Stabilized N coordinated Cu site in catalytic ozonation: The efficient generation of [rad]OH induced by surface hydroxyl groups based on the Lewis acid site

Abstract

Simultaneously maintaining perfect activity and stability of materials in catalytic ozonation system has always been an insurmountable challenge. Embedding metal ions in g-C3N4 in the form of coordination bonds made it possible, because the distinctive tri-s-triazine structure of g-C3N4 was beneficial to the expose of active sites and fixation of metal ions. A Cu doped g-C3N4 material was synthesized by a simple pyrolysis method. The material presented a 16 times enhancement of rate constants in comparison with ozonation and high stability with limited Cu leaching in the catalytic ozonation system. Owing to the positive linear relationship between Cu-N contents and rate constants, the Cu-N active site was revealed. Unexpectedly, the Cu-N site as the Lewis acid site did not directly catalyze O3 to generate OH, but relied on the surface hydroxyl groups to carry out according to the experimental and theoretical studies. It differed from the traditional catalytic path of the Lewis acid site. Finally, a novel catalytic mechanism that the Cu-N site as the Lewis acid site induced the surface hydroxyl groups, thus promoting the generation of OH by catalyzing O3 was proposed. This work would provide a new way to optimize and modify the materials equipped with Lewis acid site in catalytic ozonation system.