Efficient removal of U (VI) from aqueous solution by the synergistic mechanism of “adsorption enrichment-dual pathway reduction” based on HCN

Some uranium removal materials face recovery challenges, while magnetic NiFe₂O₄ enables rapid solid-liquid separation and recovery through an external magnetic field but exhibits limited U(VI) removal capacity. To address this limitation, a magnetic HAP/Cu₂O/NiFe₂O₄ (HCN) ternary composite was synthesized for efficient uranium removal. HCN combines several advantages: HAP provides abundant U(VI) adsorption sites; NiFe₂O₄ and Cu₂O form an S-scheme heterojunction, which exhibits excellent visible light response ability, enabling the reduction of U(VI) to U(IV) under solar irradiation. Fe(II) and cu(I) species in HCN reduce U(VI) to U(IV) while undergoing self-regenerating by capturing photogenerated electrons, sustaining Fe(II)/Fe(III) and cu(I)/cu(II) redox cycles. Moreover, HCN retains magnetic separation capability of NiFe₂O₄. Experimental results showed that the adsorption of U(VI) by HCN followed the Langmuir isotherm and pseudo-second-order kinetic model under dark conditions, with a maximum of 237.7 mg g⁻¹. Under solar illumination, the U(VI) removal capacity increased to 380.1 mg g⁻¹—A 60.1 % improvement over adsorption alone—Demonstrating the importance of synergistic effect between photocatalysis and adsorption. Mechanism studies revealed that the superior adsorption performance of HCN originates from its abundant adsorption sites and ion exchange capacity, while the photocatalytic activity is attributed to strong visible-light absorption. U(VI) is initially captured by ion exchange and surface complexation, followed by U(IV) via dual pathway (direct electron transfer and Fe(II)/cu(I) mediation). HCN also exhibits recyclability, long-term stability and excellent ion-interference resistance. In summary, HCN demonstrates strong potential for the stable and efficient removal of uranium in water