Removal of tetracycline in aqueous solution by metastable aluminum cluster ions

Tetracycline (TC), as an antibiotic, is widely used in medical and veterinary fields. However, the misuse of TC has caused significant harm to water bodies and rivers. Traditional Fenton and Fenton-like reactions are limited by a narrow pH range or high cost and low efficiency. In this work, metastable aluminum cluster ions [Al(H₂O)₆³⁺]* produced by Al-water reaction were adopted, which were as direct catalyst to decompose H₂O₂ and generate hydroxyl radicals (HO^•) for degradation of TC in aqueous solution. The effects of H₂O₂ concentration, reaction temperature, TC concentration, pH value, and inorganic salt ions or organic acids on TC degradation were studied. The results showed that [Al(H₂O)₆³⁺]* ions are effective for degrading TC across a wide pH range (2.0–12.0), and 100 % of TC can be degraded in neutral solution. Under optimal condition, TC was completely degraded within ∼1 h and >65 % of total organic carbon was removed after 24-hour reaction. Among inorganic salt ions and organic acids, CO₃²⁻ ions have an obvious negative influence on TC degradation due to quenching HO^•. The result of 10 recycling tests indicated that [Al(H₂O)₆³⁺]* ions have an excellent reusability. The degradation byproducts of TC were determined, indicating that hydroxylation, dehydroxylation, demethylation, amide bond breaking, and ring opening reactions are the main degradation pathways. This study provides a new homogeneous approach for TC degradation.