Removal of methylene blue dye from aqueous solutions by adsorption on levulinic acid-modified natural shells

This study has developed an innovative and environmentally friendly approach for the removal of methylene blue (MB) dye by natural shells (NShs) chemically modified with levulinic acid (LA). Almond shell (ASh), walnut shell (WSh), and apricot kernel shell (AKSh) were used as waste fillers. The adsorption behavior of MB onto the biosorbents was investigated with respect to parameters such as sorbent dosage (0.4-6 g/L), pH (3-10), initial dye concentration (10-500 mg/L), and temperature (25-65 °C). The biosorbents were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) analysis. The isotherm and kinetic adsorption data can be said to fit the Freundlich isotherm model and the pseudosecond-order model, respectively. The maximum adsorption capacity (q_max) of LA-modified walnut shell (LA-WSh), almond shell (LA-ASh), and apricot kernel shell (LA-AKSh) calculated by the Langmuir equation at 25 °C was 294.1, 270.2, and 180.0 mg/g, respectively. The results of thermodynamic analysis showed that adsorption was feasible, endothermic, and spontaneous.