Do we need to wash the commercial CNTs with conc. Nitric Acid before use?
Yes. If you make it activated by conc. HNO3, then it will be more dispersed in water than its pure form. This is because after CNT treatment its surface will be oxidized to -COOH.
If you don't want to activate, you should use surfactant to make it disperse.
Depends of the proposal of application. When you wash the CNT's wiht nitric acid, defects are inserted on the surfaces of the tubes.
Indeed you have to wash with nitric acid to avoid from CNT forming aggregates
Well, as Wellington Marcos Silva said, it really depends on what you need those CNTs for. And what type of CNTs do you have? Multi-walled CNTs usually already have more defects than single-walled CNTs on the surface so they have a higher risk of being oxidized. On the other hand, single-walled CNTs are very sensitive to doping and nitric acid is a very strong dopant for them. So if you’re interested in their electrical properties, then you should apply a mild nitric acid treatment and consider removing it afterwards via a heat treatment, or use a non-oxidizing acid for purification and avoid this problem. Acid washing is usually done to remove catalyst impurities from your CNTs. There are other ways you can do that, if that is what you’re trying to remove.
If you just want to prepare a dispersion of CNTs then using a surfactant and a centrifuge is enough since it will already separate your tubes from other impurities. And multi-walled CNTs can be dispersed in some common solvents without the addition of surfactant. If you do want to functionalize your tubes, you should probably try to control the amount of defects you’re introducing.
We used acid washing to remove metal catalyst impurities and amorphous carbon from CNT materials. Unfortunately, one cannot remove all metal nanoparticles, because part of these are embedded within graphene layers in the CNT material. Indeed, surface oxidation occurs during acid treatment of carbon nanotubes. Nitro groups could be introduced to the surface of CNTs by nitric acid treatment.
We investigated the effect of acid treatment on the electrocatalytic activity of carbon nanotubes towards oxygen reduction. See, for example, N. Alexeyeva, K. Tammeveski, Electrochemical reduction of oxygen on multi-walled carbon nanotubes modified glassy carbon electrodes in acid media, Electrochemical and Solid-State Letters 10 (2007) F18-F21; I. Kruusenberg, N. Alexeyeva, K. Tammeveski, J. Kozlova, L. Matisen, V. Sammelselg, J. Solla-Gullón, J.M. Feliu, Effect of purification of carbon nanotubes on their electrocatalytic properties for oxygen reduction in acid solution, Carbon 49 (2011) 4031-4039.
The purpose of using acid to treat CNTs is to purify the CNTs by removing the metal catalyst, and to functionize CNTs with functional group such as -COOH or -OH group to improve the dispersion CNTs in water or organic solvent. The downside is that it will introduce oxidative defects on sidewall due to the attach by conc acid to break up CNTs into small segments, which will be detrimental to the conductivity properties of CNTs.
Liang Tian Thank you for the paper that you refer me!! I think it is connected with my study.
I have asked a question before about my the peaks of my cyclic voltammogram. I hope you are familiar - https://www.researchgate.net/post/What_does_this_peak_in_cyclic_voltammogram_mean
Is it possible that the peaks in cyclic voltammogram are due to the defects present in CNT (Sample is cellulose with carbon - the carbon I'm refering to is CNT)?? Because you have said in your paper that cleaning CNT will introduce oxidative defects. It possible that's the reason.
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