Recognizing adsorption of aqueous Cr(VI), As(III), Cd(II), and Pb(II) ions by amino groups hollow polymer adsorbent

The mechanism from the molecular level and the selectivity for the removal of metal ions from aqueous has become a hotspot in current water treatment . In this study, a sulphydryl-modified hollow polymer adsorbent was designed with intrinsic amine and grafted sulphydryl groups for efficient uptake of Cr(VI), As(III), Cd(II), and Pb(II) by taking advantage of their properties of abundant functional groups, discrete hollow chambers, and high porosity. Interestingly, the benzenoid amine/quinoid imine functional groups have a stronger affinity for Cr(VI) than Cd(II) or As(III) and Pb(II). The formation of approximately 65.7% Cr(III) indicates the redox reaction from Cr(VI) to Cr(III). The electron-donating comes from benzenoid amine and oxidized to quinoid imine or protonated oxidized nitrogen units (-N =  + ) with Cr(VI) reduced to Cr(III) for the increase of more than double of quinoid imine and a new functional group of -N =  + . Ion exchange between –COO - groups and As(III)/Cd(II), the chelation of –SH groups for Pb(II)/As(III) are plausible mechanisms.