Influence of different heat treatments on the surface properties and catalytic performance of carbon nanotube in ozonation

The influences of treatment conditions, gas atmosphere (N₂ and H₂) and temperature (450°C and 950°C), on the surface properties and catalytic performance of carbon nanotube (CNT) were investigated for the degradation of oxalic acid in aqueous solution by the process of catalytic ozonation. No obvious change on the textural properties of CNT is found after heat treatment, while the results of Boehm titration clearly indicate the reduction of acidic groups and the increase of basic groups on CNT surface after heat treatment under different conditions, and then a significant improvement on oxalic acid removal by CNT catalytic ozonation is obtained. The heat treatment of CNT under H₂ atmosphere is more effective in eliminating acidic groups and increasing basic groups than the case of N₂ atmosphere at the same temperature, which results in higher catalytic activity and lower total organic carbon (TOC) release in ozonation correspondingly. A linear relationship is observed between the pH at the point of zero charge (pH_PZC) of CNT and the rate constant for ozonation of oxalic acid in the presence of CNT with different treatments. It is suggested that heat treatment can increase the basic property of CNT, which can enhance the contribution of surface reactions to the whole reactions for ozonation of oxalic acid.