Removal of methylene blue dye from aqueous solution using citric acid modified apricot stone

Abstract

In this study, apricot stones were modified with citric acid and used in the adsorption of methylene blue. Fourier transform infrared (FT-IR) Scanning electron microscopy (SEM), and X-Ray Diffraction (XRD) were used to characterize the adsorbent. The influence of the initial pH, temperature, contact time, and initial concentration on the adsorption process was investigated. The thermodynamic investigation showed that adsorption was spontaneous and the adsorption process was endothermic. In experimental studies, isotherm models by Langmuir, Freundlich, Temkin, and Dubinin – Radushkevich (D-R) were analyzed and experimental data showed the best agreement with the Temkin isotherm model. We found that the maximum monolayer adsorption capacity for the Langmuir isotherm model was 19.01 mg/g. Pseudo-first and second-order models were examined and, according to the results of the kinetic model analysis, the highest correlation coefficient (R2> 0.99) belongs to the pseudo-second-order kinetic model. It was concluded that the adsorption mechanism was carried out in both the intra-particle diffusion and the liquid film diffusion model.