Jinfen Wang

Determination of trace mercury in water based on N-octylpyridinium ionic liquids preconcentration and stripping voltammetry

A novel method for determination of trace mercury in water is developed. The method is performed by extracting mercury firstly with ionic liquids (ILs) and then detecting the concentration of mercury in organic media with anodic stripping voltammetry. Liquid-liquid extraction of mercury(II) ions by four ionic liquids with N-octylpyridinium cations ([OPy](+)) was studied. N-octylpyridinium tetrafluoroborate and N-octylpyridinium trifluoromethylsulfonate were found to be efficient and selective extractant for mercury. Temperature controlled dispersive liquid phase microextraction (TC-DLPME) technique was utilized to improve the performance of preconcentration. After extraction, precipitated IL was diluted by acetonitrile buffer and mercury was detected by differential pulse stripping voltammetry (DPSV) with gold disc electrode. Mercury was enriched by 17 times while interfering ions were reduced by two orders of magnitude in the organic media under optimum condition. Sensitivity and selectivity for electrochemical determination of mercury were improved by using the proposed method. Tap, pond and waste water samples were analyzed with recoveries ranging from 81% to 107% and detection limit of 0.05 μg/L.

Arsenate reduction and methylation in the cells of Trichoderma asperellum SM-12F1, Penicillium janthinellum SM-12F4, and Fusarium oxysporum CZ-8F1 investigated with X-ray absorption near edge structure.

Synchrotron radiation-based X-ray absorption near edge structure (XANES) was introduced to directly analysis chemical species of arsenic (As) in the cells of Trichoderma asperellum SM-12F1, Penicillium janthinellum SM-12F4, and Fusarium oxysporum CZ-8F1 capable of As accumulation and volatilisation. After exposure to As(V) of 500 mg L(-1) for 15 days, a total of 60.5% and 65.3% of the accumulated As in the cells of T. asperellum SM-12F1 and P. janthinellum SM-12F4, respectively, was As(III), followed by 31.3% and 32.4% DMA (dimethylarsinic acid), 8.3% and 2.3% MMA (monomethylarsonic acid), respectively. However, for F. oxysporum CZ-8F1, 54.5% of the accumulated As was As(III), followed by 37.8% MMA and 7.7% As(V). The reduction and methylation of As(V) formed As(III), MMA, and DMA as the primacy products, and the reduction of As(V) might be more easily processed than the methylation. These results will help to understanding the mechanisms of As detoxification and its future application in bioremediation.

Spectroscopic and TEM studies on poly vinyl carbazole/terbium complex and fabrication of organic electroluminescent device

Abstract Terbium acetyl salicylate complex containing 1,10-phenanthroline was synthesized. Element analysis showed that the composition of the complex was Tb(C 9 O 4 H 7 ) 3 (C 12 N 2 H 8 ). A single layer electroluminescent device using polyvinyl carbazole doped with the terbium complex as an emitting layer was fabricated. The device showed bright green EL emission. The dispersion of the terbium complex in PVK matrix was investigated using transmission electron microscopy.

Primary study of structures of r.f.-sputtered MoS2 films

Abstract The composition and structures of r.f.-sputtered MoS2 films have been determined by X-ray diffractometry (XRD), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and laser Raman spectroscopy (LRS). The r.f.-sputtered films were deposited on 440 C stainless steel substrate temperature control. We conducted XRD and LRS studies of approximately 0.8 μm thick r.f. sputter deposited MoS2 fils to determine the structure, finding that the crystal raction of the films has a hexagonal layer structure with a distorted unit cell having a greatly elongated c0 axis and a rather compressed a0 axis which differ from those of the ordinary 2H-MoS2. The concentrations of the surface and bulk atom species were determined by XPS and AES with depth profiling; the S:Mo atom ratio was found to be in the range 1.8–9, and certain amounts of oxygen are present in the bulk film. The XPS study was focused on the role of oxygen in the films, which differs from that of both the MoS2 powder and target. This indicates that there is mainly non-chemisorbed oxygen in the films, where some oxygen atoms were probably substituted into the sulphur sites in the films to form an MoSO solid solution. Discussion of the mechanism of film growth and the orientation of the crystal fraction, which is primarily considered as a solid solution, and its crystallite sized related to lubrication are included.

A Palladium-Tin Modified Microband Electrode Array for Nitrate Determination

A microband electrode array modified with palladium-tin bimetallic composite has been developed for nitrate determination. The microband electrode array was fabricated by Micro Electro-Mechanical System (MEMS) technique. Palladium and tin were electrodeposited successively on the electrode, forming a double-layer structure. The effect of the Pd-Sn composite was investigated and its enhancement of catalytic activity and lifetime was revealed. The Pd-Sn modified electrode showed good linearity (R2 = 0.998) from 1 mg/L to 20 mg/L for nitrate determination with a sensitivity of 398 μA/(mg∙L−1∙cm2). The electrode exhibited a satisfying analytical performance after 60 days of storage, indicating a long lifetime. Good repeatability was also displayed by the Pd-Sn modified electrodes. The results provided an option for nitrate determination in water.

Comparison of Two Types of Overoxidized PEDOT Films and Their Application in Sensor Fabrication

Poly(3,4-ethylenedioxythiophene) (PEDOT) films were prepared by electro-oxidation on Au microelectrodes in an aqueous solution. Electrolyte solutions and polymerization parameters were optimized prior to overoxidation. The effect of overoxidation time has been optimized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), which results in the film overoxidized for 45 s at 1.35 V presenting a strong adsorption. The other one-step overoxidation film prepared by direct CV ranging from −0.6 V to 1.35 V was polymerized for comparison. Scanning electron microscope (SEM) analysis and Fourier transform infrared (FTIR) spectroscopy were used for monitoring morphological changes and the evolution of functional groups. Both of them indicate increased abundant oxygen functional groups and roughness, yet the products exhibit dendritic morphology and piles of spherical protrusions, respectively. Moreover, double-step overoxidized film showed better electrochemical performance toward lead ion sensing. These characterizations highlight some novel properties that may be beneficial for specific sensing applications.

Modification of Graphene on Ultramicroelectrode Array and Its Application in Detection of Dissolved Oxygen

This paper investigated two different modification methods of graphene (GN) on ultramicroelectrode array (UMEA) and applied the GN modified UMEA for the determination of dissolved oxygen (DO). The UMEAs were fabricated by Micro Electro-Mechanical System (MEMS) technique and the radius of each ultramicroelectrode is 10 μm. GN-NH2 and GN-COOH were modified on UMEA by using self-assembling method. Compared with GN-NH2 modified UMEA, the GN-COOH modified UMEA showed better electrochemical reduction to DO, owing to better dispersing and more active sites. The GN-COOH on UMEA was electroreduced to reduced GN-COOH (rGN-COOH) to increase the conductivity and the catalysis performance. Finally, the palladium nanoparticles/rGN-COOH composite was incorporated into DO microsensor for the detection of DO.

Synthesis and electrochemical sensing application of poly(3,4-ethylenedioxythiophene)-based materials: A review

As a significant and promising conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) has attracted considerable attention in the last decade. This review aims at giving a comprehensive illustration about current progress on the synthesis and electrochemical sensing applications of PEDOT-based materials in environmental monitoring, food and drug analysis and health care. PEDOT-based materials, such as PEDOT, functionalized PEDOT and PEDOT composites were fabricated mainly by chemical polymerization and electrochemical polymerization. Various nanostructures with large surface area, high conductivity, fast electron transfer rate, hydrophobic interaction and good biocompatibility were displayed by the PEDOT-based materials. Synergetic effects were enhanced dramatically in electrochemical (bio) sensors by PEDOT composites, especially by those incorporated with versatile nanomaterials. Through this paper, we hope to attract attention from a wider community and inspire researchers to take advantage of PEDOT in approaching scientific challenges and developments.

Electrochemical detection of toxic tetrabromobisphenol a with boron-doped diamond thin film electrode

The electrochemical detection of tetrabromobis-phenol A (TBBPA) with boron-doped diamond (BDD) thin film electrode is demonstrated. The electrode is synthesized by filament-assisted chemical vapor deposition. An irreversible oxidation peak is observed for TBBPA in phosphate buffer on BDD surface. A method to renew the electrode is developed by sweeping in H2SO4 at 3V for 100s first and at −3V for 100s afterwards. The electrode gets higher oxidation peak current in phosphate buffer of pH 8. The linear range is from 500nM to 10µM.

A rapid and sensitive BOD biosensor based on ultramicroelectrode array and carboxyl graphene

Biochemical oxygen demand (BOD) is an important index for the assessment of organic water pollution, which needs to be detected rapidly and sensitively. In this paper, a BOD biosensor has been developed based on the direct immobilization of microorganisms around carboxyl graphene (GN-COOH) modified ultramicroelectrode array (UMEA). UMEA is designed in ring shape and hexagon distribution, which shows nonlinear diffusion in electrochemical tests, indicating fast mass transfer. The modification of UMEA comprises the electrodeposition of GN-COOH and the covalent bonding bacteria immobilization. The potential and time for electrodeposition have been optimized. The deposited GN-COOH facilitates the electron transfer and increases the current responses. The response time of the detection has been shortened to 3 min. The proposed biosensor shows a linear range from 2 to 15 mg/L with the sensitivity of 3.04 nA/(mg/L), which is about 3-times to that of our previous study without GN-COOH.