Rationally Designed Ag@polymer@2-D LDH Nanoflakes for Bifunctional Efficient Electrochemical Sensing of 4-Nitrophenol and Water Oxidation Reaction

A bifunctional MoS2/SGCN nanocatalyst for the electrochemical detection and degradation of hazardous 4-nitrophenol

Herein, we reported the dual functions of molybdenum disulfide/sulfur-doped graphitic carbon nitride (MoS2/SGCN) composite as a sensing material for electrochemical detection of 4-NP and a catalyst for 4-NP degradation. The MoS2 nanosheet, sulfur-doped graphitic carbon nitride (SGCN) and MoS2/SGCN were characterized using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) spectroscopy and X-ray photoelectron spectroscopy (XPS). Electrochemical characterization of these materials with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) in 1 mM K4[Fe(CN)6]3-/4- show that the composite has the lowest charge transfer resistance and the best electrocatalytic activity. The limit of detection (LOD) and the linear range of 4-nitrophenol at MoS2/SGCN modified glassy carbon electrode (MoS2/SGCN/GCE) were computed as 12.8 nM and 0.1 - 2.6 μM, respectively. Also, the percentage recoveries of 4-NP in spiked tap water samples ranged from 97.8 - 99.1 %. The electroanalysis of 4-NP in the presence of notable interferons shows that the proposed electrochemical sensor features outstanding selectivity toward 4-NP. Additionally, the results of the catalytic degradation of 4-NP at MoS2/SGCN show that the nanocatalyst catalyzed the transformation of 4-NP to 4-aminophenol (4-AP) with a first-order rate constant (k) estimated to be 4.2 ×10-2 s-1. The results of this study confirm that the MoS2/SGCN nanocatalyst is a useful implement for electroanalytical monitoring and catalytic degradation of the hazardous 4-NP in water samples.

Hollow CoVOx/Ag nanoprism with tailored electronic structure for high efficiency oxygen evolution reaction

Developing high-active and inexpensive electrocatalysts for oxygen evolution reaction (OER) is very important in the field of water splitting. The catalytic performance of electrocatalysts can be significantly improved by optimizing the electronic structure and designing suitable nanostructure. In this work, we represent the synthesis of hollow CoVOx/Ag-5 for OER. Due to the interaction of CoVOx and Ag nanoparticles, the electronic structure is optimized to improve the intrinsic catalytic activity. Additionally, the extrinsic catalytic activity of CoVOx/Ag is enhanced by the abundant active sites from the hollow structure. As a result, the CoVOx/Ag-5 demonstrates significantly enhanced OER catalytic activity with a low overpotential of 247 mV at 10 mA cm-2. In addition, it also exhibits excellent durability, without obvious attenuation in performance after continuous operation for 60 h. Furthermore, the catalyst can enable full water splitting with appropriate 100 % Faraday efficiency, demonstrating its practical application.

Nanozyme-Enhanced Electrochemical Biosensors: Mechanisms and Applications

Nanozymes, as innovative materials, have demonstrated remarkable potential in the field of electrochemical biosensors. This article provides an overview of the mechanisms and extensive practical applications of nanozymes in electrochemical biosensors. First, the definition and characteristics of nanozymes are introduced, emphasizing their significant role in constructing efficient sensors. Subsequently, several common categories of nanozyme materials are delved into, including metal-based, carbon-based, metal-organic framework, and layered double hydroxide nanostructures, discussing their applications in electrochemical biosensors. Regarding their mechanisms, two key roles of nanozymes are particularly focused in electrochemical biosensors: selective enhancement and signal amplification, which crucially support the enhancement of sensor performance. In terms of practical applications, the widespread use of nanozyme-based electrochemical biosensors are showcased in various domains. From detecting biomolecules, pollutants, nucleic acids, proteins, to cells, providing robust means for high-sensitivity detection. Furthermore, insights into the future development of nanozyme-based electrochemical biosensors is provided, encompassing improvements and optimizations of nanozyme materials, innovative sensor design and integration, and the expansion of application fields through interdisciplinary collaboration. In conclusion, this article systematically presents the mechanisms and applications of nanozymes in electrochemical biosensors, offering valuable references and prospects for research and development in this field.

Rapid and efficient removal of methylene blue dye from aqueous solutions using extract-modified Zn-Al LDH

Environmental pollution, particularly water pollution caused by organic substances like synthetic dyes, is a pressing global concern. This study focuses on enhancing the adsorption capacity of layered double hydroxides (LDHs) to remove methylene blue (MB) dye from water. The synthesized materials are characterized using techniques like FT-IR, XRD, SEM, TEM, TGA, EDS, BET, BJH, AFM, and UV-Vis DRS. Adsorption experiments show that Zn-Al LDH@ext exhibits a significant adsorption capacity for MB dye compared to pristine LDH. In addition, Zn-Al LDH@ext shows a significant increase in stability, which is attributed to the presence of phenolic compounds in the extract and the interactions between the functional groups of the extract and LDH. The pH and adsorbent dosage optimizations show that pH 7 and 0.7 g of Zn-Al LDH@ext are optimal conditions for efficient MB removal. The study assessed adsorption kinetics through the examination of Langmuir, Freundlich, and Temkin isotherms. Additionally, four kinetic models, namely pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich, were analyzed. The results indicated that the Temkin isotherm (R2 = 0.9927), and pseudo-second-order (R2 = 0.9999) kinetic provided the best fit to the experimental data. This study introduces a novel approach to enhance adsorption efficiency using modified LDHs, contributing to environmentally friendly and cost-effective water treatment methods.

A single-site porphyrin (Cu)-based COF electrocatalyst for the electrochemical detection of gallic acid sensitively

Sensitive and convenient determination of gallic acid (GA) is vital for food safety. Here, a novel porphyrin (Cu)-based covalent organic framework named as COF(Cu) was successfully synthesized by condensing pre-metalated 5,10,15,20-tetrakis (para-aminophenyl) porphyrin copper (II) and 2,3,6,7-tetra (4-formylphenyl) tetrathiafulvalene ligands. By combining the advantages of porphyrin with tetrathiafulvalene, it may be possible to create a COF with an intrinsically effective charge-transfer channel. In addition, the Cu-N4 type in the COF(Cu) can be regarded as the single-site electrocatalyst. Benefiting from these advantages, the COF(Cu) based electrochemical sensor demonstrated outstanding response to gallic acid (GA). Under the optimal conditions by square wave voltammetry technique, the COF(Cu) modified electrode showed a wide linear range (0.01-1000 μM), a low detection limit (2.81 nM), good reproducibility, acceptable selectivity as well as high stability. Moreover, the established approach was adopted to detect GA in real tea samples with good recoveries, indicating that the COF(Cu) based electrochemical sensor may pave the way for the application in food analysis.

Synthesis of a Cd-MOF Fluorescence Sensor and Its Detection of Fe3+, Fluazinam, TNP, and Sulfasalazine Enteric-Coated Tablets in Aqueous Solution

A Cd-based metal-organic framework (Cd-MOF), named after {[Cd(ttc)(H₂O)]·H₂O}_n (ttc = 1-imidazole-1-yl-2,4,6-benzene-tricarboxylic acid), was synthesized using the solvothermal reaction. The single-crystal structure was determined by single X-ray diffraction analysis, and crystalline characteristics and composition were confirmed by powder X-ray diffraction (PXRD) and thermogravimetric analysis (TG), respectively. Structural analysis showed that the Cd²⁺ ion is in the seven-coordinated mode, in which ttc^2- ion adopts the μ₄-η¹-η¹-η²-η² coordination mode. It is worth noting that the Cd²⁺ ion is connected to ttc^2- to form a 2D network, and the adjacent 2D network is expanded into a 3D supramolecular network structure through weak hydrogen bonds. The fluorescence sensing experiments indicated that Cd-MOF could not only be used as a fluorescence sensor for Fe³⁺, fluazinam (FLU), and 2,4,6-trinitrophenolol (TNP) but also for sulfasalazine detection in aqueous solution. To verify the sensitivity of the fluorescent probe, we calculated its detection limit: 5.34 × 10^-8 M (Fe³⁺), 7.8 × 10^-8 M (FLU), 1.21 × 10^-7 M (TNP), and 2.67 × 10^-7 M (SECT). In addition, the quenching mechanism was thoroughly studied.

High-Symmetry Co/Ni Triazine Polycarboxylate Diverse Frameworks Constructed by Mx(COO)y Building Blocks: Characterization and Catalytic Performance Evaluation of p-Nitrophenol

Three new triazine compounds [Co_1.5(H₃TDPAT)(H₂O)₃]·6H₂O (1), [Co₂(TCPT)(μ₂-H₂O)₂]·OH (2), and [Ni₃(TCPT)]·3OH (3) were designed and synthesized via the reaction of the symmetrical triazine ligand connected by C-N-C and C-O-C bonds with triazine poly(carboxylic acid)s ligands as the side arms: H₆TDPAT (H₆TDPAT = 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine) and H₃TCPT (H₃TCPT = 2,4,6-tris(4-carboxyphenoxy)-1,3,5-triazine) as well as the corresponding metal salts under the solvothermal condition. Three triazine polycarboxylate frameworks were characterized by elemental analysis, infrared spectroscopy, ultraviolet spectroscopy, thermogravimetric analysis, X-ray powder diffraction, and solid fluorescent spectra in detail. The structural analysis results showed that the three-dimensional porous cage framework of compound 1 was constructed by three different polyhedral cages connected with [Co(COO)₄(H₂O)₂] building blocks. One of the compounds, 2, is formed by twin propeller Co₂(μ₂-H₂O)(COO)₃ building blocks connecting two-dimensional layers and the intermolecular π-π interactions involved the triazine rings between the layers. While the structure of compound 3 is similar to that of 2, assembly is by Ni(COO)₃ building blocks and adjacent layers of the face-to-face π-π interaction between the triazine rings. In order to explore functional properties, the catalytic reduction of p-nitrophenol (PNP) of compounds 1-3 was investigated. They exhibit excellent catalytic activity of more than 95% for reduction of PNP with a dose of 2.5 mg of the compounds.