Efficient removal of Eosin Yellow dye using solvothermal synthesised Ni/Al layered double hydroxide and layered double oxide: insights into adsorption kinetics and thermodynamics

The accumulation of organic pollutants in the environment is swelling steadily and raising the alarm for their redressal. Layered double hydroxides (LDH) and layered double oxides (LDO) are gaining prominence for their potential to address this challenge. This work includes an eco-friendly facile solvothermal synthesis of Ni/Al LDH and their calcination to Ni/Al LDO. The prepared nanomaterials were characterised by XRD, FE-SEM, HR-TEM, FT-IR, BET and TGA techniques, which confirm the highly porous structure of synthesised nanomaterials with a high specific area of 109.94 m2g−1 and 188.94 m2g−1 for Ni/Al LDH and Ni/Al LDO, respectively. A systematic study was conducted to explore the adsorptive potential of these materials towards the removal of organic dye Eosin Yellow (EY). The adsorptive efficiency was found to be 95% and 99% for Ni/Al LDH and Ni/Al LDO, respectively, under the optimised conditions of pH, adsorbent dose, contact time, dye concentration and temperature on adsorptive removal of EY dye, which was analysed by BBD-RSM (Box-Behnken Design Response surface methodology). The adsorption data fits best with the Freundlich isotherm model and pseudo-second-order kinetics. The thermodynamic study confirms the exothermic adsorptive process. The durability and reusability of the synthesised adsorbents were ascertained by their retention of the adsorptive efficiency even after five adsorption-desorption cycles which were as high as 91% and 85% for Ni/Al LDH and Ni/Al LDO, respectively. The mechanism of adsorption involves electrostatic interaction and hydrogen bonding between the surface of adsorbent and adsorbate as well as intercalation of dye molecules.