Spatiotemporally ordered topological transformation in layered double hydroxides enables synergistic mineralization of AsIII/Cd2+

The co-contamination of arsenite (AsIII) and cadmium (Cd2+) poses a significant challenge in environmental remediation due to their divergent chemical speciation and transformation pathways. Here, a redox-active layered double oxide (MgMn-LDO) is designed, and achieves adsorption capacities of 821.7 mg g‒1 for AsIII and 1895.6 mg g‒1 for Cd2+ in their coexisting system, presenting a state-of-the-art performance. Unexpectedly, the co-adsorption system not only enhances individual adsorption capacities but also accelerates the adsorption rate by 181‒fold compared to single-component systems. The LDO undergoes a four-stage spatiotemporally ordered topological transformation, which effectively decouples the oxidation of AsIII from the adsorption of Cd2+ and reverses the conventional competitive sequence. This stepwise mechanism ensures preferential oxidation of AsIII to AsV, followed by the alteration of Cd2+ adsorption pathway to isomorphous substitution, expanding diffusion pathways and accelerating As immobilization. Large-scale experiments demonstrate this material’s potential in synergistic remediation As/Cd in mining wastewater and contaminated soils. Here authors prepare a defect-rich Mg–Mn layered double hydroxide, which via a spatiotemporally ordered topotactic transformation, achieving synergistic comineralisation of AsIII and Cd2+.