Adsorption of Remazol Brilliant Violet 5R dye from aqueous solution onto melunak and rubberwood sawdust based activated carbon: interaction mechanism, isotherm, kinetic and thermodynamic properties

In this work, melunak and rubberwood-based activated carbon (MAC and RAC) were prepared via microwave induced KOH activation for Remazol Brilliant Violet 5R (RBV5R) dye removal from aqueous solution. Batch adsorption experiments were carried out to evaluate the influence of pH, initial dye concentration, and contact time. The textural characterization shows high BET surface area of 914.0 and 796.0 m2/g for MAC and RAC, respectively, which indicate that they are comprised of a micro-mesoporous structure. Langmuir isotherms provided the best model for MAC and RAC adsorption data. The adsorption capacities of RBV5R onto MAC and RAC estimated by the Langmuir model were 238.33 and 204.08 mg/g, respectively. The pseudo-first-order, pseudo-second-order, and Elovich model equations were used to analyse the kinetic data of the adsorption process, and both data fitted well with the pseudo-second-order kinetic model. Film diffusion was the rate-limiting step controlling adsorption based on intraparticle diffusion and the Boyd plot. The adsorption mechanisms involved are pore filling, hydrogen bonding, n–π interactions, and π–π interactions. The thermodynamic parameters confirmed that the adsorption was spontaneous, feasible, and endothermic. Furthermore, a mechanism including physisorption and chemisorption of RBV5R on MAC and RAC has been proposed. The desorption study predicts excellent regenerative efficacy of both MAC and RAC for up to four cycles.