Revisiting the influence of chemical oxidation on the adsorption properties of carbonaceous materials with different structures: Non-dispersible versus dispersible structure

Abstract

Chemical oxidation is often used to modify the surface properties of carbonaceous materials and improve their environmental benefits in removal of organic pollutants. However, there are some controversial observations and explanations about the influence of chemical oxidation on the adsorption performance of carbonaceous materials that need to be revisited. We studied the influence of chemical oxidation on the adsorption of methylene blue (MB) and bisphenol A (BPA) as model compounds on activated carbon (AC) and carbon nanotubes (CNTs). The kinetics results showed that chemical oxidation prolonged the adsorption of MB and BPA on AC and CNTs, and it accelerated the overall adsorption on CNTs. The adsorption of BPA on oxidized AC was weaker, whereas that of MB was stronger. Furthermore, oxidation treatment of dispersible CNTs greatly increased the adsorption rate and capacity of the CNTs for BPA. The adsorption kinetics and capacity of AC and CNTs are closely related to their structural characteristics (non-dispersibility vs. dispersibility). 1H NMR relaxation measurements showed that the dispersibility of oxidized CNTs can be increased in a liquid environment. After oxidation, significantly more adsorption sites are exposed, which are responsible for the increased sorption capacity and adsorption rate. This work clarifies the structural dependence of the adsorption performance of modified carbonaceous materials via chemical oxidation.