Water- and pH-Stable Methylthio-Containing Metal–Organic Frameworks as Luminescent Sensors for Metal-Ion Detection

Abstract

Currently, metal–organic frameworks (MOFs) with thiol functionalities are used as advanced robust materials to solve the problems of pollution and damage caused by metal ions in water. Herein, we report a framework assembled by reacting cadmium nitrate with a new ligand, 4-methylthiopyridine-2,6-dicarboxylic acid, which possesses methylthio and carboxyl functional groups. The resultant MOFs exhibit 5-c net, fnb-type, uninodal net topology with {33·4·64·72} point symbols. The thiol-functionalized MOF features good thermal, water, and pH stabilities and luminescence emission at different temperatures. The methylthio-containing cadmium MOF (Cd-MOF) selectively detects the heavy-metal ions Cu2+, Hg2+, and Pb2+ in water by luminescence quenching, with low limits of detection (LODs) of 22.60 × 10–7, 11.07 × 10–6, and 9.58 × 10–6 M, respectively. The highly selective response and performance of the Cd-MOF probe toward Cu2+, Hg2+, and Pb2+ ions were determined by investigating the effects of other interfering ions and different pH values, and the reusability performance was evaluated.

Tactile Sensors: Hydroxyl Decorated Silver Metal–Organic Frameworks for Detecting Cr2O72–, MnO4–, Humic Acid, and Fe3+ Ions

“…Moreover, the role of pH as a critical factor can be elucidated by more quenching in the fluorescence intensity in an acidic medium compared to a basic medium . The acidic and basic medium effects on Ag-MOF detection for Cr 2 O 7 2– (Figure S26), MnO 4 – (Figure S27), HA (Figure S28), and Fe 3+ ions (Figure S29) were determined by emission intensity changes in a pH range (1–13).…”

“…Moreover, the role of pH as a critical factor can be elucidated by more quenching in the fluorescence intensity in an acidic medium compared to a basic medium. 44 The acidic and basic medium effects on Ag-MOF detection for Cr 2 O 7 2− (Figure S26), MnO 4 − (Figure S27), HA (Figure S28), and Fe 3+ ions (Figure S29) were determined by emission intensity changes in a pH range (1−13). In addition, the reusability of the alcohol-washed Ag-MOFs was determined by recording the fluorescence intensity changes with Cr 2 O 7 2− , MnO 4 − , HA, and Fe 3+ ions (30 × 10 −5 M).…”

Thiol and thioether-based metal–organic frameworks: synthesis, structure, and multifaceted applications

“…Owing to these exceptional attributes, thiol and thioether-based MOFs find extensive utility across a diverse spectrum of applications, encompassing catalysis, sensing, adsorption, and conductivity. 67–70 In case of linkers where only thiol or thioether groups are present, the MOFs are generally synthesized by inert atmosphere interfacial assisted methods as these ligands are air and moisture sensitive. 71,72 MOFs of this category are well-known for their unique two-dimensional (2D) sheet structures, which are responsible for their high conductive nature.…”

“…8) by a solvothermal reaction with Cd(NO 3 ) 2 ·4H 2 O in water solvent. 69 The colourless compound crystallized in the triclinic R 3̄ space group and formed a 3D coordination network with the free –SCH 3 group. This water- and pH-stable MOF acts as a luminescence sensor for heavy metals.…”

Recent advances in fluorescent materials for mercury(ii) ion detection

“…In contrast, the new reverse PET process in materials often causes “urn-off” fluorescence, which has also been shown to be useful in designing Hg 2+ ion sensors. 70–72 Hou et al 73 synthesized a novel zinc phosphonate with a one-dimensional chain structure based on (2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene)triphosphonic acid (H 4 L) and 2,2′-biimidazole (2,2′-biim). The as-synthesized [Zn(H 4 L)(2,2′-biim)] can act as a highly selective fluorescent probe for Hg 2+ ions.…”