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Capturing of uranium from the natural seawater is considered to be one of the most promising methods to meet the current demand for nuclear energy. Herein, we prepared a reduced graphene oxide-based (rGO-based) covalent organic framework hydrogel (KTG) with three-dimensional porous structure as a platform for enhancing uranium capture capacity through photothermal desalination. Under light irradiation, the KTG produces a local heat that can be used to generate steam while promoting the rapid diffusion of uranium inside the hydrogel 3D network, thereby increasing the adsorption efficiency and capacity of uranium. KTG can achieve exceptional uranium capture capacity (521.6 mg g−1) under one sun irradiation, which is 42.4% higher than that under dark conditions. In addition, excellent photocatalytic activity and mechanical properties make KTG possess high anti-biofouling activity, good reusability, and achieving continuous uranium capture and solar distillation.

So far, it remains a challenge to synthesize uranium adsorbents with robust stability, high adsorption capacity, excellent photocatalytic activity and easy regeneration. Herein, we report the first example of vinylene-linked covalent organic framework (Tp-TMT) with enhanced uranium adsorption through combined selective ligand binding, chemical reduction and photocatalytic reduction. The unique structure and excellent photocatalytic activity of Tp-TMT make it very suitable for photo-enhanced uranium adsorption through three synergistic mechanisms, thus exhibiting an outstanding uranium adsorption capacity (2362.4 mg g−1). In the dark, a large number of hydroxyl groups in the Tp-TMT framework serve as selective binding sites for uranium, and reduce part of U(VI) to U(IV), thereby greatly improving the adsorption capacity. Meanwhile, the synergistic effect of the triazine units and hydroxyl groups in the highly conjugated framework greatly decreases the optical band gap of Tp-TMT, and an additional U(VI) photocatalytic reduction process can occur under light irradiation, further increasing the adsorption kinetics and capacity. This work explored the structural and functional design of covalent organic frameworks for the adsorption and reduction of uranium in nuclear industry wastewater.

Highly effective and reliable adsorbents for uranium extraction are vital significant for environmental protection and social development. Herein, inspired by the interaction between imidazole affinity ligand of histidine and uranium, a series of varying degree hydroxylation imidazole linked covalent organic polymers were developed for the first time via one step facile reaction without any post treatment between 2,4,6-triformylphloroglucinol (Tp), 2,4,6-triformylresorcinol (Bd), 2,4,6-triformylphenol (Hb) and 3,3′-diaminobenzidine (DAB), denoted as TpDAB, BdDAB, and HbDAB, respectively. Benefiting from the hierarchical structure of the covalent organic polymer and synergistic effects originating from hydroxyl groups and imidazole linkages, TpDAB, BdDAB, and HbDAB displayed as the promising adsorbents for uranium extraction with high extraction ability and fast capture kinetics. X-ray photoelectron spectroscopy results revealed that both nitrogen atoms in imidazole and oxygen atom in hydroxyl took part in uranium coordination. With the increasing of hydroxyl group amounts, TpDAB achieved highest extraction capacity of uranium. Furthermore, TpDAB with imidazole affinity group possessed eminent selectivity for uranium in the multiple metal ions solution, and especially overcome the unavoidable problem of vanadium interfering with amidoxime adsorption uranium. This work provided a promising uranium extraction strategy with high selectivity and easy preparation for environmental protection and human health.