Colloidal Stability of Nanosoil/Nanofiber Aqueous Suspensions From Natural Environment in Hawaii

Nanoparticles from iron-oxide rich soil and nanofibers from bark of the plumeria tree in Hawaii have been studied using photon correlation spectroscopy (PCS). Particles with sizes of several hundred nanometers have been investigated in aqueous suspension. The zeta potentials have been determined as a function of pH for soil, fiber, and the soil/fiber mixture. It is found that all three suspensions have negative zeta potentials and no isoelectric point within the pH range from 4 to 11. This shows that the suspensions are stable over a wide range of conditions. Both soil and fiber samples have approximately constant zeta potentials within this range. However, the zeta potential changes significantly for the nanosoil/nanofiber mixture when the pH is varied. We conclude that the nanoparticles of soil and fiber interact in the suspension and that this depends on the pH value of the suspension.