Efficient and Superstable Mineralization of Toxic Cd²⁺ Ions through Defect Engineering in Layered Double Hydroxide Nanosheets

Water and soil pollution caused by toxic cadmium ions (Cd²⁺) is a serious threat to animals, plants, and human health. Discovering low-cost mineralizers which can efficiently and stably immobilize Cd²⁺ ions is therefore imperative for wastewater treatment and soil remediation. In this work, we report the successful development of a novel mineralizer for Cd²⁺ ion capture. A magnesium-aluminum layered double hydroxide (MgAl-LDH) with a monolayer structure (MgAl-mono) was first prepared and then calcined at 350 °C for 4 h to produce a defective MgAl-mono-350. MgAl-mono-350 offered a very high Cd²⁺ removal capacity (1385.5 mg/g at 25 °C) and the ability to reduce the concentration of Cd²⁺ in aqueous solution from 100 ppm to less than 50 ppb in 15 min (meeting the discharge standard of industrial wastewater). Detailed characterization and computational studies revealed that MgAl-mono-350 possessed abundant oxygen defects, thereby enabling superstable mineralization of Cd²⁺ via isomorphous substitution process,and the Cd²⁺ ions are immobilized in the generated CdAl-LDH structure. MgAl-mono-350 also offered outstanding selectivity for Cd²⁺ ions over other common ions. This work demonstrates the potential of defect-engineered LDH materials for the selective removal of heavy metals from polluted water.