Modeling and optimization of cationic dye adsorption onto modified SBA-15 by application of response surface methodology

Abstract

SBA-15 mesoporous silica was modified with melamine-based dendrimer amine (MDA) via grafting approach and used as adsorbent for the removal of methylene blue (MB) cationic dye from aqueous solution. The synthesized material, denoted MDA-SBA-15, was characterized by means of X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and N₂ adsorption–desorption, in order to prove the 2D hexagonal mesoporous structure and covalent grafting of MDA onto SBA-15. Central composite design combined with response surface methodology (RSM) was employed for statistical modeling, optimization, and analysis the effects of influence variables such as the initial pH (3–10), adsorbent doses (0.5–3.5 g L⁻¹), temperature (25–40°C), and initial concentrations (10–30 mg L⁻¹) onto the MB removal. From the analysis of variance, pH and temperature were identified as the most influential factors onto each experimental design response. Maximum percentage removal (98%) under optimum conditions of variables (pH of 10, adsorbent dose of 3 g L⁻¹, MB concentration of 10 mg L⁻¹, and temperature of 25°C), as predicted by RSM, was found to be very close to the experimentally determined value (95.5%). The Langmuir, Freundlich, and Temkin isotherm models were used to describe the equilibrium sorption of MB by MDA-SBA-15, and the Langmuir isotherm showed the best concordance as an equilibrium model. The obtained kinetic data manifested that adsorption kinetics was more accurately exposed by a pseudo-second-order model and film diffusion was the rate-determining step for the adsorption of MB onto MDA-SBA-15. The associated thermodynamic parameters reveal that the process of adsorption is spontaneous and exothermic nature within the studied temperature range.

Keywords:

• Adsorption
• Cationic dye
• SBA-15
• Response surface methodology

Acknowledgments

Authors wish to thank the Iranian Nano Technology Initiative Council for financial support. The authors also wish to thank Shahid Beheshti University for considerable laboratory support.