Removal of tetracycline onto KOH-activated biochar derived from rape straw: Affecting factors, mechanisms and reusability inspection

A porous biochar (BC) was prepared using the recycled agricultural waste rape straw as resources by combining high temperature carbonization with KOH activation procedure, and applied into tetracycline hydrochloride (TC) adsorption. The multiple characteristic techniques were adopted to investigate the structures and properties of as-prepared BC. The results demonstrated that the BC activated by KOH would possess the more graphite-like structures, more abundant oxygen-containing functional groups, and larger specific surface area (1531 m2/g) comparing with unactivated BC, which were favorable for the TC adsorption. The effects of initial TC concentration, solution pH value, salt ionic strength and adsorption temperature on the adsorption performances were explored in detail. The adsorption data could be well fitted by the pseudo-second-order kinetic model and Freundlich isothermal model. The maximum adsorption capacity of KOH activation BC could reach 325.07 mg/g at 30 °C. The endothermic and spontaneous properties of the adsorption system was implied by thermodynamic study. The adsorption TC mechanism of KOH activation BC was involved in the pore filling, π-π electron donor-acceptor interaction, hydrogen bonding and electrostatic action. Regeneration experiments showed that the TC removal efficiency could still attain 97.0% even after six cycling experiment, suggesting that the BC had the excellent reusability and stability. These results indicate the feasibility of a win-win strategy for the application of agricultural waste to water remediation.