Removal of toxic Congo red dye from water employing low-cost coconut residual fiber.

The coconut residual fiber (CRF) is the major byproduct obtained during production of virgin coconut oil. Its application as a biosorbent for adsorption of Congo red was investigated. The CRF was subjected to different pretreatments, namely, pressure cooking, hexane treatment, acid treatment and their combinations. The pretreatment of CRF with the combination of hexane, acid, and pressure cooking resulted in the highest degree of adsorption. The equilibrium data were analyzed and found to fit best to both Langmuir and Freundlich isotherms. Thermodynamic parameters such as standard free energy (ΔG kJ mol), standard enthalpy (ΔH, kJ mol) and standard entropy (ΔS, kJ mol K) of the systems were calculated by using the Langmuir constant. The ΔG, ΔH and ΔS were found to be 16.51 kJ mol, -19.39 kJ mol and -0.12 kJ mol K, respectively, at 300 K. These thermodynamic parameters suggest the present adsorption process to be non-spontaneous and exothermic. The adsorption process was observed to follow pseudo-second-order kinetics. The results suggest that CRF has potential to be a biosorbent for the removal of hazardous material (Congo red dye) with a maximum adsorption capacity of 128.94 mg g at 300 K.