ADSORPTION AND STRUCTURE OF METAL-ION COMPLEXES WITH PIPERAZINE GROUPS GRAFTED ON SILICA-GEL SURFACE

Silica gel, chemically modified with piperazine [Si(CH2)3N(CH2CH2)2)NH], abbreviated as SiP, was used to adsorb metal ions from ethanol solutions. The adsorption capacity was for each metal (in mmol g-1): Co(II) = 0.44, Ni(II) = 0.37, Cu(II) = 0.74, Zn(II) = 0.28, Cd(II) = 0.46, and Hg(II) = 0.51. The electronic spectra of MCl2 [M(II) = Co and Cu], adsorbed on SiP, indicate that one metal ion is coordinated to two free amines and the other adsorbed metal ion is coordinated exclusively with Cl- ions. Presumably for other metal ions, the coordination scheme is similar. The protonated organofunctionalized silica, abbreviated as SiPH+Cl-, was also used to adsorb the above metal ions, except Ni(II), from ethanol solutions. It was possible to conclude from the adsorption isotherms that the structure of the adsorbed metal ions can in every case be represented as (SiPH+)nMClz+nn-. © 1991.