displayed that the post-addition method yielded nanoparticles with the narrowest size distributions, having attractive dispersity values. The pre- and simultaneously-introduced methods produced smaller nanoparticles but had relatively higher size distributions. Crystallite size determined from pXRD showed that the post-addition method had the highest crystallite size, even compared to the uncapped nanoparticles, while the pre-introduced were much less crystalline. From the magnetic studies, the post-introduction method was shown to yield the highest magnetic saturation values, even when taking magnetically dead layers into account. It was also shown that the simultaneous and pre-introduction methods yielded similar magnetic saturation values despite size differences.