OK - we know little about your CNTs - not even whether your catalyst is still 'on board' or removed.

On the other hand, seems you missed a quite good source of information: wikipedia

https://en.wikipedia.org/wiki/Carbon_nanotube#Electrical_properties   clearly states that you could have 'metallic' behavior (which I'd cenominate - not completely correct - as n-type conduction) as well as several kinds of semiconducting behavior.

The paragraph starting with "Due to the role" is quite interesting - stating that adsorbed alkali metals result in n-type conduction. And hydrogen can easily be assessed to behave similar to alkali metals - even if not denominated a such. Searching a bit about experiments with alkali metal absorption might come up with a deeper insight into the conductivity modulation mechanisms.

Regards

Mr. Natheer,

Adding to Dr. Dreher,,

From the conceptual point of view, the enhancement of conductivity can be due to either an increase in the carrier concentration or an increase in the mobility. I think  the increase in the mobility due to the attachment of hydrogen to the graphine manotube atoms is not probable due to perhaps the additional scattering at the surface of the nanaotubes. So, one may expect that the electron concentration increases with he the attachment of hydrogen as hinted by Dreher.

In case of the decrease of the conductivity it is expected also that the attachment of the oxygen as an electron acceptor will decrease the electron concentration and thereby decrease the electron concentration reducing the conductivity.

Nitrogen may also capture electrons when attached to carbon reducing also he electron concentration.

More investigations and search in the literature to verify these mechanisms.

wish you success 

I am grateful to all of you to pay attention

Thank you Dr Abdelhalim

Can you give me some referance about this subject?

Thank you