Synthesis of Mg–Al layered double hydroxides-functionalized hydrochar composite via an in situ one-pot hydrothermal method for arsenate and phosphate removal: structural characterization and adsorption performance

Abstract In recent years, hydrochar has been recognized as an ideal and eco-friendly adsorbent for the removal of various pollutants, while it has a relatively low adsorption affinity toward negatively charged contaminants, such as arsenate and phosphate. Thus, to address serious worldwide water pollution caused by arsenate and phosphate, the Mg–Al layered double hydroxides-functionalized hydrochar (Mg–Al LDHs-FHC) composite was synthesized via an in situ one-pot hydrothermal method. The Mg:Al molar ratios (2:1–4:1) and hydrothermal temperatures (150–210 °C) played significant roles in influencing the structural properties of the Mg–Al LDHs-FHC composites. Specifically, the Mg–Al LDHs-FHC composite prepared at Mg:Al molar ratio of 2:1 and hydrothermal temperature of 150 °C showed the best arsenate (100%) and phosphate (99.7%) removal due to the highest charge density (4.132 e/nm2) and the largest interlayer d-spacing (0.8371 nm), facilitating strong electrostatic adsorbent–adsorbate interaction and easy intercalation into the interlayer. Single-component isotherm data fit Langmuir and Freundlich models, while binary-component data used extended and ideal adsorbed solution theory combining these models. Overall, the adsorption affinity of the composite followed the order arsenate > phosphate (single-component system) and arsenate