Biotemplated fabrication of a 3D hierarchical structure of magnetic ZnFe₂O₄/MgAl-LDH for efficient elimination of dye from water

A novel hierarchically porous magnetic ZnFe₂O₄/MgAl-layered double hydroxide (LDH) was reported as an effective adsorbent for the elimination of Congo Red (CR) from water. Three-dimensional stackable MgAl-LDH nanosheets synthesized through hydrothermal method were attached to the surface of ZnFe₂O₄ microsphere, using the inexpensive, non-toxic, quick and simple bio-template technique. Mg/Al molar ratios played a crucial role in crystal phase synthesis and adsorption capacity. Adsorption kinetics and thermodynamics of CR adsorption by ZnFe₂O₄/MgAl-LDH were also investigated. The adsorption kinetics followed the pseudo-second-order. The maximum adsorption capacity (294.12 mg g⁻¹) was obtained by the ZnFe₂O₄/MgAl-LDH with Mg/Al molar of 2, which was more productive than the base adsorbent without MgAl-LDH attaching (28.58 mg g⁻¹). Adsorption isotherm revealed Langmuir-type monolayer adsorption. The adsorption processes were spontaneous and endothermic in nature. Absorbents fabricated in this work could be easily regenerated by rinsing the material in methanol and magnetically separated from the solution. Adsorbent synthesized in this work is very promising composite for purification of water from toxic chemicals.