[Adsorption Mechanism of Phosphate on Layered Double Hydroxide-loaded Biochar and DFT Study]

This study utilized layered double hydroxides （LDHs） loaded with potato straw biochar （SBC） to prepare a composite material （LDHs@SBC）. The adsorption performance of LDHs@SBC for phosphate was investigated， and the adsorption mechanism was analyzed at the molecular level using density functional theory （DFT）. The results showed that the adsorption kinetics of phosphate by LDHs@SBC could be well-fitted by a pseudo-second-order kinetic model （R²=0.983）， with the main adsorption process being chemical adsorption. Thermodynamic analysis indicated that the adsorption process of phosphate by LDHs@SBC was a spontaneous exothermic reaction. DFT calculations revealed that the adsorption energy of phosphate by LDHs@SBC was -5.34 eV， confirming that the adsorption process was chemical adsorption and a spontaneous exothermic reaction. The adsorption of phosphate by LDHs@SBC was due to the hybridization of P-p/s， O-p， and M-p/s orbitals forming a coordination bond P-O-M， along with significant electron transfer and orbital contribution. The pH of the solution affected the speciation of phosphate and the charge distribution of LDHs@SBC. The adsorption of phosphate by LDHs@SBC reached its maximum through the formation of ordinary hydrogen bonds （OHB） and charge-assisted hydrogen bonds （CAHB）. The main mechanisms for phosphate adsorption by LDHs@SBC included electrostatic attraction， precipitation， ligand exchange， and charge-assisted hydrogen bonding. LDHs@SBC exhibited strong adsorption performance for phosphate and good reusability， making it a promising， efficient， and renewable adsorbent material for the treatment of phosphorus-containing wastewater.