Electron spin polarization of C-doped carbon nitride enhancing PMS activation for deep degradation of Emerging Contaminants

The poor stability and metal leaching of transition metal-based catalysts for peroxymonosulfate (PMS) activation cause practical challenges in Emerging Contaminants (ECs) degradation. It is necessary to explore non-metallic catalyst with high activity and stability. Herein, carbon-doped graphitic carbon nitride (C-C₃N₄) is synthesized through sample thermal polymerization. The morphology and chemical structure of C-C₃N₄ are analyzed in detail through multiple characterizations combining density functional theory (DFT) calculation. The tetracycline (TC) can be nearly 100% removed in 15 min with the high mineralization rate (∼70%) in 50 min by C-C₃N₄/PMS system. The continuous reaction and recycle using experiments exhibit the excellent stability of C-C₃N₄ and the tetracycline (TC) remove rate still exceeds 80% after 360 min. The high applicability of C-C₃N₄ to different water sources, anions and pollutants is also tested. Qualitative and quantitative analysis of reactive oxygen species (ROSs) proves the enhanced generation of ^•OH, SO₄^•−, ¹O₂. C doping leads to the electron spin polarization and regulates electronic structure thus enhances the electron transfer between PMS and C-C₃N₄. In situ analysis combining DFT calculation identifies that doped C is the active site for PMS activation and dual-site adsorption of PMS on doped C and N‒(C)₂ greatly decreases the energy barrier for ^•OH generation (from 1.52 to 0.27 eV). Fukui function calculation combining the intermediate detection by LC-MS concludes the detailed degradation pathway. This study provides a valuable insight for the development of efficient metal-free catalysts and the deep degradation of ECs through Fenton-like catalysis.