Upgrading of agro-industrial green biomass residues from chocolate industry for adsorption process: diffusion and mechanistic insights

In the last decades, the world suffers from the wastes those results from unprecedented growth in the food industry. This context investigated the characteristics and suitability of utilizing cocoa shell (CS), an agro-industrial residual biomass waste from the chocolate industry, without any chemical and/or physical treatment. It is an abundant, low-cost, and green adsorbent that can be utilized for the effective removal of basic blue (BB41) as an example of cationic dye from aqueous solutions. The CS showed high adsorption potential (90.04%) with the mild operating condition, 45 min adsorption time, pH 6, CS dose 4 g/L, BB41 concentration 10 mg/L, stirring speed 400 rpm at 295 K. The kinetic, equilibrium, isotherms and mechanism studies revealed that the BB41 adsorption onto CS was attained mainly by electrostatic interaction, π–π stacking interaction, hydrogen bonding, covalent bond, and physical mechanisms. Besides, the organic functional groups played an important role during the adsorption process. The thermodynamic parameters suggested that the adsorption of BB41 dye was the non-spontaneous endothermic process with an activation energy 18.28 kJ/mol. From the industrial point of view, this work offers an economical push in waste management and also a green approach for the effective removal of toxic dyes from textile wastewater.