Hexagonal-prism-shaped optical sensor/captor for the optical recognition and sequestration of Pd^II ions from urban mines

In this work, we have developed a hexagonal-prism-shaped optical sensor/captor (OSC) based on the immobilization of an organic probe into hexagonal, micrometric monoliths of mesoporous aluminosilica scaffolds for the colorimetric monitoring, selective sequestering, and effective recovery of Pd^II ions from urban mines as a promising technology for industrial applications. In such a solid OSC, H-type aggregation and face-to-face (π-π∗ stacking) interactions between the heteroatoms-coordinated organic probe and the active acid sites of the scaffolds lead to the formation of 1D molecular probe assemblies parallel to the interior pore walls. The design patterns of hexagonal-prism-shaped and open cylindrical pores (ca. 4 nm) exhibited suitable accommodation to protect the organic probe from extra H-aggregates, as evidenced by the high affinity of the Pd^II-probe binding events. The OSC shows evidence of controlled Pd^II ion assessment in terms of the optical recognition of Pd^II ions down to sub-nanomolar concentrations (3.3 × 10^-9 mol/L). Our study shows that the developed OSC can be used as an effective tool for urban mining development, particularly for secondary resources in industrial countries.