Adsorption modeling by two sites Langmuir type isotherm for adsorption of bisphenol-A and diethyl phthalate onto activated carbon in single and binary system

Adsorption of bisphenol-A (BPA) and diethyl phthalate (DEP) onto activated carbon has been studied. The experimental adsorption data is reasonably well fitted by a two site Langmuir isotherm model. The estimated two equilibrium adsorption constants were almost the same even though the adsorbates were different. This suggested that the existence of two types of adsorption sites with different equilibrium adsorption constants for strong and weak sites on the present activated carbon surface. The equilibrium adsorption constant of strong site was 130 times larger than that of weak site, and the saturated adsorption density of weak site was 2.6 and 3.6 times larger than that of strong site for BPA and DEP, respectively. In addition, adsorption experiments of the binary system have also been carried out. Based on suggesting two type sites, two models, competitive adsorption or noncompetitive adsorption models, were attempted to apply to the experimental results. Judging from the model consideration, the noncompetitive model could describe well the adsorption isotherm in the binary system. Compared with the single system, in the binary system, the equilibrium adsorption constants were almost the same, but the saturated adsorption densities were 10% to 30% lower than that of the single system.