Regulation of defects and nitrogen species on carbon nanotube by plasma-etching for peroxymonosulfate activation: Inducing non-radical/radical oxidation of organic contaminants

The structural defects and heteroatom dopants of carbonaceous materials play critical roles in their activation of peroxymonosulfate (PMS) for organic pollutants' removal. This study uses plasma-etching technology to control the levels of structural defects and nitrogen species in nitrogen-doped carbon nanotubes (N-CNTs) for excellent PMS activation. The vacancy defects, CO, pyrrolic N and graphitic N could be rationally designed by controlling the plasma-etching time. Obviously, the ID/IG (from 0.56 to 0.94) and CO contents (from 0.07 to 0.44 at%) of N-CNTs increase with rising etching time, exhibiting good linear positive correlations with phenol oxidation rates. Furthermore, through active species identification, quantitative structure-activity relationships analysis and theoretical calculations, vacancy defects (adsorbing PMS O1 site) and CO are confirmed to be the active sites for the generation of 1O2, which is major pathway (82%) for phenol degradation. While radicals induced by pyrrolic N and graphitic N adsorbing PMS O2 site are the minor pathway (18%). Overall, this study sheds new light on the crucial roles of defects and N species in inducing PMS non-radical/radical activation by carbocatalyst via efficiently controlled plasma-etching technology.