Anion recognition by urea metal-organic frameworks: remarkable sensitivity for arsenate and fluoride ions

Functionalized metal-organic frameworks (F-MOFs) are known as a promising chemical sensors since they have specific merits like fixed functionalized ligands projecting into the pores which can be utilized to enhance sensitivity and selectivity. Due to the important role of anions in biological process and environmental systems, there is an increasing interest in synthesis and design of new receptors for anions. Urea groups can operate as a hydrogen bond donating site with hydrogen bond acceptor molecules. Strong and directional hydrogen-bonding between the positive urea groups and anions could reduce vibrational quenching and enhance the fluorescence intensity. In this study, two luminescent porous urea decorated MOFs have been successfully assembled and structurally characterized. Luminescence studies of these MOFs toward anions revealed that these F-MOFs exhibit high sensitivity and selectivity toward H₂AsO₄^- and F^- anions as two major ground water pollutants. Moreover, the proposed materials have been applied for the removal of arsenate and nitrate in contaminant well water samples. Graphical abstract.