Extraction of luminescent compounds from wastewater by ionic liquids for fabricating fluorescence/afterglow anti-counterfeiting materials

Abstract

Dyes in industrial wastewater are often toxic, polluting the environment, and harmful to animals and humans. The conventional methods of removing the dyes from wastewater are physical adsorption, precipitation, biodegradation, and photodegradation. Here we report the use of ionic liquids (ILs) to extract dyes from wastewater for the fabrication of fluorescence/afterglow materials. This method not only reduces the dye concentration by two to three orders of magnitude, but also obtains luminescent materials for anti-counterfeiting application. Diverse dyes such as rhodamine, acridones, difluoroboron compounds, and polycyclic aromatic hydrocarbons (PAHs) have been tested as model dyes in wastewater. In the case of rhodamine and some PAHs, fluorescence materials that exhibit diverse colors can be obtained after extraction by ILs. For difluoroboron compounds, room-temperature phosphorescence (RTP) materials have been achieved after extraction. Interestingly, in the case of acridones, the emergence of RTP/TADF dual afterglow emission has been evidenced in ILs, where TADF represents thermally activated delayed fluorescence. By the combination of these luminescent materials, lifetime-coded and multicolor-coded anti-counterfeiting functions have been demonstrated.