Highly Versatile and Efficient Process for CNT Oxidation in Vapor Phase by Means of Mg(NO3)2‒HNO3‒H2O Ternary Mixture

Nitric acid vapor phase oxidation of carbon nanotubes using Mg(NO3)2‒HNO3‒H2O ternary mixture is proposed as a further development and significant improvement of the method employing the sole azeotropic HNO3 solution. Based on the so-called “salt effect,” the addition of Mg(NO3)2 to HNO3‒H2O solution allows varying the acid vapor concentration within a wide range, even beyond the azeotropic one (>68wt%). Ternary mixture containing 20wt% Mg(NO3)2 and variable amount of liquid HNO3 (30–58wt%) is used for the functionalization process, achieving nitric acid vapor concentrations in the range 25–93wt%. The increase of acid concentration in vapor phase produces a significant augment of the functionalization degree and a linear increase of the concentration of carboxylic acids groups, which can thus be simply tuned.