KOH activated biochar loaded with MnAl-layered double hydroxides for superior adsorption of tetracycline from the aquatic environment

In this study, a promising KOH activated biochar/MnAl-layered double hydroxides (K-BC-LDHs) composite was synthesized using the in-situ chemical co-precipitation method. The results showed that the LDH particles were successfully distributed across the activated biochar during the modification process. More functional groups (Mn − O, Mn − O − Mn) and crystalline minerals (Mn4Al2(OH)12CO3·3H2O) were created and appeared on the surface of the composite. The LDHs modification process decreased the surface area, but increased the pore volume of the activated biochars. In addition, a mesoporous structure was formed, predominately due to the introduction of LDHs particles. The adsorption capacity for TC by K-BC-LDHs reached 1477.67 mg·g−1 and this increase was attributed to the combined actions of pore filling, complexation, and ion exchange, followed by hydrogen bonding, electrostatic attraction, and π-π interactions. The pseudo-second-order kinetics, intra-particle diffusion kinetics, and Langmuir isotherm models well described the adsorption behavior of TC by K-BC-LDHs. Furthermore, TC adsorption by K-BC-LDHs was a spontaneous and endothermic process. The K-BC-LDHs composite exhibited strong adsorption toward TC over a wide pH range (3–9) and there was a certain resistance to coexisting ionic interference. Additionally, the K-BC-LDHs composite showed high adsorption performance toward other pollutants and can potentially be recycled.