Zn-La staged modification of reed biochar for adsorption of tetracycline hydrochloride and mechanism study

Staged modification significantly improved the adsorption capacity of BC. • The adsorption capacity of Zn-La@BC is 11.28 times that of the original BC. • Zn-La@BC retains 80% of its adsorption capacity after 5 cycles. • Zn-La@BC exhibits strong resistance to interference from low-valent ions. • Metal complexation and electrostatic interactions are the primary mechanisms. A Zn La co-doped reed biochar (BC) adsorbent was prepared using a staged optimization and a two-step bimetallic modification method to enhance its adsorption capacity for tetracycline hydrochloride (TC). The optimal process conditions for the Zn La co-doped biochar (Zn-La@BC) adsorbent were determined using the response surface method (BBD): Calcination at 300 °C for 120 min under N 2 protection with a Zn@BC to LaCl 3 mass ratio of 1:0.6. Maximum adsorption occurred at a pH of 9, a dosage of 0.20 g·L −1 , and a reaction temperature of 35 °C. Fitting the Langmuir model revealed a maximum adsorption capacity of 594.65 mg·g −1 , which is an 11.28-fold increase on pristine BC. This adsorbent exhibit strong resistance to low-valent ion interference, retaining 80% adsorption capacity after 5 cycles and demonstrating excellent cyclic stability. Its adsorption mechanism primarily involves metal surface complexation and electrostatic adsorption, supplemented by hydrogen bonding, π-π interactions, and pore filling. This study provides a novel approach for preparing high-capacity reed-derived BC adsorbents.