Mechanism-Property Correlation in Coordination Polymer Crystals towards Design of Superior Sorbent.

Abstract

A development of methodology for designing superior sorbents of oxoanions is performed. To integrate high efficiency of chemi-sorption, selectivity and recyclability into one sorbent, understanding the nature of oxoanions-sorbent interactions and the struc-tural evolution of the sorbents is essential. Three cationic Ag(I) coordination polymers (CPs) are synthesized for dichromate (Cr2O72-) removal and three distinct oxoanion-exchange mechanisms are identified, namely the replacement, breath, and recon-struction processes, depending on degree of the framework distortion induced by the dichromate-CP interactions. The single-crystal to single-crystal transformation during the oxoanion-exchange has been investigated by using single-crystal X-ray diffrac-tion, energy dispersive X-ray microanalysis. The replacement process due to a weak chemisorption shows excellent recyclability in cost of reduction of efficiency and selectivity of adsorption. The reconstruction process may achieve a high efficiency and selec-tivity, but it loses recyclability. Due to the formation of Ag-O(dichromate) bond and breathing effect of the framework, the sorbent with the breath mechanism shows both superior efficiency and high recyclability in dichromate removal. Study of per-rhenate (ReO4-) removal using the same CPs demonstrates that one CP performing the reconstruction process in dichromate re-moval turns to the breath process in removal of perrhenate anions. These results of mechanism-property correlation provide an in-sight into improvement of the methodology to fabricate the most superior CP sorbent for oxoanion removal.