Metal organic frameworks for electrochemical sensor applications: A review

Metal-organic frameworks (MOFs) are broadly known as porous coordination polymers, synthesized by metal-based nodes and organic linkers. MOFs are used in various fields like catalysis, energy storage, sensors, drug delivery etc., due to their versatile properties (tailorable pore size, high surface area, and exposed active sites). This review presents a detailed discussion of MOFs as an electrochemical sensor and their enhancement in the selectivity and sensitivity of the sensor. These sensors are used for the detection of heavy metal ions like Cd²⁺, Pb²⁺, Hg²⁺, and Cu²⁺ from groundwater. Various types of organic pollutants are also detected from the water bodies using MOFs. Furthermore, electrochemical sensing of antibiotics, phenolic compounds, and pesticides has been explored. In addition to this, there is also a detailed discussion of metal nano-particles and metal-oxide based composites which can sense various compounds like glucose, amino acids, uric acid etc. The review will be helpful for young researchers, and an inspiration to future research as challenges and future opportunities of MOF-based electrochemical sensors are also reported.

Isomers of Terpyridine as Ligands in Coordination Polymers and Networks Containing Zinc(II) and Cadmium(II)

The use of divergent 4,2′:6′,4″- and 3,2′:6′,3″-terpyridine ligands as linkers and/or nodes in extended coordination assemblies has gained in popularity over the last decade. However, there is also a range of coordination polymers which feature 2,2′:6′,2″-terpyridine metal-binding domains. Of the remaining 45 isomers of terpyridine, few have been utilized in extended coordination arrays. Here, we provide an overview of coordination polymers and networks containing isomers of terpyridine and either zinc(II) and cadmium(II). Although the motivation for investigations of many of these systems is their luminescent behavior, we have chosen to focus mainly on structural details, and we assess to what extent assemblies are reproducible. We also consider cases where there is structural evidence for competitive product formation. A point that emerges is the lack of systematic investigations.

Recent advances in metal-organic frameworks for pesticide detection and adsorption

The large-scale use of pesticides such as organophosphate pesticides (OPPs) and organochlorine pesticides (OCPs) has led to serious environmental problems worldwide, and their high toxicity could cause serious damage to human health. It is crucial to remove and track them precisely in the environment and food resources. As novel nanomaterials, metal-organic frameworks (MOFs) have attracted significant attention in the fields of adsorption and luminescence sensing due to their rich topology, tunable pore size and shape, high surface area, and abundant active sites. Luminescent metal-organic frameworks (LMOFs) have sprung up as great potential chemical sensors to detect pesticides with fast response, high sensitivity, high selectivity and easy operation. Therefore, in this highlight, we focus on recent progress of MOFs in sensing and adsorbing pesticides, as well as in the possible mechanism of sensing, so as to attract more attention to pesticide detection and adsorption.

A three-dimensional metal–organic framework with high performance of dual cation sensing synthesized via single-crystal transformation

BUT-26, synthesized via a ligand exchange reaction, can detect trace amounts of Cu²⁺ and Fe³⁺ ions in aqueous solutions.

A water-stable zinc(ii)-organic framework as a multiresponsive luminescent sensor for toxic heavy metal cations, oxyanions and organochlorine pesticides in aqueous solution

A novel metal-organic framework with the formula [Zn3(DDB)(DPE)]·H2O (1) (H5DDB = 3,5-di(2',4'-dicarboxylphenyl)benzoic acid and DPE = 1,2-di(4-pyridyl)ethylene) has been solvothermally synthesized by employing a rigid carboxylate ligand H5DDB to assemble with Zn(ii) ions in the presence of a flexible bis(pyridyl) linker DPE. The Zn-MOF is a 3D framework with six-nuclear clusters and possesses remarkable water stability and pH stability. Interestingly, complex 1 can sensitively and selectively sense Fe(iii), Cr(iii), Cr(vi), Mn(vii) and the pesticide 2,6-Dich-4-NA with low detection limits in aqueous solution. Moreover, complex 1 also exhibits selectivity for 2,6-Dich-4-NA detection in real samples including carrot, grape and nectarine extracts, and its detection ability is almost unchanged in the presence of the surfactant sodium dodecyl sulfate (SDS). The possible mechanisms of luminescence quenching have been explained by the weak affinity of nitrogen atoms, resonance energy transfer, and photoinduced electron transfer. To our knowledge, this is the first example of a MOF-based multiresponsive fluorescent probe for the simultaneous detection of Fe(iii), Cr(iii/vi), Mn(vii) and the pesticide 2,6-Dich-4-NA in aqueous solution.

A mesoporous NNN-pincer-based metal–organic framework scaffold for the preparation of noble-metal-free catalysts

A terpyridine-based mesoporous 3D MOF was synthesized as a general scaffold for catalyst preparation.

An Isoreticular Series of Zinc(II) Metal-Organic Frameworks Derived from Terpyridylcarboxylate Ligands

An isoreticular family of seven microporous metal-organic frameworks of the general form [ZnL] have been synthesized, where L is a 4'-substituted 2,2':6',2″-terpyridine-4,4″-dicarboxylate ligand. Each framework adopts an interpenetrated zeolitic gismondine (gis-c) topology and possesses one-dimensional square channels with ca. 9.0 Å apertures running down the crystallographic c axis. Gas adsorption measurements with N₂, H₂, CH₄, and CO₂ confirm their permanent porosity. The ligand functional groups, which include phenyl, 2-tolyl, 4-chlorophenyl, 4-nitrophenyl, 2-thienyl, 3-thienyl, and 4-pyridyl, line the channel walls and tune the gas adsorption properties of these materials.

Mechano-, thermo-, solvato-, and vapochromism in bis(acetato-κ1O)[4′-(4-(diphenylamino)phenyl)](2,2′:6′,2′′-terpyridine-κ3N,N′,N′′)zinc(ii) and its polymer

The titled complex undergoes multi-functional luminochromism in the solid state and polymer form.

Selective gas adsorption and fluorescence sensing response of a Zn(ii) metal–organic framework constructed by a mixed-ligand strategy

By means of a mixed-ligand strategy, a novel metal–organic framework was obtained, which remarkably exhibits bi-functional properties, i.e., selective gas adsorption of CO₂ over CH₄ and fluorescence sensing response for nitrobenzene.