P2O5로 표면개질한 활성탄에 의한 Bisphenol A의 흡착특성

Abstract

The objective of this work is to investigate the adsorption characteristics of bisphenol A (one of phenolic endocrine disrupting chemicals) by surface modified activated carbons prepared with various P2O5 concentrations using the activated carbon (WCP-AC) prepared from waste citrus peel (WCP) which is abandoned in large quantities in Jeju Island and the coconut-based activated carbon (C-AC) which is marketed in large amounts. The surface properties and the adsorptivity of bisphenol A of the activated carbons before and after surface modification with P2O5 are compared, and the adsorption parameters are calculated by appling adsorption date to adsorption isotherms and adsorption kinetic models. Moreover, the effects of P2O5 concentration, solution temperature, pH and ionic strength on the adsorption of bisphenol A onto the activated carbons before and after surface modification. The results obtained are summarized as follows.

The contents of C, H and N of the activated carbons after surface modification are similar to those of the activated carbons before surface modification, but the content of P2O5 for the former increases greatly than for the latter, due to the impregnation of P2O5 into the pores. For the activated carbons after surface modification, the surface pores retrogrades due to the impregnation of P2O5 into the pores, the specific surface area, total pore volume, average pore diameter and iodine adsorptivity decrease, compared to the activated carbons before surface modification. The adsorption equilibrium of bisphenol A by the activated carbons before and after surface modification is obtained at nearly 48 h, and the amounts of adsorption equilibrium of bisphenol A for the latter are higher than those for the former, although specific surface area, total pore volume, average pore diameter and iodine adsorptivity for the latter is lower than those for the former. The adsorption of bisphenol A by the activated carbons before and after surface modification fits the Langmuir isotherm better than the Freundlich isotherm, although it can be described by both isotherms. The maximum amounts of adsorption of bisphenol A by the activated carbons after surface modification with 1,000 mg/L P2O5 are 1.3 ～ 1.5 times higher than those by the activated carbons before surface modification. The adsorption kinetics of bisphenol A by the activated carbons before and after surface modification fits the pseudo-second-order model better than the pseudo-first-order model. The values of rate constant of bisphenol A by the activated carbons after surface modification with 1,000 mg/L P2O5 are 1.22 ～ 1.90 times higher than those by the activated carbons before surface modification. With increasing P2O5 concentration in surface modification of activated carbons, the amounts of adsorption of bisphenol A increase, but do not increase above 1,000 mg/L of P2O5. With increasing solution temperature, the reaction rate increases, but the amount of adsorption equilibrium decreases, especially for the activated carbons before surface modification. The adsorption of bisphenol A by the activated carbons before and after surface modification occurs by physisorption and chemisorption, respectively, from the activation energy obtained by applying the adsorption data with solution temperature to the Arrhenius equation. The amounts of adsorption of bisphenol A by the activated carbons before and after surface modification are similar in the pH range of 5 ～ 9, but decrease greatly at pH 11, and increase with increasing ionic strength due to its screening effect and salting out effect.