Enhanced adsorption performance of tetracycline in aqueous solutions by KOH-modified peanut shell-derived biochar

Modification of biochar is essential to improve its properties and then promote its adsorption effect. In this study, modified biochar derived from peanut shell was prepared by KOH treatment. Adsorption behavior and mechanisms toward tetracycline (TC) by biochar were investigated. The results showed that KOH modification significantly changed the surface morphology, pore structure, elemental composition, functional groups, minerals, and carbon defects of biochar. The content of C, H, N, and S of biochar decreased as well as the content of O and ash increased after KOH modification. Surface area and pore volume of KBC were 1271.97 m2·g−1 and 0.653 cm3·g−1, which was 5.8 and 5.4 folds than that of BC, respectively. KOH modification also changed the Ca, Si minerals components in biochar. Moreover, the functional groups in biochar also significantly changed after modification, especially O- and N-containing groups. More carbon defects occurred in KBC due to the KOH reactions. Pseudo-second-order model and Langmuir model can better describe the adsorption processes of TC on biochars. The maximum adsorption capacity of TC on KBC reached 356.19 mg∙g−1 at 318.15 K. KBC has a stable removal effect to TC in a wide pH range and under the interference of co-existing ions. Pore filling and π-π interaction were the main adsorption mechanisms for TC removal by KBC. Therefore, KOH-modified peanut shell-derived biochar has a potential to act as an adsorbent to remove TC from aqueous solutions or immobilization in soils.