Orange peel-derived bio-adsorbents for methylene blue removal: Surface characteristics, experiments, kinetics, and density functional theory mechanism

• Orange peel was chemically and thermo-chemically converted into a new bio-adsorbent • Bio-adsorbent was used for Methylene Blue Removal • Kinetic and equilibrium data fitted to various models • Density Functional Theory (DFT) identified the main adsorption mechanisms. Orange peel was transformed through chemical and thermochemical processes to produce materials that were tested for their ability to adsorb methylene blue from aqueous solutions and the results showed that some of these materials have a high adsorption capacity for methylene blue, which is influenced not only by their surface area but also by the functional groups on their surfaces. Kinetic and equilibrium data fitted to various models indicated that multiple interactions drive the adsorption process and the adsorption capacities of these materials (exceeding 192.31 mg g⁻¹) were found to be comparable to those of activated carbon and other agro-industrial adsorbents. Additionally, Density Functional Theory studies identified the main adsorption mechanisms as (i) electrostatic interactions, (ii) hydrogen bonding, and (iii) π-π interactions between methylene blue and the bio-char and these findings suggest that orange peel-derived materials are a promising and effective alternative for removing methylene blue dye from water.