Green iron oxides/amino-functionalized MCM-41 composites as adsorbent for anionic azo dye: Kinetic and isotherm studies

Abstract

In this work, green iron oxide nanoparticles (FeONPs) were prepared from Fe(III) precursor and Camellia sinensis (black tea) extract, and were anchored on amino-functionalized mesoporous silica MCM-41. The multicomponent composite named BTFe/MCM-41-NH2 was characterized and applied in the adsorption of the anionic azo dye methyl orange. The results indicated that BTFe/MCM-41-NH2 is 11 times more adsorbent than MCM-41 and 2.5 times more adsorbent than MCM-41-NH2, showing the improved adsorption property of the multifunctional material. Adsorption parameters such as adsorbent dosage, initial dye concentration, pH and time, were screened for BTFe/MCM-41-NH2, a provided an experimental adsorption capacity at equilibrium of qe,exp = 105.3 mg g−1 at 298 K. Zeta potential measurements showed the favored electrostatic interaction with the negatively charged dye at acid pH when BTFe/MCM-41-NH2 is positively charged. Kinetic studies revealed pseudo-first-order model characteristic of reaction-controlled adsorption. The experimental data at equilibrium was fit by several adsorption isotherms models. Freundlich and Temkin were the most suitable isotherms to describe the prepared material, suggesting an adsorption through a heterogeneous surface with multiple sites of adsorption, such as protonated amino groups, FeONPs, besides the tea polyphenols that provided extra sites of adsorption through π-π interactions with the aromatic rings of the dyes.