Enhancing Pt/Co separation selectivity of P204-P507/XAD-4 resins through Dual-Site modulation involving alkaline activation and HFIP masking

Dual-site modulated P204-P507/XAD-4 resin separates Pt/Co efficiently. • Alkaline activation of P-OH groups significantly boosts Co(II) capture. • HFIP effectively shields P=O sites to suppress Pt(IV) co-adsorption. • The Co/Pt separation factor achieves a nearly ten-fold improvement. • DFT and XPS reveal decoupled pathways via synergy-through-inhibition. The efficient recovery of platinum (Pt) and cobalt (Co) from spent proton exchange membrane fuel cell (PEMFC) catalysts is vital for the sustainable hydrogen economy, yet their deep separation from acidic leachates is hindered by the inherent affinity property of organophosphorus extractants. In this study, a dual-site regulation strategy was developed using a synergistic P204-P507/XAD-4 solvent-impregnated resin (SIR). By combining alkaline activation to enhance P–OH cation-exchange capacity (boosting Co(II) uptake from 40.19 ± 0.31 to 47.26 ± 0.58 mg/g at pH 7.0) as well as the hexafluoroisopropanol (HFIP) masking to selectively shield P=O sites via competitive hydrogen bonding (suppressing Pt(IV) adsorption from 7.60 ± 0.66 to 3.78 ± 0.47 mg/g at pH 3.0), the competing adsorption pathways were effectively decoupled. Experimental results showed that the dual-modified resin achieved a Co(II) adsorption capacity of 47.26 ± 0.58 mg/g and an exceptional separation factor (SF Co/Pt ) of 248.85 ± 10.19 at pH 7.0, representing an approximately ten-fold improvement over the unmodified composite. Mechanistic investigations via XPS and DFT calculations indicated that Co(II) is predominantly captured through P–OH sites, while the binding energy shifts in P=O groups are primarily attributed to a secondary inductive effect rather than direct coordination. Furthermore, in continuous fixed-bed operation, the resin exhibited a wide separation window with Co(II) breakthrough delayed to 55 bed volumes, delivering a Pt-enriched effluent with 99.1% purity at 97.0% recovery, while the retained Co(II) was quantitatively eluted at 96.6% purity. The resin also retained over 90% of its initial Co(II) adsorption efficiency after three consecutive adsorption–desorption cycles. and offering a mechanism-driven approach for precision metal adsorbent design.