Synergistic effect of hierarchical pores and self-doped heteroatoms of biochar in rapid and efficient adsorption of PPCPs residues

Abstract

Pore structure and surface activities synergistically enhanced the adsorption performance of self-doped heteroatoms biochar for PPCPs (Pharmaceuticals and Personal Care Products). This biochar was prepared by two-step pyrolysis (TSP) using UPs (Ulmus pumila L. samara) with cavity structure, nitrogen and sulfur atoms, and higher cellulose and hemicellulose. UPBC-2 was prepared using the optimal dose of activator with a specific surface area of 2401 m²g⁻¹ and a pore volume of 1.984 cm³g⁻¹. Micropores in the hierarchical porous played a decisive role in the adsorption capacity of UPBC-2. Nitrogen (1.67 at. %) and sulfur (0.35 at. %) atoms were rapid adsorption sites for PPCPs, which were rapidly diffused into the interior of UPBC-2 through the hierarchical pores. The synergistic effect of pore structure and surface activity resulted in short equilibrium time (5, 7, and 5 min) and high saturation capacity (655.6, 754.0, and 601.7 mg g^-1) of CBZ, CQ, and DCF by UPBC-2. The adsorption capacity of UPBC-2 on PPCPs was almost independent of pH, ionic strength, coexisting ions, and adsorption–desorption cycles, but was influenced by molecular size and hydrophilicity of PPCPs. The dominant interaction in the adsorption process was the rapid π-electron sharing between PPCPs and graphitic N / thiophenic S.