Synthesis of MgAl-LDH@ZIF-8 composites by in situ growth method for highly efficient phosphate removal

Abstract

Removal of phosphate from wastewater by adsorption has become one of the effective ways to mitigate the negative effects of eutrophication in water bodies, and efficient adsorbent is the key. In this study, MgAl-LDH@ZIF-8 composites were prepared by in situ growth of zeolite imidazole framework-8 (ZIF-8) on layered double hydroxide (MgAl-LDH) for efficient removal of phosphates in wastewater. Compared with pure ZIF-8 and MgAl-LDH, MgAl-LDH@ZIF-8 has higher phosphate removal efficiency of up to 99%. Its maximum adsorption capacity was 68.53 mg P g⁻¹. The adsorption process conformed to the pseudo-second-order kinetic model and Langmuir isotherm model. The thermodynamic results indicate that the adsorption process is spontaneous and endothermic. The adsorption mechanism is mainly electrostatic attraction, ion exchange, and ligand exchange. The MgAl-LDH@ZIF-8 with the dosage of 2.5 g L⁻¹ can remove 30 mg P L⁻¹ of simulated wastewater containing phosphate and meets the discharge standard of the U.S. Environmental Protection Agency (0.5 mg P L⁻¹). The results show that MgAl-LDH@ZIF-8 is an effective adsorbent for the removal of phosphate from wastewater, with potential for practical applications.