| Since the discovery of carbon nanotubes(CNTs) by Iijima in 1991, they have been the targets of numerous investigations due to their outstanding chemical, physical and mechanical properties. Carbon nanotubes have and could been applied in many fields, such as emission electron sources, scanning probes, chemical sensors, field-effect transistors nano-electronic devices, and so on. In this paper, carbon nanotubes were applied in the electrochemical analysis for the determination of trace metals lead and cadmium; meanwhile, a polymer-CNTs composite thin film was prepared by layer-by-layer self assembly techniques, some results were achieved as following:First, a glassy carbon electrode modified by functionalized carbon nanotubes was used as working electrode for the square wave adsorptive stripping voltammetric measurement of trace lead. Possible adsorption and stripping mechanism were discussed. The electrochemical response was characterized with respect to accumulation time, lead concentration, supporting electrolyte, pH value of the solution and possible interferences. It is found that glassy carbon electrode modified with carboxylic acid group by carbon nanotube functionalized had more sensitivity in adsorption of lead. During the potential scanning from -1.0 V to 0 V, a sensitive anodic stripping peak appears at -0.544 V. The peak current is linear with the concentration of Pb2+ in the range of 1.0×10-7～1.0×10-5mol/L. The detection limit is 1.0×10-8 mol/L after 1 h accumulation. Using this electrode, trace lead in water sample was successfully determined, the recoveries are between 92% and 102%.Second, water-soluble carboxylic carbon nanotube was used as a sensitizing agent for the square wave anodic stripping voltammetric measurement of trace cadmium. Possible adsorption and stripping mechanism were discussed. The electrochemical response was characterized with respect to accumulation time, cadmium concentration, supporting electrolyte, influence of hydrochloric acid added and possible interferences. The method was successfully applied to determine trace cadmium in water sample. The results show that a sensitive stripping peak potential of cadmium is about -0.65V, and the peak current is linear with the concentration of Cd2+ in the range of 2.0×10-9～1.0×10-8 mol/L. The detection limit is 1.0×10-10mol/L, and the recovery is 94%～103%.Third, using water-soluble of carboxylic carbon nanotube as a sensitizing agent, the method of determination of trace lead in water by square wave stripping voltammetry was introduced. The results show that in a supporting electrolyte of 1 mol/L HCI, using water-soluble of carboxylic carbon nanotube as a sensitizing agent, a sensitive stripping peak potential of lead is about -0.46V. The linear relationship between the stripping current and concentration ration of Pb2+ existed in the range of 2.0×10-9～1.0×10-8 mol/L, The linear regression equation is as following: Ip (μA)=9.6656+0.6407 C(10-9 mol/ L), and the correlation coefficient is 0.9985. The detection limit is 1×l0-10 mol/L, and the recovery is 96%～104%.Fourth, purification of carbon nanotubes was performed based on the literature method, during the washing to the neutral and the next separating process, we found that CNTs suspended in the water, unable to be separated by centrifugation with larger loss of CNTs by filtration. In order to solve this problem, 50 V DC voltage was gradually applied to the graphite electrode for 1 hour to deposition carbon nanotubes electrically, and then centrifugal separation. By using the method we proposed, the yield of pure CNTs can be increased from 41.29% to 75.76%.Fifths, Poly(styrene sulfonate)/carbon nanotubes and quaternary ammonium type cationic starch/carbon nanotubes were used to prepared composite thin film by layer-by-layer self assembly techniques. The polymer wrapping CNTs were dissolved in water and used to form electrostaticself-assembled multilayer films. Multilayer thin films were characterized by transmission electron microscopy (TEM) and UV spectrum.
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