Layered double hydroxides/biochar composites for adsorptive removal of tetracycline and ciprofloxacin

Abstract

Modification of biochar (BC) using layered double hydroxides (LDHs) is an anticipated strategy to strengthen the adsorption performance of BC. In this work, sawdust was used to prepare pristine BC to act as a matrix, and the MgFe-LDHs were selected as typical LDHs to prepare BC-LDHs composites via a coprecipitation technique, and the adsorption mechanisms toward tetracycline (TC) and ciprofloxacin (CIP) were evaluated. The effect of LDHs amount on the characteristics of BC-LDHs composites and the adsorption behavior and mechanisms of TC and CIP were also studied. Results showed that the loading of LDHs reduced the specific surface area and total pore volume of BC but developed more mesoporous structure in composites, created metal oxygen-containing functional groups (Mg–OH, Mg–O, Fe–O), and introduced a typical mineral (Mg6Fe2(OH)16CO3·4H2O) on the surface of the BC. The BC-1/3LDHs obtained by loading LDHs on 3 g BC exhibited the maximum adsorption capacity toward TC and CIP, and reached 77.04 mg∙g−1 and 66.74 mg∙g−1, respectively. The introduction of MgFe-LDHs greatly intensified the complexation interaction and hydrogen bonding of the composites. The Freundlich and pseudo-second-order models well-described the adsorption process of TC and CIP on BC-1/3LDHs. In addition, BC-1/3LDHs could adsorb TC and CIP in a wide range of pH values despite the interference of coexisting ions and also presented a good recycle utilization potential. Furthermore, the introduction of LDHs, especially BC-1/3LDHs, shifted the adsorption thermodynamic properties of BC. Overall, the prepared BC-1/3LDHs could be used as a promising adsorbent for the removal of TC and CIP from water environments.