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

Abstract

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 (ΔG⁰ kJ mol^-1), standard enthalpy (ΔH⁰, kJ mol^-1) and standard entropy (ΔS⁰, kJ mol^-1 K^-1) of the systems were calculated by using the Langmuir constant. The ΔG⁰, ΔH⁰ and ΔS⁰ were found to be 16.51 kJ mol^-1, -19.39 kJ mol^-1 and -0.12 kJ mol^-1 K^-1, 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^-1 at 300 K.