Synergistic Enhancement of Palladium Adsorption on Covalent Organic Polymers via Hydrazone Linkages and Pyridine (Invited)

To address the bottlenecks of poor stability and low selectivity of traditional adsorbents when dealing with strongly acidic palladium-containing wastewater, this study proposed a synergistic “stable skeleton–functional site” design strategy. Highly stable hydrazone linkages were used as the backbone connection moieties, while pyridine and triazine groups with strong coordination capability were incorporated, which realized the unification of structural stability and adsorption activity. Based on this strategy, two novel hydrazone-linked covalent organic polymers, TFPT-BPY and TFPT-BPH, were successfully prepared, and their physicochemical properties were systematically characterized by techniques including FTIR, XRD, and nitrogen adsorption–desorption measurements. Adsorption performance studies showed that both materials maintained high Pd(II) removal efficiency (>94%) over a wide pH range of 1~5, and the maximum adsorption capacity of TFPT-BPY (205.08 mg·g⁻¹) was 31.7%, which was higher than that of TFPT-BPH (155.74 mg·g⁻¹). X-ray photoelectron spectroscopy (XPS) analysis indicated that Pd(II) was primarily captured through coordination with nitrogen atoms in the triazine and pyridine rings. The additional pyridine nitrogen within TFPT-BPY structure provided many more binding sites, thereby enhancing its palladium adsorption capacity. Both materials exhibited exceptional stability, retaining over 70% adsorption efficiency after five adsorption–desorption cycles. This study provides a new approach for developing novel adsorbent materials with high stability, high adsorption capacity, and excellent selectivity.