A Hexanuclear Cadmium Metal-Organic Framework Exhibiting Dual Mechanisms to Trigger a Fluorescence-Quenching Response toward Iron(III) Ions

An effective procedure used metal-organic framework for determination of cadmium ions in real tap water and human blood plasma samples

A newly developed 2H5MA-MOF sensor by covalently linking NH2-MIL-53(Al) with 2'-Hydroxy-5'-methylacetophenon, designed for highly sensitive and selective detection of Cd2+ ions using fluorometric methods. Detailed structural and morphological analyses confirmed the sensor's unique properties. It demonstrated an impressive linear detection range from 0 to 2 ppm, with an exceptionally low detection limit of 5.77 × 10-2 ppm and a quantification limit of 1.75 × 10-1 ppm, indicating its high sensitivity (R2 = 0.9996). The sensor also responded quickly, detecting Cd2+ within just 30 s at pH 4. We successfully tested it on real samples of tap water and human blood plasma, achieving recovery rates between 96 % and 104 %. The accuracy of these findings was further validated by comparison with ICP-OES. Overall, the 2H5MA-MOF sensor shows great potential for fast, ultra-sensitive, and reliable detection of Cd2+ ions, making it a promising tool for environmental and biomedical applications.

Highly Sensitive Detection of Iron Ions in Aqueous Solutions Using Fluorescent Chitosan Nanoparticles Functionalized by Rhodamine B

Detection of iron ions in aqueous solutions is of significant importance because of their important role in the environment and the human body. Herein, a fluorescent rhodamine B-functionalized chitosan nanoparticles probe is reported for the efficient detection of iron ions. The chitosan nanospheres-rhodamine B (CREN) was prepared by grafting rhodamine B onto the surface of chitosan nanospheres through an amidation reaction. The as-prepared CREN fluorescent probes exhibit high fluorescence intensity under ultraviolet light. When iron ions are added to the CREN solution, they can be coordinated with weak-field ligands such as N and O on the surface of chitosan nanoparticles (CSNP) by a high-spin method. The self-assembly of Fe³⁺ on the surface of the CREN led to the generation of single electrons and the presence of high paramagnetism, resulting in fluorescence quenching. The quenching effect of Fe³⁺ on the CREN fluorescent probe can achieve the efficient detection of Fe³⁺, and the detection limit reaches 10^-5 mol/mL. Moreover, this fluorescence quenching effect of Fe³⁺ on the CREN fluorescent probe is specific, which could not be disturbed by other metal ions and counteranions.

Response of a Zn(II)-based metal-organic coordination polymer towards trivalent metal ions (Al3+, Fe3+ and Cr3+) probed by spectroscopic methods

A new zinc-based two-dimensional coordination polymer, [Zn(5-AIP)(Ald-4)]·H2O (5-AIP = 5-amino isophthalate, Ald-4 = aldrithiol-4), 1, has been synthesized at room temperature by the layer diffusion technique. Single-crystal X-ray diffraction analysis of 1 showed a two-dimensional bilayer structure. An aqueous suspension of 1 upon excitation at 300 nm displayed an intense blue emission at 403 nm. The luminescence spectra were interestingly responsive and selective to Al3+, Cr3+ and Fe3+ ions even in the presence of other interfering ions. The calculated detection limits for Al3+, Cr3+ and Fe3+ were 0.35 μM ([triple bond, length as m-dash]8.43 ppb), 0.46 μM ([triple bond, length as m-dash]22.6 ppb) and 0.30 μM ([triple bond, length as m-dash]15.85 ppb), respectively. Notably, with the cumulative addition of Al3+ ions, the luminescence intensity at 403 nm decreased steadily with a gradual red shift up to 427 nm. Afterward, this red shifted peak showed a turn-on effect upon further addition of Al3+ ions. On the other hand, for Cr3+ and Fe3+ ions, there was only drastic luminescence quenching and a large red shift up to 434 nm. This indicated the formation of a complex between 1 and these metal ions, which was also supported by the UV-Visible absorption spectra of 1 that showed the appearance of a new band at 280 nm in the presence of these three metal ions. The FTIR spectra revealed that these ions interacted with the carboxylate oxygen atom of 5-AIP and the nitrogen atom of the Ald-4 ligand in the structure. The luminescence lifetime decay analysis manifested that a charge-transfer type complex was formed between 1 and Cr3+ and Fe3+ ions that resulted in huge luminescence quenching due to the efficient charge transfer involving the vacant d-orbitals, whereas for Al3+ ions having no vacant d-orbital, turn-on of luminescence occurred because of the increased rigidity of 1 upon complexation.

Dramatic luminescence signal from a Co(ii)-based metal–organic compound due to the construction of charge-transfer bands with Al3+ and Fe3+ ions in water: steady-state and time-resolved spectroscopic studies

A Co(ii)-based metal–organic compound exhibits luminescence turn-on by Al³⁺ and quenching by Fe³⁺ due to the formation of charge-transfer complexes/adducts.

A water-stable europium-MOF as a multifunctional luminescent sensor for some trivalent metal ions (Fe3+, Cr3+, Al3+), PO43− ions, and nitroaromatic explosives

Eu-MOF having a layered structure exhibits high sensitivity, selectivity, and recyclability towards sensing Fe³⁺, Cr³⁺, Al³⁺, and PO₄³⁻ ions and TNP.

A novel fluorescence phenomenon caused by amine induced ion-exchange between Cd2+ and Fe3+ ions

A 3D metal–organic framework {[Cd(5-Brp)(dpa)]·0.5DMF·H₂O}_n (1) was successfully synthesized and characterized, which markedly recognized iron ions under the induction of an amino group. With the concentration of Fe³⁺ increasing, the emission of 1 first declined, then enhanced with a red shift and was finally quenched, which was different from the reference compound [Cd(5-Brp)(bpp)(H₂O)]_n (2). This result drew our attention to amine induced ion-exchange. This peculiar phenomenon inspired us to construct an effective ion detector.

A 3D metal–organic framework {[Cd(5-Brp)(dpa)]·0.5DMF·H₂O}_n (1) was successfully synthesized and characterized, which markedly recognized iron ions under the induction of an amino group.