Here we report a nanoadsorbent design, which integrates the high affinity of amidoxime (AO) groups and size effect of nanomaterials in nanofibrous composite mats prepared by a two-nozzle electrospinning process, for the adsorption of uranium in simulated seawater with an uptake capacity of 1.6 mg U g⁻¹ adsorbent in the presence of massive amounts of interference ions.