Adsorption isotherms studied on synthesized corn cob-based activated carbon as an adsorbent for removal of methyl orange dye from aqueous solution

Abstract

The synthesized corn-based activated carbon (CCAC) is used as an adsorbent to remove the methyl orange (MO) dye from the dye’s aqueous solution. By using X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) analysis and comparing the results with activated carbon (AC), the CCAC was shown to have been formed accordingly. Also, analysis of the Zero-point Charge of the CCAC (pH_PZC = 5.12), moisture contents (12.5%), ash content (4.56%), pore volume (25%), and surface area (346.2 m²/g). The batch process was used to investigate the effect of different parameters on adsorption such as contact time, initial concentration, temperature, and % of Coke. At 30 min, 99.1% of the MO was removed at room temperature, and at 45 °C 98.4% within 20 min. Scanning electron microscopy (SEM) images were taken to see the surface morphology of the CCAC before and after adsorption, and calculated the average particle size of the adsorbent (1.955 µm). The experiment was designed at three different temperatures (25 °C, 35 °C, and 45 °C) to study adsorption isotherms using one-, two-, and three-parameters of adsorption isotherm models, which were fitted using the origin lab program. Among the three different temperatures, considering the R² value in different adsorption isotherms, the temperature 45 °C condition was well-fitted with all the adsorption isotherms, balancing with other parameters. The better-fitted adsorption isotherms were like—Langmuir > Freundlich > Temkin > Toth > Redlich–Peterson > Dubinin-Radushkevich > Fowler–Guggenheim > Henry’s Isotherm. Analyzing the thermodynamics and kinetics of the adsorption process indicates the adsorption was a spontaneous, exothermic, and pseudo-second-order adsorption process. Therefore, the results of this study reveal that the two-parameter adsorption isotherms (like Langmuir > Freundlich > Temkin) were well fitted for the removal of the MO dye by using the easily available, eco-friendly and cheap agricultural waste- corn cob-based activated carbon which could be a choice as an adsorbent.