Tailoring the sorption properties of crystal violet by activated carbon extracted from waste onion

Crystal violet (CV), a cationic dye is not only toxic for plant and animals but also for human, due to its resistance to biodegradation. It is, therefore, highly important to remove CV dyes from water resources. Adsorption is cost-effective and ecofriendly technique to remove CV dyes. Herein, we report the synthesis of novel waste onion-based porous biosorbent and its chemical activation through KOH. N-2 adsorption/desorption isotherms show that activated carbon was found to be highly mesoporous with average particles size of 17 nm. The BET surface area was calculated to be 292.8 m(2)/g. To characterize the materials for structural, morphological and thermal stability, various analytical techniques like X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy and thermogravimetric analysis were performed. For comparison purpose both carbon and activated carbon samples were used to remove CV dyes from water resources. Freundlich isotherm model provides the best correlation for adsorption of CV on both the samples. Monolayer adsorption capacity (q(m)) for carbon and activated carbon was 8.7 and 18.6 mg/g respectively, which declared that activated carbon is more effective adsorbent then carbon. To explore the mechanism of adsorption thermodynamics and spectroscopic analysis were investigated. Positive value of delta H and negative value of delta G indicated that reaction is endothermic and spontaneous. Value of E-a < 40 kJ/mol indicates that mechanism of adsorption is physisorption. Overall onion waste provides an effective and novel biosorbents for removal of crystal violet dye from water resources.