Experimental and simulated TD-DFT study of malachite green dye and tetrahydroquinoxaline hybrid blend: Its application removal from wastewater

Abstract

2-Carbethoxy-3-oxo-1,2,3,4-tetrahydroquinoxaline (CTQ) was synthesized using a condensation reaction between o-phenylenediamine and diethylbromomalonate under regulated conditions. CTQ compound was used as a powerful adsorbent in the elimination of harmful malachite green (MG) dye from wastewater using the spectrophotometer technique. By applying Hartree-Fock (HF) and density functional theory (DFT-B3LYP) with 6-31G(d,p) as the basis, the optimized geometries, vibrational wavenumbers, intensities of vibrational bands, and various atomic charges of 9VC have been investigated. The basic vibrational modes measured experimentally are analyzed and compared to theoretical predictions. Density functional theory (DFT) was used to examine the geometry, electronic structure, polarizability, and hyperpolarizability of the hybrid blend organic dye (CTQ+MG)HB, which contains π-conjugated tetrahydroquinoxaline unit with an electron donor-acceptor moiety, and time-dependent DFT (TD-DFT) with several hybrid functionals were used to examine the electronic absorption spectrum. Various factors affecting the removal of this toxic dye like adsorbent dose, contact time, initial dye concentration, and dye solution temperature were examined. To show the equilibrium of the adsorption, Freundlich and Langmuir isotherm models were utilized. Freundlich and Langmuir's equations' correlation coefficient values were found to be in perfect agreement. The transfer of MG to quinoxaline is regulated by a pseudo-second-order procedure. The adsorption approach was a spontaneous and exothermic type. A suitable reaction mechanism has also been described and explored in this study along with an analysis of the thermodynamic parameters.