Yongling Du

Fabrication of β-cyclodextrin-coated poly (diallyldimethylammonium chloride)-functionalized graphene composite film modified glassy carbon-rotating disk electrode and its application for simultaneous electrochemical determination colorants of sunset yellow and tartrazine

We proposed a green and facile approach for the synthesis of β-cyclodextrin-coated poly(diallyldimethylammonium chloride)-functionalized graphene composite film (β-CD-PDDA-Gr) by using L-ascorbic acid (L-AA) as the reducing agent at room temperature. The β-CD-PDDA-Gr composite film modified glassy carbon-rotating disk electrode (GC-RDE) was then developed for the sensitive simultaneous determination of two synthetic food colorants: sunset yellow (SY) and tartrazine (TT). By cyclic voltammetry (CV), the peak currents of SY and TT increased obviously on the developed electrochemical sensor. The kinetic parameters, such as diffusion coefficient D and standard heterogeneous rate constant kb, were estimated by linear sweep voltammetry (LSV). Under the optimal conditions, the differential pulse voltammetry (DPV) signals of SY and TT on the β-CD-PDDA-Gr modified GC-RDE were significantly enhanced. The enhanced anodic peak currents represented the excellent analytical performance of simultaneous detection of SY and TT in the range of 5.0×10(-8) to 2.0×10(-5) mol L(-1), with a low limit of detection (LOD) of 1.25×10(-8) mol L(-1) for SY and 1.43×10(-8) mol L(-1) for TT (SN(-1)=3). This proposed method displayed outstanding selectivity, good stability and acceptable repeatability and reproducibility, and also has been used to simultaneously determine SY and TT in some commercial soft drinks with satisfactory results. The obtained results were compared to HPLC of analysis for those two colorants and no significant differences were found. By the treatment of the experimental data, the electrochemical reaction mechanisms of SY and TT both involved a one-electron-one-proton-transfer process.

Simultaneous electrochemical determination of uric acid, xanthine and hypoxanthine based on poly(l-arginine)/graphene composite film modified electrode

Poly(l-arginine)/graphene composite film modified electrode was successfully prepared via a facile one-step electrochemical method and used for simultaneous determination of uric acid (UA), xanthine (XA) and hypoxanthine (HX). The electrochemical behaviors of UA, XA and HX at the modified electrode were studied by cyclic voltammetry and differential pulse voltammetry (DPV), and showed that the modified electrode exhibited excellent electrocatalytic activity toward the oxidation of the three compounds. The calibration curves for UA, XA and HX were obtained over the range of 0.10-10.0, 0.10-10.0 and 0.20-20.0 μM by DPV, respectively and the detection limits for UA, XA and HX were 0.05, 0.05 and 0.10 μM (S/N=3), respectively. With good selectivity and high sensitivity, the modified electrode has been applied to simultaneous determination of UA, XA and HX in human urine with satisfactory result.

Sensitive determination of thymol based on CeO2 nanoparticle–decorated graphene hybrid film

A novel thymol electrochemical sensor based on a CeO2 nanoparticle–decorated graphene hybrid was introduced. The hybrid was characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The electrochemical behavior of thymol on the CeO2/graphene modified glassy carbon electrode was investigated in pH 7.0 phosphate buffer solution by cyclic voltammetry and differential pulse voltammetry. Compared with the bare glassy carbon electrode, the proposed electrode showed improved analytical performance characteristics in catalytic oxidation of thymol. Under the selective conditions, the modified electrode showed a linear voltammetric response for the thymol within a concentration range of 1.0 × 10−7 to 1.8 × 10−5 mol L−1, and a value of 5.0 × 10−8 mol L−1 was calculated for the detection limit (S/N = 3). Furthermore, good selectivity with high sensitivity was obtained for the determination of thymol in real samples.

High electrocatalytic activity of non-noble Ni-Co/graphene catalyst for direct ethanol fuel cells

The electrocatalytic oxidation of ethanol is studied on the non-noble catalysts Ni-Co/graphene and Ni/graphene supported on glass carbon electrode (GCE) in alkaline medium. The synthesized materials are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and scanning transmission electron microscopy. The elements of Ni-Co/graphene and Ni/graphene catalysts are characterized using energy-dispersive X-ray spectroscopy. The electrocatalytic properties of Ni-Co/graphene and Ni/graphene for ethanol oxidation are investigated by cyclic voltammetry, chronoamperometry, and Tafel plot. Compared with Ni/graphene catalyst, Ni-Co/graphene has the higher electroactivity and better stability for ethanol oxidation. The rate constant (ks) and charge-transfer coefficient (α) are calculated for the electron exchange reaction of the modified GCE. The results indicate that Co addition could promote the oxidation reaction at the Ni/graphene catalyst. Our study demonstrates that the low-cost electrocatalyst Ni-Co/graphene has a great potential for real direct ethanol fuel cells’ application.

Sensitive determination of vanillin based on an arginine functionalized graphene film

An arginine (Arg) functionalized graphene (Arg-G) nanocomposite was produced successfully and the procedure was environment-friendly. An electrochemical sensor based on the Arg-G nanocomposite was developed for the determination of vanillin. The Arg-G modified glassy carbon electrode (GCE) showed excellent sensitivity properties by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under the optimized conditions, the oxidation peak current was proportional to vanillin concentration in the range of 2.0 × 10−6 to 7.0 × 10−5 mol L−1 with the correlation coefficient of 0.9986 and the detection limit of 1.0 × 10−6 mol L−1 (S/N = 3). Moreover, the sensor could be used for the detection of vanillin in real food samples with satisfactory results.

Synthesis of Platinum Nanoparticles by using Molybdenum Disulfide as a Template and its Application to Enzyme‐like Catalysis

Platinum nanoparticles were synthesized with molybdenum disulfide (MoS2) as a template through a facile hydrothermal method. The as‐prepared nanocomposites (Pt‐MoS2) were characterized by TEM, HRTEM, electrochemical impedance spectroscopy, and X‐ray photoelectron spectroscopy, and they were then used to fabricate a biosensor for enzyme‐like catalysis of hydrogen peroxide (H2O2). The electrochemical activity for the reduction reactions of H2O2 was evaluated in N2‐saturated phosphate buffer solution. The cyclic voltammetry and amperometry results demonstrated that the biosensor modified by the nanocomposites exhibited a fast amperometric response and excellent electrocatalytic activity for reduction of H2O2 with a wide linear range from 0.004 to 48.5 mM and a low detection limit of 0.001 mM at 3σ. Thus, the present work indicates that Pt nanoparticles can be synthesized on the surface of few‐layer MoS2 owing to interfacial PtS bonds and that the composites show a clear enhancement in the catalytic activity relative to that of the platinum nanoparticles alone. This method provides a new way to prepare metal nanoparticles for extensive applications in the field of catalysis.

Fabrication of a CuS/graphene nanocomposite modified electrode and its application for electrochemical determination of esculetin

In this paper, a CuS/graphene nanocomposite modified glassy carbon electrode (GCE) was successfully constructed and used for determination of esculetin. The electrochemical behavior of esculetin was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results indicated that the synergistic effect between CuS nanoparticles (NPs) and graphene enhanced the electrochemical response of esculetin. Under optimal conditions, the DPV peak current increased linearly with the esculetin concentration in the range from 1.0 × 10−7 to 1.0 × 10−4 mol L−1, and the detection limit (S/N = 3) was 5.8 × 10−8 mol L−1. Furthermore, a good selectivity with high sensitivity was obtained for the determination of esculetin in real samples.

Electroless deposition of Au nanoparticles on reduced graphene oxide/polyimide film for electrochemical detection of hydroquinone and catechol

An electrochemical sensor for determination of hydroquinone (HQ) and catechol (CC) was developed using Au nanoparticles (AuNPs) fabricated on reduced graphene oxide/polyimide (PI/RGO) film by electroless deposition. The electrochemical behaviors of HQ and CC at PI/RGO-AuNPs electrode were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under the optimized condition, the current responses at PI/RGO-AuNPs electrode were linear over ranges from 1 to 654 mol/L for HQ and from 2 to 1289 mol/L for CC, with the detection limits of 0.09 and 0.2 mol/L, respectively. The proposed electrode exhibited good reproducibility, stability and selectivity. In addition, the proposed electrode was successfully applied in the determination of HQ and CC in tap water and the Yellow River samples.

Hexagram-like CoS-MoS2 composites with enhanced activity for hydrogen evolution reaction

Hexagram-like CoS-MoS2 composites were prepared on indium tin oxide (ITO) conductive glasses via cyclic voltammetry electrodeposition using Co(NO3)2 and (NH4)2MoS2 as precursors and tested for application in hydrogen evolution reaction (HER). The structure of CoS-MoS2 composites was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectrum (XPS). Electrochemical characterizations indicate that CoS-MoS2 composites exhibit more excellent catalytic activity and stability than MoS2. Compared with pure MoS2, the hexagram-like CoS-MoS2 composites with increased specific surface area improved the density of exposed active sites, and the Co binding S edges in CoS-MoS2 composites promote the number of highly catalytic edge sites and decreased the binding energy △GH. Moreover, the effects of different substrates on the CoS-MoS2 composites were also investigated. Our further understanding of this highly active hydrogen evolution catalyst can facilitate the development of economical electrochemical hydrogen production systems.