Different methodologies for synthesis of nitrogen doped carbon nanotubes and their use in catalytic wet air oxidation

In this work, a comprehensive study was performed regarding the incorporation of N-groups into the multi-walled carbon nanotube sp2 network, namely, quaternary nitrogen, pyrrolic and pyridinic groups. An easy to handle, solvent-free post-doping method, combining a mechanical treatment under ball-milling followed by thermal treatments under inert atmosphere or ammonia was developed. Different nitrogen precursors (melamine, urea, NH3), different precursor/CNT ratios, presence of O-containing surface groups and final temperatures of the thermal treatment were evaluated towards the generation of active and stable N-species. The materials were characterized in terms of texture and surface chemistry by several techniques: N2 adsorption, XPS, TPD, TGA and elemental analysis. The catalytic performance of the novel N-doped CNTs was evaluated in the oxidation of oxalic acid and phenol (used as model pollutants) by catalytic wet air oxidation (CWAO). Catalytic oxidation of model pollutants is faster in the presence of samples rich in nitrogen, and also favoured in the absence of O-containing surface groups on the CNT surface.