I am trying to disperse ZnO nanoparticles (APS < 60 nm) into chloroform. But after sonication (about 15-20 minutes) sometimes the NPs get agglomerated in form of huge chunks of masses and get stick to inside surface of the flask. What may be the possible reason for this? Photograph attached.
I would suggest diluting the concentration of ZnO and using less sonication power/ time. Also, are you sure that its ZnO that is agglomerating? it might be some sort of sonochemistry modifying ZnO.
Thank you sir for your suggestions. Yes I tried with different concentrations and time of sonication but could not draw any conclusion as this happens randomly. Can you suggest me what concentration would be safe to avoid this.
I have not tried to characterize it assuming it was lump of Nanoparticles. I will have to check if there is some sonochemical changes occurring.
What is the concentration that you are using? I have worked with carbon nanotubes, and the lowest concentration for them in water was around 0.5 wt% (if i remember correctly).
At higher concentrations, i believe that two things are happening simultaneously. More and more nanoparticles are being sepearated from the agglomerates. On the other hand, suspension is becoming more and more crowded with nanoparticles. so the distance between particles is decreasing. According to DVLO theory, at a certain point and van der waals attraction will be too strong and they will agglomerate again. This is what i think is happening. maybe someone else can comment according the his/her experience. I would suggest start from 0.1 wt % and increase until the agglomeration can be seen.
Some points which might be considered: temperature (increase), match between the dispersing medium and the surface of the particles, what is originally on the surface of the particles ((acetic acid?)charge stabilization will not be optimal in your dispersion medium, is the "modification" alternated by the process)). Some hinds to analyze the surface might be found in the publication.
Article Synthesis and testing of ZnO nanoparticles for photo-initiat...
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