Redox potentials of sulfonamide antibiotics mediating the electron transfer process in single-atom Cu catalyst/peroxymonosulfate system: Selective removal mechanisms for sulfonamides

The oxidative behaviors of target pollutants in single-atom catalysts-activated peroxymonosulfate (SACs/PMS) system has mostly been studied from the loaded metal and coordination structure of SACs. However, the origin of the altered degradation behavior caused by the specific properties of pollutants has been neglected. Herein, Cu atoms coordinated with four N atoms embedded in biochar (Cu_SA30@C) was prepared to establish the relationship between the selective degradation behavior of sulfonamide antibiotics in Cu_SA30@C/PMS system and their own properties. Four representative sulfonamide pollutants (SAs) were selected and their redox potentials were determined by measuring half-wave potentials (φ_1/2). Results showed that a good correlation (R²=0.916) between the φ_1/2 values of different SAs and their corresponding degradation rate constants (k_obs) in Cu_SA30@C/PMS system was established. Additionally, the φ_1/2 values of SAs correlate well with the energy gap between SAs and the Cu_SA30@C/PMS complexes, further proving that the redox potential of SAs played a crucial role for electron-transfer oxidation in Cu_SA30@C/PMS system. This work contributes to the understanding of the selective degradation activity of sulfonamide antibiotics in Fenton-like systems from the perspective of pollutants properties, and provides new ideas for the efficient treatment of sulfonamide antibiotic wastewater.