Influence of pH and surface oxygen-containing groups on multiwalled carbon nanotubes on the transformation and adsorption of 1-naphthol.

The pH-dependent behavior, including the transformation of 1-naphthol by oxidative polymerization to form precipitates in solution and the adsorption of 1-naphthol onto carbon nanotubes (CNTs), was examined. Neglecting the precipitate loss of 1-naphthol and possibly of similar chemicals may result in the overestimation of their adsorption and inadequate interpretation of the underlying adsorption mechanisms. Surface oxygen-containing groups on CNTs and the dissociated species of these groups can interact with the dissociated and neutral species of 1-naphthol in a way similar to polymerization, thus promoting the adsorption of 1-naphthol onto CNTs. Adsorption onto CNTs may reduce the polymeric precipitates of 1-naphthol in solution by possibly decreasing aqueous 1-naphthol concentrations. These observations and the underlying mechanisms are important for predicting the fate and risks of naphthalene and carbaryl in the environment because 1-naphthol is a primary metabolite of naphthalene and carbaryl. In addition, it is possible to enhance the removal of 1-naphthol and similar chemicals by controlling the pH and designing specific surface functional groups for CNTs.