Huakun Xing

Nickel clusters grown on three-dimensional graphene oxide–multi-wall carbon nanotubes as an electrochemical sensing platform for luteolin at the picomolar level

This study focuses on enhancing the catalytic activity of metallic Ni by using various nanostructured carbon materials, including 1D multi-wall carbon nanotubes (MWCNTs), 2D graphene oxide (GO) and graphene (GR), and 3D graphene oxide–multi-wall carbon nanotubes (GO–MWCNTs) as supporting matrices for the fabrication of an electrochemical sensor for detecting the flavonoid luteolin. Ni clusters were prepared by a facile electrochemical approach and the metallic Ni on various carbon supports exhibited different morphologies, which were characterized by scanning electron microscopy (SEM) and Raman spectra. The electrocatalytic performance of Ni-based materials towards luteolin oxidation was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that Ni clusters supported on GO–MWCNTs (Ni/GO–MWCNTs) were profoundly superior to other carbon materials, with a greatly enhanced current. This is attributed not only to the excellent electric conductivity and large surface-to-volume ratio of Ni/GO–MWCNTs, but also to the unique 3D carbon nanostructure that facilitates the easy access of the electrolyte and analyte to the modified electrode surface and promotes the reaction kinetics. Under the optimal conditions, the anodic peak current was linear to the concentration of luteolin in the range from 1 pM to 15 μM with a detection limit of 0.34 pM (S/N = 3). The good analytical performance, low cost and straightforward preparation method made this novel electrode material promising for the development of an effective luteolin sensor.

A universal strategy for the facile synthesis of a sandwich-structured Pt–graphene–Pt nanocomposite for salbutamol sensing

In this work, a sandwich-structured Pt–graphene–Pt (P–Gr–P) nanocomposite has been prepared by a two-step method including (i) a chemical and (ii) an electrochemical reduction process. The P–graphene oxide–P (P–GO–P) nanocomposite was firstly synthesized by an in situ growth method, during which platinum nanoparticles (PtNPs) grew on both sides of GO. In the second step, P–GO–P was coated onto a glass carbon electrode (GCE). In this process, GO in the P–GO–P nanocomposite was reduced to a more conductive form of graphene (Gr). The obtained sandwich-structured P–Gr–P can effectively separate the individual layers of Gr sheets from each other, prevent the agglomeration of Gr sheets and improve the conductivity of the Gr film. In addition, the electrocatalytic properties of the as-prepared P–Gr–P nanocomposite towards the oxidation of salbutamol (SAL) were investigated. Results revealed that the sandwich-structured P–Gr–P nanocomposite with higher electrochemically active surface area showed better electrocatalytic activity toward SAL oxidation than PtNPs–Gr prepared by using the one-step electrochemical co-deposition method. On the basis of the excellent electrochemical activity of the P–Gr–P nanocomposite, a highly sensitive electrochemical platform was developed for the rapid detection of SAL. The present work provides an interesting strategy to prepare a Gr-based nanocomposite for electrochemical sensors.

Simple and green synthesis of piperazine-grafted reduced graphene oxide and its application for the detection of Hg(II)

In this paper, piperazine-grafted reduced graphene oxide (NH-rGO) was synthesized via a simple and green two-step procedure: (i) opening of the resulting epoxides of graphene oxide (GO) with piperazine (NH) through nucleophilic substitution; (ii) reduction of GO with ascorbic acid. Its structure and morphology were characterized by scanning electron microscopy and x-ray photoelectron spectroscopy. The NH-rGO modified glassy carbon electrode was explored as an electrochemical sensor for the determination of Hg(II) using a differential pulse anodic stripping voltammetry technique. Hg(II) can be efficiently accumulated and deposited on the surface of a modified electrode by strong coordination chemical bonds formed between Hg(II) and NH. And then the anodic stripping current can be significantly enhanced by rGO with the merits of large specific surface area and high conductivity, which served as a signal amplifier, finally realizing the highly sensitive determination of Hg(II). The experimental parameters including the pH value of the acetate buffer, deposition potential and deposition time were optimized. Under optimal conditions, the developed sensor exhibited a wide linear range from 0.4-12 000 nM with a low limit of detection of 0.2 nM, which is well below the guideline value in drinking water set by the WHO. Moreover, the practical application of this method was confirmed by an assay of Hg(II) in tap water samples with acceptable results.

Preparation and characterization of poly(2′-aminomethyl-3,4-ethylenedioxythiophene) by chemical oxidative polymerization

Poly(2′-aminomethyl-3,4-ethylenedioxythiophene) was synthesized by the chemical oxidative polymerization of 2′-aminomethyl-3,4-ethylenedioxythiophene in the presence of different oxidants, such as FeCl3, Ce(SO4)2, (NH4)2Ce(NO3)6, and (NH4)2S2O8. The as-formed polymer was investigated by FTIR, UV–Vis, and Raman spectroscopy, fluorescence, thermogravimetry, and X-ray diffraction to determine the structure, photophysical properties, thermal stability, and polymer phase. FTIR and Raman spectra measurements indicated that the formation of macromolecules occurred exclusively via α,α-coupling of thiophene rings. Moreover, polymer obtained in polymerization using Ce(SO4)2 as the oxidant displayed superior thermal stability. All the characterizations indicated that FeCl3 was the more suitable oxidant for oxidative polymerization of the monomer and provided formation of polymer with higher yield.