New insight into remarkable tetracycline removal by enhanced graphitization of hierarchical porous carbon aerogel: Performance and mechanism

Tetracycline (TC) as an organic pollutant causes serious harm due to its difficulty in natural decomposition, and improving its removal performance has become the focus of attention. In this study, carbon aerogel (CA) with hierarchical porous structure was successfully synthesized by cross-linking polymerization of chitosan with glutaraldehyde and combined with high-temperature carbonization procedure. Through optimization, the CA800 obtained by carbonization at 800 °C has a good graphitization structure, which is the essential for its excellent adsorption performance, and the maximum adsorption capacity of TC can reach 210.79 mg/g under the optimal conditions. The process conforms to the pseudo-second-order kinetic model and the Freundlich isotherm model, indicating that chemisorption and multilayer adsorption play a dominant role; thermodynamic analysis confirms that the present adsorption system possesses endothermic and spontaneous properties. In addition, the CA800 adsorbent exhibits good reusability and convenient recovery properties. Normally, pore filling, π-π EDA interactions, hydrogen bonding and electrostatic interactions are considered as the main adsorption mechanisms for TC adsorption on carbon-based materials, but beyond that, the n-π EDA interactions present in this paper also play a prominent role. Consequently, this study makes it possible to optimize the graphitization of carbon-based adsorbents to improve their adsorption performance.