Enrichment and activation of cyano in cobalt hexacyanoferrate for specific recovery of ultra-low concentrations of platinum

Adsorption recovery of ultra-low concentrations (1 ppm) of platinum (Pt) was challenging due to the inferior sensitivity response and poor specific affinity between sorbents and target ions. Herein, enrichment and activation of the cyano group (CN) on cobalt hexacyanoferrate (CoHCF) were achieved by crystal facets engineering to capture Pt(II) efficiently and specifically. The Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and density-functional theory (DFT) calculations results revealed that the activity and density of CN on the (220) facets were higher than that on the (200) facet. The Pt(II) adsorption efficiency on the CN-enriched and -activated CoHCF (CoHCF(2 2 0)) reached 92.5%, which was 1.56 times higher than that on the original CoHCF (59.2%). The specific adsorption of Pt(II) was driven by the coordination interaction between Fe-CN- and Pt, leading to the Pt(II)-Pd(II) separation efficiency attained 98.95% within 20 min. In addition, CoHCF(2 20) equipped with Pt(II) could be further chemically reduced as a photocatalyst for hydrogen evolution. This study suggested an attractive strategy for the practical recovery of Pt(II) and comprehensive utilization of ultra-low concentration Pt-containing wastewater.