Reductive ethylenediamine group immobilized in hybrid Pd-based nanocomposite for efficiently sequestrating selenate

Abstract

Reductive sequestration of selenate [Se(VI)] has emerged as an effective and promising approach in consideration of the poor adsorptive selectivity toward Se(VI) by regular adsorption processes, where the adsorption efficiency for Se(VI) would be typically compromised by the coexisting anions, especially sulfate anion, which has similar structure and property as that of selenate. Herein, we propose a synergistic strategy of ion-exchange and catalytic reduction for this purpose; that is, a Pd-embedded hybrid nanocomposite (Pd-EDA@CMPS) was subtly assembled by in situ nucleating Pd-nanoparticle inside a porous polystyrene adsorbent possessing ethylenediamine (EDA) functional group, which is a reversible redox unit and served as electron donator for Se(VI) reduction, and the embedded Pd nanoparticle exhibited superior catalytic reduction activity and stability for sustainable use. The reduction product, i.e., Se(IV), was immediately in-situ sequestrated inside the hybrid nanocomposite. Macroscopic batch experiments verified the outstanding anti-interference of Se(VI) removal by Pd-EDA@CMPS against the ubiquitous competing anions such as sulfate, chloride, bicarbonate, and phosphate even with 100-times higher concentration. Furthermore, the notable applicability of Pd-EDA@CMPS in a wide pH range (i.e., 3.0 ∼ 11.0) was confirmed, and an interesting pH-buffering effect may be responsible for such a satisfied performance. Besides the excellent hydraulic properties and mechanical strength, the exhausted Pd-EDA@CMPS can be regenerated by successive treatment with NaOH and NaBH4 solution for reuse without obvious loss in capacity.