Hello all,
I've been trying to functionalise some CNTs with a carboxylic acid side-chain but I've been having difficulty with my end-product, resulting in negligible yield.
My current protocol is based off a previous publication; 100mg of CNTs are refluxed in HNO3 (70%) for 10 hours at 110C. Afterwards I'm left with a homogenous black suspension. I left it covered over night to allow the CNTs to deposit at the bottom of the flask and to remove the supernatant.
I noticed that the CNTs appear to be much smaller than what I originally had, and through centrifugation and washing in attempt to achieve a neutral pH, a large quantity of the potential yield is being lost.
Can anyone propose alternative methods or a potential change in this method?
Regards,
Edit: I do not have access to certain equipment, such as vacuum ovens, a CVD. I'm limited to basic chem equipment and on a tight budget.
My first thought is you're using a too high concentration of nitric acid. Why don't you try milder conditions and see if you get higher yields?
Or you could use milder oxidants such as (NH4)2S2O8.
have a look at this reference
Firstly it depends on the CNTs you are using. Some are weaker and some are stronger (according to the tube crystallinity and the wall number). If the CNT's quite weak then less concentrated HNO3 (try 3M) can be used for 6 hours. Or if you want to use the 70% one then limit the treatment for 1 hour and wash afterwards.
I think you used a hard condition in your work that CNTs can be damaged, because SWCNTs are more vulnerable compared to MWCNTs, is better that CNTs be refluxed in milder condition such as HNO3 (70%) for 8 hours at 70C.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4287712/
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