Catalytic performance of heteroatom-modified carbon nanotubes in advanced oxidation processes

Multi-walled carbon nanotubes (CNTs) were submitted to chemical and thermal treatments in order to incorporate different heteroatoms on the surface. O-, S- and N-containing groups were successfully introduced onto the CNTs without significant changes of the textural properties. The catalytic activity of these heteroatom-modified CNTs was studied in two liquid phase oxidation processes: catalytic ozonation and catalytic wet air oxidation (CWAO), using oxalic acid and phenol as model compounds. In both cases, the presence of strongly acidic O-containing groups was found to decrease the catalytic activity of the CNTs. On the other hand, the introduction of S species (mainly sulfonic acids) enhanced the removal rate of the model compounds, particularly in the CWAO of phenol. Additional experiments were performed with a radical scavenger and sodium persulfate, in order to clarify the reaction mechanism. Nitrogen functionalities improve the catalytic performance of the original CNTs, regardless of the process or of the pollutant.

Graphical AbstractCatalytic ozonation and catalytic wet air oxidation of oxalic acid and phenol using carbon nanotubes functionalized with O-, S- and N-containing surface groups.Figure optionsDownload full-size imageDownload as PowerPoint slide