Modified walnut shell for enhanced adsorption for methylene blue from aqueous solution: Preparation, characterisation, isotherm, kinetics and mechanism study

Abstract

Human and aquatic health is frequently at risk due to methylene blue (MB) dye pollution in aquatic environments. In order to remediate water contaminated with MB dye, a chemically modified walnut shell (CMWS) adsorbent is developed in the present study. The physico-chemical characteristics of modified walnut shell have been investigated using a variety of characterisation techniques, including pH_pzc, FTIR, BET, FE-SEM, and EDS. After optimising the impact of the most important parameters, a maximum removal of 85.6% is noted at pH 6. The MB uptake by chemically modified walnut shell is explained by the multilayer layer adsorption onto energetically equivalent sorption sites. The linear Freundlich model yielded a maximal adsorptive capacity of 66.6 mg MB per g CMWS. The kinetic models also showed that the rate depends on the adsorbent's adsorptive capacity. The pseudo-second order model works well for MB adsorption and R² >0.999. Thermodynamic studies indicated that adsorption is feasible, spontaneous and endothermic in nature. This work suggests that CMWS be investigated further as a possible adsorbent for the removal of MB dye.