Biochar Derived from Chinese Herb Medicine Residues for Rhodamine B Dye Adsorption

[Image: see text] In this study, one well-known CHM residue (Atropa belladonna L., ABL) was used to prepare biochar capable of adsorbing rhodamine B (RhB) with an ultrahigh surface area for the first time. Three micropore-rich ABL biochars including ABL@ZnCl(2) (1866 m(2)/g), ABL@H(3)PO(4) (1488 m(2)/g), and ABL@KOH (590 m(2)/g) were obtained using the one-step carbonization method with activation agents (ZnCl(2), H(3)PO(4), and KOH) via chemical activation and carbonization at 500 °C, and their adsorption performance for RhB was systematically studied with adsorption kinetics, isotherms, and thermodynamics. Through pore diffusion, π–π interaction, and hydrogen bonding, ABL biochar had excellent adsorption performance for RhB. Moreover, when C(0) was 200 mg/L, biochar dosage was 1 g/L, and the contact time was 120 min; the maximum RhB adsorption capacity and removal efficiency on ABL@ZnCl(2) and ABL@H(3)PO(4) were 190.63 mg/g, 95% and 184.70 mg/g, 92%, respectively, indicating that it was feasible to prepare biochar from the ABL residue for RhB adsorption. The theoretical maximum adsorption capacities of ABL@ZnCl(2) and ABL@H(3)PO(4) for RhB were 263.19 mg/g and 309.11 mg/g at 25 °C, respectively. Furthermore, the prepared biochar showed good economic applicability, with pay back of USD 972/t (ABL@ZnCl(2)) and USD 987/t (ABL@H(3)PO(4)), respectively. More importantly, even after five cycles, ABL@H(3)PO(4) biochar still showed great RhB removal efficiency, suggesting that it had a good application prospect and provided a new method for the resource utilization of traditional CHM residues. Additionally, pore diffusion, π–π interactions, and hydrogen bonding all play roles in the physical adsorption of RhB on ABL biochar. π–π interactions dominated in the early stage of RhB adsorption on ABL@H(3)PO(4), while pore diffusion played a crucial role in the whole adsorption process on both adsorbents.