Fluorescent naphthalimide containing polyurethanes for the detection and removal of Hg2+/Hg+ and Fe3+ ions

Heavy metal (HM) pollution is getting worse with the society progress. Identification and separation of HM ions are urgent issues in environmental protection and social development. In this work, 4-bromo-1,8-naphthalic anhydride was first reacted with amino-propylene glycol to synthesize naphthimide fluorophores bearing two hydroxyl groups. And then, -Br was substituents by 8-mercaptoquinoline, 2-mercaptoimidazole, and 4-mercaptopyridine, respectively. Eventually, it was reacted with 1,5-naphthalene diisocyanate (NDI) to synthesize fluorescent polyurethane (PU) films through the reaction between -OH and -NCO. It is found that the PU film not only has a specific identification ability to Hg2+/Hg+ and Fe3+ ions, but also can efficiently remove Hg2+/Hg+ and Fe3+ ions through adsorption. In addition, selective identification by fluorescence quenching was investigated. It is due to the photoinduced electron transfer mechanism (PET). Furthermore, the lowest detection limits for Fe3+, Hg2+, and Hg+ were 6.0 x 10(-7) M, 4.7 x 10(-7) M, and 9.7 x 10(-7) M, respectively, which reflected the sensitivity of the probe and made it fluorescence probes. The three fluorescent small molecules were incorporated into PU, which not only retain their identification function, but also serve the purpose of adsorption and separation of HM ions.