Terpyridine-based silica supports prepared by ring-opening metathesis polymerization for the selective extraction of noble metals

The synthesis of a terpyridine-based sorbent for solid-phase extraction (SPE) of noble metal ions is described. For this purpose, 4′-(norborn-2-en-5-ylmethylenoxy)terpyridine was copolymerized with norborn-2-ene via Mo(N-2,6-i-Pr2-C6H3)(CHCMe2Ph)(OC(CH3)(CF3)2)2-catalyzed ring-opening metathesis polymerization (ROMP) to give a poly(norbornene900-b-4′-(norborn-2-en-5-ylmethylenoxy)terpyridine60) block-copolymer. This block-copolymer was used for the preparation of polymer-coated silica 60 (4.8 wt.% coating), which was investigated for its extraction capabilities for Cr(III), Mn(II), Re(II), Fe(III), Ru(III), Co(II), Rh(III), Ir(III), Ni(II), Pd(II), Pt(II), Cu(II), Ag(I), Au(III), Zn(II), Cd(II) and Hg(II), at different pH. Under competitive conditions and at pH <0.6, the selectivity order was Pd ≈ Ag ≈ Au ≈ Pt > Re > Ir > Rh > Ru > Fe > Cr ≈ Mn ≈ Cd ≈ Zn. Enhanced selectivity was observed at pH = 3.5, the order was Au > Hg > Pd ≈ Ag > Rh > Pt > Ir ≈ Re > Cu > Co ≈ Zn ≈ Cd ≈ Ni > Cr > Mn. The maximum metal loading that was achieved under non-competitive conditions was >6 mg/g for Au(III), Hg(II), Pd(II) and Ag(I). Even under competitive conditions, loadings of >6 mg/g were realized for Au(III) and Hg(II). Quantitative recoveries >97% were observed for all metals in case loading was stopped before reaching the point of breakthrough.