The pH of a solution has a significant impact on the measured zeta potential of a metal oxide particle. Zeta potential is a measure of the electrostatic repulsion or attraction between particles in a colloidal suspension, which influences the stability of the suspension. In the case of metal oxide particles, the surface of the particle can either gain or lose protons H+ depending on the pH of the surrounding solution, leading to changes in the surface charge and, consequently, the zeta potential.At low pH values acidic conditions , metal oxide particles tend to gain protons, resulting in a positive surface charge and a positive zeta potential. Conversely, at high pH values alkaline conditions , metal oxide particles tend to lose protons, leading to a negative surface charge and a negative zeta potential. The point at which the zeta potential is zero is called the isoelectric point IEP or point of zero charge PZC , and it is specific to each metal oxide.Understanding the relationship between pH and zeta potential can be utilized for controlling the stability of colloidal suspensions in different pH conditions. A colloidal suspension is considered stable when the particles do not aggregate or settle out of the suspension. This is achieved when the electrostatic repulsion between particles is strong enough to overcome the attractive van der Waals forces. Generally, a zeta potential value greater than +30 mV or less than -30 mV indicates a stable suspension.By adjusting the pH of the solution, one can control the zeta potential of the metal oxide particles and, in turn, the stability of the colloidal suspension. For example, if the suspension is unstable at a certain pH, the pH can be adjusted to a value where the zeta potential is either more positive or more negative, thus increasing the electrostatic repulsion between particles and stabilizing the suspension.In summary, the pH of a solution has a significant impact on the zeta potential of metal oxide particles, which in turn affects the stability of colloidal suspensions. By understanding and controlling the pH-zeta potential relationship, one can optimize the stability of colloidal suspensions for various applications, such as drug delivery, coatings, and catalysts.