Graphene Composites Modified Carbon Paste Electrode For Heavy Metal Ions

As a new type of carbon material, graphene has excellent properties in the electrical, mechanical and optical fields. Composite with other materials, it is a hot issue to improve the properties of graphene. In this paper, the application of the carbon paste electrode in the determination of heavy metal ions was explored in graphene/polyaniline, graphene/silver, graphene/nickel foam and graphite/barium ferrite as modifier. It is introduced the chemical modified carbon paste electrode and based on this method, cyclic voltammetry was used for the detection of some heavy metal ions such as cadmium, copper, mercury and zinc. The main research contents are as follows:（1） The determination of cadmium ions in carbon paste electrode was made by using graphene/polyaniline composite as modifier, and the optimum conditions were discussed. The mass ratio of graphene/polyaniline composites and graphite powder was 0.005:1; the NH3-NH4 Cl was buffer; pH value was 10.75; the scanning speed was 100 mV·s-1. Peak current and the concentration of Cd²⁺ in the 1.0×10-8 mol·L-1 2.0×10-5 mol·L-1 range showed a good linear relationship, linear equations for Ipc = 0.15551 + 0.01726 c（Ipc for the peak current, the unit is mA; c for concentration of Zn2+, the unit is μmol·L-1）, the correlation coefficient was 0.9974, detection limit for 2.24×10-9 mol·L-1. The experimental results show that the graphene/polyaniline composite modified carbon paste electrode has high selectivity, and high detection limit for the determination of Cd²⁺.（2） Studied the graphene/silver composites modified carbon paste electrode, cyclic voltammetry determination of copper ions, to explore the optimum testing conditions. The results found that G/Ag（G: Ag = 1.5:1.5） and the best ratio of graphite powder was 0.005:0.5; pH 7.00 buffer solution for PBS buffer solution; in the scanning range of 0.4 V 1.4 V and the scanning rate of 100 mV·s-1 the peak value of the oxidation reduction was maximum. In the range of 1.0×10-8 mol·L-1 3.5×10-7 mol·L-1, the peak current had good linear relationship with the concentration of Cu2+, linear equation for the Ipc = 0.44156 + 0.13936 c（Ipc as the peak current, the unit mA; c for Cu2+ concentration, the unit is μmol·L-1）, the linear correlation coefficient R = 0.9955, the detection limit of 3.6×10-9 mol·L-1. Other ions to experiment without interference.（3） The preparation of graphene/nickel foam composites modified carbon paste electrode, determination of the concentration of 1.0×10-4 mol·L-1 Hg2+ by 100 mV·s-1 scan rate, the oxidation peak appeared at about 0.41 V, and the optimum condition was obtained for the NH3-NH4 Cl buffer solution with pH value of 10.20, Peak current and the concentration of Hg2+ in the 5.0×10-8 mol·L-1 3.0×10-7 mol·L-1 range showed a good linear relationship, the linear correlation coefficient and detection limit were 0.9921 and 2.9×10-8 mol·L-1, linear equation for the Ipa = 5.336 + 1.212 c（Ipa for peak current, the unit mA; c for Hg2+ concentration, the unit is μmol·L-1）. Other interfering ions has no effect on the result of the experiment.（4） Through the preparation of graphene/barium ferrite modified carbon paste electrode, the zinc ion was detected, and the best experimental conditions were examined. The results show that the barium ferrite, graphene, graphite powder quality than for 0.015:0.0016:1.5; cyclic voltammetry in nh3-nh4 cl buffer. At about 0.216 V appear in good shape of the reduction peak and oxidation peak at about 0.274 V; peak current and the concentration of Zn2+ in the 1.0×10-8 mol·L-1 1.6×10-5 mol·L-1 range showed a good linear relationship, the correlation coefficient is 0.9970. The detection limit for 1.89×10-9 mol·L-1. Interference experiment results show that the interference ions has no effect on the experiment.