Hexavalent Cr ion adsorption and desorption behaviour of expanded poly(tetrafluoro)ethylene films grafted with 2-(dimethylamino)ethyl methacrylate.

A new polymeric adsorbent for Cr(VI) ions based on an expanded poly(tetrafluoroethylene) (ePTFE) film was prepared by the combined use of the pretreatment with oxygen plasma and photografting of 2-(dimethylamino)ethyl methacrylate (DMAEMA). The grafting of DMAEMA was characterized by XPS and FT-IR spectroscopic measurements. The adsorption behaviour of DMAEMA-grafted ePTFE (ePTFE-g-PDMAEMA) films was investigated as a function of the experimental parameters, such as the initial pH value, temperature, and grafted amount. The adsorption capacity and initial adsorption rate had the maximum values at the initial pH value of 3.0. On the other hand, the adsorption capacity became almost constant at temperatures higher than 30°C, although the adsorption rate increased over the temperature. The adsorption behaviour obeyed the pseudo-second-order kinetic model and well expressed by the Langmuir isotherm equation with higher correlation coefficients. These results indicate that the adsorption of Cr(VI) ions occurs through the electrostatic interaction between protonated dimethylamino groups on a grafted PDMAEMA chain and ions. Cr(VI) ions were successfully desorbed from Cr(VI)-loaded ePTFE-g-PDMAEMA films in the eluents, such as NaCl at 0.50 M, NHCl at 0.50M, and NaOH at 1.0 mM, and ePTFE-g-PDMAEMA films were repeatedly used for adsorption of Cr(VI) ions without appreciable loss in the adsorption capacity. It should be noted that Cr(VI) ion adsorptivity with a high initial rate was conferred to the ePTFE films. The results obtained in this study emphasize that ePTFE-g-PDMAEMA films can be applied as an adsorbent for Cr(VI) ions.