A Boric Acid-Functionalized Lanthanide Metal–Organic Framework as a Fluorescence “Turn-on” Probe for Selective Monitoring of Hg²⁺ and CH₃Hg⁺

Abstract

Mercury detection remains an important task because of its high toxicity. Herein a new dual-signal probe based on a boric acid (BA)-functionalized lanthanide metal–organic framework (BA-Eu-MOF) was developed for the detection of Hg2+ and CH3Hg+ ions for the first time. The BA-Eu-MOF was synthesized by coordination of Eu3+ with 5-boronobezene-1, 3-dicarboxylic acid (5-bop) through a one-pot method. The 5-bop ligand not only acted as the “antenna” to sensitize the luminescence of Eu3+ but also provided reaction sites for Hg2+ and CH3Hg+. Owing to the electron-withdrawing effect of the BA group, the “antenna” effect of the ligand was passivating and the BA-Eu-MOF showed weak red emission in water. Upon addition of Hg2+ or CH3Hg+ into the system, a transmetalation reaction took place, i.e., BA groups were replaced by Hg2+ or CH3Hg+; therefore, the “antenna” effect of the ligand was triggered, leading to the enhancement of red emission. As Hg2+ or CH3Hg+ concentration increased, the red emission was gradually enhanced, and the color change was also observed with the naked eye under 365 nm ultraviolet light. Owing to the porous characteristics and the surface effect of the MOF, as well as the unique transmetalation reaction between the BA group and Hg2+ or CH3Hg+, the developed nanoprobe showed excellent characteristics for simultaneous detection of Hg2+ and CH3Hg+, such as simple preparation, convenient operation, “turn-on” signal output, high sensitivity, and selectivity. The unique features of the BA-Eu-MOF make it an attractive probe for monitoring Hg2+ and CH3Hg+.

Alkali Metal Ion-exchange in a Metal-Organic Framework Based on Lanthanum and 1,4-Phenylenebis(methylidyne)tetrakis(phosphonic acid)

“…4,5 The ion-exchange reactions of MOFs have also been applied to various methods for the removal, separation, 6,7 and detection of metal ions. [8][9][10] Although in most cases, selectivity of the metal exchange reactions in MOFs exhibits a common trend as often observed in conventional ion-exchange systems, 11,12 unusual selectivity has been observed in ion-exchangeable MOFs. For example, Plabst et al 13 reported an exceptional selectivity for the ion-exchange reaction between alkali metal ions in an MOF comprising of 1,4-phenylenebis(methylidyne)tetrakis(phosphonic acid) (L; Fig.…”

Recent Advances in Developing Lanthanide Metal–Organic Frameworks for Ratiometric Fluorescent Sensing

“…Moreover, the boric acid exhibits a strong affinity to fluoride ions, while its interaction with other anions is relatively weak, making it perfect for fluoride selective sensing. Reports on enhancing antenna effect resulted in "turn-on" sensing are rather few comparing to the "turn-off" mechanism discussed above (Karmakar et al, 2019;Fueyo-González et al, 2020;Min et al, 2020;Wang et al, 2020;Yue et al, 2020). However, it is obvious that "turn-on" sensors have advantages over the "turn-off" sensors, especially in the quantitative determination of an analyte in low concentration (Luo et al, 2020).…”

Nanoscale Metal-Organic Frameworks as Fluorescence Sensors for Food Safety

“…Over the past few years, lots of research groups tried to rapidly detect kinds of cations by the usage of NMOFs-based fluorescence sensors and have borne fruit [4]. In addition, many of them shared a similar sensing mechanism, in which NMOFs-based fluorescence sensors were selectively quenched by certain metal cations through the PET [93][94][95][96]. In this part, the latest and novel NMOFs sensors for cation detection will be introduced.…”