Metal-Organic Frameworks for Flexocatalytic Uranium Recovery from Mining Wastewater

Designing materials with high flexoelectric responses is important for developing advanced catalytic systems. Metal-organic frameworks (MOFs), featuring flexible, tunable, and typically centrosymmetric structures, are promising high-performance flexocatalysts. Herein, we report a MOF, [Co2(4,4'-bpy)3(H2O)2V4O12]·2H2O (4,4'-bpy = 4,4'-bipyridine), as a flexocatalyst for uranium recovery from uranium mining wastewater. Its pronounced mechanical anisotropy and low shear and Young's moduli endow the rod-like crystal with excellent deformability. Finite-element simulations show that the MOF undergoes significant nonuniform deformation under external stress, generating a flexoelectric polarization of 0.6 C·m-2. Electronic structure analysis reveals that Co 3d and O 2p states dominate the band edges of the MOF and regulate their alignment with relevant redox potentials during the flexocatalytic process. Under ultrasonic conditions, the MOF converts soluble UO22+ into insoluble (UO2)O2·2H2O, enabling efficient separation and recovery of uranium from wastewater. It remains highly active over a wide pH range and at high salinity. In a dynamic system, the catalyst treated 1390 bed volumes of mining wastewater over 48 h, decreasing the uranium concentration from 5.22 ppm to below the industrial discharge limit of 300 ppb. This work establishes MOFs as promising flexocatalysts for uranium recovery and expands their potential in other flexocatalytic applications.