The zeta potential of S1 nanoparticles was 63.5 mV indicating good dispersion stability. This is in agreement with the results reported by other studies done at pH 5.5–6. The zeta potential values of iron containing samples, S2 and S3, were 55 and 52.4 mV, respectively. Similar decrease of the zeta potential values with the addition of iron has been reported by other researchers. Knowledge about zeta potential of nanoparticles can have an important impact on their applications in solutions e.g. water purification. The hydrodynamic size of the particle varied from 183 nm to 187 nm (Table 3). There is a large difference between the hydrodynamic size and the aggregate size of the particles observed from TEM images (see Table 3). It can be attributed to inadequate dispersion of nanoparticles to water during the preparation of the suspensions.