An improved method of MgFe-layered double hydroxide/ biochar composite synthesis

Layered double hydroxides (LDHs) and their composites are a promising platform for a wide range of applications, especially in the environmental field. However, the facile and efficient synthesis of high-quality LDHs and their composites remains a challenge. Here, an improved co-pyrolysis method has been developed to synthesize LDH/biochar composites. A composite material was prepared by directly anchoring MgFe-LDH on corn stover by co-precipitation with FeCl₃ and Mg(OH)₂, and then through pyrolysis. The main features of this improved method are the use of the solubility product Mg(OH)₂ to maintain the pH of the mixture at ∼10 (the optimum for LDH precipitation), eliminating the cumbersome pH control steps of the traditional co-precipitation method, and the low rate of solid-liquid reaction to obtain high LDH crystallinity and purity. This produces improved properties of the MgFe-LDH/biochar composite after pyrolysis: higher loading of MgFe-LDH, larger specific surface area of the composite, a more stable layered structure, and a more customizable LDH. The theoretical maximum adsorption capacity of phosphorus for the composite was 379.4 mg L⁻¹ according to an adsorption isotherm study, and the dominant adsorption mechanism is chemical adsorption accompanied by physical adsorption. In actual wastewater applications, >80% of total phosphorus in biogas slurry was removed via adsorption, indicating that the composite is highly efficient in phosphorus selectivity in wastewaters with complex components. Here, a more sustainable synthesis method of LDH/biochar composite has been developed with high application potential. Copyright © 2023 Published by Elsevier Ltd.