Hydrazone-linked COFs with N/O synergistic sites achieving ultrahigh and fast Pd(II) capture under acidic conditions
Yumei Luo1, Kaiyu Xia1, Yuancheng Qin1
1Key Laboratory of Jiangxi Province for Persistent Pollutants Prevention Control and Resource Reuse, Nanchang Hangkong University, Nanchang 330063, China.
Abstract:
The selective adsorption of palladium (Pd) from acidic wastewater is of great importance for sustainable resource utilization and environmental remediation. Herein, covalent organic frameworks (COFs) employing hydrazide-containing amine monomers as linkage units are successfully synthesized. At pH= 1, the pyridyl-functionalized COF (BTHN) exhibited a record-high Pd(II) adsorption capacity of 898.09 mg g-1, achieving 96.3 % removal of Pd(II) ions within 30 min at an initial concentration of 100 mg L-1. Meanwhile, both COFs (BTHN and BTHO) demonstrated remarkable recyclability and selectivity, maintaining over 94 % removal efficiency after five adsorption-desorption cycles and achieving nearly 100 % Pd(Ⅱ) removal even in the presence of 16 coexisting competitive ions. Notably, BTHN showed a high dynamic adsorption capacity (443.69 mg g-1) under continuous-flow conditions and enabled efficient Pd(II) recovery from real spent catalyst leachates, highlighting its practical applicability. XPS and DFT analyses revealed that the outstanding performance originates from a coordination-enriched pore microenvironment, where locally concentrated and spatially proximate N/O donor sites enable synergistic coordination with Pd(II) ions, together with favorable electrostatic interactions. This study highlights the potential of hydrazone-linked COFs as efficient and regenerable adsorbents for noble metal recovery under strongly acidic conditions.
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