We determine the zeta potential (ZP) by using electrophoretic laser light scattering and Laser Doppler Velocimetry (LDV). Particle sizes are measured by photon correlation spectroscopy (PCS). We studied the ZP for colloidal suspensions of TiO2 and Ag metal particles in order to determine the kinetic interaction and charge exchange between the particles. We investigated the natural tendency of the particles for aggregation and varied the pH of the solution. It was found that the ZP versus pH curve for the mixed TiO2/Ag did not behave as the average of the individual TiO2 and Ag curves as one would expect, and instead there was a slight horizontal shift towards higher pH values which implies that the particles in the mixed TiO2/Ag colloid are interacting with the result of charge exchange. The average particle size was measured in terms of effective diameter, for the TiO2, Ag and the mixed TiO2/Ag particles. The results indicated an increase of approximately 100 nm in the effective diameter of the mixed TiO2/Ag particles size compared to the size of the individual TiO2 particles. This can be explained as the fact that 50 nm Ag particles are adsorbed on the surface of the TiO2 particles.

One of the most common herbicides in the world, Atrazine, was used as a model pollutant in this study. The photocatalytic activities of the nanocomposite of TiO2/Ag, with nanopaticles of TiO2 and Ag, were investigated by photodegradation of atrazine under the natural sun. It was found that the efficiency of solar-photocatalytic activity was increased significantly by using the nanocomposites of TiO2/Ag, compared to the use of TiO2 alone. The mechanism of the TiO2/Ag composite for enhancement of photocatalytic activity was elucidated in this work.

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.