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/SiO2) 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 HNO3 concentration environments, with excellent kinetics (similar to 60 min) and outstanding adsorption capacities (60.02 mg/g in 3 M HCl, 92.59 mg/g in 3 M HNO3) 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/SiO2 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.