Can anybody please tell me color of cobalt nanoparticles synthesised in ethylene glycol? or what is generally color of cobalt nanoparticles?

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Muhammad Ismail Popular answer

Dear Manoj Yadav

The color of your cobalt nanoparticles will be probably grayish..........For detailed please see the article.

Materials Sciences and Applications, 2011, 2, 1307-1312

Muhammad Ismail

Manoj Yadav

Thank you...but bulk cobalt looks greyish ..and i guess Co NPs should look different in colour from them.

Aaron Bloomfield

The color will depend on the size: very small particles may have plasmonic resonance with visible light. When I have made them previously (big, r ~100 nm) the color is very dark grey, almost black.

Thank you @ Dr. Aaron Bloomfield for sharing experience ... Now, I have understood and I have done colloidal synthesis of a Co-NP sample which shows black colour in solution. But only concern which my supervisor was telling me that there may some cobalt oxide NP also.

Lotanna Ezeonu

Hi Manoj,

I have been synthesizing Co NPs for some time now and my observation is that one has to try as much as possible to carryout the synthesize in an airless system otherwise the colour of the colloidal suspension may change indicating either oxidation or increase in size of the Co NPs

Yes, thanks sharing experience and what you said is correct, Lotanna!

By the way, I have had challenges with preventing the oxidation of my Co NPs during synthesis even after deaerating my 3necked flask by a vacuum pump (prior to addition of my reductant) and flowing N2 gas over the colloidal suspension of my Co NPs.

Please can anyone recommend something that may help me prevent oxidation of my Co NPs in aqueous solution?