Xueping Hu

In-situ synthesis of reduced graphene oxide/gold nanoparticles modified electrode for speciation analysis of copper in seawater

In this paper, reduced graphene oxide/gold nanoparticle/Nafion (rGO/AuNP/Nafion) modified electrode was fabricated through in-situ synthesis and used for determination of copper ions in strong salt electrolyte (0.5M NaCl) by differential pulse anodic stripping voltammetry (DPASV). This in-situ synthesis procedure was based on the ion-exchange and electrochemical reduction. The use of rGO provided a larger electrode surface and the presence of more active sites, while electron transfer was accelerated by incorporating AuNPs. Nafion was utilized as a cation exchange polymer in which rGO and AuNPs could be tightly attached to the electrode surface. The physical and electrochemical characterizations of the as-prepared modified electrode were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and cyclic voltammetry. AuNPs with diameter of 5-10nm on rGO decorated in the gold electrode surface were observed. Under the optimal conditions, the rGO/AuNP/Nafion electrode had a linear response to copper ions in the concentrations range from 20nM to 1μM (R2 = 0.998), with the lowest detectable concentration of 8nM and the detection limit of 4nM (S/N = 3). Additionally, this electrode was successfully applied to the speciation analysis of copper (free, dissolved and total) in seawater.

A tin-bismuth alloy electrode for the cathodic stripping voltammetric determination of iron in coastal waters

We employed a home-made tin–bismuth alloy electrode (SnBiE) as the working electrode with 1-(2-piridylazo)-2-naphthol (PAN) as the complexing ligand to detect trace iron. This method is based on the cathodic reduction of Fe(III)–PAN complex to Fe(II)–PAN complex at the SnBiE by using adsorptive cathodic stripping voltammetry. The experimental parameters, such as the pH value, concentration of buffer solution, accumulation potential, accumulation time and the concentrations of PAN, were optimized, and the interference by other ions was investigated in detail. The response of Fe(III) was linear in the range of 1 nM to 900 nM with a detection limit of 0.2 nM (after 60 s of accumulation, s/n = 3). This method can also be applied to the determination of iron in coastal rivers and seawater with satisfactory results.

Distribution and contamination assessment of arsenic and mercury in surface sediments from the intertidal zone of Yantai Sishili Bay, China

ABSTRACT Sixty surface sediment samples from the intertidal zone of Yantai Sishili Bay (YSB) have been analyzed for arsenic (As) and mercury (Hg) to evaluate their contamination levels and potential ecological risks. Concentrations of As and Hg ranged from 7.01–23.56 and 0.00–0.01 μg g−1 in the dry season; during the wet season, the corresponding data were 1.44–6.17 and 0.00–0.02 μg g−1. The geoaccumulation index (Igeo) and potential ecological risk index (Eri) were used to conduct a pollution assessment. The results demonstrated that the intertidal zone of YSB has good sediment quality and that As and Hg are not likely to cause negative environmental impacts in the region.

Cathodic stripping voltammetric determination of chromium in coastal waters on cubic Nano-titanium carbide loaded gold nanoparticles modified electrode

The novel cubical nano-titanium carbide loaded gold nanoparticles modified electrode for selective and sensitive detection of trace chromium (Cr) in coastal water was established based on a simple approach. Nano-titanium carbide is used as the typical cubical nanomaterial with wonderful catalytic activity towards the reduction of Cr(VI). Gold nanoparticles with excellent physical and chemical properties can facilitate electron transfer and enhance the catalytic activity of the modified electrode. Taking advantage of the synergistic effects of nano-titanium carbide and gold nanoparticles, the excellent cathodic signal responses for the stripping determination of Cr(VI) can be obtained. The detection limit of this method is calculated as 2.08 μg L-1 with the linear calibration curve ranged from 5.2 to 1040 μg L-1. This analytical method can be used to detect Cr(VI) effectively without using any complexing agent. The fabricated electrode was successfully applied for the detection of chromium in coastal waters collected from the estuary giving Cr concentrations between 12.48 and 22.88 μg L-1 with the recovery between 96% and 105%.

Determination of iron in seawater: From the laboratory to in situ measurements

The marine biogeochemistry of iron plays a significant role in regulating climate change. Trace dissolved iron in oceanic surface water can limit phytoplankton growth which in turn limits the carbon dioxide flux at the air/sea interface. To better understand the relationship between iron and its different species with phytoplankton, as well as the biogeochemical cycle of iron in seawater, accurate, sensitive, and in situ methods are needed for iron determination. This paper reviews the methods for determining iron in seawater from the laboratory, shipboard to in situ measurements, including such strategies as atomic spectrometry, spectrophotometry, chemiluminescence, and voltammetry, which will provide the foundation for developing reliable long-term iron monitoring and sensing platforms in the future.

Speciation determination of iron and its spatial and seasonal distribution in coastal river

In this study, the speciation of iron (Fe), including total Fe (TFe) and acidified dissolved Fe (ADFe), was assessed by fast cathodic absorption stripping voltammetry, using a gold electrode and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) as a novel complexing agent for Fe. The validity and accuracy of this method were compared with the standard spectrophotometry and tested by the standard samples. Under optimized conditions, the Fe response was linear within the range of 0.01 to 1 μM with a detection limit of 1.2 nM. To further validate this method, the variation in concentrations of TFe and ADFe were investigated at twelve sampling stations in a local coastal river, in both the dry and wet season. Additionally, to further understand the interaction between Fe and environmental factors, the relationships between the concentration of Fe species and dissolved oxygen (DO) and salinity were also discussed.

Vertical profile, contamination assessment of mercury and arsenic in sediment cores from typical intertidal zones of China

The vertical profiles, contamination levels, and potential ecological risks of mercury and arsenic were studied from the sediment cores of seven typical intertidal zones, including the Liaohe River Estuary, the Jianhe River Estuary, the Dagu River Estuary, Yancheng Shoal, the Dongtan Yangtze River Estuary, Hangzhou Bay, and the Pearl River Estuary. Marine sediment quality standards, the threshold effect level (TEL), and the probable effect level (PEL) were used as guidelines to evaluate sediment quality. In addition, the geo-accumulation index (Igeo) and potential ecological risk index (Eri

Corrosion resistance properties of electroless nickel composite coatings

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