Competitive adsorption of a phthalate esters mixture by chitosan bead and alpha-cyclodextrin-linked chitosan bead

The competitive adsorption effect by chitosan bead and alpha-cyclodextrin-linked chitosan bead on a mixture of six phthalate esters (PAEs) was investigated. The adsorption efficiency of short-chain hydrophilic PAEs was reduced when long-chain hydrophobic PAEs co-existed in the solution. Moreover, the adsorption efficiency of adsorbents for PAE is correlated to the distribution ratio (Kd), which shows that the Kd of hydrophobic PAEs is higher than that of hydrophilic PAEs. Both chitosan bead and alpha-cyclodextrin-linked chitosan bead exhibit the same phenomenon. The effect of alpha-cyclodextrin (CD)-linked chitosan bead is more significant compared with that of chitosan bead. Furthermore, it is observed that both adsorbents spontaneously adsorb PAEs by free energy (deltaG0), but the hydrophilic PAE co-existing with DMP (dimethyl phthalate) results in less entropy (deltaS0) change compared with a hydrophobic PAE co-existing with DMP. In a continuous system to treat a PAE mixture, hydrophobic PAE shows a higher breakthrough capacity than hydrophilic PAE. Moreover, the competitive adsorption results in the laboratory were comparable with those in field studies.