Effective recognition of multiple anions by an azobenzene--Al$^{\mathbf{3+}}$ system

Authors: YE ZHANG, PING JIA, ZHANGFA TONG, HAI-BO LIU, JING WANG

Abstract: A ready-to-use multifunctional coordinative system, 2,2'-dihydroxyazobenzene --aluminum (III) (DHAB--Al$^{3+})$, was created to recognize several anions effectively through three channels, namely colorimetric detection, UV-Vis spectroscopy, and fluorescence spectroscopy. Under naked eye visualization, the H$_{2}$PO$_{4}^{-}$ can be readily distinguished from the other anions by the DHAB--Al$^{3+}$ system through a change in color from reddish-orange to light yellow. H$_{2}$PO$_{4}^{-}$ was qualitatively detected by using UV-Vis and fluorescence spectra. Differentiating SO$_{3}^{2-}$, HPO$_{4}^{2-}$, and HCO$_{3}^{-}$ anions colorimetrically is difficult; thus, CO$_{3}^{2-}$, SO$_{3}^{2-}$, HPO$_{4}^{2-}$, and HCO$_{3}^{-}$ were discriminated by adopting distinct changes in the UV-Vis spectra. CO$_{3}^{2-}$, HPO$_{4}^{2-}$, and HCO$_{3}^{-}$ were accurately quantified using fluorescence spectra. The DHAB--Al$^{3+}$ system responded to H$_{2}$PO$_{4}^{-}$ and CO$_{3}^{2-}$ via a sensing mechanism based on a displacement approach. By contrast, the system responded to SO$_{3}^{2-}$, HPO$_{4}^{2-}$, and HCO$_{3}^{-}$ based on a binding site--signaling subunit approach. The DHAB--Al$^{3+}$ system can determine the concentration ranges of H$_{2}$PO$_{4}^{-}$ with the naked eye and quantify CO$_{3}^{2-}$, SO$_{3}^{2-}$, HPO$_{4}^{2-}$, and HCO$_{3}^{-}$ through UV-Vis spectra.

Keywords: Multifunctional, colorimetrically, DHAB--Al$^{3+}$ system, anions

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