Re: pH drift method for determining PZC of adsorbent


rekuci@xxxxxxxxx wrote:
> I'm assuming "point of zero charge" is the same as the isoelectric
> point (pI or IEP) or pH where zeta potential = 0. Are you specifically
> trying to measure it for carbon

Yes for the carbon made from corncobs.

>or are you just trying to demonstrate
> the concept? This sounds like a simplified version of this type of
> measurement (zeta potential is usually directly measured with various
> electrokinetic techniques, which can require some semi-complicated
> setups).

I am not aware of eletrokinetic techniques. Are there any common ones
which can be easily done? But the pH drift method is quite common with
those who are into adsorption studies, since most of authors who have
reported PZC have utilized this method. Some call it suspension tests.
Even the suspension time is variable, some soak for 24 hours some for 6
hours.


>
> Your carbon is probably pretty dirty and could be slowly releasing
> residue salts into solution.

It is indeed dirty. I assume this is residual sulfuric acid leaching
in, the corncobs wer carbonized with sulfuric acid and heated at 150
oC.

>It doesn't necessarily have to be
> something acidic leaching out, because the presence of salts will
> change the surface charge properties by providing ionic species that
> can adsorb other than H+ and OH-. The authors of the cited paper
> specifically have to qualify that the method can be used for carbonized
> wheat because of 'enrichment', whatever that is, to eliminate pH drift
> from dissolution of salts.

Yes, this is what they have said.

.