Chirality control is one of the biggest challenge in the field of carbon nanotubes. However synthesis of controlled chirality is possible experimentally. One way to separate metallic from semi-conducting nanotube is ultra-centrifugation of nanotube in the liquid environment. Lately, people have also synthesized in-situ growth of precise chiral controlled nanotube by using sulphur and/or  metals during the CVD process. There are many articles on that. I am attaching one review article.

http://www.nature.com/nature/journal/v510/n7506/full/nature13434.html 

Dear Shashank Shekhar,

Thank you very much for your reply and the attached link.

Best regards,

Dr Brahim Attaf

This may also be of interest:

http://iopscience.iop.org/article/10.1088/0957-4484/14/6/317/pdf