Mn-Cu co-doped graphitic carbon nitride accelerates permonosulfate to generate more singlet oxygen in pollutant degradation

Abstract

Graphitic carbon nitride (g-C3N4), a nitrogen-rich polymeric semiconductor, has gained significant attention as a photocatalyst. However, its potential to activate permonosulfate (PMS) has been somewhat limited. Prior research has demonstrated that manganese-doped g-C3N4 can effectively activate PMS to degrade pollutants, with Mn3+ playing a pivotal role. Consequently, enhancing the Mn3+ content within the system is of paramount importance. In this study, we developed a novel class of manganese‑copper doped g-C3N4 materials using a hydrothermal-calcination process. The optimized material, denoted as Mn5Cu5-CN, was synthesized at a Mn/Cu molar ratio of 1:1. When applied to degrade a model contaminant, acetaminophen (ACP), the Mn5Cu5-CN/PMS system demonstrated remarkable efficiency, degrading nearly 20 mg/L of ACP within 30 min (material dosage = 0.4 g/L, PMS concentration = 2.0 mM). The Mn5Cu5-CN exhibited favourable performance across a broad pH range. Singlet oxygen (1O2) was identified as a major player in the degradation of ACP. X-ray photoelectron spectroscopy (XPS) analyses revealed that the cyclic redox reactions of Mn3+/Mn4+ and Cu+/Cu2+ led to the abundant generation of 1O2. Superoxide (O2•-) was identified as an important intermediate product in these processes. Additionally, the g-C3N4 present in the material also facilitated the generation of reactive oxygen species (ROS). This study provides a fresh perspective on the utilization of g-C3N4 for pollutant degradation, highlighting the potential of MnCu doped g-C3N4 materials in environmental remediation.