I have been trying to synthesize copper nanoparticles in open atmosphere by reducing copper nitrate using NaBH4 and using collagen as a capping agent. I had few doubts regarding the order of addition of the reagents:
1. Initially pH of the copper nitrate solution was increased to 10 and then addition of collagen was performed.I let the solution stir for 60mins and then added NaBH4 but after some 10 mins, I could observe black color copper oxide precipitate. What could be the reason behind this? Since capping agent was added there should be no formation of copper oxides.
2. Or was my order of addition of reagents not proper?
3. Using another method, after changing the pH of copper nitrate solution I added some two drops of NaBH4 to copper nitrate solution and then immediately two drops of collagen. In this way I kept on adding some amount of NaBH4 and some amount of collagen intermediately. But I ended up in forming a dark green color solution (Which doesn't mean formation of copper nanoparticles)
4. Can someone point out the mistake I have been making? For effective yield,should I consider the critical micelle concentration of collagen in Cu(NO3)2 solution? How do I go finding about the CMC?
5.Can I add some amount of LiAlH4 and then some amount of NaBH4 and use these two reducing agents intermediately?
I have been using 0.1M Cu(NO3)2 and 0.5M NaBH4 and 1 M NaOH (for pH change.) I have been perfoming drop wise addition of NaBH4 till color of the solution changes to reddish brown.
How do you confirm that the particles formed are copper oxide? Did you characterize the precipitate/particles formed due to the addition of NaBH4?
As we know, the color of solution containing colloids varies depending on the size of the solid particles dispersed in the liquid. Most common and popular example is the colloidal solution of metallic gold.
By changing the condition of synthesis, for example, using capping agent or changing the order of addition of capping agent, I think the size of particles formed changes, resulting in different color. Therefore, without characterizing particles formed with some spectroscopic technique (surface plasmon) or XRD or any other relevant techniques, the answer of your question is not straightforward.
MMI
I was sure that the precipitate formed is of copper oxide because it has been mentioned in many of the research articles that " brown precipitate indicates the presence of copper nanoparticles". But what you are saying also sounds correct. I will try to verify it using xrd and other relevant methods.
Dear Bhubesh,
I agree with your 1st Situation its formation of copper oxide particles. As per my experience in copper nano particles formation its is quite difficult to synthesis in open atmosphere as Cu immediately react with atmospheric Oxygen before capped with your collagen. I suggest to use Microwave for rapid formation of CuNP with other reducing agent.
now regarding your 2nd query of Green color particles I seen that the before formation of Red/brick red color CuNP green color particles forms it means that you reach up to 1000 nm but due to some amount of uncapped Cu, atmospheric O2 and less amount/concentration of reducing agent its not reached less than 1000 nm.
From my suggestion synthesize in inert atmosphere in spite of open atmosphere with calculated capping agent:Cu atom ratio for more stability and less particles.
Best of Luck
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