In-Depth Study of Heavy Metal Removal by an Etidronic Acid-Functionalized Layered Double Hydroxide

Sorption methodologies play a pivotal role in heavy metal removal to meet the global requirements for uninterrupted access to drinkable water. Standard sorption technologies lack efficiency due to weak adsorbent-metal interaction. To this end, a layered cationic framework material loaded with phosphonate was first fabricated by a facile intercalation method to capture hazardous metals from an aqueous solution. To inquire the removal mechanisms, batch experiments, detection technologies, and simulation calculations were employed to study the interactions at the interface of clay/water. Specifically, the functionalized layered double hydroxide possessed excellent chelation adsorption properties with Zn²⁺ (281.36 mg/g) and Fe³⁺ (206.03 mg/g), in which model fitting results revealed that the adsorption process was chemisorption and monolayer interaction. Further, the interfacial interaction between the phosphonate and clay surface was evaluated by molecular dynamics simulation, and a new concept named the interaction region indicator was used to characterize weak interaction and coordinate bonds. The deep insight into the chelation mechanism was visually presented via the orbital interaction diagram. In addition, the regeneration of the spent adsorbent, adsorption column test, and acute toxicity analysis demonstrated that the synthesized material has immense potential in terms of practical usage for the treatment of toxic pollutants. These results provide a novel path for researchers to properly understand the adsorption behavior.