Unveiling the Uncommon Fluorescent Recognition Mechanism towards Pertechnetate Using a Cationic Metal–Organic Framework Bearing N‐Heterocyclic AIE Molecules

Abstract

As one of most problematic radionuclides, technetium‐99, mainly in the form of anionic pertechnetate (TcO4−), exhibits high environmental mobility, long half‐life, and radioactive hazard. Due to low charge density and high hydrophobicity for this tetrahedral anion, it is extremely difficult to recognize it in water. Seeking efficient and selective recognition method for TcO4− is still a big challenge. Herein, a new water‐stable cationic metal‐organic framework (ZJU‐X8) was reported, bearing tetraphenylethylene pyrimidine‐based aggregation‐induced emission (AIE) ligands and attainable silver sites for TcO4− detection. ZJU‐X8 underwent an obvious spectroscopic change from brilliant blue to flavovirens and exhibited splendid selectivity towards TcO4−. This uncommon fluorescent recognition mechanism was well elucidated by batch sorption experiments and DFT calculations. It was found that only TcO4− could enter into the body of ZJU‐X8 through anion exchange whereas other competing anions were excluded outside. Subsequently, after interaction between TcO4− and silver ions, the electron polarizations from pyrimidine rings to Ag+ cations significantly lowered the energy level of the π* orbital and thus reduced the π–π* energy gap, resulting in a red‐shift in the fluorescent spectra.

Two-Fold Interlocking Cationic Metal–Organic Framework Material with Exchangeable Chloride for Perrhenate/Pertechnetate Sorption

“…The maximum sorption capacity of ZJU-X4 toward ReO 4 – was calculated to be 395 mg/g (Figure S6), lower than the theoretic sorption capacity of 615 mg/g due to incomplete anion exchange. The maximum sorption capacity of ZJU-X4 was higher than those of some reported materials, such as Yb 3 O­(OH) 6 Cl (48.6 mg/g), SCU-101 (271 mg/g), ZJU-X8 (326 mg/g), LDHs (130 mg g –1 ), and D318 resin (351 mg/g), but there was still a certain gap with polymers, including TbDa-COF (952 mg/g), CPN-tpm (1133 mg/g), and SCU-CPN-2 (1467 mg/g) (Table S1).…”

3D Ionic Olefin-Linked Conjugated Microporous Polymers for Selective Detection and Removal of TcO4–/ReO4– from Wastewater

“…Conjugated microporous polymers (CMPs) are a class of organic porous polymers that combine a π-conjugated backbone with a permanent nanoporous structure . They have attracted increasing attention due to their tunable structure, high specific surface area, extended conjugated backbone, and excellent chemical stability. − The extended π-conjugated structure endows CMPs with strong fluorescence properties, making them have great application potential in the sensing field. − From this point of view, CMP materials may be suitable candidates for the detection of TcO 4 – /ReO 4 – . However, to date, no application of CMPs for this purpose has been developed.…”

Constructing Cationic Metal–Organic Framework Materials Based on Pyrimidyl as a Functional Group for Perrhenate/Pertechnetate Sorption

“…However, there are rare reports that a pyrimidyl group has been used for the fabrication of cationic MOFs to date. 62 In this work, pyrimidyl was incorporated into various organic skeletons to explore the superiority of pyrimidyl ligands to construct cationic MOFs in the elimination of radioactive anions (Scheme 1). Three new crystal structures of cationic MOFs, ZJU-X11, ZJU-X12, and ZJU-X13 (Zhejiang University, Xiao's group), were constructed by different organic ligands with pyrimidyl and AgNO 3 .…”

“…Compared to pyridyl, imidazolyl, and pyrazinyl, pyrimidyl can provide more binding sites through two nitrogen atom coordination with metal ions. However, there are rare reports that a pyrimidyl group has been used for the fabrication of cationic MOFs to date . In this work, pyrimidyl was incorporated into various organic skeletons to explore the superiority of pyrimidyl ligands to construct cationic MOFs in the elimination of radioactive anions (Scheme ).…”