Enhancing phosphorus removal through layered double hydroxide-decorated biochars: Unveiling pore structure and surface functionalization

Background: This study provided a sustainable solution to enhance phosphate (P) removal in aqueous solution using biochar (BC) surface modification techniques with multilayer double hydroxide coating (LDH@BC).Methods: Various LDH@BC composite materials were synthesized using the coprecipitation method, and their properties were measured using BET, SEM, EDS, surface zeta potential, FTIR, and XPS to investigate P adsorption behaviors.Significant Findings: The LDH layer played an important role in regulating the amplified mesoporous structure and diverse surface functional groups of BC for P removal enhancement. Specifically, Mg/Al-LDH@BC exhibited a larger specific surface area of 148 m2 g-1, creating more active sites and achieving the highest removal efficiency of 95.90 mg g-1. Zn/Al-LDH@BC demonstrated an amplified mesoporosity of 0.90, facilitating the transport of P ions and resulting in a higher removal rate of 0.017 g mg-1 h-1. Mg/Al-LDH@BC, with a higher pHpzc of 9.7, exhibited less susceptibility to changes in the pH of the solution within the range of 2 to 10. Additionally, Mg/Al-LDH@BC displayed excellent selectivity over other ions in multisalt solution of 40.26 for NH4+, 10.55 for NO3 , and 3.97 for SO42  . Several important proposed P removal mechanisms are involved in electrostatic attraction, complexation/ligand exchange, precipitation, and physical adsorption.