Boric acid–driven surface charge reconstruction on surface–oxidized zero–valent iron enhances uranium capture efficiency

The reduction and removal of uranyl ions (UO 2 2+ ) using highly active zero–valent iron (Fe⁰) are crucial for efficient uranium capture in environmental and nuclear waste management. However, the reported utilization efficiency of Fe⁰ for uranyl reduction remains limited due to surface passivation and inadequate electron transfer. Herein, we demonstrate an advanced approach by introducing boric acid to reconstruct the surface charge on oxygen–rich Fe⁰, effectively repelling oxygen adsorption and enhancing uranium capture efficiency. Combining theoretical calculations with modern characterization techniques, the interaction process between UO 2 2+ and surface boric acid–modified Fe⁰ was studied. Surface modification with boric acid can alter the isoelectric point of Fe⁰, increasing the adsorption of U(VI). Additionally, the empty p orbitals of boron can promote delocalization of electron clouds around shell iron atoms and oxygen atoms, thereby facilitating the outward transfer of electrons from the iron core within Fe⁰ and enhancing the reduction of U(VI). Furthermore, the surface boric acidification of Fe⁰ can enhance the removal of U(VI) through improved adsorption and reduction pathways. Density functional theory calculations revealed that the interfacial electron transfer pathway provided by surface boric acid enhances the reduction capability and inhibits the adsorption of oxygen molecules. This effect reduces the ineffective consumption of Fe⁰ electrons and increases the proportion of U(IV) in the products. This charge redistribution effectively prevents surface passivation while promoting stronger interaction with uranyl ions.