Competitive adsorption of diethyl phthalate (DEP), dibutyl phthalate (DBP) and di (2-ethylhexyl) phthalate (DEHP) onto corn cob biochar

Abstract

Phthalates are ranked among the most dangerous pollutants and often exist simultaneously in the terrestrial and marine environment. Their adsorption to biochar can have an impact on their behavior. So far, the competitive adsorption of phthalates on biochar has not been reported. In this study, biochar from corn cobs was produced and characterized for the competitive adsorption of diethyl phthalate (DEP), dibutyl phthalate (DBP) and di (2-ethylhexyl) phthalate (DEHP). Kinetics, isotherms experiment and pH effect were also carried out. Langmuir and Freundlich models, pseudo-first and pseudo-second-order kinetic models were used to simulate the experimental data. The result shows that in the single component phthalate system, biochar showed a higher adsorption capacity for DEHP (7.53 mg/g for BC400 and 14.71 mg/g for BC700) than for DEP (2.71 mg/g for BC400 and 5.00 mg/g for BC700) and DBP (6.59 mg/g for BC400 and 10.14 mg/g for BC700). In addition, a rapid adsorption rate for DEP was observed, which can be attributed to the smaller size and shorter carbon chains in the DEP molecule, resulting in faster diffusion into the pores of the biochar. In the three-component system, a competition between DEHP, DEP and DBP in their adsorption on biochars was observed, and DEHP (7.78 mg/g for BC400 and 12.05 for BC700 mg/g) was preferred to the detriment of DEP and DBP. The higher adsorption of DEHP can be explained by a stronger hydrophobic interaction with biochar. Compared to DEP and DBP, DEHP has a high octanol-water partition coefficient (logK ow ) and low solubility in water. This present work improves the understanding on the interaction between phthalates and the properties of biochar, and demonstrates that these properties are important for the control of environmental pollution.