In-situ growth of multi-active-site COFs on peony pod-derived aerogel for three-dimensional synergistic adsorption of oxytetracycline: design and mechanism.

Efficient sequestration of oxytetracycline (OTC) from aqueous environments is limited by the single interaction force of conventional adsorbents, stemming fundamentally from the insufficient understanding and translation of adsorption mechanisms into rational material design. In this study, based on the molecular structure complexity of OTC, a new type of waste-derived macroscopic adsorbent with high adsorption capacity was developed from the perspective of multi-site and multiple intermolecular forces synergy design. A covalent organic frameworks (COFs) rich in secondary amine, ketone, and sulfonic acid groups was grown in situ on peony pod-based cellulose-sodium alginate composite aerogel (PCSA). The composite PCSA@COFs showed an effective OTC adsorption capacity of 43.44 mg/g at 298 K, following pseudo-second-order and Langmuir models, indicating spontaneous, endothermic chemisorption. Density functional theory calculations further revealed a strong binding energy of -55.11 kcal/mol between COFs and OTC with multiple interaction sites. Topological analysis via Atoms in Molecules theory demonstrated a multi-site three-dimensional synergistic mechanism through the identification of ring critical points and cage critical points, while the topological parameters revealed a partially covalent character in the interaction between sulfonic acid groups and OTC. This work provides a novel design concept for developing effective and eco-friendly adsorbents for antibiotic removal from aqueous environments.