Removal of methyl green dye using activated carbon prepared from corn cobs

Dyes released into hydrological systems in textile manufacturing, printing and other dyeing processes are hazardous and toxic to human and aquatic lives. Activated carbons have been remarkably used to treat dye contaminated waste water due to their large surface area and porosity, however regeneration and high cost have limited their applications. This study investigated the use of activated corn cobs (ACC) on the adsorption of methyl green dye from aqueous solution. The raw cobs were collected, crushed into particle size of about 600 μm and modified in-situ with KOH to prepare ACC which was characterized using some analytical techniques such as Fourier Transform Infra-Red (FTIR), Energy Dispersive X-ray (EDX) spectroscopy and Scanning Electron Microscopy (SEM). The absorbance of the dye solution was monitored at 620 nm with UV-Visible spectrophotometer. FTIR analysis showed the vibration frequency for C‒H, O‒H, C=O and C‒O stretches at 2950, 3400, 1710, and 1150 cm-1 respectively. SEM results revealed the ACC has a porous surface with heterogeneous pores which became compact after dye adsorption. EDX confirmed the presence of C, O, H and K in the adsorbent. The suitability of the pseudo-first, pseudo second and Elovich kinetic models for the sorption of methyl green onto ACC was examined. The equilibrium data were subjected to Langmuir, Freundlich, Tempkin and Dubinin-Radushkevich isotherm models. The pseudo-second order kinetic model provided the best correlation and was found to be more statistically significant. Langmuir model was found to fit well based on the high values of the coefficient of regression R2 and low % standard error values. The monolayer adsorption capacity Qmax was found to be 85.83 mgg-1. Thermodynamic adsorption processes showed the spontaneous, endothermic and randomness of the systems with free energy change less than zero, enthalpy change (∆H) of 62.47 kJmol-1and entropy change (∆S) of 125.37 Jmol-1K-1.