Enhanced Removal of Oil Droplets from Oil-in-Water Emulsions Using Polyethylenimine-Modified Rice Husk

Abstract

Although several nano-materials have been used to adsorb oil droplets in water, preparing these materials requires complex procedures and expensive reagents. Their implication to the environment also remains unclear. Thus, in this study, we propose to develop efficient, inexpensive and environmental-friendly oil-removing adsorbents. To this end, we select an agricultural waste, rice husk (RH), as an adsorbent. To enhance the oil-removing performance, RH are modified with a biocompatible cationic polymer, polyethylenimine (PEI). The as-prepared PEI–RH was characterized using SEM, FT-IR, and TGA, and used to adsorb oil droplets in water. PEI–RH was found to exhibit a much higher oil adsorption capacity than RH. The oil adsorption kinetics and isotherm were measured and analyzed using theoretical models. The thermodynamic parameters of the oil adsorption were also determined. The factors affecting the oil adsorption to PEI–RH were examined including temperature, size of PEI–RH, pH, salt and surfactants. The higher temperature was found to enhance the oil adsorption capacity, whereas smaller size of PEI–RH exhibited a much higher adsorption capacity. The adsorption capacity of PEI–RH remained quite stable in the pH range of 5–7, while the highly acidic and basic conditions were not preferable for PEI–RH to separate oil-in-water emulsions. The addition of NaCl slightly improved the oil adsorption capacity but the presence of surfactants decreased the oil adsorption capacity of PEI–RH. PEI–RH also could be reused for multiple cycles after a simple ethanol washing method. These features enable PEI–RH a promising and low-cost adsorbent for the separation of oil-in-water emulsions.