Efficient Fe/CuFeO2/rGO nanocomposite catalyst for electro‐Fenton degradation of organic pollutant: Preparation,characterization and optimization

The nanocomposite of zero‐valent iron and delafossite CuFeO₂ supported on reduced graphene oxide was synthesized for the first time to evaluate its performance as the heterogeneous catalyst toward electro‐Fenton (EF) removal of catechol. X‐ray diffraction, Fourier transform‐infrared, scanning electron microscopy and Brunauer–Emmett–Teller (BET) were used to characterize the nanocomposite. It was found that the rhombohedral structure of CuFeO₂ remained stable during the nanocomposite preparation. The BET surface area of the nanocomposite increased about 102 times in comparison with bare CuFeO₂. The influence of the operating parameters was investigated. The optimum operating conditions were pH 3, Fe/CuFeO₂/rGO: 1 g/l; catechol: 7.5 × 10^?4 mol/l; and I: 150 mA, which led to 99% and 78.4% catechol and chemical oxygen demand removal in 120 min, respectively. The stability of the catalyst by leaching measurements was studied. Only 2% and 3.1% of iron and copper, respectively, was leached in the solution. The obtained results introduced Fe/CuFeO₂/rGO as a stable and appropriate catalyst for removal of organic compounds by the EF process. It was inferred from the scavenger utilization that hydroxyl radical plays a major role in catechol elimination and EF reaction followed by the Haber–Weiss mechanism at optimum conditions. The gas chromatography–mass spectrometry analysis was performed to detect the intermediate products, and an acceptable degradation pathway was proposed. The EF degradation of catechol follows a pseudo‐first‐order kinetics model with a rate constant of 3.69 × 10^?2 min^?1 for the optimum operating conditions. The reusability of Fe/CuFeO₂/rGO was investigated for six cycles, and the catalytic efficiency almost remained.     

Alcohol‐based deep eutectic solvent as a carrier of SiO2@Fe3O4 for the development of magnetic dispersive micro‐solid‐phase extraction method: Application for the preconcentration and determination of morin in apple and grape juices,diluted and acidic extract of dried onion and green tea infusion samples

In this study, a hydrophilic deep eutectic solvent was synthesized as a carrier and disperser of magnetic nanoparticles based on ferrofluid and used to develop the dispersive micro‐solid‐phase extraction method. Ethylene glycol/tetramethylammonium chloride deep eutectic solvent and SiO₂@Fe₃O₄ were used to provide the highly stable ferrofluid with strong sorbing properties without any additional stabilizer, which was employed to extract and determine morin in apple and grape juices, diluted and acidic extract of dried onion, and green tea infusion samples. The dispersibility of SiO₂@Fe₃O₄ and prevention of its aggregation in the sample solution were improved using the deep eutectic solvent‐based ferrofluid. Also, it facilitated the fast injection of sorbent into the sample solution that led to an increase of the contact surface between the sorbent and analyte, and reduction of the extraction time and consumption of the sorbent. The important experimental parameters influencing the extraction efficiency of morin were examined. Under the optimal conditions, a linear calibration curve was obtained in the range of 3–500 µg/L with a determination coefficient of 0.9994. The limits of detection and quantification were of 0.91 and 2.98 µg/L, respectively. While an extraction recovery of 97.7% with relative standard deviation of 3.8% (interday) was obtained via three replicated measurements on a 30 µg/L of morin standard solution, the enrichment factor was 39.1. Finally, this method was successfully used to extract and preconcentrate morin in various samples, followed with their determination by high‐performance liquid chromatography with ultraviolet detection.     

A characterization of well-posedness for the second order abstract Cauchy problems with finite delay

In this work, we introduce a strongly continuous one-parameter family of bounded linear operators that completely describes the well-posedness of a second order abstract differential delay equation in the initial history space $L^p([-r,0];X)$, $r>0$. This family, which satisfies a specific functional equation is applied to characterize the mild solution of the considered second order delay equation.