The effect of surface modification of coconut shell-based activated carbon on methomyl adsorption

• Main Author: Tanala, Francis Narvin Arenas
• Format: text
• Language: English
• Published: Animo Repository 2011
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/4096
• Institution: De La Salle University

In this study, ITDI-AC, which is an activated carbon prepared from physical activation of coconut shells in steam atmosphere, was used as the primary adsorbent for pesticide removal from water. The Industrial Technology Development Institute (ITDI) of the Department of Science & Technology (DOST) prepared this type of AC using their designed activation reactor. In addition, methomyl was selected as the pesticide to be used as adsorbate due to its high persistency and solubility in water. This study aims to modify the surface of the ITDI-AC to improve its surface properties and adsorption performance through thermal treatment in air at 250°C (ACA), nitrogen at 600°C (ACNT), and hydrogen at 600°C (ACHT). The resulting modified samples were characterized through Autosorb, SEM-EDX, TGA, FTIR, and PZC. Equilibrium time, kinetic behavior, and rate-controlling step were also determined from the kinetic adsorption data of methomyl adsorption on ITDI-AC. Characterization results showed that thermal treatment improves the surface and pore properties of ITDI-AC. The increase in the presence of basic groups was found using hydrogen and nitrogen atmosphere while the surface chemistry was not altered when using air atmosphere. The equilibrium time was found out to be 16 hours with the kinetic data following the pseudo-second order kinetic reaction while external diffusion is the rate-controlling step. The best AC sample was determined to be ACHT with a highest methomyl adsorption capacity of 10.53 and 10.36 mg/g derived from the Langmuir and Freundlich equations at Ce = 5mg/L as compared to ITDI-AC (5.67 and 5.98 mg/g), ACA (5.29 and 5.61 mg/g), and ACNT (8.97 and 9.21 mg/g). The batch adsorption data was found to be predicted the both isotherm models. The effect of pH, initial methomyl concentration, and temperature on adsorption capacity was also determined from batch adsorption tests using the ACHT sample. It was found out that initial methomyl concentration is the most significant factor at 95% while both initial concentration and temperature were significant at 90% confidence interval. The adsorption of methomyl on ACHT was found to be thermodynamically feasible, spontaneous, and endothermic, and classified as physical adsorption.