Efficiency and mechanisms of tetracycline removal from water by enhanced peroxymonosulfate activation via carboxylated Fe2+
The persistence of tetracycline (TC) in aquatic environments poses significant ecological risks. This study developed a homogeneous reaction system based on carboxylated Fe2+ enhanced peroxymonosulfate (PMS) activation, using citric acid (CA) as a ligand. Carboxylation improved Fe2+ stability and catalytic activity, while solid PMS served as the oxidant, circumventing issues of traditional Fenton processes such as H2O2 instability, complex heterogeneous catalyst preparation, high disposal costs, and toxic metal leaching. The acidic pretreatment enabled by CA inhibited Fe2+ oxidation and promoted sustained PMS activation without external energy input. Under optimized conditions (TC 5 mg·L−1, Fe2+ 0.02 mmol·L−1, CA 0.001 mmol·L−1, PMS 2 mmol·L−1), 88.80% TC degradation was achieved within 60 min. Mechanistic studies revealed that CA protected Fe2+ active sites via carboxyl coordination, facilitating continuous generation of reactive species, including singlet oxygen (1O2) and sulfate radicals (SO4•−). 1O2 was the dominant species (50.5% contribution), followed by SO4•− (35.7%), synergistically driving efficient TC degradation while significantly reducing iron sludge production. Phytotoxicity assays confirmed that treated water exhibited no significant toxicity to wheat seedlings (P > 0.05), indicating effective ecological risk elimination. This work provides a low-energy, operationally simple, and environmentally friendly technology for antibiotic-contaminated water treatment, with promising practical application potential.