You can try steam method..

pubs.acs.org/doi/pdfplus/10.1021/jp0631883

But, depending upon the location of Fe nano particles, some of them may leach out..

Other alternative is thermal annealing in Ar or other inert atmosphere.. this will graphitize most of the amorphous carbons..

Now coming to electrochemical performance.. presence of amorphous carbons are reported to be beneficial.. refer papers by Prof. Pumera of NTU ex: 10.1021/ac4010748 and others from his group..

You can try oxidation below 200 C or hydogen peroxide treatment. See papers of Gallego et. al.

(Functionalization of Carbon nanotubes by water plasma)

Http://iopscience.iop.org/0957-4484/23/38/385604/

and

(Nitrogen plasma functionalization of carbon nanotubes for supercapacitor applications)

http://link.springer.com/article/10.1007/s10853-013-7579-z ()

If amorphous-phase and metal-oxide phase can be rendered into separate particles, it may be possible to separate them by magnetic levitation

See for example

http://www.rsc.org/chemistryworld/News/2012/March/magnetic-levitation-measures-protein-binding-for-disease.asp

http://osdir.com/patents/Sorting-solids/Method-separation-plastic-mixtures-based-magneto-archimedes-levitation-06902065.html

For CNT purification. Nitric acid remove amorphous carbon and hydrogen chloride remove iron.

As suggested by others....acid treatment in a mixture of HNO3 and H2SO4 will be the best way to purify CNTs....there is a lot of literature available on this topic.

what about trying CS2?

Heat at about 350 to 400 C in AIR say about for 1 hour, followed by dilute HCL (pH 3 to 3.5) with 20 g/L sodium citriate to dissolve the iron, about 30 minutes at ambient temperature, Repeat until there is no color change. The citrate will complex the iron and speed up the reaction.

Based on some thermogravimetric analyes we had done on CNT product materials, CNTs are somwhat more resistant to oxidation than amorphous carbon. It's possible that the amorphous carbon could be selectively burned off by carefully controlling the temperature and amount of oxygen inside the reaction tube.

Be aware that the oxidation of amorphous carbon will release heat (like hot charcoals) in close proximity of the CNTs which could increase the likelihood CNT oxidation and damage. If the Raman data indicates this, my suggestion would be to reduce the O2 concentration going into the reactor to like 10% or 5% with argon making up the remainder. Some experimentation and patients will undoubtedly be required to yield the best product material.

Viney's suggestion is good. Stick to temperature well below 400oC to avoid burning off SWCNT

Oxidation in air if the best way to remove amorphous carbon with minimal or no modification of nanotubes (see the attached papers). Fe can be removed by HCl treatment after oxidation. Use of nitric acid and other liquid oxidizers may lead to strong side-wall functionalization of nanotubes.

An additional paper

The original question was

"method to remove amorphous carbon without affecting metal oxide (iron) phase?".....

Chemical methods like oxidation with acids, peroxides, thermal annealing in air, etc. will no doubt remove amorphous carbon but it will also affect iron oxide.. so, a better option will be annealing in N2 or some inert atmosphere.. not only will this lead to catalytic graphitization of amorphous C, it will have minimal effect on iron oxide.... and even if it does affect iron oxide, N-doped iron oxides can be very beneficial in applications such as Lithium ion batteries, super capacitors, catalysts etc.

BTW glad to see expert researchers like Prof. Gogotsi contributing in discussions....

My suggestion would be after selectively burning off the amorphous carbon in air, or a reduced oxygen atmosphere, to purge out any remaining oxygen and then introduce hydrogen at about 5%. This should reduce the oxidized iron catalyst.

Thank you all very much for your suggestions regarding my question. I will definitely consider your suggestions, I wish you all the best with your research too.

I did the procedure of Viney Saini in 2005-06 and it had worked fine with me at IISc, Bangalore.

you can pourify your CNT by oxidation by acid, it's depend on your CNTs that which acid could be use.

 Dear Kolla Praveen ,

   Take TG/DT analysis of your material. You should be able to differentiate at which temperature the amorphous carbon and CNT burns to form CO or CO2. Based on that temperature at which the amorphous carbon burns out; heat your sample. It should be able to remove the amorphous carbon present in your CNT sample without affecting other elements. Because amorphous carbon's oxidation temperature is lower than the oxidation temperature of carbon nanotubes.

Hope this will help you.

I used low concentration nitric acid to remove a carbon on CNT.