Diameter-Dependent Degradation of 11 Types of Carbon Nanotubes: Safety Implications

Understanding the biodegradation profiles of various types of carbon nanotubes (CNTs) is important for their safe use according to their structural characteristics. To investigate the relationship between the biodegradation and the physicochemical properties of CNTs, sodium hypochlorite was used to degrade CNTs because it is believed to be a key oxidizer of CNTs inside macrophages and neutrophils. The complete degradation of CNTs in response to sodium hypochlorite was confirmed, and the half-lives of 11 different types of commercially available single-wall CNTs (SWNTs), carbon nanohorns (CNHs), and multiwall CNTs (MWNTs) in sodium hypochlorite were determined. The degradation of CNTs generally correlated with diameter, as follows: SWNTs ≥ CNHs > thinner MWNTs > thicker MWNTs. In addition, defects and the degree of dispersion also affected the degradation rate, but these were not the primary factors determining CNT degradation.