Pyrene Bearing Azo-Functionalized Porous Nanofibers for CO₂ Separation and Toxic Metal Cation Sensing

A novel luminescent azo-linked polymer (ALP) has been constructed from 1,3,6,8-tetra­(4-aminophenyl)­pyrene using a copper­(I)-catalyzed oxidative homocoupling reaction. The polymer displays high porosity with a Brunauer–Emmett–Teller surface area of 1259 m² g^–1 and narrow pore size distribution (1.06 nm) and is able to take up a significant amount of CO₂ (2.89 mmol g^–1) at 298 K and 1.00 bar with a high isosteric heat of adsorption of 27.5 kJ mol^–1. Selectivity studies applying the ideal adsorbed solution theory revealed that the novel polymer has moderately good selectivities for CO₂/N₂ (55.1) and CO₂/CH₄ (10.9). Furthermore, the ALP shows fluorescence quenching in the presence of Hg²⁺, Pb²⁺, Tl⁺, and Al³⁺ ions. Compared with these ions, the ALP showed no sensitivity to light metal ions such as Na⁺, K⁺, and Ca²⁺ in ethanol–water solution, clearly indicating the high selectivity of the ALP toward heavy metal ions. The exceptional physiochemical stability, high porosity, and strong luminescence make this polymer an excellent candidate as a fluorescent chemical sensor for the detection of heavy metal ions.