Interactions at the CMC/magnetite interface:Implications for the stability of aqueous dispersions and the magnetic properties of magnetite nanoparticles

Magnetite NPs modified with CMC, a polysaccharide containing carboxylic groups derived from cellulose, were prepared. Two different methods were used: addition of CMC to a dispersion of magnetite NPs previously synthesized (ex situ preparation) and addition of NaOH to an aqueous solution of Fe(II) and Fe(III) in the presence of CMC (in situ preparation). The aim of this study was to characterize in detail the interactions between magnetite NPs and CMC and to elucidate the effect of the polymer on the magnetite NP agglomeration. FTIR spectroscopy was used to shed light onto the nature of the interactions between CMC and Fe3O4 NPs. The morphological characterization of the NPs was carried out by FESEM. The size and the ζ-potential of the NPs in various aqueous media were determined by DLS. XRD measurements indicate that the presence of CMC does not modify, within the uncertainty of the measurement, the size of the primary particle (ca. 10 nm). FTIR spectra suggest that CMC chains are anchored to magnetite NPs via carboxylate groups interacting with iron ions at the surface. The FESEM images show that magnetite NPs prepared by the in situ method form aggregates which are significantly smaller than those prepared by the ex situ procedure. The FESEM images reveal a different morphology of the polymeric matrix between the CMC/magnetite NPs prepared following the two procedures. The hydrodynamic diameter of the CMC/magnetite NPs in water at neutral pH prepared in the presence of CMC is 280 nm. The ζ-potential (ca. −80 mV) measured for the dispersions in water at neutral pH of CMC/magnetite NPs prepared according to the two methods explains their long-term stability. The magnetic behaviour of the CMC/magnetite NPs can be explained considering the different size of the aggregates in the two kinds of sample.