Enhanced removal of Ni²⁺ and Co²⁺ from wastewater using a novel 2-hydroxyphosphonoacetic acid modified Mg/Fe-LDH composite adsorbent

While technological advancements in treating electroplating wastewater continue, removing high concentrations of Ni²⁺ and Co²⁺ remains a challenge. Surface functionalization of clay has emerged as a pivotal approach for effectively removing heavy metals, rivaling intercalation modification in its effectiveness. This study investigated the adsorption performance and mechanisms of a phosphonate-modified layered double hydroxide material, employing batch experiments and simulation calculations to elucidate the impact of surface modification on adsorption behavior. Briefly, various characterization techniques confirmed that the layered double hydroxide synthesized through co-precipitation exhibited a sheet-like morphology, with phosphonate groups anchoring onto the clay surface following functionalization. Under optimal conditions (pH=6.0, t = 60 min, and C₀=300 mg/L), the material demonstrated high uptake capacities for Ni²⁺ (198.01 mg/g) and Co²⁺ (180.18 mg/g), surpassing most previously reported adsorbents. The adsorption kinetics for Ni²⁺ and Co²⁺ on the modified material followed a pseudo-second-order model, and the isotherms conformed to the Langmuir equation, indicating a monolayer chemical adsorption process. Moreover, after five adsorption-desorption cycles, the adsorbent demonstrated exceptional reusability and stability, and its potential for practical application preliminarily assessed using electroplating wastewater containing Ni²⁺. To further clarify the adsorption mechanism, a molecular dynamics simulation employing the CLAYFF-CVFF force field was conducted to examine the electrostatic interaction of modifiers at the clay surface. Wavefunction analyses derived from quantum chemical calculations provided insights into interactions, identified molecular reactive sites, and elucidated orbital interactions within chelation complexes. This research presents a feasible approach for developing high-performance materials for wastewater remediation in practical applications.