Before drying, I washed the nanoparticles with ethanol and then kept them for drying in an oven by pouring the solution onto a petri dish. After drying for 24 hours, I observed that a white layer had formed above the nanoparticles, whereas the nanoparticles were clearly identified because of their non-white color. Please suggest a suitable explanation for this.
Dear Vivek Chandel, answering your question will require a detailed description of your experimental system, which you haven't provided. There are a few general suggestions:
- analyze the white precipitate experimentally
- do you have any capping polymer used in the reaction? It could be that, and it would make sense that it is "above" the particles.
- some nanoparticles absorb in the VIS range due to the surface plasmon resonance, but this peak is lost upon aggregation. However, the aggregated particles would have to float above your particles according to your description. That is a possible case, but not very frequent, provided the densities of common solvents and nanoparticles.
- is there some other additive in your mixture that may precipitate?
A thin white layer that occurs while drying over desired nanoparticles could be due to agglomeration, precipitation, coagulation and evaporation of a solvent.
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