Diameter dependent degradation of single walled carbon nanotubes

This study investigates the degradation of single walled carbon nanotubes via chemical method (3: 1 ratio of sulfuric acid to nitric acid) and enzymatic method by Horseradish peroxidase (HRP). Two sets of carbon nanotubes (CNTs), pristine and carboxylated (functionalized) CNTs were used for degradation studies. Chemical degradation of CNTs was conducted using pristine CNTs whereas enzymatic degradation by HRP was conducted using both pristine and carboxylated CNTs. Chemical degradation of pristine CNTs was observed within one hour whereas enzymatic degradation of carboxylated CNTs was observed after 20 days. No observable degradation was noticed for enzymatic degradation of pristine CNTs. The CNT diameter dependence for degradation was studied using Radial Breathing Mode (RBM) of the Raman spectra for CNTs[1]. Three distinct RBM peaks corresponding to three different diameter CNTs were observed, i.e. the sample contained at least three different types of CNTs varying in diameter. It was observed that smaller and medium diameter CNTs were degraded more than the larger diameter CNTs via chemical degradation whereas a reverse trend of larger diameter CNTs being degraded was observed for enzymatic degradation.