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• A new double-network hydrogel is explored for uranium recovery from seawater. • U-adsorption capacity of the hydrogel is greatly enhanced by added nanoclay. • Mechanical property of the hydrogel is largely improved by th double-network. • Used materials are lowcost and the hydrogel owns good U-adsorption reusability. Massive uranium recovery from seawater is a key project to provide the long-time consumption of global nuclear power, while it is still greatly difficult to achieve high-efficient adsorbents with high mechanical property. In this work, a new nanoclay-poly(amidoxime) (NC-PAO) high-strength double-network (DN) composite hydrogel adsorbent with high-efficient and fast uranium extraction capacity has been explored. The uranium adsorbing performance can be significantly enhanced by the small content of added super-hydrophilic NC (Laponite RDS sheets), because of the largely improved hydrophilicity of the hydrogel. Compared with the blank PAO DN hydrogel without nanoclay, the uranium adsorbing capacity of this NC-PAO DN hydrogel can largely increase 73.4% from 4.97 mg/g to 8.62 mg/g, after in seawater only 25 days. The uranium adsorption rate of this hydrogel from natural seawater, can reached 0.345 mg/(g∙day), which is excellent among existing uranium adsorbents. Furthermore, this hydrogel has high mechanical performance with 2.42 MPa of tensile strength and 16.13 MPa of compressive strength, which can be used in seawater for relatively longer time than traditional low-strength single-network hydrogel, owing to its double network (DN) structure (the weakly crosslinked gelatin soft network and the strongly crosslinked cellulose nanofiber (CNF) hard network). This NC-PAO DN hydrogel adsorbent will be an excellent candidate for fast uranium recovery from seawater in largescale. Most importantly, this work will inspire the development of new hydrogel-based adsorbents and even other type of adsorbents for high-efficient uranium extraction, through compositing various low-cost and super-hydrophilic nanomaterials to significantly improve the hydrophilicity of the adsorbent and designing double-network structure to largely enhance the mechanical property. [ABSTRACT FROM AUTHOR]