Green synthesis of mesoporous Ni-Co layered double hydroxide and its application for removal of 2,4-dinitrophenol from water: A theoretical study complemented by the first principle density functional theory-Monte-Carlo approach

This paper describes the synthesis of a novel mesoporous Ni-Co layered double hydroxide(LDH) and its application for the adsorptive removal of 2,4-dinitrophenol(2,4-DNP) from an aqueous solution. A green synthetic method was used involving a non-aqueous `soft chemical' ethanol: acetone mixture in order to avoid intercalation or interlayer contamination by CO2 gas, which is responsible for carbonate formation. The synthesized material was characterized using PXRD, HR-TEM, FESEM, XPS, FT-IR, TGA-DTA, etc. The experimental and model fitting results of adsorption studies showed that equilibrium Freundlich adsorption isotherm and kinetic pseudo-second-order were the best-fitting models. Also, thermodynamic adsorption parameters Delta H-o,Delta S(o)and Delta G(o) were found to be favorable, non-spontaneous, and endothermic. Furthermore, theoretical molecular dynamic simulation (MD) revealed that the nature of adsorbate-substrate (2,4-DNP- Ni-Co LDH) interactions were favorable hydrophobic interactions. DFT-based DMoL3 approach showed that the adsorbate-substrate energy gap (eV) increases with the increase in the interfacial region, explaining the high chemical stability after the adhesion of adsorbate molecules. The regeneration adsorption cycles showed that the Ni-Co LDH acts with an excellent removal affinity towards the 2,4-DNP molecule within 150-180 min from cycles 1-4.