Wei Huang

Nonenzymatic amperometric response of glucose on a nanoporous gold film electrode fabricated by a rapid and simple electrochemical method

An enzyme-free amperometric method was established for glucose detection using a nanoporous gold film (NPGF) electrode prepared by a rapid one-step anodic potential step method within 5 min. The prepared NPGF had an extremely high roughness and was characterized by scanning electron microscopy (SEM) and cyclic voltammetry. Electrochemical responses of the as-prepared NPGF to glucose in 0.1M phosphate buffer solution (PBS, pH 7.4) with or without Cl(-) were discussed. In amperometric studies carried out at -0.15 V in the absence of Cl(-), the NPGF electrode exhibited a high sensitivity of 232 μA mM(-1)cm(-2) and gave a linear range from 1mM up to 14 mM with a detection limit of 53.2 μM (with a signal-to-noise ratio of 3). In addition, the oxidation of ascorbic acid (AA) and uric acid (UA) can be completely eliminated at such a low applied potential. On the other hand, the quantification of glucose in 0.1M PBS (pH 7.4) containing 0.1M NaCl offered an extended linear range from 10 μM to 11 mM with a sensitivity of 66.0 μA mM(-1)cm(-2) and a low detection limit of 8.7 μM (signal-to-noise ratio of 3) at a detection potential of 0.2V.

Preparation of AuPt Alloy Foam Films and Their Superior Electrocatalytic Activity for the Oxidation of Formic Acid

AuPt alloy films with three-dimensional (3D) hierarchical pores consisting of interconnected dendrite walls were successfully fabricated by a strategy of cathodic codeposition utilizing the hydrogen bubble dynamic template. The foam films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Due to the special porous structure, the electronic property, and the assembly effect, the AuPt alloy foam films show superior electrocatalytic activity toward the electrooxidation of formic acid in acidic solution, and the prepared 3D porous AuPt alloy films also show high activity and long stability for the electrocatalytic oxidation of methanol, where synergistic effect plays an important role in addition to the electronic effect and assembly effect. These findings provide more insights into the AuPt bimetallic nanomaterials for electrocatalytic applications.

Facile preparation of a variety of bimetallic dendrites with high catalytic activity by two simultaneous replacement reactions

Herein, two simultaneous replacement reactions were explored to prepare a variety of bimetallic dendrites (AgCu, AgPd, AuPd, CuAu, CuPt and CuPd) in one step, using commercial Mg powder as a sacrificial metal to reduce the bimetallic precursors in aqueous solution. We demonstrate in detail how the morphologies and compositions of the bimetallic dendrites are affected by factors such as the potential difference between the metal redox couples, molar ratios of precursors, ligands, reaction times and total precursor concentrations, taking dendritic AgCu as an example. In addition, monometallic Ag and Cu dendrites were also prepared for comparison. The application of these prepared dendrites as high performance catalysts for the reduction of 4-nitrophenol in aqueous solution at room temperature was further explored. The order of activity CuPd > CuPt > CuAu > Cu > Ag1Cu1 > Ag3Cu1 > AuPd > Ag1Cu3 > AgPd > Ag was established for the prepared dendrites based on normalized kinetic parameters according to our proposed formula.

Fabrication of nano-network gold films via anodization of gold electrode and their application in SERS

We report here a green and facile one-step method to fabricate nano-network gold films of low roughness via anodization of gold electrodes in an aqueous solution of l-ascorbic acid (AA) or hydroquinone (H2Q) at the oxidation peak potential. The preparation involves the formation of thin gold oxide layer by anodization of gold and its simultaneous and/or subsequent reduction by AA or H2Q. The as-fabricated nano-network gold films show very strong SERS activity in comparison with the substrates prepared by some other electrochemical roughening methods.

Nanoassemblies of colloidal gold nanoparticles by oxygen-induced inorganic ligand replacement.

This article reports a novel method of the fabrication of floating ultrathin nanoporous films and superlattice-like bottom sediment flakes of colloidal gold nanoparticles (Au NPs) by the oxygen-induced ligand replacement of inorganic species. The two nanoassemblies were realized in a weighing bottle simply by aging the Au colloid, which was synthesized and stabilized using more divalent tin Sn(II) than required for the reduction of HAuCl(4). In situ Raman spectroscopy was employed to trace the assembly process, and we found that the protective Sn(II) species (mostly SnCl(3)(-)) of the gold colloid could be gradually replaced by Cl(-) ions in the solution, while the strongly chemically adsorbed Sn(II) species on the Au NPs was oxidized by O(2) from the air contact. The destabilized colloidal Au NPs by the ligand replacement of SnCl(3)(-) with Cl(-) first assembled into an ultrathin nanoporous film at the air-water interface and then sedimentated to the bottom. Superlattice-like sediment flakes of Au NPs can be obtained at lower temperature (approximately 5 degrees C). Particularly, this method does not involve any organic substances, providing clean ultrathin nanoporous films and superlattice-like flakes of Au NPs. The ultrathin nanoporous films and superlattice-like flakes of Au NPs can serve as SERS substrates with strong and long activity.

Rapid and high-capacity adsorption of sulfonated anionic dyes onto basic bismuth(III) nitrate via bidentate bridging and electrostatic attracting interactions

A new adsorbent of octahedron-structured basic bismuth(III) nitrate (OBBN), [Bi6O5(OH)3](NO3)5·3H2O, was synthesized by a mild hydrolysis route and used for the adsorption removal of sulfonated anionic dyes (SADs) from aqueous solutions. A typical SAD, methyl orange (MO), was taken to investigate the adsorption processes at different pH, adsorbent dosage, contact time, temperature and initial MO concentration. The equilibrium adsorption data were well fitted by the Langmuir isotherm model and showed high adsorption capacity (qmax = 1298 mg g−1). The adsorption kinetics was well described by the pseudo-second-order model and exhibited a short adsorption equilibrium time (<14 min for 20 mg L−1 MO). Adsorption thermodynamic parameters revealed that the adsorption is endothermic, random and spontaneous. The adsorption behavior was closely related to the combined interactions of bidentate bridging and electrostatic attraction between [Bi6O5(OH)3]5+ polycations on the OBBN surface and –SO3− groups of the SAD. The adsorbent was successfully applied to remove MO from model wastewater with a satisfactory result.

Facile preparation of Sb and oxide-coated Sb nanoparticles via cathodic dispersion of bulk Sb in different media

We report here a facile electrochemical method on the preparation of antimony nanoparticles (NPs) by dispersing a bulk antimony electrode under highly cathodic polarization in different media at room temperature, requiring neither precursor ions nor organic capping agents. The dispersion of bulk antimony in a tetrabutyl ammonium bromide (TBAB) acetonitrile solution involved the formation and oxidation of an unstable Zintl compound of antimony, and the as-prepared Sb NPs were readily transferred into Sb–Sb2O3 core–shell NPs during the post treatment and characterization because of the surface oxidation of Sb NPs by oxygen in the air. In contrast, Sb NPs prepared by dispersing the bulk antimony cathode in a blank aqueous NaOH solution were oxygen-resistant in the air because the strongly adsorbed hydroxide ions from the solution could stabilize the Sb NPs. The incorporation of sodium, the formation/oxidation of polyanions of antimony (Zintl ions), and the formation/decomposition of unstable antimony hydrides may all take effect for the cathodic dispersion of bulk antimony electrodes in the NaOH solution. Transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy were used to characterize these NPs.

Facile preparation of ordered arrays of polystyrene spheres dissymmetrically decorated with gold nanoparticles at air/liquid interface and their SERS properties

Ordered arrays of polystyrene (PS) spheres dissymmetrically decorated with gold nanoparticles (NPs) were facilely assembled at air/liquid interface by the combination of colloidal crystal templating and modified conventional electroless plating. Distinguishingly, Sn2+ ions served as the reductant and stabilizer in the preparation of Au colloid, and the immersed part of a floating monolayer of pristine PS spheres was also sensitized by the excessive amounts of Sn2+ ions in the Au colloid. Colloidal Au NPs spontaneously aggregated onto the sensitized portion of PS spheres due to oxygen-induced ligand replacement of SnCl3− with Cl−, forming asymmetric PS/Au composite sphere arrays. Moderate heating (60 °C) accelerated the assembly process. The method presented here is convenient, cost-effective and can be extended to prepare asymmetric composite sphere arrays of PS/Pd and PS/Au–Pd. Furthermore, the surface enhanced Raman scattering (SERS) performance of the ordered arrays of asymmetric PS/Au composite spheres was examined.

Ultra-rapid fabrication of highly surface-roughened nanoporous gold film from AuSn alloy with improved performance for nonenzymatic glucose sensing

Using one-step anodization strategy, a nanoporous gold film (HNPG) with large surface area was rapidly fabricated on Au80Sn20 (wt%) alloy in just 80 s. The formation of highly surface-roughened nanoporous structures results from a complex process of electrochemical dealloying of Sn component from AuSn alloy, anodic electrodissolution, disproportion and deposition of Au component, and spontaneous redox reaction between electrodissolved Sn2+ and AuCl4－species at the applied anodic potential. As-prepared HNPG/AuSn shows enhanced electrochemical performance for glucose oxidation in alkaline electrolyte. At a low potential of 0.1 V (vs. SCE), it offers a short response time of 4 s, a wide linear detection range of 2 μM to 8.11 mM, an ultralow detection limit of 0.36 μM (S/N = 3), an ultrahigh sensitivity of 4374.6 μA cm-2 mM-1, and satisfactory selectivity and reproducibility. Specifically, after 6 weeks, no obvious loss of glucose amperometric signal was observed on HNPG/AuSn. The facile preparation and excellent sensing performance of HNPG/AuSn electrode make sure that it is a promising candidate for advanced enzyme-free glucose sensors.

Potential Oscillations during the Pb Electro-oxidation in H2SO4 with SCN − Involving Interfacial Phase Transitions

Potential oscillations have been observed for the first time during the electro-oxidation of Pb electrode in sulfuric acid with SCN - . The oscillations occur in the phase transition region of PbSO 4 /PbO 2 accompanying periodic. oxygen evolution. Raman spectroscopy and X-ray diffraction results show that the PbO 2 film formed by electro-oxidation can be reduced to PbSO 4 chemically by SCN - . Therefore, the oscillatory phenomena found here could be ascribed to the alternate formation and reduction of PbO 2 films on electrode surface, namely, the PbO 2 film formed by the electro-oxidation of Pb via PbSO 4 can be reduced to PbSO 4 again by S 2- which comes from the dissociation of SCN - . Oxygen evolution can promote the formation of PbO 2 and vice versa. The oscillatory mechanism has been further proved either by the replacement of SCN - with another source of S 2- from thiourea or by the recurrence of oscillations on an electrodeposited PbO 2 film.