Simultaneous removal of anionic dyes onto Mg(Al)O mixed metal oxides from ternary aqueous mixture: Derivative spectrophotometry and Density Functional Theory study

Abstract

A simultaneous removal of Eriochrome Black T (EBT), Indigo Carmine (IC) and Methyl Orange (MO) anionic dyes in ternary mixture onto mixed metal oxides (Mg(Al)O) was studied. Mg(Al)O nanoparticles were obtained through one-step by pyrolysis of MgAl-layered double hydroxide compound as precursor. In view of the significant interferences in visible light absorbance, second-order derivative spectrophotometric method was adopted for simultaneous analysis of MO, EBT and IC concentrations. Thermodynamic parameters indicated that the removal of the three anionic dyes were exothermic and spontaneous in nature. Theoretical studies carried out on the dyes structures using density functional theory (DFT) calculations were of use to evaluate the relative electron donating/accepting character of each dye molecule, and are in good agreement with experimental data. Quantum chemical results suggested that MO (N = 4.2414) is more nucleophilic than EBT (N = 3.7960) and IC (N = 3.9797); the assumption has been that MO molecules were favorably adsorbed and interacted first with Mg(Al)O nanoparticles in the mixture media. Moreover, according to the local molecular reactivity results the nitrogen atoms, exhibiting the higher nucleophilic Parr functions PK−, could be the main active sites. In the light of these results, a possible removal mechanism was suggested.