M.R. Mahmoudian

Synthesis and characterization of Co3O4 ultra-nanosheets and Co3O4 ultra-nanosheet-Ni(OH)2 as non-enzymatic electrochemical sensors for glucose detection.

The present study examines the synthesis of Co3O4 ultra-nanosheets (Co3O4 UNSs) and Co3O4 ultra-nanosheet-Ni(OH)2 (Co3O4 UNS-Ni(OH)2) via solvothermal process and their application as non-enzymatic electrochemical sensors for glucose detection. X-ray diffraction and transmission electron microscopy results confirmed the Co3O4 UNS deposition on Ni(OH)2 surface. The presence of Co3O4 UNSs on Ni (OH) 2 surface improved the sensitivity of glucose detection, from the increase of glucose oxidation peak current at the Co3O4 UNS-Ni(OH)2/glassy carbon electrode (current density: 2000μA·cm(-2)), compared to the Co3O4 UNSs. These results confirmed that Ni(OH)2 on glassy carbon electrode is a sensitive material for glucose detection, moreover the Co3O4 UNSs can increase the interaction and detection of glucose due to their high surface area. The estimated limit of detection (S/N=3) and limit of quantification (S/N=10) of the linear segment (5-40μM) are 1.08μM and 3.60μM respectively. The reproducibility experiments confirmed the feasibility of Co3O4 UNS-Ni(OH)2 for the quantitative detection of certain concentration ranges of glucose.

Solid-phase electrochemical reduction of graphene oxide films in alkaline solution

Graphene oxide (GO) film was evaporated onto graphite and used as an electrode to produce electrochemically reduced graphene oxide (ERGO) films by electrochemical reduction in 6 M KOH solution through voltammetric cycling. Fourier transformed infrared and Raman spectroscopy confirmed the presence of ERGO. Electrochemical impedance spectroscopy characterization of ERGO and GO films in ferrocyanide/ferricyanide redox couple with 0.1 M KCl supporting electrolyte gave results that are in accordance with previous reports. Based on the EIS results, ERGO shows higher capacitance and lower charge transfer resistance compared to GO.

A sensitive electrochemical Hg2+ ions sensor based on polypyrrole coated nanospherical platinum

We report the synthesis and characterization of polypyrrole coated on nanospherical platinum (Pt/PPy NSs) composites for the detection of mercury ions. The synthesis was completed via the direct reduction of potassium tetrachloro platinate(II) aqueous solution in the presence of pyrrole monomers in NaOH. X-ray diffraction and field emission scanning electron microscopy results indicated that the Pt cations were completely reduced to Pt with the concurrent formation of Pt/PPy NSs nanospherical morphology, respectively. The electrochemical properties of Pt/PPy NSs electrode were studied by cyclic voltammetry, differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy. From the DPV results, a linear working range for the concentration of mercury ions between 5 to 500 nM with LOD 0.27 nM (S/N = 3) was obtained. The sensitivity of this linear segment is 1.239 μA nM−1 cm−2. The interference from Ag+, Fe2+, Mn2+, K+, Pd2+, Cu2+, Ni2+, Pb2+, Sn2+ and Zn2+ was negligible, thus is a bright prospect for the electrochemical detection of Hg(II).

Graphene oxide electrocatalyst on MnO2 air cathode as an efficient electron pump for enhanced oxygen reduction in alkaline solution

Graphene oxide (GO) was deposited on the surface of a MnO2 air cathode by thermal evaporation at 50°C from a GO colloidal suspension. Fourier transformed infrared spectroscopy and field emission scanning electron microscopy confirmed the presence of GO on the MnO2 air cathode (GO-MnO2). Voltammetry and chrono-amperometry showed increased currents for the oxygen reduction reaction (ORR) in 6 M KOH solution for GO-MnO2 compared to the MnO2 cathode. The GO-MnO2 was used as an air cathode in an alkaline tin-air cell and produced a maximum power density of 13 mW cm−2, in contrast to MnO2, which produced a maximum power density of 9.2 mW cm−2. The electrochemical impedance spectroscopy results suggest that the chemical step for the ORR is the rate determining step, as proposed earlier by different researchers. It is suggested that the presence of GO and electrochemically reduced graphene oxide (ERGO) on the MnO2 surface are responsible for the increased rate of this step, whereby GO and ERGO accelerate the process of electron donation to the MnO2 and to adsorbed oxygen atoms.

A sensitive dopamine biosensor based on ultra-thin polypyrrole nanosheets decorated with Pt nanoparticles

A sensitive and selective electrochemical sensor to determine dopamine (DA) was successfully fabricated from ultra-thin polypyrrole nanosheets (UltraPPy) that were decorated with Pt nanoparticles (Pt/UltraPPy–GCE). The morphology and structure of the modified electrode were characterized using transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction and Fourier-transform infrared spectroscopy (FTIR). This new electrode displayed a synergistic effect of UltraPPy and Pt on the electro-oxidation of DA in phosphate buffer solution at pH 7. The Pt/UltraPPy–GCE demonstrated excellent electrochemical activity towards DA oxidation compared with the bare GCE, UltraPPy–GCE and Pt NPs–GCE, possibly because of the larger surface area of the UltraPPy, which increased the interactions between the polymer and the K2PtCl4 solution during Pt NP deposition. The small size of the deposited Pt NPs resulted in a large surface area of Pt, which is suitable for the reaction with DA. Furthermore, polypyrrole (PPy) in the nanocomposite material could crosslink to improve its stability with the Pt NPs. By applying the differential pulse voltammetry technique under optimized experimental conditions, a good linear ratio of oxidation peak currents and DA concentrations over a range of 0.01–400 μM was achieved with a limit of detection of 0.67 nM. This electrode was used to determine the DA concentration in a DA hydrochloride injection.

Influences of anionic and cationic dopants on the morphology and optical properties of PbS nanostructures

Selenium and zinc are used as anionic and cationic dopant elements to dope PbS nanostructures. The undoped and doped PbS nanostructures are grown using a thermal evaporation method. Scanning electron microscopy (SEM) results show similar morphologies for the undoped and doped PbS nanostructures. X-ray diffraction (XRD) patterns of three sets of the nanostructures indicate that these nanostructures each have a PbS structure with a cubic phase. Evidence of dopant incorporation is demonstrated by X-ray photoelectron spectroscopy (XPS). Raman spectra of the synthesized samples confirm the XRD results and indicate five Raman active modes, which relate to the PbS cubic phase for all the nanostructures. Room temperature photoluminescence (PL) and UV—Vis spectrometers are used to study optical properties of the undoped and doped PbS nanostructures. Optical characterization shows that emission and absorption peaks are in the infrared (IR) region of the electromagnetic spectrum for all PbS nanostructures. In addition, the optical studies of the doped PbS nanostructures reveal that the band gap of the Se-doped PbS is smaller, and the band gap of the Zn-doped PbS is bigger than the band gap of the undoped PbS nanostructures.

Excellent photocatalytic performance under visible-light irradiation of ZnS/rGO nanocomposites synthesized by a green method

ZnS/graphene nanocomposites with different graphene concentrations (5, 10 and 15 wt.%) were synthesized using L-cysteine as surfactant and graphene oxide (GO) powders as graphene source. Excellent performance for nanocomposites to remove methylene blue (MB) dye and hexavalent chromium (Cr(VI)) under visible-light illumination was revealed. TEM images showed that ZnS NPs were decorated on GO sheets and the GO caused a significant decrease in the ZnS diameter size. XRD patterns, XPS and FTIR spectroscopy results indicated that GO sheets changed into reduced graphene oxide (rGO) during the synthesis process. Photocurrent measurements under a visiblelight source indicated a good chemical reaction between ZnS NPs and rGO sheets.

Synthesis and Characterization of Zinc/Polypyrrole Nanotube as a Protective Pigment in Organic Coatings

This study deals with the synthesis and characterization of zinc/polypyrrole nanotube (Zn/PPy) as a protective pigment in organic coatings. The PPy nanotube is synthesized by chemical oxidative polymerization, and zinc nanoparticles are deposited onto the surface of the synthesized PPy nanotube in the presence of sodium dodecyl sulfate. Field emission scanning electron microscopy, transmission electron microscopy, and X-ray diffraction results confirm the existence of the nanotube morphology and the zinc nanoparticles. Electrochemical impedance spectroscopy and potentiodynamic polarization are performed on steel plates coated with polyvinyl butyral incorporated with the Zn/PPy nanotube. The results show that the existence of zinc can improve the protective properties of the pigment. The existence of zinc leads to a cathodic protection and the main product of zinc corrosion is the stale zinc hydroxide which can block the pores in the coating. In addition, the zinc nanoparticles can increase conductivity of the PPy nanotube leading to increasing nanotube’s ability to form protective layers of metal oxides on the steel surface.

Studies on the Effects of the Potential Sweep Rates and pH on the Corrosion Rate of Polyaniline Coated Steel

Polyaniline (PAni) film was successfully electrodeposited on the surface of steel substrates in oxalic acid electrolyte by cyclic voltammetry at different potential sweep rates (dE/dt) (10, 20 and 30 mVs-1) and different pH values (1.55, 2.55 and 3.55). The coated steel with PAni was characterized by Field Emission Scanning Electron Microscopy (FESEM) and Fourier Transform Infrared Spectroscopy (FTIR) techniques. The corrosion resistance of the electrodeposited layers was evaluated by potentiodynamic polarization in 0.1 M NaCl aqueous solution. The results showed that with increasing pH and sweep rate the amount of corrosion rate decreased and increased respectively. Moreover, the correlation between variation of anodic charge (Qa) with pH and sweep rate has been evaluated. The variation of anodic charge confirmed that the growing rate of polymer decreased with increasing sweep rate and pH. The result of potentiodynamic polarization showed that the coated steel with synthesized PAni in pH 3.5 and sweep rate 0.01Vs-1 had better protective properties against corrosion.