Magnetite nanoparticles functionalized with citrate: A surface science study by XPS and ToF-SIMS

The surface composition of magnetite nanoparticles, bare and functionalized with citrate, was investigated by means of XPS and ToF-SIMS. Magnetite nanoparticles were prepared by co-precipitation and two different procedures were used to functionalize them with citrate ions. By means of XPS we found that the composition of the oxide is not modified, within the uncertainty of the analysis, by the functionalization swith citrate. Moreover, the amount of citrate ions adsorbed at the surface of the nanoparticles is the same, independently on the functionalization procedure. The thickness of the citrate shell is consistent with that of a single layer of citrate ions covering only partially the surface of the nanoparticles. XPS and ToF-SIMS analyses revealed the presence of ammonia molecules, resulting from the Fe(II) salt used to prepare the oxide nanoparticles, adsorbed at the surface of nanoparticles.