Voltammetric determination of catechol based on a glassy carbon electrode modified with a composite consisting of graphene oxide and polymelamine

The authors describe an voltammetric catechol (CC) assay based on the use of a glassy carbon electrode (GCE) modified with a composite consisting of graphene oxide and polymelamine (GO/PM). The modified GCE was characterized by field emission scanning electron microscopy, elemental analysis, Raman spectroscopy and FTIR. Cyclic voltammetry reveals a well-defined response to CC, with an oxidation peak current that is distinctly enhanced compared to electrodes modified with GO or PM only. The combined synergetic activity of GO and PM in the composite also results in a lower oxidation potential. Differential pulse voltammetry (DPV) shows a response that is linear in the 0.03 to 138 μM CC concentration range. The detection limit is 8 nM, and the sensitivity is 0.537 μA⋅μM−1 ⋅cm−2 . The sensor is selective for CC even in the presence of potentially interfering compounds including hydroquinone, resorcinol and dopamine. The modified GCE is highly reproducible, stable, sensitive, and shows an excellent practicability for detection of CC in water samples

Investigation of the Interaction of Sertraline with Calf Thymus DNA by Spectroscopic Methods

The interaction of the antidepressant drug, sertraline, with calf thymus double stranded DNA (dsDNA) in physiological buffer (pH 7.4) was investigated by UV-Vis spectrophotometry, spectrofluorimetry, circular dichroism, Fourier transform infrared spectroscopy (FTIR), viscosity measurements and DNA melting studies. The absorption spectra of the drug with DNA showed a hyperchromic effect. Using Hoechst reagent as a fluorescence probe, quenching of the emission peak occurred in the DNA-Hoechst mixture when sertraline was added. The FTIR spectra revealed minor groove binding mode between the drug and the dsDNA. The binding constant of sertraline to DNA was calculated using spectroscopic data. The calculated thermodynamic parameters suggested that electrostatic interactions are important forces in the formation of sertraline-DNA complex

Voltammetric Determination of Gabapentin by a Carbon Ceramic Electrode Modified with Multiwalled Carbon Nanotubes and Nickel-Catechol Complex

Sol-gel technique was used for the fabrication of a renewable carbon ceramic electrode (CCE) modified with nickel-catechol complex (Ni-CA). The complex was deposited on the surface of a multiwalled carbon nanotubes-CCE by potential cycling in the range of 0.0-0.8 V (vs. saturated calomel electrode, SCE). Ni-CA showed electrocatalytic activity towards the redox reaction of gabapentin. A linear relationship of anodic peak current with gabapentin concentration was observed in a range of 1.25-63.23 µmol L-1 with a limit of detection of 0.5 µmol L-1. The electrode response towards gabapentin was quite reproducible and a long-term stability of the electrode (more than 2 months) was observed. The electrode was successfully applied to the determination of gabapentin in pharmaceutical preparations

Preparation, characterization and application of iron (III)-loaded chitosan hollow fiber membranes as a new bio-based As (V) sorbent

Fe (III)-loaded chitosan (CS) hollow fibers (CS-Fe (III) HF) were successfully prepared according to the dry-wet spinning technique. The CS-Fe (III) HFs were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analysis (TGA). Removal of pentavalent arsenic was studied through biosorption on CS-Fe (III) HF adsorptive membranes. The response surface methodology (RSM) was applied to investigate the influence of the main operating parameters such as contact time, pH, initial As (V) concentration and HFs dosage on the adsorption capacity of As (V). From the Pareto analysis, pH, [As (V)]o, [CS-Fe (III) HF membranes] and squared effect of [As(V)]o were found to produce the largest effect on biosorption of As (V). Kinetic studies showed that the pseudo-second-order kinetic model provides the best correlation to the experimental results. Equilibrium data fitted well with the Langmuir model with maximum adsorption capacity of 3,703 \u3bcg g 121. A laboratory scale glass membrane module consisting of three CS-Fe(III) HFs has also been prepared and tested for biosorption of As (V) at a real scale. Permeability of As (V) ions through the CS-Fe (III) HF membranes was 0.145 \u3bcmol m 122 h 121 bar 121

Performance of chitosan based nanocomposite hollow fibers in the removal of selenium(IV) from water

Fe3O4-chitosan nanocomposite hollow fibers were prepared via impregnation of Fe3O4 nanoparticles on dry-wet spun chitosan hollow fibers (CS-HFs) and its performance in the removal of selenium(IV) from water was investigated. The prepared nanocomposite was characterized using XRD, SEM and TEM analyses confirming the formation of Fe3O4 nanoparticles throughout the heterogeneous surface of CS-HFs. Response surface methodology (RSM) was utilized to optimize Se(IV) adsorption and investigate operational parameters including nanocomposite amount, Se(IV) concentration, pH and contact time. The polynomial second order regression, which is conventionally developed in RSM for describing the process, did not accurately fit the experimental data owing to significant lack of fit. However, in modified polynomial third order regression, all model evaluation criteria had been confirmed the accuracy of the developed model. The adsorption of Se(IV) on prepared Fe3O4-CS HFs followed from pseudo-second-order kinetics with participating both intraparticle and boundary layer diffusion in the rate-controlling step

Improving photocatalytic activity of the ZnS QDs via lanthanide doping and photosensitizing with GO and g-C3N4 for degradation of an azo dye and bisphenol-A under visible light irradiation

In this research, insertion of Gd ions (2 wt%) into the crystalline lattice of the ZnS QDs enhanced the photocatalytic activity of the QDs. In addition, the influence of graphene oxide (GO) and graphitic carbon nitride (g-C3N4) was assessed on the photocatalytic activity of the ZnS QDs through degradation of acid red 14 (AR14) and bisphenol-A (BA) under visible light. Higher photocatalytic degradation efficiency (97.1% for AR14 and 67.4% for BA within 180 min) and higher total organic carbon (TOC) removal (67.1% for AR14 and 59.2% for BA within 5 h) was achieved in the presence of ZnS QDs/g-C3N4 compared with ZnS QDs/GO nanocomposite. Finally, the Gd-doped ZnS QDs were hybridized with g-C3N4 as optimal support to fabricate a potent visible-light-driven photocatalyst for the decomposition of organic contaminants. The maximum photocatalytic degradation of 99.1% and 80.5% were achieved for AR14 and BA, respectively, in the presence of Gd-doped ZnS QDs/g-C3N4 nanocomposite. The photosensitization mechanism was suggested for the improved photocatalytic activity of the ZnS QDs/GO, ZnS QDs/g-C3N4, and Gd-doped ZnS QDs/g-C3N4 nanocomposites under visible light. © 2022 Elsevier Lt