Novel amidoxime-functionalized covalent organic frameworks synergistically promote UO22+removal via photocatalytic reduction and adsorption

Efficient enrichment and recycling of uranyl ion (UO22+) from wastewater are crucial for preventing radioactive contamination and protecting human health. Herein, two novel covalent organic frameworks (Tp-PDAN and TpPDAN-AO) were synthesized by a simple two-step method. Tp-PDAN-AO exhibits excellent hydrophilicity, thermal stability, and chemical stability, making it suitable for UO22+ removal from acidic wastewater. The highdensity amidoxime chelate groups in Tp-PDAN-AO confer high adsorption capacity and selectivity for UO22+, with a maximum adsorption capacity of 565.30 mg g-1, reaching equilibrium within 2 h. Additionally, Tp-PDAN-AO exhibits strong photocatalytic activity under UV irradiation, which further enhances U(VI) reduction, boosting both adsorption kinetics and capacity. The maximum adsorption capacity increases to 757.62 mg g- 1 with photocatalytic reduction. Density functional theory (DFT) calculations reveal six distinct COF-U(VI) interaction modes, explaining the chelation mechanism between hydrated uranyl ions and Tp-PDAN-AO (eta 2 mode), providing insights into the application of COFs with customizable functional groups for UO22+ adsorption.