Xiaoquan Lu

Simultaneous determination of ascorbic acid, dopamine and uric acid based on tryptophan functionalized graphene.

A new type of tryptophan-functionalized graphene nanocomposite (Trp-GR) was synthesized by utilizing a facile ultrasonic method via π-π conjugate action between graphene (GR) and tryptophan (Trp) molecule. The material as prepared had well dispersivity in water and better conductivity than pure GR. The surface morphology of Trp-GR was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The electrochemical behaviors of ascorbic acid (AA), dopamine (DA), and uric acid (UA) were investigated by cyclic voltammetry (CV) on the surface of Trp-GR. The separation of the oxidation peak potentials for AA-DA, DA-UA and UA-AA was about 182 mV, 125 mV and 307 mV, which allowed simultaneously determining AA, DA, and UA. Differential pulse voltammetery (DPV) was used for the determination of AA, DA, and UA in their mixture. Under optimum conditions, the linear response ranges for the determination of AA, DA, and UA were 0.2-12.9 mM, 0.5-110 μM, and 10-1000 μM, with the detection limits (S/N=3) of 10.09 μM, 0.29 μM and 1.24 μM, respectively. Furthermore, the modified electrode was investigated for real sample analysis.

Plasma degradation of dyes in water with contact glow discharge electrolysis.

Contact glow discharge electrolysis (CGDE) of two dyes, weak acid brilliant red B and weak acid flavine G, was investigated under different concentrations, temperature and mediums. From the variation of their concentration with the reaction time, it was demonstrated that the oxidation would be a first-order reaction. On the base line of UV spectra of solution in the degradation process, we deduced that two dyes underwent the oxidative degradation in CGDE. The rate constants, relevant coefficients and the decolorization degree were displayed under different conditions.

Preparation of ultrafine nickel powder and its catalytic dehydrogenation activity

Nanocrystalline nickel powders were prepared from aqueous solution by reducing their corresponding metal salts under suitable conditions. The experimental conditions including the types and concentration of protective agents, feeding order and the pH of the solution that influence the average particle size were studied in detail. X-ray powder diffraction patterns show that the nickel powder is cubic crystallite. The average particle size of the ultrafine nickel powder is 50 nm. In addition, we also studied the effect of particle size in liquid phase dehydrogenation of 2-butanol. The results show that the smaller particle size is favored of increasing catalytic activity.

Electrochemical behavior of rutin on a multi-walled carbon nanotube and ionic liquid composite film modified electrode

The electrochemical behavior of hydroquinone (HQ) was studied by cyclic voltammetry at a glassy carbon electrode (GCE) modified by a gel containing multi-walled carbon nanotubes (MWNTs) and room temperature ionic liquid (RTIL) of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF(6)). At the modified electrode, HQ showed a pair of quasi-reversible redox peaks. The cathodic peak current value (I(pc)) of HQ was 9.608 x 10(-4)A, which is 43 times larger than the one at the GCE, and 11 times larger than that of I(pc) at the MWNTs/GCE. Furthermore, the capabilities of electron transfer on these three electrodes were also investigated by electrochemical impedance spectroscopy (EIS), and the similar conclusion as cyclic voltammetry has drawn. Besides, we also characterized the surface morphology of the prepared composite film using the scanning electronic microscopy (SEM). The MWNTs were pulled away from the tangle in RTIL. The solvent effect of RTIL may be the reason of higher adsorption amount.

High loading Pt nanoparticles on functionalization of carbon nanotubes for fabricating nonenzyme hydrogen peroxide sensor

A very efficient, simple approach was developed to fabricate a high Pt nanoparticles-loading multiwall carbon nanotube (MWCNTs) amperometric sensor for hydrogen peroxide (H2O2) determination. In this strategy, MWCNTs were first functionalized with an anionic surfactant, sodium dodecyl sulfate (SDS); then the Pt nanoparticles (NPs) were loaded on MWCNTs-SDS by electrodepositing. The large amounts of Pt nanoparticles could be well deposited on the surface of the MWCNTs-SDS modified electrode, as revealed by scanning electron microscopy (SEM). In addition, the PtNPs/MWCNTs-SDS composite was also characterized by electrochemical methods including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The experimental results demonstrated that the constructed electrode exhibited good catalytic activity toward the hydrogen peroxide, and obtained a wide linear range from 5.8×10(-9) to 1.1×10(-3) M with a limit of detection (LOD) of 1.9×10(-9) M, which was superior to that obtained with other H2O2 electrochemical sensors reported previously. Moreover, it can also be applied to real samples analysis. The excellent performance of hydrogen peroxide sensor was ascribed to the MWCNTs-SDS composites being used as effective load matrix for the deposition of PtNPs and the synergistic amplification effect of the two kinds of nanomaterials-PtNPs and MWCNTs.

Highly dispersive Ag nanoparticles on functionalized graphene for an excellent electrochemical sensor of nitroaromatic compounds

A facile carbon radical reaction procedure and a chemical reduction method were proposed to synthesize Ag nanoparticles on functionalized graphene with uniform, high dispersion and excellent stability. The resultant material showed excellent electrocatalytic activity to nitroaromatic compounds and high sensitivity to the detection of nitroaromatic compounds.

A sensor based on the carbon nanotubes-ionic liquid composite for simultaneous determination of hydroquinone and catechol

MWNTs-IL-Gel/GCE, a glassy carbon electrode modified with multiwalled carbon nanotubes (MWNTs) and ionic liquids (IL), was developed to serve as a sensor for simultaneous determination of Hydroquinone (HQ) and catechol (CC) in this paper. The modified GCE showed two well-defined redox waves for HQ and CC in both CV and DPV with a peak potential separation of ca. 0.1 V, which was large enough for simultaneous detection. The results revealed that the oxidation of HQ and CC with the enhancement of the redox peak current and the decrease of the peak-to-peak separation exhibit excellent electrocatalytic behaviors. A high sensitivity of 1.8×10(-7)M with detection limits of 6.7×10(-8)M and 6.0×10(-8)M (S/N=3) for HQ and CC were obtained. Moreover, the constants of apparent electron transfer rate of HQ and CC at MWNTs-IL-Gel/GCE were calculated as 7.402 s(-1) and 8.179 s(-1), respectively, and the adsorption quantity of HQ and CC was 1.408×10(-6) mol cm(-2) with chronocoulometry. The developed sensor can be applied to determinate directly of HQ and CC in aqueous solution.

Acetylsalicylic acid electrochemical sensor based on PATP–AuNPs modified molecularly imprinted polymer film

A novel electrochemical sensor based on molecularly imprinted polymer film has been developed for aspirin detection. The sensitive film was prepared by co-polymerization of p-aminothiophenol (p-ATP) and HAuCl(4) on the Au electrode surface. First, p-ATP was self-assembled on the Au electrode surface by the formation of Au-S bonds. Then, the acetylsalicylic acid (ASA) template was assembled onto the monolayer of p-ATP through the hydrogen-bonding interaction between amino group (p-ATP) and oxygen (ASA). Finally, a conductive hybrid membrane was fabricated at the surface of Au electrode by the co-polymerization in the mixing solution containing additional p-ATP, HAuCl(4) and ASA template. Meanwhile, the ASA was spontaneously imprinted into the poly-aminothiophenol gold nanoparticles (PATP-AuNPs) complex film. The amount of imprinted sites at the PATP-AuNPs film significantly increases due to the additional replenishment of ASA templates. With the significant increasing of imprinted sites and doped gold nanoparticles, the sensitivity of the molecular imprinted polymer (MIP) electrode gradually increased. The molecularly imprinted sensor was characterized by electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), and cyclic voltammetry (CV). The linear relationships between current and logarithmic concentration were obtained in the range from 1 nmol L(-1) to 0.1 μmol L(-1) and 0.7 μmol L(-1) to 0.1 mmol L(-1). The detection limit of 0.3 nmol L(-1) was achieved. This molecularly imprinted sensor for the determination of ASA has high sensitivity, good selectivity and reproducibility, with the testing in some biological fluids also has good selectivity and recovery.

INVESTIGATION ON THE ELECTROCHEMISTRY OF RUTIN AND ITS ANALYTICAL APPLICATION

ABSTRACT An electrochemical investigation for rutin on glassy carbon electrode is presented. An adsorptive process is observed. The maximum coverage on the electrode surface is 5.09 × 10−10 mol/cm2, this area corresponding to a benzene ring with 3′,4′-dihydroxides adsorbed on the electrode surface; the other parts of rutin keep away from the surface. In the meantime, a new electrochemical method for determining rutin is presented. In a medium of 0.1 M acetate buffer solution (pH = 4.46), a very sensitive polargraphic adsorptive wave is observed by using a differential pulse voltammetry at about 0.29 V (vs. Ag/AgCl). The linear relationship between the peak current and the concentration of rutin exists in a range from 3.28 × 10−7 to 3.28 × 10−5 M. The detection limit of rutin is down to 2.51 × 10−8 M. This method has been applied to determine rutin in several samples of Chinese medicines. The results are satisfactory.

A new electrochemical sensor of nitro aromatic compound based on three-dimensional porous Pt–Pd nanoparticles supported by graphene–multiwalled carbon nanotube composite

In this study, an electrochemical sensor of nitro aromatic compound based on three-dimensional porous Pt-Pd nanoparticles (Pt-Pd NPs) supported by reduced graphene oxide (rGO) nanosheets-multiwalled carbon nanotube (CNTs) nanocomposite (marked as Pt-Pd NPs/CNTs-rGO) was investigated for the first time. This hybrid nanocomposite has been prepared via a facile and versatile hydrothermal synthetic strategy while its structure and property are evaluated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electrochemical impedance spectroscopy (EIS). The result shows that 3D porous Pt-Pd NPs/CNTs-rGO nanocomposite has a large specific surface area of 326.6m(2)g(-1) and exhibited ultrahigh rate capability and good cycling properties at high rates. Electrochemical studies have been performed for the nitro aromatic compounds detection by using different pulse voltammetry (DPV) techniques. The proposed nanocomposite exhibited much enhanced elctrocatalytic activity and high sensitivity toward the detection of nitro aromatic compounds which compared with Pt-Pd NPs dispersed on functionalized rGO, Pt-Pd NPs dispersed on functionalized CNTs, rGO-CNTs and bare glass carbon electrode (GCE). On the basis of the above synergetic electrochemical sensing and synthesis procedure, the hybrid material can be recommended as a robust material for sensor-related applications. Moreover, the proposed sensor exhibits high reproducibility, long-time storage stability and satisfactory anti-interference ability.