Constructing boron and oxygen dual coordination in g-C3N4 for robustcatalytic ozonation and iopamidol degradation

Abstract

In this study, a series of boron (B) and oxygen (O) dual doped g-C3N4 (BOCNx) composites with different boric acid dopant dosages were successfully synthesized through one-step thermal condensation method. Amongst, BOCN50 exhibited the best catalytic ozonation activity, achieving 97 % of iopamidol (IPM) degradation within 15 min and the highest k value (0.3166 min−1), which was 8 times higher than that of ozonation alone. Multiple characteristic techniques were used to explore the surface properties of BOCNx catalysts and it was found that B and O primarily coordinated in g-C3N4 as the forms of C-O, C = O and B-N bonds. Further investigation in the structure–activity relationship of BOCNx catalyst indicated that the increasing contents of oxygen-containing functional groups and B-N bonds were linearly correlated with the IPM degradation rate. The results of scavenger experiments and ESR analysis demonstrated that the main reactive oxygen species involved were hydroxyl radicals, superoxide radicals, and singlet oxygen (•OH, •O2− and 1O2). Additionally, up to 12 intermediate products of IPM during the reaction were detected, and the corresponding degradation pathways were elucidated. Finally, the structure of BOCN and the active sites for O3 adsorption were determined by density functional theory (DFT) calculation, thus providing theoretical support for studying the mechanism of catalytic ozonation degradation.