Adsorption and mechanism study for methylene blue dye removal with carbonized watermelon (Citrullus lanatus) rind prepared via one-step liquid phase H2SO4 activation

In this study carbonized watermelon (Citrullus lanatus) rind (CWMR) was prepared and reported as a low-cost and renewable material for adsorption of methylene blue (MB) from aqueous solution. Sulphuric acid (H2SO4) was chosen as a chemical activator to modify watermelon rind via a one-step chemical activation at relatively low activation temperature (110 degrees C) for 24 h. The adsorption study in batch mode was performed by taking into account the effects of the CWMR dosage (0.02-0.25 g), solution pH (3-9), initial MB concentration (50-400 mg/L), and contact time (0-300 min). A comprehensive kinetic, equilibrium, and thermodynamic study was carried out. The kinetic results are described by a pseudo-second-order kinetic model, while the adsorption process at equilibrium followed the Langmuir isotherm model with maximum adsorption capacity of 200 mg/g at 303 K. Thermodynamic parameters reveal that the adsorption process is endothermic in nature that is driven mainly by electrostatic, hydrogen bonding, and pi-pi stacking interactions. These findings indicated that the CWMR developed in this research is an efficient, low cost, and renewable adsorbent for the effective removal of cationic dyes from wastewaters.