Highly fluorescent conjugated microporous polymers for concurrent adsorption and detection of uranium

Abstract

Uranium is one of the most important elements in the nuclear industry, but it also causes potential health risks to human beings when released into the natural environment. It is highly desired to develop a strategy that enables concurrent uranium detection and adsorption for sustainable development of nuclear energy and environmental conservation. In this work, a fluorescent conjugated microporous polymer consisting of 1,3,5-triethynylbenzene and amidoxime/carboxylate-substituted fluorene (CMPAO) is designed and synthesized for efficient extraction and detection of uranyl ions. The amidoxime ligands on CMPAO provide selective uranium-binding properties, while hydrophilic carboxylate groups largely enhance aqueous dispersibility leading to adequate contact with uranyl ions. As a consequence, CMPAO is capable of selective and efficient extraction of uranyl ions, achieving an optimal sorption capacity of 251.9 mg U g⁻¹. Moreover, the adsorption of uranium on CMPAO leads to dramatic fluorescence quenching, allowing selective and sensitive detection of uranyl ions by fluorescence spectroscopy. Importantly, thanks to the signal amplification by the conjugated skeleton, CMPAO has a fairly low detection limit of 1.7 × 10⁻⁹ M for uranyl ions in deionized water, which is far below the maximum contamination standard in drinking water of the World Health Organization (6.3 × 10⁻⁸ M).