Weak electric field enabling enhanced selectivity of tannic acid-graphene aerogels for Pb2+ harvesting from wastewater

Abstract Selective recovery of Pb2+ is always a high concern in the industrial application but challenging. Recycling Pb2+ as a sort of resource from contaminated water not only can significantly cut down the resource depletion but also reduce environmental pollution. Herein, a feasible electrochemistry-driven adsorption approach (ECDA) is employed to aid adsorbents for the selective removal of Pb2+ from metal-laden wastewaters. The distribution coefficient (Kd) of Pb2+ on the conductive tannic acid-graphene aerogel (TA@GO) is 370.53 mL g−1 at −0.2 V which is 3 times that of the corresponding adsorbent (118.80 mL g−1) without applying a weak electric field. Compared with pure adsorbent, TA@GO achieves an enhanced selectivity coefficient (α) from 1.39 to 4.18 for Pb2+/Cu2+ at −0.2 V. The weak electric field can drive Pb2+ ions migrates rapidly from the bulk solution to the surrounding binding sites (phenolic hydroxyl) of adsorbent forming pre-aggregation, increasing the accessibility and availability of the active sites with target pollutants. And then a strong coordination interaction occurs between Pb2+ and the binding sites on TA. By applying different potentials, the selective properties of TA@GO can be tuned. Moreover, TA@GO shows a high selectivity coefficient of 12.44 for Pb2+/Cu2+ after being improving the electrical conductivity using electro-reduction, which is up to 2.5 times higher than the original TA@GO. We elucidated a new Pb2+ removal mechanism that involves a synergic effect by anchoring additional electric fields on functional adsorbents to improve the selective performance. This study highlights a novel direction for selective Pb2+ recovery by introducing electric fields onto adsorbents in practical application.