Their unique layered structure, large specific surface area, good stability, high negative charge density between layers, and customizable composition give layered double hydroxides (LDHs) excellent adsorption and detection performance for heavy metal ions (HMIs). However, their easy aggregation and low electrical conductivity limit the practical application of untreated LDHs. In this work, a ternary MgZnFe-LDHs engineered porous biochar (MgZnFe-LDHs/PBC) heterojunction was proposed as a sensing and adsorption material for the effective detection and removal of Cd²⁺ from wastewater. The growth of MgZnFe-LDHs in the PBC pores not only reduces the accumulation of MgZnFe-LDHs, but also improves the electrical conductivity of the composite. The synergistic effect between MgZnFe-LDHs and PBC enables the composite to achieve a maximum adsorption capacity of up to 293.4 mg/g for Cd²⁺ in wastewater. Meanwhile, the MgZnFe-LDHs/PBC-based electrochemical sensor shows excellent detection performance for Cd²⁺, presenting a wide linear range (0.01 ng/L–1 mg/L), low detection limit (3.0 pg/L), good selectivity, and stability. The results indicate that MgZnFe-LDHs/PBC would be a potential material for detecting and removing Cd²⁺ from wastewater.

Herein, MnMgFe-layered double hydroxides/biochar (MnMgFe-LDHs/BC) composite was fabricated by immobilizing MnMgFe-LDHs on BC via the coprecipitation method, which was employed as an effective material for the detection and removal of Cd²⁺ from aqueous media. A lamellar structure of MnMgFe-LDHs with abundant surface-hydroxyl groups and various interlayer anions inside present a greater chance of trapping Cd²⁺. Meanwhile, the conductive BC with a porous structure provides numerous channels for the adsorption of Cd²⁺. Using the MnMgFe-LDHs/BC-based sensor, Cd²⁺ can be detected with a low limit of detection down to 0.03 ng/L. The feasibility of detecting Cd²⁺ in paddy water was also carried out, with satisfactory recoveries ranging from 97.3 to 102.3%. In addition, the MnMgFe-LDHs/BC material as an adsorbent was applied to remove Cd²⁺ from water with adsorption capacity of 118 mg/g, and the removal efficiency can reach 91%. These results suggest that the as-prepared MnMgFe-LDHs/BC can serve as a favorable platform for efficient determination and removal of Cd²⁺ in water.