In-situ synthesis of MIL-100(Fe)@chitosan composite beads with hierarchical porous structure for efficient adsorption of chlortetracycline hydrochloride: Synthesis, performance and mechanisms

The widespread use of chlortetracycline hydrochloride (CTC) inevitably poses a potential threat to human health and the biological system, and its environmental pollution and ecotoxicological effects cannot be ignored. Herein, we adopted an in-situ growth method to immobilize the powder form of MIL-100(Fe) adsorbent into lowcost chitosan (CS) matrix for the CTC removal. Metal hydroxide (or metal oxide)/CS beads from the aciddissolved/alkali-solidified self-sphering shaping method were employed as the substrates for MIL-100(Fe) immobilization, allowing it grow uniformly and stably. Notably, this strategy not only reduced the loss in the separation and regeneration process of powdery MIL-100(Fe), but also improved the adsorption capacity of the CS. Isotherm and kinetic studies showed that the Freundlich and PSO models can describe the experimental data better, respectively, and the maximum adsorption capacity of Langmuir can reach 578.03 mg g-1. Further, the performance of MIL-100@CS-2 composite beads was thoroughly explored by batch experiments and response surface methodology (RSM) to obtain the optimized operating conditions with the highest CTC removal rate. By combining the density functional theory (DFT) calculation with experimental analysis, the adsorption mechanisms of pore filling, hydrogen bonding, electrostatic interaction, pi-pi EDA interaction, and hydrophilic interaction were proposed. This work provides a reliable basis for the development of shaping adsorbents and has potential application prospects in the treatment of wastewater containing antibiotics.