High selectivity and excellent reproducibility of Mg-UiO-66@rGO in phosphate electro-adsorption: Regulating structural defects to establish coordinative unsaturated metal sites

The flow-through electroactive membrane adsorption method has been proved to be a promising strategy to enrich low-concentration phosphate. However, the challenges of selective adsorption of phosphate and poor regeneration restrict its industrial application. Here, this study proposed a novel bimetallic Mg-UiO-66@rGO electrode material through the introduction of Mg(II) into UiO-66, which possessed remarkable adsorption selectivity and optimal reproducibility among the reported electrode materials. The maximum phosphate adsorption capacity of Mg-UiO-66(13)@rGO (Zr/Mg = 3:1) was 62.81 mg⋅g⁻¹ at 3.2 V. Furthermore, it maintained the excellent adsorption properties in the presence of all competitive anions and after 30 times of continuous adsorption–desorption. In actual wastewater, Mg-UiO-66(13)@rGO still represented excellent adsorption kinetics of 0.51 mg⋅(g⋅min)⁻¹ and equilibrium adsorption capacity of 61.2 mg⋅g⁻¹. The superior selectivity of Mg-UiO-66@rGO was attributed to the establishment of coordinative unsaturated metal sites (CUMSs), thus increasing the adsorption sites. The synergic effect of electric field facilitates the breaking and formation of coordination bonds between charged ions and deeper binding sites, boosting the adsorption–desorption ability. Notably, the structural stability is also a key factor in promoting repeated material regeneration. This study advances electrode material to a new level by introducing CUMSs and bimetallic synergies.