Enhanced electrochemical uranium extraction by three-dimensional zero-valent iron aerogels via dynamic Fe(II)/Fe(III) cycling

Hierarchically porous 3D Fe 0 aerogel overcomes agglomeration and passivation of Fe 0 nanoparticles. • Aerogel achieves 9590.25 mg/g uranium capacity which is 1.5 times that of conventional Fe 0 nanoparticles. • Electric field drives dynamic Fe(II)/Fe(III) cycling on the aerogel to sustain active site regeneration for uranyl reduction. • Hierarchical pores create a localized microenvironment that enhances active site accessibility and Fe(II) retention. Electrochemical uranium extraction (EUE) is a promising strategy, yet conventional Zero-Valent Iron (Fe 0 ) nanoparticles suffer from severe agglomeration and surface passivation. Herein, we designed a hierarchically porous 3D Fe 0 aerogel that overcomes these limitations by providing an interconnected conductive network and abundant accessible active sites. At −0.2 V vs. RHE and an initial U(VI) concentration of 500 mg/L, the Fe 0 aerogel exhibited a maximum capacity of 9590.25 mg/g after 48 h electrolysis, which is approximately 1.5 times that of conventional Fe 0 nanoparticles under identical conditions. The aerogel also exhibited excellent selectivity against competing ions and good tolerance to carbonate interference. Operando Raman spectroscopy and quasi-operando XPS revealed that the external electric field drove the dynamic Fe(II)/Fe(III) redox cycle at the solid-liquid interface, which enabled the continuous in-situ regeneration of Fe(II) as the active electron-shuttling mediator for uranyl reduction. This electrochemically mediated mechanism effectively mitigates the severe surface passivation that plagues conventional iron-based electrodes. In-situ FTIR spectroscopy hinted at the formation of a distinct interfacial microenvironment within the porous architecture, potentially involving enhanced hydrogen-bonding interactions, which may further contribute to the extraction performance. Additionally, a continuous-flow reactor employing the aerogel as a flow-through cathode operated steadily in natural seawater for 10 days, achieving a stable extraction rate of 1.26 mg/g/day. This work elucidates the molecular-scale mechanisms of interfacial electroreduction, providing an innovative paradigm for the scalable mining of critical nuclear resources from real aquatic environments. Schematic illustration of efficient uranium extraction by Fe 0 aerogels via dynamic Fe(II)/Fe(III) cycling. Download: Download high-res image (410KB) Download: Download full-size image