Redox-active Fe-modified MnMg layered double hydroxide for highly efficient arsenic removal: Dual oxidation-adsorption mechanisms

Arsenic is a widely acknowledged environmental pollutant commonly found in both natural and industrial water systems, posing critical risks to both ecosystems and human health. This study introduces an iron-modified MnMg layered double hydroxide (FeMnMg-LDH) engineered to enhance arsenic removal efficiency for both As(III) and As(V) under environmentally relevant conditions. The materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The incorporation of Fe into MnMg-LDH led to increased surface area, optimized surface chemistry, and mitigated particle aggregation, thereby exposing additional active sites. The FeMnMg-LDH demonstrated remarkable adsorption capacities of 106.67 mg g(-1) for As(III) and 107.63 mg g(-1) for As(V), representing a sixfold and twofold enhancement, respectively, over the pristine MnMg-LDH. Adsorption kinetics and isotherms aligned closely with pseudo-second-order and Langmuir models, indicating monolayer chemisorption. Competitive anion experiments revealed minimal interference except for PO43-, underscoring the material's selectivity. The FeMnMg-LDH retained > 80 % of its initial capacity after three regeneration cycles, demonstrating robust reusability. The mechanisms investigation reveals a synergistic oxidation-adsorption process, where Fe/Mn redox couples facilitated As(III) oxidation to more adsorbable As(V), coupled with immobilization via coprecipitation, surface complexation, electrostatic interactions, and ion exchange. These findings reveal that FeMnMg-LDH is a promising sorbent for arsenic-contained wastewater treatment, offering practical advantages in stability, efficiency, and scalability.