The zeta potential of a colloidal solution is a measure of the electrostatic repulsion between particles in the solution. It is an important factor in determining the stability of colloidal systems, as it influences the degree of aggregation or dispersion of the particles. The pH of the solution can have a significant effect on the zeta potential, as it influences the ionization of functional groups on the surface of the particles, which in turn affects the overall charge of the particles.In general, the zeta potential of a colloidal solution tends to become more negative as the pH increases, and more positive as the pH decreases. This is because, at low pH values, the surface of the particles is more likely to be protonated, leading to a positive charge. Conversely, at high pH values, the surface of the particles is more likely to be deprotonated, leading to a negative charge.Experimental evidence supporting this relationship can be found in numerous studies. For example, a study by Kosmulski et al. 2002 investigated the effect of pH on the zeta potential of various metal oxide particles, including alumina, silica, and titania. They found that the zeta potential of these particles became more negative as the pH increased, consistent with the general trend described above.Another study by Zhang et al. 2015 examined the effect of pH on the zeta potential of graphene oxide GO particles in aqueous solutions. They found that the zeta potential of GO particles decreased became more negative as the pH increased from 2 to 10, which they attributed to the ionization of carboxyl and hydroxyl groups on the surface of the particles.These studies, along with many others, provide experimental evidence that the pH of a colloidal solution can significantly affect the zeta potential of the particles, which in turn influences the stability and behavior of the colloidal system.References:1. Kosmulski, M., Gustafsson, J., & Rosenholm, J. B. 2002 . The pH-dependent surface charging and points of zero charge: V. Update. Journal of Colloid and Interface Science, 253 1 , 77-87.2. Zhang, L., Wang, Y., Zhang, Y., & Chen, Y. 2015 . The influence of pH on the zeta potential of graphene oxide in aqueous solutions. RSC Advances, 5 129 , 106498-106504.