The PZC can be defined as the pH-values at which the net surface charge is zero
(Stumm, 1992). Under such conditions, there is no electrostatic repulsion among
neighboring molecules and/or colloids of the compound and they tend to coalesce and
flocculate. At a pH other than the PZC of the compound in a colloids system, colloidal
particles have a net electric charge of the same sign so they repel each other, making the
colloid suspension stable, which prevent flocculation. A substance-specific PZC is
determined by its functional groups that are found on its surface.