A research team led by Prof. CAO Hongbin from the Institute of Process Engineering (IPE) of the Chinese Academy of Sciences has revealed the catalytic reaction mechanism of O₃ activation and singlet oxygen (¹O₂) generation on N-doped defective nanocarbons.

This work was published in Environmental Science & Technology on May 26 (DOI: 10.1021/acs.est.1c08666).

Catalytic ozonation is promising for water purification due to its excellent performance in pollutants abatement, which generally relies on the efficient conversion of O₃ into reactive oxygen species. However, the reaction mechanism of catalytic ozonation remains unclear.

In this study, the researchers chose eight representative configurations of N-doped defective nanocarbons (N-DNCs) and 10 active sites, and systematically mapped out the O₃ decomposition processes on these active sites by density functional theory (DFT) calculations.

They found that O₃ could decompose into an adsorbed atomic oxygen species (Oads) and an ³O₂ on the active sites. The Oads may not only act as an initiator for generating reactive oxygen species, but also directly attack the organics on partial sites.

On the N site and C site of the N₄V₂ system (quadri-pyridinic N with two vacancies) and the pyridinic N site at edge, O₃ could be activated into ¹O₂ in addition to ³O₂. The N₄V₂ system is predicted to have the best activity among the N-DNCs studied, said Dr. YU Guangfei from IPE.

Furthermore, based on the DFT results, the machine learning models were utilized to correlate the O₃ activation activity with the local and global properties of the catalyst surfaces. Among several models, XGBoost performed the best, with the condensed dual descriptor being the most important feature. 

"This contribution not only provides insights into the molecular mechanism of catalytic ozonation process on N-DNCs, but also demonstrates the power of combining the DFT calculation with machine learning for predicting catalytic performance of novel materials," said Prof. XIE Yongbing from IPE. "This approach can be extended to search for and design efficient catalysts for environmental and other applications."

Schematic diagram of main research contents in this study (Image by YU Guangfei)

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LI Xiangyu
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