A facile “one-pot” synthesized CaAl MnO4 LDH with a high loading capacity of oxidants for the sustained oxidation of oxytetracycline in soil

Abstract

This study aims to address previous issues such as low payload of sustained release materials and excessive consumption of oxidants by developing novel sustained-release oxidation agents. Through a one-pot synthesis method, MnO4- intercalated Ca-Al-layered double hydroxide (CaAl MnO4 LDH) was synthesized with an oxidant payload of 4.82mmol/g, constituting 53.2% of the total mass. MnO4- exists in the sustained-release material in two forms: 57% in free state and 43% intercalated. The free MnO4- rapidly degrades oxytetracycline (OTC), while the intercalated MnO4- is gradually released from the LDH interlayers through ion exchange and interface dissolution, continuously degrading OTC desorbed from the soil. Additionally, CaAl LDH readily releases Ca2+; the small molecular acids and CO2 generated after OTC degradation will re-fix Ca2+ to form CaCO3, achieving carbon sequestration and enhancing the utilization efficiency of Ca2+. In simulated OTC contaminated soil columns (50mg/kg) treated with 0.5wt% MnO4 LDH at a water flow rate of 0.04mL/min, it was confirmed that the oxidant utilization efficiency of MnO4 LDH was 3.5 times higher than that of the KMnO4 system, removing 99.8% of OTC within 40 days. This study provides new insights for the design of sustained-release materials and theoretical support for the remediation of organic pollutants.