Improved adsorption properties of tetracycline on KOH/KMnO₄ modified biochar derived from wheat straw

Modification of pristine biochars has received increasing attentions due to the significant potential in enhancing adsorption performance. In this work, the co-modification of KOH and KMnO₄ on biochar (K-Mn-BC) was performed, with the effect of KOH/KMnO₄ modification on biochar properties and their adsorption toward tetracycline (TC) being extensively explored. Results showed that KOH/KMnO₄ modification can significantly regulate biochars to form hierarchical structure. The obtained K-Mn-BC was characterized with a high specific surface area (1524.6 m² g^-1) and total pore volume (0.85 cm³ g^-1). In addition, the K-Mn-BC exhibited a high adsorption capacity of 584.19 mg g^-1 toward TC at 318 K, and pseudo-second-order (R²:0.993～0.998) and Langmuir (R²: 0.834～0.874) models can fit well with the adsorption behavior. Moreover, the obtained K-Mn-BC can efficiently adsorb TC within a wide pH range (3.0-10.0), and were not affected by the co-existing ions. The possible mechanisms for the high adsorption capacity were ascribed to the pore filling and π-π interaction, following by hydrogen bonding and metal complexation. The obtained K-Mn-BC is a suitable adsorbent for TC removal from water due to the hierarchical structure, high adsorption capacity, and stable adsorption effect.