Greetings,
I need the surface charge density of particulate solid at diferent pH. I have tried from the surface complexation model but there are several things missing. I only have the zeta potential data in water.
Is there another method experimental or mathematical to obtain the surface charge density?
kind regards.
If you already have the zeta potential of the particle, you can use a relationship that connect the zeta potential with the charge, q, (in C per m3) of your particule : q=4*pi*eps*a(1+kappa*a)*zeta. This equation describes the electroneutrality around a sphere : the excess of charge in the electrostatic double layer is equal to the opposite of the particle charge.
You can also run titration experiments that can give you directly the charge of your particle.
Good luck.
Hi Gonzalo,
With only zeta-potential you will not be able to calculate surface charge density, unfortunately. Zeta-potential is only the potential but it is not related to the number of charges causing this potential. If you want to know surface charge density you need to perform streaming potential titrations.
For some surfaces you could use common acid-base titrations but since you want to know at different pH-values, acid-base titrations are not the way to go.
In streaming potential titration, a flow is generated dislocating counter ions from a sample specimen, this causes a compensating streaming current which you can measure. Next you titrate the surface with an oppositely charged polyelectrolyte until the streaming current (or potential) is zero. From the polyelectrolyte consumption you can calculate the exact surface charge density.
I looked at your affiliation, so found a link that relates to your field of interest, water management....... Please review this paper for details on the method: Article Streaming current titration for coagulation of high turbidity water
Kind regards, Leo
I fully agree with Leo.
It's worth reading in detail about the origins of the double layer which will explain why it is not a good idea to assume that the zeta potential is the same (or similar) to the true surface charge. The zeta potential measures the potential at the point where the particle and all its adsorbed ions etc move relative to the liquid - also known as the electrokinetic potential. I gave a related answer here:
https://www.researchgate.net/post/Can_I_measure_electrostatic_force_by_using_zeta_potential
Here's an article by a good friend of mine that explains the origin and features of the double layer. You'll see that it is possible to have a negative zeta potential even when the surface charge is positive.
https://www.americanpharmaceuticalreview.com/Featured-Articles/133232-An-Overview-of-the-Zeta-Potential-Part-1-The-Concept/
Hope this helps,
John.
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