A study of oxidizing centers in carbon nanotubes by solid-state NMR

Abstract

Functionalized carbon nanotubes (CNTs) play an important role as catalysts in several oxidation reactions. Active centers, present in a catalyst, are mainly associated with oxidizing functional groups. Therefore, determining the concentration of oxidizing centers from the various functional groups present on the surface of CNTs is very important, but it is yet to be achieved. In the present study, solid-state NMR SSNMR techniques were employed to study the adsorption behavior of trimethylphosphine (TMP) in CNTs using TMP as a probe molecule. The results show that TMP gets oxidized to TMPO (trimethylphosphine oxide). The concentration of oxidizing centers was also selectively measured in the order of sub-mmol per g, employing SSNMR. The oxidizing centers comprise a very small portion among the various functional groups present on the surface of CNTs. The concentration of oxidizing centers was found to increase as the degree of functionalization of CNTs increased. Further studies are required to understand the exact structure of oxidizing centers present in CNTs.