Hierarchical porous Ni/Co-LDH hollow dodecahedron with excellent adsorption property for Congo red and Cr(VI) ions

High-performance adsorption toward Congo red and Cr(VI) depends on the design of hierarchical nanostructures. Herein, hierarchical porous Ni/Co-layered double hydroxide (NiCo-LDH) hollow dodecahedra were synthesised by etching zeolitic imidazolate framework-67 (ZIF-67) as a self-sacrificing template with Ni(NO₃)₂. The synthesised NiCo-LDH showed better adsorption property for adsorbing Congo red and Cr(VI) ions (Cr₂O₇²⁻) than NiCo₂O₄-NiO, which was obtained by calcining NiCo-LDH at 350 °C. The adsorption processes of Congo red and Cr(VI) ions very well fitted the pseudo-second-order model. The Langmuir model was more suitable than the Freundlich model in describing the adsorption isotherm, and the theoretical maximum adsorption capacities of Congo red and Cr(VI) ions were 909.2 and 99.9 mg g⁻¹ at 30 °C, respectively. Furthermore, the synthesised NiCo-LDH was recyclable and could selectively adsorb anionic dyes. This work can serve as a basis for designing and manufacturing excellent adsorbents for water treatment.