Insights into the Mechanism of Ozone Activation and Singlet Oxygen Generation on N-Doped Defective Nanocarbons: A DFT and Machine Learning Study

N-doped defective nanocarbon (N-DNC) catalysts have been widely studied due to their exceptional catalytic activity in many applications, but the O-3 activation mechanism in catalytic ozonation of N-DNCs has yet to be established. In this study, we systematically mapped out the detailed reaction pathways of O-3 activation on 10 potential active sites of 8 representative configurations of N-DNCs, including the pyridinic N, pyrrolic N, N on edge, and porphyrinic N, based on the results of density functional theory (DFT) calculations. The DFT results indicate that O-3 decomposes into an adsorbed atomic oxygen species (O-ads) and an O-3(2) on the active sites. The atomic charge and spin population on the O-ads species indicate that it may not only act as an initiator for generating reactive oxygen species (ROS) but also directly attack the organics on the pyrrolic N. On the N site and C site of the N4V2 system (quadri-pyridinic N with two vacancies) and the pyridinic N site at edge, O-3 could be activated into O-1(2) in addition to O-3(2). The N4V2 system was predicted to have the best activity among the N-DNCs studied. Based on the DFT results, machine learning models were utilized to correlate the O-3 activation activity with the local and global properties of the catalyst surfaces. Among the models, XGBoost performed the best, with the condensed dual descriptor being the most important feature.

Automated summary

In this study, the O-3 activation mechanism and active sites of N-doped defective nanocarbon catalysts in catalytic ozonation were systematically investigated using density functional theory calculations. The results revealed the decomposition mechanism of O-3 and identified the N4V2 system as the most active catalyst. Furthermore, machine learning models were applied to correlate the O-3 activation activity with catalyst surface properties, with XGBoost performing the best and the condensed dual descriptor being the most important feature.