It depends on the the wall structure of your CNT also. Try just nitric acid as Murat said. We refluxed it in there for 2-15 h depend on the raw CNT and the application.

We used centrifugation for washing. It is working fine until the ionic strength of your soulition is enough high to precipitate the funcionalized CNTs. We keep such properties at high with adding a small amount of HCl to the suspension before centrifuging (which is gone after by the drying process).

If u wanna be sure to get -COOH, that case u can use a KMnO4/HClO4 treatment after the acid treatment at RT, freezed by citric acid.

For the first one, I have understood that the first step to functionalize the carbon nanotube is always using strong acids, like the way you describe...

And for the second one, I think that maybe you can dilute (in water) the mixture of acids to avoid the degradation of the filters.... I am just guessing...

I agree with Jose Salazar. I also faced the same problem while functionalizing the CNT. Other options are usage of dilute agents like H2O2, but it can produce only -OH functionalities.

I'm now trying to do in a low temperature to avoid the cnt being degraded by the acids. hopefully it works. I've tried using citric acid functionalization before but the FTIR results are just so poor.

I used only concantrate nitric acide in ultrasonic bath during six hours. Then filter with filter paper and store in acetone. After that process i used cnt to electrodeposition.

It depends on the the wall structure of your CNT also. Try just nitric acid as Murat said. We refluxed it in there for 2-15 h depend on the raw CNT and the application.

We used centrifugation for washing. It is working fine until the ionic strength of your soulition is enough high to precipitate the funcionalized CNTs. We keep such properties at high with adding a small amount of HCl to the suspension before centrifuging (which is gone after by the drying process).

If u wanna be sure to get -COOH, that case u can use a KMnO4/HClO4 treatment after the acid treatment at RT, freezed by citric acid.

Hi Brayan ,

Did you found any approach?I have same problem.

See this question please:

https://www.researchgate.net/post/Anyone_have_experience_treating_CNTs_with_H2SO4_HNO3_mixture_31_sonication_for_4_H

Dear Bran & All Question followers..

As I just started my project on CNT functionalization, can you please help....

How feasible is the treatment of mix acid to functionalize the CNTs? (% of functionalization)

How to filter the functionalize CNTs from acidic solution? (what kind of filter & filtration process)

How to preserve the functionalize CNTs?

Thanks & Regards,

Vishal

I want to highlight that base wash is a crucial step after acid treatment. Because the oxidation debris is produced by acid treatment, and they will somehow prevent CNT itself from functionalization in the next step. And in acidic and neutral environment oxidation debris prefer to attach on the outer wall of CNT via pi-pi stacking. They can be removed from the surface of CNT due to the deprotonation of carboxylic group in alkaline solution.

See：http://pubs.acs.org/doi/abs/10.1021/ja906267g

Hi, guys is it important to use a polycarbonate membrane. Is it okay to use a regular membrane?

Thank you

what is important of functionalized carbon nanotube?

Dear all, i have one basic question regarding functinalization of carbon nanotubes with 3:1 acid mixtures(H2SO4:HNO3).  After functionalization of carbon nanotubes we found only oxygen functionalities such as (-COOH, -OH etc), but why not -NO2 group? because we are using conc.H2SO4 and CONC.HNO3 acids?

HNO3 + H2SO4 ---- NO2+ + H3O+  + 2HSO4-

@kaptan, the importance of functionalization can be attributed to increase the oxidation properties of CNTs. Also, with funcitonalized groups like -COOH, =C-O, the proportion of conductive nano-tubes to semi conductive nano-tubes increases.

It is better to use dilute solutions of this mixture, to avoid both issues. 

hello

How to make centrifuge if this corrosive solution? tubes will be destroyed!!!!

Is it possible to functionalize PLA by using 3:1 acid mixture by using microwave synthesis process to get carboxylated PLA.