Enhanced adsorption of methylene blue on modified silica gel: equilibrium, kinetic, and thermodynamic studies

Abstract

The present work was undertaken to chemically modify silica gel (SG) with citric acid (CA) to enhance its adsorption power for methylene blue (MB) dye from aqueous solution. Citric acid-modified silica gel (CAMSG) was synthesized thermochemically and was characterized by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and elemental analysis. Influences of various parameters such as adsorbent dose, pH, initial dye concentration, contact time, and temperature on adsorption were studied. Equilibrium data were analyzed using Langmuir, Freundlich, and Temkin isotherm models. Kinetic studies show that the adsorption follows pseudo-second-order kinetics and intraparticle diffusion model. Negative values of Gibb’s free energy change (ΔG°) show that the adsorption was feasible and spontaneous in nature and the negative values of enthalpy change (ΔH°) confirm exothermic adsorption.

Keywords:

• Adsorption
• Isotherm
• Kinetics
• Methylene blue
• Silica gel

Acknowledgments

The authors are thankful to Dr. Dinesh Deva of Nanoscience, IIT Kanpur, India for recording SEM and Council of Scientific and Industrial Research (CSIR), New Delhi, India, for the financial support.