I have my ZnO nanoparticles and I have to check the zeta potential at various different pH range from 2-12. But usual chemistry of ZnONP tells that they might start dissolving below 5.5 pH or so. In such case how do I go about?
How to prepare sample for just normal zeta measurement and for various pH? Which solvent (I use deionized water as of now)? Concentration?
If i choose phosphate buffer at various pH does that help?
I am very new to this method I have never done this before so I have no clues. If someone can guide me through how to go about from sample preparation to interpretation.
Can DLS be measured with same sample preparation?
You cannot measure the zeta potential of a system (particles + environment) without taking into account the chemistry. As you indicate ZnO dissolves in acidic environments. Thus there is no concept of zeta potential in such situations. Take a look at: Guidance to improve the scientific value of zeta-potential measurements in nanoEHS Gregory V. Lowry et al Environ. Sci.: Nano, 2016, 3, 953 - 965
DOI: 10.1039/C6EN00136J
You can prepare pH2 phosphate buffer solution with deionized water and dissolve your nano particle at optimum amount (NPs should not collapse) Follow the size and zeta at each pH. Size data should give a average data with small std deviation.
For ph 2 dissolving is the correct wording. Please neither start with acid conditions or with pH 9 (pzc).
Use a large concentration of inert salts (like KCl) so that the activity is not influenced by the variation in pH and the zeta potential is as near to the surface charge as possbile (keyword Deby screening).
You even find a table for ZnO (zeta potential measurement) in the uploaded information for the following article
Article Synthesis and testing of ZnO nanoparticles for photo-initiat...
concerning the measurement the second artic might be interesting
Article Functionalized polymer colloids bearing primary amino groups
concering the dynamic determination of the diameter: Our old equipment had two separated measuring positions but as far as I know most of the newer equipments use the same cell for both techniques.
Dilara ma'am, thank you for answering my question. So you mean to say I can prepare my dillutions in Phosphate buffer for all pH ranges and will be able to measure the Zeta potential? And what concentration will be optimum?
Michael Sir, thank you so much for providing the information and the attached papers. Papers are really helpful.
So just to confirm I need to use KCl based system or just pure KCl system to prepare my dillutions?
Farooq sir I want to see stability and charge present on particle at various pH to understand best conditions and even want to compare one of my coated system. I have particles with amine functionalization which i want to confirm with Zeta that is really amine group present or not.
You cannot measure the zeta potential of a system (particles + environment) without taking into account the chemistry. As you indicate ZnO dissolves in acidic environments. Thus there is no concept of zeta potential in such situations. Take a look at: Guidance to improve the scientific value of zeta-potential measurements in nanoEHS Gregory V. Lowry et al Environ. Sci.: Nano, 2016, 3, 953 - 965
DOI: 10.1039/C6EN00136J
Dear Mithesh. Firs of all, if you are not sure if the particles are dissolving, try to prepare acidic suspension of NP (pH of 2) and monitor it. For example wait for 5 minutes and centrifuge the suspension and if the supernatural is colored, NP most probably dissolve. Also if it is slightly coloured this means that or the particles are small or really small amout of NP dissolves- which is not problem for zeta potential meassurment.
So then you prepare on site the suspension with various pH, measure (this takes about approximately 1 minute - different conditions different measuring time). And you will get your result.
By preparing the solution on site and for each pH separately, you will avoid possible effect of dissolving (if NP dissolve completely).
You really do not need to confirm the fact that ZnO dissolve in acid media. If you need a reference simply take a look in the reference list of our publications dealing with ZnO. I remember a study analysing the dissolving of ZnO layers in PH 4, which I cited in the open access publication.
Concering your question: The salt should screen the particles so that they do not influence each other and so that the hydrodynamic diameter is small. Of course the activty (non ideal behaviour of the concentration) of the solution should be constant which is also ensured if you use inert salts. Especially for the determination of the diameter the concentration should be low.(one scattering event)
Indeed, based on amphoteric nature of ZnO and presense of hydroxide and other groups at its surface, you have to to take into account its solubility both at acidic and alkaline pH as well as adsorption at the surface of the solution components (ions and surface active compounds). It seems you can also find some useful data in the paper Article Stability of ZnO Nanoparticles in Solution. Influence of pH,...
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