Effects of the Cationic Structure on the Adsorption Performance of Ionic Polymers toward Au(III): an Experimental and DFT Study

Ionic
polymers have been proven to be promising adsorbents in recovering
Au­(III) due to their advantages of simple synthesis and high adsorption
efficiency. However, the unclarity of the relationship between the
adsorption ability of ionic polymers and their cationic structures
hinders further optimization of their adsorption performance. This
study synthesized a series of ionic polymers with pyridinium, imidazolium,
piperidinium, pyrrolidinium, and triethylammonium cations to discover
the effects of the cationic structure on their adsorption properties.
Experimental results show that the existence of anion−π
interaction between aromatic cations and [AuCl4]− makes the aromatic cations–anion interaction stronger, which
does not enhance the adsorption performance of the aromatic-based
ionic polymer. This is due to the charge delocalization in the aromatic
ring, resulting in a lower electrostatic potential (ESP) of aromatic
cations than that of aliphatic cations with a localized charge. The
higher the ESP of cations, the better the adsorption performance of
the corresponding ionic polymer. This study serves as a deep understanding
of the cationic structure–adsorptive performance relationship
of the ionic polymer at the molecular level and further provides a
theoretical guidance to optimize the adsorption performance of ionic
polymers.