Selective Phosphate Adsorption Using Topologically Regulated Binary-Defect Metal-Organic Frameworks: Essential Role of Interfacial Electron Mobility

Metal-organic framework (MOF)-modified biochars (BC) have gained recognition as potent adsorbents for phosphate. However, essential insights into the electronic interfacial state of the MOFs remain lacking. In this study, we propose a novel topological transformation strategy to directionally regulate the interfacial electronic states of BC/MOFs composites. The optimized BC/MOFs exhibited an excellent selective phosphate adsorption capacity of 188.68 mg·g^-1, coupled with rapid sorption kinetics of 6.81 mg·(g·min^0.5)⁻¹ in simulated P-laden wastewater. When challenged with real bioeffluent, such efficacy was still maintained (5 mg·L^-1, 25.92 mg·g^-1). This superior performance was due to the Fe(III) → Fe(II) transition, promoting electron mobility and leading to the anchoring of Mg(II) to form specific coordination unsaturated sites (Mg-CUS) for phosphate adsorption. Importantly, the simultaneous regulation of binary defects further enhances electron mobility, resulting in the formation of sp³ unequal hybrid orbitals with a stronger internal coupling capability between Mg 3s in Mg-CUS and O 2p in phosphate. Furthermore, the high electron affinity of Mg effectively promotes electron cycling, endowing BC/MOFs with a distinct self-healing capability to facilitate phosphate desorption. The outcomes of this study provide novel perspectives for electronic regulated phosphate adsorption.