Degradation performance and mechanisms of tetracycline by 3D anode-driven electrocatalysis synergized anchored Co3O4 nanoneedles activated peroxymonosulfate

In this work, a dual three-dimensional porous system (3D-SFS + CoNN@SFF) with anchored Co3O4 nanoneedles for peroxymonosulfate activation (CoNN@SFF) and coating optimized porous electrodes for electrocatalysis (3D-SFS) coupling is constructed based on SiC foam filler for the degradation of high concentrate tetracycline (TC). The results indicate that the coupled system demonstrates favorable synergistic performance. Its reaction kinetic constant (k) is 2.29, 2.45, and 8.47 times that of the single system of CoNN@SFF, 3D-SFS, and conventional BDD-driven electrocatalytic oxidation. Meanwhile, the energy consumption of the coupled system is low at 0.00151 kWh·g−1. Experiments under different operating parameters reveal that the 3D-SFS + CoNN@SFF system exhibits good performance under multiple anion coexistence conditions or over a wide pH range of 2–10. Furthermore, EPR and quenching experiments reveal that active species hydroxyl radical (•HO), sulfate radical (SO4∙-), and singlet oxygen (1O2) are involved in TC degradation reactions. 1O2 is the most dominant active species, followed by •HO. Based on this, TC degradation mechanisms dominated by 1O2 and •HO are further calculated via density functional theory (DFT). Results show that the dominant initial reaction channels are •OH abstracting hydrogen atom on the hexatomic ring with dimethylamino group (A-ring, OH-RH9) and the addition reaction to a carbon atom on the adjacent ring (B-ring, OH-RC7) with apparent rate constants (kapp) of 2.29 × 109 and 1.52 × 109 M−1s−1. Although it is difficult for 1O2 to attack TC directly, it plays an essential role in the subsequent ring-cleaving reaction of TC. The three most probable ring cleaving pathways with low energy barriers for the rate-determining step are screened, which include reactions of 1O2 addition, •HO2 elimination, ortho-position H-transfer, and •HO addition. This work not only constructs an efficient coupled 3D catalytic system, but also provides a universal reference for the degradation mechanism of TC with •OH and 1O2 as the main active species.