It is not meaningful. In that case, it is recommended to repeat the measurements. Sometimes, sample can show two PZC due to aggregation of suspension.

Even if my material is a hybrid composite consisted of three different phase with significant content?

Depends on the chemistry of the system. Does one phase dissolve at high or low pH? More details about your system would allow a specific response and not a general one.

Alan F Rawle

Thank you for your reply. My sample is composed of Al2TiO5, TiO2 and Al2O3. I do not know how Al2TiO5 behaves at high and low pH values.

Alumina is amphoteric and dissolves at low and high pH's. Thus the composition of the solids in suspension will change as will the continuous phase. TiO2 also will dissolve at low pH's. Thus you have a complex situation. Have you a zeta-pH plot that you can display?

Alan F Rawle

You can find my zeta potential plot in your p.v.

Alan F Rawle

Could you please introduce me some literature mentioning these points?

Any basic chemistry text should illustrate the pH-dependent behavior of amphoteric oxides such as alumina.

You may find this blog of interest for typical titration behavior of metal oxide nanoparticles: https://www.materials-talks.com/blog/2017/07/27/isoelectric-points-of-nanomaterials-qa/

Md. Aminul Islam Alan F Rawle Ulf Nobbmann

Thank you for your guidance.

pzc is when the surface charge is zero.

iep is when the electric potential at the slipping plane is zero.

These are not the same. You cannot measure pzc via zeta potential. You can estimate it if you know enough about the interfacial chemistry. Typically, this isn't the case.

See https://www.liquisearch.com/isoelectric_point/isoelectric_point_versus_point_of_zero_charge for good discussion.