Shimaa M. Ali

Improved host–guest electrochemical sensing of dopamine in the presence of ascorbic and uric acids in a β-cyclodextrin/Nafion®/polymer nanocomposite

A voltammetric analytical method based on a combination of β-cyclodextrin (CD), Nafion® (NF) and a gold electrode modified with poly(3,4-ethylene-dioxythiophene) (PEDOT) has been successfully developed (Au/PEDOT/NF/CD) for the determination of dopamine (DA) in the presence of ascorbic acid (AA) or uric acid (UA). Optimization of the sensor was conducted, including variables such as the type of substrate, concentration of each modifier, pH of the electrolyte, method of deposition of the polymer and immobilization of CD, and also the time for accumulation of the compound at the modified surface. The synergistic effect of the high conductivity of PEDOT and NF, in addition to the pre-concentrating effect of CD, its different host–guest inclusion complexes and its formation of hydrogen bonds with each compound, was used to construct a stable electrochemical sensor for the determination of these compounds. Under optimized conditions a linear calibration curve was obtained for the determination of dopamine in urine within the range 0.6–320 μmol L−1, with a correlation coefficient of 0.996 and detection limit of 5.84 nmol L−1. The proposed sensor was successfully used for the determination of tertiary mixtures of DA, AA and UA, of DA, AA and acetaminophen (APAP), and of binary mixtures of DA and serotonin (ST). It has been demonstrated that Au/PEDOT/NF/CD can be used as a sensor with excellent reproducibility, sensitivity and stability.

Control of zinc corrosion in acidic media: Green fenugreek inhibitor

Abstract Fenugreek seeds extract was examined as a green corrosion inhibitor for Zn in 2.0 mol/L H 2 SO 4 and 2.0 mol/L HCl solutions by mass loss and electrochemical measurements. Scanning electron microscope (SEM) images show that the surface damage is decreased in the presence of the inhibitor. X-rays photoelectron spectroscopy (XPS) analysis was performed to identify the corrosion product, ZnO, and to prove the inhibitor adsorption mechanism. The maximum inhibition efficiency values are 90.7% after 1 h and 66.6% after 0.5 h by 200 mL/L of fenugreek extract in H 2 SO 4 and HCl solutions, respectively. Addition of I − ion greatly improves the inhibition efficiency of fenugreek seeds extract for Zn corrosion in HCl due to the synergistic effect. Potentiodynamic polarization and EIS measurements prove the inhibition ability of fenugreek for Zn corrosion in HCl as indicated by the decreased corrosion current density and increased charge transfer resistance values in the presence of fenugreek.

Synthesis and Characterization of Nano-Conducting Copolymer Composites: Efficient Sorbents for Organic Pollutants

Nano-conducting copolymers of aniline (ANI) and pyrrole (Py) with silica of different starting monomer ratios are prepared by oxidative chemical polymerization. X-ray diffraction (XRD) data showed that polyaniline (PANI) is the predominant phase in copolymer composites with a higher starting ANI monomer ratio while polypyrrole (PPy) is the major phase for other prepared samples. Transmission and scanning electron microscope images ascertained XRD results where hexagonal-shaped particles are assigned to PANI/SiO2 and poly(9ANI-co-1Py)/SiO2 samples; the cauliflower morphology can be observed for PPy/SiO2, poly(1ANI-co-9Py)/SiO2, poly(1ANI-co-2Py)/SiO2, and poly(1ANI-co-1Py)/SiO2 samples. One-dimensional nano-fibers can be obtained by using a starting monomer ratio of 2ANI:1Py during synthesis. Thermal analysis showed that copolymerization increases the thermal stability as compared with PANI/SiO2 and PPy/SiO2 composites. All prepared samples were applied as sorbents for Congo red dye from aqueous solutions. It was found that the sorption capacity value was affected by the starting monomer ratio; poly(2ANI-co-1Py)/SiO2 has the highest sorption capacity; the qm value is 142.9 mg g−1 due to its highly-stabilized nano-structure.

Perovskites of Type LaBO3 Prepared by the Microwave-Assisted Method for Oxygen Production

LaBO3 (B = Ni, Mn, Cr and Co) were prepared by microwave-assisted citrate method. The electrocatalytic activity toward oxygen evolution reaction was investigated by dc linear polarization and electrochemical impedance measurements. XRD characterization showed that pure perovskite crystals were formed. FESEM images showed that changing the type of the B-site metal ion affected the morphology of the prepared perovskites. HRTEM images confirmed the formation of the orthorhombic phase LaCrO3 and the rhombohedral phases of LaNiO3, LaMnO3 and LaCoO3. The order of the electrocatalytic activity was LaNiO3 > LaFeO3 > LaMnO3, that was related to the calculated values of the activation energy 11.38, 20.13 and 22.01 kJ mol-1 for LaBO3 (B = Ni, Fe and Mn), respectively. LaCrO3 and LaCoO3 showed no catalytic activity toward OER due to the dissolution and the formation of passive layer of Co3O4 when being tested in HClO4 medium. The reaction order and mechanism were identified.