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In the present article, the synthesis of zeolite imidazole framework-11 (ZIF-11) by ultrasonic-assisted hydrothermal process and its application as an electrode modifier for electrochemical determination of uric acid in urine are demonstrated. The obtained materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and nitrogen adsorption/desorption isotherms. It was found that the ZIF-11 with rhombic dodecahedron topology and high surface area (1066 m2.g-1) was synthesized in a certain temperature and found in around 25–40°C, and other crystalline phases of zinc benzimidazolate deferring from ZIF-11 phase were found in less 25°C or higher than 40°C. The ZIF-11 is stable in the pH range 6-10. The modification of glassy carbon electrode was performed with ZIF-67 using the drop-casting procedure. The present ZIF-11 modified electrode was employed to study the electrochemical behavior of uric acid (UA). UA oxidation is catalyzed by this electrode in aqueous buffer solution (pH 7) with a decrease of 70 mV in overpotential compared to glassy carbon electrode. With the differential pulse–anodic stripping voltammetry (DP-ASV) method, the oxidation current of UA versus its concentration shows good linearity in the range 20–540μM (R=0.998) with a detection limit of 0.48 μM (S/N=3). The obtained ZIF-11 modified electrode was applied in the detection of UA content in urine samples, and satisfied results were obtained.

Herein, the single-atom Ni site heterogeneous catalysts supported by the UiO-66 structure (University of Oslo-66 metal organic framework) were successfully synthesized by a postsynthetic metalation method, where Ni ions are covalently attached to the missing-linker defect sites at zirconium oxide clusters (Zr6O4(OH)4) in as-prepared UiO-66 structure, [Zr6O4(OH)4(BDC)(DMF)10(OH)10] (BDC (benzene-1,4-dicarboxylate), DMF (dimethylformamide)). The structure properties of the catalysts were characterized using powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), N2 adsorption-desorption isotherms (BET), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy (PL). It was found that single-atom Ni heterogeneous catalysts supported by the UiO-66 structure, UiO-66/Ni1.0 [Zr6O4(OH)4(C8H4O4)(DMF)10(OH)8Ni2(OH)2(Cl)2], showed a sphere-like morphology with a high specific surface area as well as good thermal stability. Specifically, the as-prepared UiO-66/Ni1.0 exhibited the excellent catalytic activity and stability for 4-nitrophenol reduction in terms of low activation energy (Ea=23.15 kJ mol−1), high turnover frequency (76.19 molecules g-1 min-1), and high apparent rate constant (kapp=0.956min−1). In addition, methylene blue (MB) was also chosen as the organic dye model for catalytic reduction reaction. The kapp and TOF for the reduction of MB using UiO-66/Ni1.0 were 0.787 min−1 and 33.89×1020 molecules g−1 min−1, respectively.

This article reports the synthesis of the University of Oslo-66 (UiO-66) and its application to simultaneous voltammetric determination of ascorbic acid (AA) and acetaminophen (AC). The zirconium terephthalate samples synthesized in different solvents (the N,N′-dimethylformamide, acetonitrile, and ethanol) are characterized with XRD, SEM, TG, nitrogen adsorption/desorption isotherm, and XPS techniques. Among solvents the N,N′-dimethylformamide solvent is favorable for the UiO-66 phase formation. The synthesized UiO-66 material with spherical particles with round 100–150 nm in diameters possesses a large specific surface area. The UiO-66 is used as electrode modifier to develop UiO-66 modified glassy carbon electrode for determining simultaneous AA and AC. The UiO-66 modified electrode demonstrates excellent electrocatalytic performance towards AA and AC oxidation compared with bare GCE. The anodic peak current varies linearly to AA and AC concentration in the range of 0.02 to 2.92 μM. The level of detection (S/N = 3) was found to be 0.019 and 0.018 μM, respectively. The proposed differential pulse voltammetry method was used to determine individually or simultaneously AA and AC in pharmaceutical formulations. The results are not significant different from those analyzed by high-performance liquid chromatography.

In the present paper, the composite of zeolite imidazolate framework-11 (ZIF-11) and activated carbon derived from rice husks (RHAC) was synthesized. The obtained materials were characterized by XRD, SEM, EDX-mapping, and nitrogen adsorption/desorption isotherms. The final composite ZIF-11/RHAC exhibits an even dispersion of ZIF-11 particles on activated carbon matrix. Herein, an electrochemical sensor based on a ZIF-11/RHAC was developed for a rapid determination of triclosan (TCS). It was found that the oxidation of TCS is irreversible and involves the transfer of one electron. The linear range for TCS detection in the optimized experimental conditions was found to be 0.1-8 μM with the limit of detection of 0.076 μM. Finally, the proposed method was successfully employed to detect TCS in different personal care product samples with high accuracy, which was confirmed by a good agreement between these results and those obtained using high-performance liquid chromatography (HPLC).

In the present paper, a nanocomposite of rGO and TiO 2 nanoparticles (TiO 2 /rGO) was prepared by a facile synthesis method with peroxo titanium complexes as TiO 2 precursor. The morphology and structure of TiO 2 /rGO nanocomposite were investigated by X-ray diffraction (XRD), Raman spectroscopy, nitrogen adsorption/desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX)-elementary mapping spectroscopy. It was found that TiO 2 /rGO nanocomposites with high surface area were formed involving strong coupling interaction between TiO 2 and rGO. Based on the synergistic effect of rGO and TiO 2 nanoparticles, an electrochemical sensor for paracetamol (PAR) and codeine (COD) was fabricated by modifying the glassy carbon electrode (GCE) with TiO 2 /rGO material. The cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DP-ASV) were used to determine the electrochemical signals of these analytes. CVs of this sensor provided distinct and sharp oxidation peaks for PAR and COD. The DP-ASV parameters were optimized. It was found that the proposed electrode exhibits excellent electrochemical activity toward PAR and COD. Under the optimal conditions, the A low limit of detection of 0.28 µM for PAR and 0.25 µM for COD were achieved in the linear range from 0.4 to 2.0 µM for both PAR and COD. The proposed method was free from the interference effects of glucose, ascorbic acid, caffeine, and other inorganic salts. This electrode was also highly stable and sensitive making it applicable in the analysis of various real pharmaceutical samples. Graphical abstract

Nickel ferrite/(N,S)graphene oxide (NF/(N,S)GO) was synthesized by a facile coprecipitation-hydrothermal route using Ni 2+ and Fe 3+ mixture in (N,S)GO suspension. This material was used as a photocatalyst for the degradation of rhodamine B (RhB) as a dye model in aquatic environment. It was found that NiFe 2 O 4 nanoparticles with a particle size of 11.5 nm was highly dispersed on (N,S)GO matrix, which was prepared from graphite and thiourea. Visible-light-induced photodegradation of RhB over NF/(N,S)GO has been studied where NF/(N,S)GO presented high photodegradation activity toward RhB compared to both nickel ferrite and (N,S)GO. Furthermore, after three cycles of photodegradation of RhB, the catalyst did not exhibit significant loss of activity (with a drop of around 15% in degradation efficiency compared to fresh catalyst), confirming its stability. The chemical oxygen demand (COD) measurement revealed a gradual decrease of COD from 49.4 mg.L −1 at initial time to 4.8 mg.L −1 after 240 min of light illumination, indicating high degree of mineralization of the degradation process. In addition, kinetic and radical scavenger studies suggest that superoxide ions (·O 2 − ), hydroxyl ions (·OH) were the dominant photooxidants, followed by hole (h + ) and electron (e − ). The degradation mechanism of RhB over NF/(N,S)GO was also addressed. This study provided a possible treatment approach for organic pollutants in aqueous solution by exploiting visible light source.

This paper demonstrates the preparation of ZnMn2O4 nanoparticles through thermal hydrolysis in different solvents, such as isopropanol, ethylene glycol, glycerol, and water, combined with pyrolysis. The obtained samples were characterised by using X-ray diffraction (XRD), infrared spectroscopy (FT‒IR), scanning electron microscopy (SEM), energy-dispersive X-ray mapping, nitrogen adsorption/desorption isotherms, and a vibrating sample magnetometer. The electrocatalytic activity of ZnMn2O4 nanoparticles was investigated toward the oxidation of uric acid (UA) and xanthine (XA). The ZnMn2O4-nanoparticle-modified electrode not only enhances the oxidation currents of the two purine derivatives but also successfully separates the voltammetric signals of the analytes in their binary mixture and, hence, is employed for their simultaneous determination. The factors affecting the analysis, such as pH, scan rate, linear range, detection limit, reproducibility, and interferents, were also investigated. The results show that the UA and XA limits of detection are as low as 0.55 and 1.28 µM, and the modified electrodes have satisfactory repeatability and reproducibility. The practical application of the modified electrode was demonstrated by simultaneously determining the concentrations of UA and XA in urine samples with exceptional accuracy.

A facial differential pulse voltammetric procedure using a glassy carbon electrode modified with zeolite imidazolate framework-67/graphitic carbon nitride (ZIF-67/g-C3N4) for the diclofenac (DCF) determination is demonstrated. ZIF-67/g-C3N4 with different mass ratios of the components was synthesized in a self-assembly process. The obtained materials were characterized by using X-ray diffraction, scanning electron microscopy (SEM), EDX-mapping, and nitrogen adsorption/desorption isotherms. The peak current varies linearly with the DCF concentration in the range of 0.2–2.2 μmol·L−1 and has a detection limit of 0.071 μmol·L−1. The modified electrode exhibits acceptable repeatability, reproducibility, and selectivity towards DCF. The proposed electrode allows determining DCF in human urine without pretreatment, and the results are comparable with those determined with HPLC.

A simple approach was developed to synthesize cobalt ferrite nanoparticles/graphene quantum dots (CF/GQDs). The material was prepared from a homogeneous mixture of iron nitrate, cobalt nitrate, and starch at 140, 180 and 200 °C in a 24 h thermal hydrolysis process. The obtained materials were characterised by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, ultraviolet–visible diffuse reflectance spectroscopy, Fourier-transform infrared spectroscopy, photoluminescence spectroscopy, vibrating-sample magnetometry, and nitrogen adsorption/desorption isotherms. Cobalt ferrite crystals of around 8–10 nm and graphene quantum dots formed directly at 200 °C. Stacking GQDs sheets onto the CF nanoparticles resulted in CF/GQDs nanoparticles. The nanocomposite exhibits satisfactory fluorescent and superparamagnetic properties, which are vital for catalytic applications. The CF/GQDs catalyse significantly the degradation of methylene blue (MB) under visible light. The catalyst can be recycled with an external magnetic field and displays suitable stability. Also, it was reused in three successive experiments with a loss of efficiency of about 5%. The CF/GQDs are considered as an efficient photocatalyst for MB degradation and other dyes.

In this work, a nanocomposite based on nickel ferrite/activated carbon (NiF/AC) was used to modify a highly sensitive electrochemical sensor for the quantification of theophylline (TPL) in pharmaceutical tablets. The synthesized materials were characterized using x-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy-elemental mapping and surface area analysis via the Brunauer–Emmett–Teller method. Cyclic voltammetry was employed to study the electrocatalytic properties of the NiF/AC-GCE toward the oxidation of TPL. The dependence of the electrochemical response on the scan rate and pH was also investigated, and the working parameters were optimized. The linear range of the established electrochemical biosensor was from 0.5 to 5 μ M (R 2 = 0.997), with a detection limit of 0.21 μ M. The present method was tested using three pharmaceutical formulation standard samples with good accuracy and acceptable recovery. Thus, it is a promising candidate for the determination of TPL in pharmaceutical formulations.