Chemically modified tomato stems for methylene blue removal: Kinetic, isotherm and thermodynamic studies

Several research studies have demonstrated that adsorption is a good way to remediate methylene blue (MB) traces found in wastewater. However, the high cost of industrial activated carbons has led to the development of adsorbents from biomass in recent years. The present work is therefore aimed to develop biosorbent based on tomato stems bypassing carbonization and to provide added value to tomato stems that exist locally in large quantities and are not valued. The adsorption properties of the biosorbents on MB adsorption process were evaluated by studying several parameters like adsorbent dose, pH, contact time, temperature, biosorbent regeneration medium and initial dye concentration. Adsorption kinetics best complied with pseudo–second–order kinetic model indicating an adsorption mechanism focused on chemical process involving electron exchanges between adsorbent and adsorbate. Experimental data applied to different isotherm models revealed that Langmuir monolayer model was suitable to fit the adsorption process indicating a maximum adsorption capacity of 34.48 mg g −1 . Thermodynamic parameters determined from this study show the spontaneity and endothermic nature of the adsorption process. Material after adsorption was regenerated in hydrochloric acid medium. An overall comparison of the results of this study with similar reported methods using biomass as raw material showed that activated tomato stems could be a promising adsorbent for MB removal from wastewater.