Precise target capture and the dynamic separation of Sn(IV) in highly acidic media by combining N and P donor covalent organic framework silica-based composite adsorbents

A silica-based adsorbent (P507@COF-TpAzo/SiO 2 ) with nitrogen and phosphorus donors was prepared for industrial separation and recovery of Sn(IV) by in-situ growth of covalent organic framework (COF) on a silica substrate combined with vacuum impregnation. The materials were tested and analyzed by the scanning electron microscope (SEM), X-ray diffraction (XRD) and other characterization techniques, which demonstrated that the adsorbent has an enormous specific surface area, excellent heat resistance, and a regular morphological structure. The static experimental results showed that the adsorbent displayed remarkable selectivity for Sn(IV) in high HCl and HNO 3 concentration environments, with excellent kinetics (∼60 min) and outstanding adsorption capacities (60.02 mg/g in 3 M HCl, 92.59 mg/g in 3 M HNO 3 ) in different media at 3 M acidity. Cycle performance testing demonstrated that the adsorbent exhibited excellent stability (cycle times ≥8). Analysis using Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) showed that the synergistic adsorption results of N and P were reflected, mainly by the synergistic complexation of P=O and N=N-C. The potential sites for the adsorption of the adsorbent towards Sn(IV) were predicted by density functional theory (DFT) calculations, and the adsorbent demonstrated a more stable binding energy with Sn(IV). Finally, dynamic separation and efficient enrichment (>210) of Sn(IV) in highly acidic wastewater were realized by designing a penetrating column separation process. P507@COF-TpAzo/SiO 2 satisfied the requirements of the dynamic adsorption experiments, bridging the research gap of dynamic separation, and provides a new strategy for the industrial removal and recovery of Sn(IV), as well as a way for environmental protection and industrial green production. • A novel adsorbent (P507@COF-TpAzo/SiO 2 ) containing N and P donors was designed. • Adsorbent exhibits excellent selectivity, fast kinetics, high adsorption capacity and high chemical stability for Sn(IV). • Complete separation (nearly 100%) of Sn(IV) from the wastewater by column experiments for 72 h. • Synchronisation of column experiments to achieve efficient enrichment of Sn(IV) ( C / C o ≥ 210). • Revealing the complex structure of N and P donors to Sn(IV) by means of XPS, FT-IR, and DFT calculations.