MnNx-Carbon-Silica-Framework for highly efficient heterogeneous catalytic ozonation of electron-rich organics through nonradical pathway

Abstract

Heterogeneous catalytic ozonation (HCO) is considered as a powerful technique for wastewater treatment, whose pathway of removing organics could be adjusted by tuning the active sites of catalysts. The traditional hydroxyl radical pathway could be affected by wastewater matrices. In comparison, nonradical pathways such as 1O2 pathway and intra-electron–transfer pathway provide a promising solution to electron-rich organics degradation avoiding the impact of matrices. In this study, we proposed MnNx loaded Carbon-Silica-Framework (MnNx-CSF) as an efficient catalyst with stable mechanical strength to selectively remove electron-rich organics through HCO. The TOC removal for p-HBA was up to 81% in MnNx -CSF HCO process within 30 min, while only 44% and 22% of TOC were removed in the Mn-SiO2 HCO process and ozonation process, respectively. The N species were confirmed to be related to the catalytic efficiency. Specifically, the pyridine N and graphitic N were the relevant active N species in MnNx-CSF. The pyridine N could coordinate with Mn atoms to form the active site MnN4, demonstrating a high tendency to adsorb O3 and decompose it into 1O2. The graphitic N could further enhance the electron transfer pathway to degrade organics. Modulating N species to coordinate with metal is considered to be a possible strategy for regulating the catalysts to achieve the catalytic ozonation process through a nonradical way. With a combination of experiments and theoretical calculations, the study provides a new insight for catalytic ozonation of electron-rich organics through 1O2 pathway and intra-electron-transfer pathway.