Molecular modeling investigation on mechanism of cationic dyes removal from aqueous solutions by mesoporous materials

Abstract

Currently, mesoporous silica (MPS) adsorbents as promising material have been widely used for toxic dyes removal from wastewater but understanding the detail of adsorption mechanism still remains a big challenge. This work presents an approach for design and simulation of the cationic dyes removal through MPS and an amino-functionalized MPS (3-Aminopropyl triethoxysilane, MPS-APTES) structures in aqueous solution. The adsorption of methylene blue and malachite green dyes on the MPS and functionalized MPS were comprehensively analyzed using quantum mechanics method. The results showed that the adsorption energy of compounds was increased as follows: MPS-APTES-water-malachite green, MPS-APTES-water-methylene blue, MPS-water-malachite green and MPS-water-methylene blue structures. An improvement in adsorption of both dyes was observed in presence of amino groups in the surface of MPS. The HOMO and LUMO energy levels were calculated for dyes and adsorbents-water-dyes configurations. Other impressive quantum chemical descriptors, such as chemical potential (μ), global hardness (η), global softness (σ), polarizability and electrophilicity index (ω) were calculated using ionization energy (I) and electron affinity (A) energies. It was observed that the softness and chemical reactivity of MPS-APTES-dye systems were higher than MPS-dyes; moreover MPS-APTES-water-malachite green structure had more softness and chemical reactivity compared to MPS-APTES-water-methylene blue. As a result, the electron transfer of studied dyes on MPS-APTES structure was more facile compared to MPS structure which was in accordance with the low ∆EGAP and electrophilicity index of MPS-APTES-dyes compounds. The quantum calculations demonstrated that amino functionalization of MPS provides higher reactivity for adsorption of organic pollutants in comparison to MPS. In particular, this study shows that the theoretical molecular calculation is highly recommended for cost and time saving as this approach offers an evaluation of process feasibility before any practical analysis.