Adsorption of Cd(2+) by an ion-imprinted thiol-functionalized polymer in competition with heavy metal ions and organic acids

The simultaneous presence of heavy metals and organic acids in nature and wastewaters and their competition for adsorption sites determine the migration, transformation and fate of pollutants in the environment. A Cd(2+)-ion-imprinted polymer (Cd(2+)-IIP) with a thiol-functional group was hydrothermally synthesized by a surface imprinting technique combined with ultrasonic heating for selective adsorption of Cd(2+) from wastewaters. The adsorbent was characterized by SEM, EDS, XPS, BET and FT-IR measurements. The experimental results concerning Cd(2+) adsorption from single-, binary-, ternary- and quaternary-metal aqueous solutions containing Cu(2+), Ni(2+) and Zn(2+) revealed high selectivity. In binary-metal solutions, relative selectivity coefficients for Cd(2+) in respect to Cd(2+)/Cu(2+), Cd(2+)/Ni(2+), and Cd(2+)/Zn(2+) were as high as 3.74, 5.73 and 4.15, respectively. In multi-metal solutions, competing heavy metal ions had little effect on the adsorption of Cd(2+) attributed to the high selectivity of Cd(2+)-IIP towards Cd(2+) determined by its coordination geometry. The effect of low-molecular weight organic acids on the Cd(2+) adsorption was also studied and the results showed that the presence of tartaric, citric and oxalic acids as admixtures in Cd(2+) aqueous solutions noticeably reduced the cation adsorption in a wide range of concentrations with the minor exception of low contents of citric and tartaric acids slightly improving adsorption.