Highly active N-doped carbon nanotubes prepared by an easy ball milling method for advanced oxidation processes

The performance of novel N-doped carbon materials prepared by an easy ball milling method was evaluated in two distinct advanced oxidation processes (AOPs): catalytic wet air oxidation (CWAO) and catalytic ozonation (COZ), using oxalic acid as model pollutant. The ball milling method allows the incorporation of large amounts of N-groups onto the surface of carbon nanotubes, namely pyridine-like N atoms (N-6), pyrrole-like N atoms (N-5) and quaternary nitrogen (N-Q), resulting in highly active catalysts for the oxidation of oxalic acid by both AOPs. The material prepared by ball milling with melamine without solvent is the most promising sample, combining an easy preparation with high amount of N-functionalities. Under the operation conditions used, oxalic acid was completely mineralized in 5 min by CWAO and in 4 h by COZ. The novel metal-free catalyst developed by this easy ball milling method demonstrated to be effective, confirming that this solvent-free methodology is quite adequate for the preparation of N-doped carbon materials with enhanced properties for the mineralization of organic pollutants by the studied processes.