Preparation of P-doped biochar and its high-efficient removal of sulfamethoxazole from water: Adsorption mechanism, fixed-bed column and DFT study

Heteroatom doping technology is of great significance for adsorption. However, the effect of P with relatively lower electronegativity (2.19) doped in the π-electron system and phosphorus-containing functional groups on the adsorption has always been neglected. Herein, P-doped biochar (PBC) was successfully synthesized via the in-situ activation method and applied in a bath experiment and a long-term fixed-bed dynamic adsorption for sulfamethoxazole (SMX) removal. Compared to pristine BC, the pHpzc, ash content and graphitization degree of PBC would be reduced significantly after phosphoric acid (H3PO4) was treated, but it gained a large specific surface area (SSA = 233 m2 g−1), as well as abundant surface functional groups. In the adsorption process, the behavior of SMX adsorbed onto PBC conformed to pseudo-second-order kinetic and Langmuir models in batch experiments. Its excellent adsorption capacity (148.62 mg g−1) benefited from a large number of functional groups. DFT calculation indicates that the C3-P-O configuration mainly promoted the adsorption of SMX. It is speculated that the hydrogen-bond interaction between SMX and C3-P-O was the main adsorption mechanism, and electrostatic and π-π EDA interaction also contributed. Various parameters during the dynamic process were thoroughly explored. The saturated adsorption capacity of the column would be promoted when influent SMX concentration and bed depth increased, but negatively correlated with solution pH and influent rate. Moreover, PBC fixed-bed column for SMX removal was well fitting Thomas, Yoon-Nelson and BDST models, which provided a predictable strategy for practical application.