4-Nitrobenzaldehyde removal by catalytic ozonation in the presence of CNT

4-nitrobenzaldehyde (4-NBA) degradation pathway was studied during single and catalytic ozonation processes. Multi-walled carbon nanotubes (CNT) were used as ozonation catalysts and different textural and chemical modifications were performed to obtain samples with enhanced catalytic activity (CNT(BM) and CNT-M(BM 4 h)). Single ozonation was capable of total pollutant degradation after 180 min of reaction; however, complete mineralization was not achieved, reaching nearly 40 % of total organic carbon (TOC) removal. Catalytic ozonation presented a faster pollutant removal rate, and a high content of organic matter was removed in the first 30 min of reaction. For this specific case, the incorporation of nitrogen heteroatoms in the CNT structure (sample CNT-M(BM 4 h)) did not actively contribute to increasing the performance of the material, achieving a mineralization degree very similar to that obtained with the commercial catalyst (CNT) at the end of the reaction. The most promising catalyst was the ball-milled sample, CNT(BM), attaining 60 % of mineralization degree after 180 min of reaction. The catalyst CNT(BM) proved to be stable even after several reuses, presenting a loss of efficiency of 15 % in terms of TOC from the first to the fifth cycle. Radical scavenger experiments revealed that there is a significant contribution of OH center dot radicals during single ozonation, whereas for catalytic ozonation process the reaction mechanism is quite different with less involvement of OH center dot radicals in solution and a large contribution of the pathway involving adsorption and surface reactions.