Organic–inorganic hybrids assembled from plenary Keggin-type germanotungstate units and 3d–4f heterometal clusters

La-doped NiWO4 coupled with reduced graphene oxide for effective electrochemical determination of diphenylamine

Diphenylamine (DPA) is a harmful pesticide widely used to control post-harvest scald of fruits. In this study, rapid and sensitive determination of DPA was realized by the development of an effective electrochemical sensor, which was fabricated by coupling La-doped NiWO4 nanoparticles (La/NiWO4) with reduced graphene oxide (rGO), and the obtained rGO/La/NiWO4 nanocomposite was modified on glassy carbon electrodes (GCEs). The morphologies, structures and compositions were well characterized, and the effects of La doping and the introduction of rGO on the crystal structure and electrochemical performance were discussed. The incorporation of both La and rGO was found to enhance the active surface area and improve conductivity, resulting in the enhanced electrocatalytic performance of rGO/La/NiWO4/GCE, including a wide linear range (0.01-500 μM), a low detection limit (0.0058 μM) and high sensitivity (1.778 μA μM-1 cm-2). The fabricated sensor was further used for DPA detection in fresh apple extract to evaluate its practicality and demonstrated excellent recoveries ranging from 99.52 to 104.70%.

Polyoxometalate Functionalized Sensors: A Review

Polyoxometalates (POMs) are a class of metal oxide complexes with a large structural diversity. Effective control of the final chemical and physical properties of POMs could be provided by fine-tuning chemical modifications, such as the inclusion of other metals or non-metal ions. In addition, the nature and type of the counterion can also impact POM properties, like solubility. Besides, POMs may combine with carbon materials as graphene oxide, reduced graphene oxide or carbon nanotubes to enhance electronic conductivity, with noble metal nanoparticles to increase catalytic and functional sites, be introduced into metal-organic frameworks to increase surface area and expose more active sites, and embedded into conducting polymers. The possibility to design POMs to match properties adequate for specific sensing applications turns them into highly desirable chemicals for sensor sensitive layers. This review intends to provide an overview of POM structures used in sensors (electrochemical, optical, and piezoelectric), highlighting their main functional features. Furthermore, this review aims to summarize the reported applications of POMs in sensors for detecting and determining analytes in different matrices, many of them with biochemical and clinical relevance, along with analytical figures of merit and main virtues and problems of such devices. Special emphasis is given to the stability of POMs sensitive layers, detection limits, selectivity, the pH working range and throughput.

A series of polyoxometalate compounds by tuning N sites and numbers of ligands: syntheses, characterization and electrochemical sensing, and photocatalytic and supercapacitor properties

Using morpholine derivatives with different N sites and numbers, we synthesized seven compounds by a hydrothermal method. They can photocatalytically degrade organic dyes and reduce Cr(vi) and can be used as electrochemical sensors. 4 has capacitor performance.

Ferrocene-reduced graphene oxide-polyoxometalates based ternary nanocomposites as electrochemical detection for acetaminophen

Developing a convenient and accurate method for the determination of acetaminophen (APAP) content is very vital, and ferrocene (Fc) based nanocomposites coupled with polyoxometalates (POMs) as electrochemical sensor is a promising approach to address the issues. Herein, a new ternary nanocomposite of Fc based carbon nanomaterials (Fc-rGO) with PMo₁₂ (Fc-rGO/PMo₁₂, rGFP-n) was successfully fabricated, and the electrochemical activities and APAP detection of rGFP-n as electro-active materials were systematically investigated, and results of the differential pulse voltammetry (DPV) and electro-active surface area (0.0332 cm²) show that rGFP-1 is an excellent electrochemical sensor for APAP, and the proportion of Fc in rGFP-n can affect the charge transfer between APAP and rGFP. Under the optimal experimental conditions, rGFP-1 can be used to detect APAP with the limit of detection (LOD) of 13.27 nM (S/N = 3), the sensitivity of 36.81μA⋅μM^-1cm^-2, and the detection range from 1×10^-6 to 1×10^-3M, meeting the lowest plasma concentration of APAP (1.3 mM).

A series of polyoxometalate-based hybrid complexes constructed by a tripodal ligand containing mixed N/O donors

We designed two synthetic strategies using identical ligands to construct six POM-based complexes. These complexes can act as amperometric sensors for the detection of Cr(vi), Fe(iii) and H2O2 and fluorescence sensors for sensing Cr3+.

Two highly stable inorganic–organic hybrid 3D frameworks based on Cu–Ln incorporated polyoxometalates for selective dye removal and proton conduction

Two highly stable inorganic–organic hybrid 3D TM–Ln incorporated POM-based framework materials have been successfully synthesized. The compounds can not only exhibit moderate proton conductivity but also selectively adsorb cationic dyes.

A novel cadmium metal–organic framework-based multiresponsive fluorescent sensor demonstrating outstanding sensitivities and selectivities for detecting NB, Fe3+ ions and Cr2O72− anions

A Cd(ii) metal–organic framework (MOF) [Cd₃(L)(NTB)₂(DMA)₂]·2DMA was solvothermal prepared in the presence of ligand L (L = (E)-4,4′-(ethene-1,2-diyl)bis[(N-pyridin-3-yl)benzamide]) and ligand H₃NTB (H₃NTB = 4,4′,4′′-nitrilotribenzoic acid).

The fabrication of a chemical sensor with PANI-TiO2 nanocomposites

In this study, conjugated conducting polyaniline was fabricated onto titania nanoparticles (PANI-TiO₂ NPs) using a microwave-accelerated reaction system. The synthesized nanoparticles were characterized using the techniques of electron microscopy (e.g., FE-SEM and TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and ultraviolet-visible (UV-Vis) spectrometry. An ultrasensitive sensor using the electrochemical (I–V) approach was fabricated using a thin film of PANI-TiO₂ NPs on a glassy carbon electrode (GCE), and it was found to be selective towards 1,2-diaminobenzene (1,2-DAB) in a buffer phase. From current versus concentration studies, the calibration curve was plotted to estimate the sensor's analytical parameters. The highest sensitivity (19.8165 μA μM⁻¹ cm⁻²) and lowest detection limit (0.93 ± 0.05 pM) were obtained from the electrochemical assessment by applying a signal-to-noise ratio of 3. A linear calibration plot was attained over a large range of concentration (LDR: 1.0 pM to 0.01 mM). The selective 1,2-DAB sensor was found to be efficient and reproducible in performance, yielding significant results with a fast response time (12.0 s). Therefore, the overall results of the 1,2-DAB chemical sensor suggest that this detection approach might be an easy way to develop an efficient electrochemical sensor for the protection of the environment as well as for use in the healthcare field on a broad scale.

The conjugated conducting polyaniline was fabricated onto PANI-TiO₂ nanoparticles prepared by microwave-accelerated reaction system for the development an efficient and sensitive electrochemical sensor to protect the environment and healthcare fields in a broad scale.

Syntheses, Crystal Structure, Electrocatalytic, and Magnetic Properties of the Monolanthanide-Containing Germanotungstates [Ln(H2O) n GeW11O39]5- (Ln = Dy, Er, n = 4,3)

Two monolanthanide-containing polyanions based on monolacunary Keggin germanotungstates [Ln(H2O) n GeW11O39]5- (Ln = Dy, Er, n = 4,3) have been synthesized in simple one-pot synthetic procedure and compositionally characterized in solid state by single-crystal X-ray diffraction, powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and elemental analysis. Electronic absorption and emission spectra of the title compounds in solution were also studied. The [DyIII(H2O)4GeW11O39]5- Keggin POM exhibits a slow relaxation of magnetization. The cyclic voltammetry measurements and mass spectrometry were carried out to check the stability of the compounds in solution. Both polyanions prove efficient in the electrocatalytic reduction of nitrite. To our knowledge, this observation establishes the first example of electrocatalysis of nitrite reduction by all inorganic monolanthanide-containing germanotungstates family.

Organic-inorganic hybrid 1-D double chain heteropolymolybdates constructed from plenary Keggin germanomolybdate anions and hepta-nuclear Cu-RE-pic heterometallic clusters

Two unprecedented organic-inorganic hybrid 1-D double chain germanomolybdates containing hepta-nuclear Cu-RE-pic heterometallic clusters [NH₄]₂[RE(H₂O)₅]₂[Cu(pic)₂]₂[Cu(pic)₂(H₂O)₂]₃[α-GeMo₁₂O₄₀]₂·22H₂O [RE = La³⁺ (1), Ce³⁺ (2), and Hpic = 2-picolinic acid] were successfully obtained by the stepwise self-assembly strategy via the conventional solution method. The most striking structural feature of 1 and 2 is that the two plenary Keggin [α-GeMo₁₂O₄₀]^4- polyoxoanions are joined by an organic-inorganic hybrid hepta-nuclear Cu-RE-pic {[RE(H₂O)₅]₂[Cu(pic)₂(H₂O)₂]₃[Cu(pic)₂]₂}⁶⁺ heterometallic moiety. What is more interesting is that their adjacent structural units are connected together by {Cu(pic)₂} bridges, forming a 1-D extended double chain architecture. Furthermore, the adsorption capacity of 1 toward dyes in aqueous solutions was deeply investigated. It is fascinating that 1 shows a good adsorption capacity toward basic violet 3 (BV 3) in aqueous solutions and the adsorption kinetics conforms to the second-order kinetic model.