i want to determine the point of zero charge ( pHpzc) of perovskite. in the literature there are many methods but i want to follow pH drift method (addition of salts) and method which involve the zeta potential vs different pH values. But the problem in all these methods is their variation w.r.t use of background electrolytes, concentration of electrolytes, volume of solution, time of stirring/shaking/sonication , amount of solid used.what is the standard parameters for all these methods. changing these parameters will change the value of pHpzc?
I guess you have access to a Zeta sizer (like MALVERN Zetasizer Nano ZSP) without automatic titration unit. You have to add ions to suppress particle-particle interactions. This may lead to a variation in the activity of the solution which can influence the measured values. I would suggest using a highly concentrated solution of e.g. KCl with a small content of your particles, which forms a stable dispersion at the starting pH (?). It is possible that the particles will be non-dispersable (near to or) after passing the point of zero charge (control the count number of the detector). Some details may be found within the attached publication.
Article Functionalized polymer colloids bearing primary amino groups
To measure the zeta potential you do need an instrument that does this, as noted in the response above. But the other things like time of stirring etc. are important because you want equilibrated solids in the solution you are testing. So while the times may change the important thing is - is that enough time for the solids to equilibrate? This is because when you put solids into a solution, the surface may change and that means the surface charge may also change. That is why it is good practise to get into the habit of measuring the pH just before the zeta potential measurement as it has probably changed over the equilibration time.
The other important parameter is the background electrolyte. Don't use a concentrated electrolyte, this will only introduce error into your results. The surface charge is often a small number that has to be extracted from the large conductivity value of the background electrolyte, so don't go beyond 0.1M of electrolyte unless you have to and if you can go lower that is better. Finally, to get a good indication of the pzc, do more pH values close to the pzc than away from it. For example, if the pzc were around 6, you might do pHs 4, 5, 5.5, 6 6.5 , 7,and 8 to increase the accuracy.
thanks a lot Dr Schmitt and Dr Jones for valuable information. but how about the quantity of solid to be added and the volume of electrolyte solution .Some papers suggest 0.1 g and 50 ml while others 0.01 g etc, here i am confused. the sonication should be before the pH adjustment?
The volume of electrolyte should be a lot more than the solid but will also depend on your instrument. A Malvern type instrument needs only ~1 mL to do the measurement but you would probably prepare up 10 mL. In terms of solids you could start off with around 3wt/wt% solids. And the sonication should be just before the measurement. The pH will be stable if you allowed the system to equilibrate so you can measure it first then sonicate and do the measurement.
thanks Dr Jones. wt.% = [g solute/(g solute + g solvent)] x 100 so according to your statement 3wt/wt% means 0.3g for 10 ml total solution. i mean 3wt/wt%= 3 g/3 g solid+97 g water so for 10 ml aq solution will be 0.3 g soild. is that right?
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