Removal of Remazol Brilliant Blue Reactive Dye from Aqueous Solutions Using Watermelon Rinds as Adsorbent

Abstract

This study examined the feasibility of removing Remazol brilliant blue reactive (RBBR) dye from aqueous solutions using watermelon rind activated carbon (WRAC) as adsorbent. The surface area of WRAC prepared is 776.65 m2/g with high pore volume of 0.438 cm3/g, which is comparable to commercially expensive activated carbon. The effects of contact time, initial dye concentration, pH, and temperature on adsorption of RBBR dye were investigated. Pseudo-first-order, pseudo-second-order, Elovic, and Avrami kinetic models were used to test the experimental data in order to elucidate the kinetic adsorption process; pseudo-second-order model best fitted the data. Experimental data were analyzed using eight model equations: Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, Radke–Prausnite, Sips, Viet–Sladek, and Brouers–Sotolongo isotherms, and it was found that the Freundlich isotherm model described the equilibrium adsorption data best. The heat of adsorption (ΔH) indicated the endothermic nature of the process and the negative values of free energy (ΔG) indicated that the adsorption is spontaneous. The mechanism of adsorption was controlled by both film and intraparticle diffusions. The mean free energy obtained from Dubinin–Radushkevich model is 4.972 kJmol−1, indicating that the adsorption of RBBR dye onto WRAC follows physical adsorption process.