I prepared copper nanofluid by dispersing copper nanopowder (60-80nm purchased from Sigma Aldrich) in DI water using gum-arabic and sodium citrate. First preparation, the color of the nanofluid was bluish. After that, I needed more nanofluid, so I prepared another sample (using the same materials and following the same procedure) but the color was greenish!
When I did a literature review and asked some chemists, I found that the color must be reddish!
I would be grateful if you help me to overcome this confusion.
Surely it is due to aggregation of nanoparticles and making particles in different sizes regarding to the original ones. You need to pursue the preparation methods. For checking my opinion you may take spectra of your samples, record AFM/TEM/SEM of the samples.
The color of the Cu-based nanofluid changes from greyish black to be dark brown after one day. You should take care the suspension stability of nanofluids.
Thank you all for your response.
Dear Dilip, do you know why the colour of copper nanofluid changes from greyish black to dark brown and why after one day?
I would be grateful if you can explain more.
Not exactly after one day,,,, it may take more time also depending on concentration and surfactant used..........
Dear Aimen Zeiny
I have worked on CU and CuO nanofluids. In your work might be some problem related to stability of nanoparticles in base fluid. The color of Cu nanofluids should be dark brown or it may some effect of surfactant if you are using.
Dear Aimen, the copper get easily oxidized in an aqueous medium due to dissolved oxygen. The green color of copper signifies it got oxidized. The color of the nanofluid will vary with the base fluid as well as presences surfactants and other additives. But, the color of the copper nanofluid must be somewhat near to reddish or brownish. Color change to black also signifies the oxidation.
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