Removal of heavy metal ions from aqueous solution by azocalix[4]arene

This study presents the preparation, characterization, and sorption properties of new chromogenic azocalix[4]arene based oligomers (1a, 2a and 3a) towards some selected heavy metal (Ag+, Hg+, Hg2+, Co2+, Ni2+, Cu2+, Cd2+ and Cr3+) cations. These compounds have been synthesized via polycondensation reactions involving 25,27-diethylacetoxy-26,28-dihydroxy-5,17-bis(4-nitrophenylazo)calix[4]arene(1), 25,27-diethyl acetoxy-26,28-dihydroxy-5,17-bis(4-ethylphenylazo)calix[4]arene (2), or 25,27-diethyl acetoxy-26,28-dihydroxy-5,17-bis(4-bromophenylazo)calix[4]arene (3) with 1,4-bisamino methyl benzene. Two-phase sorption properties of azocalixarene oligomers (1a, 2a and 3a) towards the selected metal cations are reported. The binding properties of these oligomers towards the selected metal cations were observed to be higher than those of monomeric analogs. It is suggested that this increased binding ability arises from highly rigid azo (-N=N-) group moiety at the upper rim of calix[4]arene in the oligomeric skeleton.