Detection of Trace Heavy Metals Ions by Arrays of Titania Nanotubes Annealed in Nitrogen

Redox response of trace heavy metals ions（THMIs） has better performance on highly ordered vertically oriented titania nanotube arrays（TNA） annealed in nitrogen. Experimental data showed that different THMIs possess different reaction peak shapes and charge and discharge capacities. Therefore, the TNA will become an important tool used for environmental protection and facilitating the rapid determination of THMIs. THMIs of 5×10^4 mol/L concentration were measured at a scan rate of 100 mV/s. The analytical utility of TNA is demonstrated in a neutral 0.5 mol/L Na2SO4 solution. The results sufficiently show that titania nanotube arrays electrodes（TNAE） will be used to measure THMIs.

Sensitive Voltammetric Detection of Trace Heavy Metals in Real Water Using Multi-Wall Carbon Nanotubes/Nafion Composite Film Electrode

Multi-wall carbon nanotubes （MWCNTs） and Nation composite film （MWCNTs/Nafion） were used for fabricating electrochemical sensors for the voltammetric detection of trace lead（Ⅱ） and cadmium（Ⅱ） in several water samples. The morphology and structure of MWCNTsfNafion film were characterized by scanning electron microscopy （SEM） and infrared spectrum （IR）. The electron transfer of MWCNTs/Nafion composite film was examined by cyclic voltammetry （CV） and electrochemical impedance spectrum （EIS）. Various experimental parameters, which influenced the response of MWCNTs/Nation/GC to target metals, were optimized. The results showed that the synergistic effect was obtained on the MWCNTs/Nafion/GC whose sensitivity and stability were better than those of Nation-coated electrode （Nafion]GC） or CNTs/GC. Stability of the Pb（II） and Cd（Ⅱ） stripping signals was excellent with relative standard deviations （RSD） within 5% （n = 10） from one electrode preparation to another, and RSD of 30μg.L^1 Pb（Ⅱ） and Cd（Ⅱ） were 2.8% and 3.2% for 20 repeated analysis on one single CNTs/Nafion/GC. Over 50 runs, the stability of Pb and Cd detection at the MWCNTs/Nafion conposites electrode was still satisfactory with RSD lower than 6.0%. The determination limits （S/N=3） of the proposed method were determined to be 100 ng·L^-1 for Pb and 150 ng.L^-1 for Cd. Finally, the MWCNTs/Nafion/GC was successfully applied to determine Pb（Ⅱ） and Cd（Ⅱ） in different water samples with recoveries of 97%-103% for Pb and 96%-104% for Cd.

Dissolved Cu,Pb,Zn and Cd in the South China Sea surface waters

A total of 106 surface water samples were collected in the South China Sea during two transects in June and December 1998. The samples were collected with strictly contamination free proce- dure and trace metals were measured by clean laboratory methods and GFAAS. The mean concentrations for the disolved fractions are: Cu 0.100 μg/dm3, Pb 0.060 μg/dm3, Zn 0.086 μg/dm3, Cd 0.007 μg/dm3, which is close to the world open ocean'slevel. The spatial distribution of the trace heavy met- als shows higher concentrations in offshore area and lower concentrations in the central in the South Chi- na Sea, and the concentrations decrease with the distance from the offshore, which suggests the exis- tence of significant continental shelf input of the trace heavy metals. The correlationship among the ele- ments is better in surnmer than that in winter. Cu is positively correlated with Cd in both seasons and it is also found for the first time that they are positively correlated with nutrients in the South China Sea surface waters which further indicate the biogeochemical cycle of these elements in the marine environ- ment. The baseline value of Cu, Pb, Zn, Cd in the South China Sea surface waters is obtained through statistical analysis.

Experimental study on mercury content in flue gas of coal-fired units based on laser-induced breakdown spectroscopy

Accurate measurement of trace heavy metal mercury(Hg) in flue gas of coal-fired units is great significance for ecological and environmental protection.Mixed gas was used to simulate the actual flue gas of a power plant in this study.A laser-induced breakdown spectroscopy(LIBS)system for Hg measurement in mixed gas was built to study the effect of mixed gas pressure,Hg concentration in mixed gas and delay time on Hg measurement.The experimental results show that the appropriate low mixed gas pressure can obtain high Hg signal intensity and signal to noise ratio.The Hg signal intensity and signal to noise ratio increased with the increase of Hg concentration in mixed gas.The Hg signal intensity and signal to noise ratio decreased with the increase in delay time.According to the above results,the optimized measurement conditions can be determined.Different Hg concentrations in mixed gas were quantitatively analyzed by the internal standard method and traditional calibration method respectively.The relative error of prediction of the test sample obtained by the internal standard method was within 11.11%.The relative error of prediction of the traditional calibration method was less than 14.54%.This proved that the internal standard method can improve the accuracy of quantitative analysis of Hg concentration in flue gas using LIBS.