Ultra-efficient adsorption of diclofenac sodium on fish-scale biochar functionalized with H3PO4 via synergistic mechanisms

Developing safe and efficient diclofenac sodium (DS) removal technology has become a critical issue. This study synthesized the fish-scale biochar by co-pyrolysis of fish scale and phosphoric acid (H3PO4). In addition to increasing the specific surface area and pore volume of fish-scale biochar, H3PO4 assisted in the formation of Graphitic N and sp2 C, as well as reacting with C═O groups to form a significant number of phosphorus-containing groups. All these functional groups could act as major active sites for DS adsorption. Adsorption data could well fit pseudo-second-order and Langmuir models. The maximum adsorption capacity of FSB600-15 for DS was 967.1 mg g-1, which was much better than that reported in the literature. Under the synergistic effect of various mechanisms (pore-filling effect, electrostatic attraction, H-bonding, π-π, and n-π electron donor-acceptor interactions), the DS ultra-efficient adsorption on FSB600-15 was realized. Meanwhile, the DS adsorption by FSB600-15 was an endothermic, spontaneous, and entropy-increasing process. Furthermore, the DS adsorption capacity was more than 426.5 mg g-1 in the actual water, which was sufficient for practical applications.