The TEM micrographs of RH-Silica are shown in Fig. 5.
The morphology of the spherical silica and the particle size were examined by TEM. RH-Silica consists of uniform and aggregate spherical particles with a diameter range between 15 and 91 nm. In basic condition, silica particles aggregate to form negatively charged colloidal gel. These colloidal particles induce strong electrostatic repulsive energy to avoid gelation and agglomeration [21]. It can be seen that the nanoparticles are basically amorphous as shown in the XRD (Fig. 3).