A method for the synthesis of carbon nanotubes from natural rubber, including providing a first material, the first material may include natural rubber or derivatives thereof, thermally decomposing the first material at a first temperature into an intermediate material, contacting the intermediate material with a catalyst, treating the intermediate material in contact with the catalyst at a second temperature, for forming carbon nanotubes. Adjusting an average characteristic of resulting nanotubes, including carrying out the synthesis method as a reference method and for decreasing the average diameter of the nanotube: decreasing the second temperature and/or decreasing the reaction time and/or increasing the concentration of H2 in the forming gas in relation to the reference method. Or, for increasing the average diameter of the nanotube: increasing the second temperature and/or increasing the reaction time and/or decreasing the concentration of H2 in the forming gas in relation to the reference method.