One-step synthesis of high-surface-area porous biochar from reed for antibiotic adsorption: influencing factors, mechanisms, and recyclability

Abstract

It is a significant challenge to achieve high-efficiency and low-cost removal of antibiotics from water. Herein, reed was used as the raw material to prepare K₂CO₃-modified porous biochar (KRBC) via a one-step chemical activation method. At 900 °C, pyrolysis with an alkali/carbon ratio of 2 : 1 resulted in porous biochar (KRBC-2) with a high specific surface area of 2427.34 m² g⁻¹. When the aqueous solution pH was 2, the removal of doxycycline (DOX, 50 mg L⁻¹) and ciprofloxacin (CIP, 50 mg L⁻¹) reached 100% and 96.7%, respectively. K₂CO₃ facilitated the transformation of the carbon crystalline structure into an amorphous state, thereby providing more adsorption sites. KRBC-2 possessed outstanding recyclability with a high DOX removal efficiency of 86.3% in the 5-cycle adsorption. The adsorption of DOX by biochar obtained from pyrolysis under different conditions conformed to the pseudo-second-order kinetic model. More importantly, the adsorption of DOX by KRBC-2 followed a monolayer adsorption mechanism, with a maximum adsorption capacity of 1167.39 mg g⁻¹. The spontaneity and temperature positive effect of KRBC-2 on DOX adsorption were proved through thermodynamic experiments. The influence of monovalent cations on DOX adsorption by KRBC-2 was negligible, while anions competed with DOX for hydrogen-bonding sites on the KRBC-2 surface. The excellent adsorption performance of KRBC-2 for DOX was mainly related to the pore structure, electrostatic attraction, and hydrogen bonding. This work provides a new approach for the resource utilization of agricultural waste and the efficient removal of antibiotics.