Well i am really confused about the fact of dispersing ZnO nanoparticles in an appropriate solvent for taking UV-vis absorbance peak. Many questions have been asked by researchers here in RG but the suggestions are full of ambiguity or inappropriate. Here i am clarifying my confusions and askingthe queries.
1) First of all, do i need to disperse the nanoparticles in a solvent or dissolve it? Many people have mixed up the terms. In my opinion, dissolving a metal oxide will need a strong acid and reactive environment which will eventually alter the structure. So is not it necessary to disperse ZnO in a solvent for taking UV-vis absorbance peak?
2) If i need to disperse ZnO in a solvent, what will be the solvent? Some common suggestions are Distilled/DI water, DMSO, Methanol/Ethanol. What should be the right dispersing medium? Generally ethanol is a better dispersing media than water.
Someone please give me the correct and logical guideline.
Thanks for your time and gratitude in advance.
I hope these responses are helpful! 1) Disperse is the proper process, to preserve the structure of the nano particles. Note that dispersion can be done in both liquid media (solvent, with the assistance of shaking, sonication, etc.) or solid media (such as Barium Sulfate). If in liquid, coordination and hydration can alter the electronic properties. For this reason, I would err toward solid-state UV-VIS, using a standard integrating sphere. Dissolution is common for small molecules or other media. When working with solids and analyzing structure, you will find many referring to 'dispersion' as 'dissolution'. Your opinion in the case of ZnO is accurate (though not all oxides need a strong acid to dissolve in water, e.g. Cs2O! ZnO dissolution into water by reaction with HCl will form soluble Zinc Chloride, which isn't ZnO for analysis.) 2) If you need a liquid state solvent, you are correct that there are many choices. The influence of your material's physio-chemical properties, however, dictates the dispersion stability. Unstable dispersion will have changing optical properties, and introduce artifacts in your measurement. For this reason, I suggest your solvent be solid Barium Sulfate powder, and you disperse the NP by mixture there before measurement. This will allow you to preserve the structure of the ZnO without inducing coordination electronic changes or risk instability in the dispersion. This link from Shimadzu covers some basics of the technique. I've also included an application note for TiO2 band gap measurement. https://www.shimadzu.com/an/uv/support/fundamentals/integratingspheres.html Best of luck on experiments!
It is a generic problem especially if you are working on Nanoparticles synthesis. Curtis Guild has nicely explained the question and it is correct. However, I would like to add one more thing added with his answer that ----in case of nanoparticles your synthesis process exclusively holds the right for its proper solvent.
For example- if particles are the product of the co-precipitation method then the solvent is different then the product of the salvo-thermal process.
basically particles nature and charge on it govern the solvation tendency and therefore the judicious selection is "an art of basic science".
For UV-Vis spectra. , you just need to disperse .
for ZnO, Ethanol/IPA are best dispersants.
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