Carboxyl-functionalized biochar derived from walnut shells with enhanced aqueous adsorption of sulfonamide antibiotics.

The novel HNO3-modifitied biochar (NBC) was synthesized from walnut shell. The NBC was characterized from scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectrum. The NBC was then used in the adsorption of sulfadiazine, sulfamethazine and sulfachloropyridazine from aqueous solution. The material surface has carbon/oxygen-contained groups, which is benefit for the adsorption. The results showed the adsorption ability of NBC on three sulfonamides were 32, 46, and 40 mg g-1, respectively. The kinetic was found to follow the Elovich model and the isotherm conformed Freundlich. Adsorption was more favorable at weak acidic solution. The interactions mainly include π-π EDA, electrostatic interaction, Lewis acid-base interaction, hydrophobic interaction and H-bond.