Construction Of Reduced Graphene-transition Metal Oxide Nanocomposites Modified Electrodes And Their Electrochemical Detection Activity For Azo Colourants In Food Stuff

Amaranth,sunset yellow and tartrazine are widely used in foods as synthetic colourants,due to their low cost,high effectiveness and excellent stability.However,excessive addition of these colourants in foods may be harmful to human beings.For example,it can cause hyperactivity,mental decline and even cancer.The traditional detection method for colourants is mainly high performance liquid chromatography.But it is costly,time consuming and complicated in operation.Electrochemical analysis method has been proposed for the determination of azo colourants due to its easy operation and high sensitivity.But the analysis result is susceptible to be interfered by many factors.Therefore,the high spercificity of catalysis is expected to slove this problem.In this thesis,researches on the modified electrodes are deeply done in order to develop electrochemical sensor for azo colourants with high sensitivity and low cost.Graphene is used to prepare modified electrodes with high sensitivity and selectivity due to its good conductivity,larger specific surface area and excellent mechanical properties.Nanoscale transition metal oxide has big heat resistance and sensitivity to light,heat and impurity,so it is used as catalyst to improve reaction rate.The electrochemical sensors for determination of amaranth,sunset yellow and tartrazine respectively were fabricated by graphene composited with nanoscale transition metal oxide,such as MnO₂,Cu₂O and TiO_2.The electrochemical behaviours of the mentioned azo colourants were investigated by second-order derivative linear scan voltammograms.The research results show that the optimal electrochemical sensor for amaranth is based on MnO₂-graphene composited materials,the optimal electrochemical sensor for sunset yellow is based on Cu₂O-graphene composited materials and the optimal electrochemical sensor for tartrazine is based on TiO₂-graphene composited materials.The result of determination of azo colourant is better than that reported by the existing literatures.The main research contents of three colourant electrochemical sensor are as following.1.Detection of amaranth by MnO₂ NRs-ErGO/GCEMnO₂ nanorods and reduced graphene co-modified glassy carbon electrode?MnO₂NRs-ErGO/GCE?was prepared using electrochemical reduction method.Transmission electron microscope and X-ray powder diffractometer were used to characterize the modified materials such as MnO₂nanorodsandMnO₂NRs-ErGOnanocomposites.The electrochemical behaviors of amaranth on bare electrode,ErGO or MnO₂NRs-ErGO modified electrodes were investigated by cyclic voltammetry,respectively.The detection conditions?including pH value,accumulation potential,and accumulation time?were optimized systematically.The results show that MnO₂NRs-ErGO nanocomposites increased the electrochemical active area and improved the electrochemical oxidation reaction rate significantly.Under the optimized detection conditions,the peak current is found to be linear with amaranth concentration in the range from 2.0×10^-88 to 1.0×10^-55 mol/L and 1.0×10^-5to 4.0×10^-44 mol/L with the detection limit of 1.0×10^-88 mol/L?S/N=3?.Satisfactory results are obtained in the analysis of actual beverage samples by using the modified electrode.2.Detection of sunset yellow by Cu₂O-ErGO/GCECu₂O and reduced graphene co-modified glassy carbon electrode?Cu₂O-ErGO/GCE?was prepared by electrochemical reduction of Cu₂O-GO on electrode surface.Scanning electron microscope and X-ray powder diffractometer were used to characterize the modified materials such as Cu₂O nanoparticles and Cu₂O-ErGO nanocomposites.The electrochemical behavior of sunset yellow on bare glassy carbon electrode,ErGO or Cu₂O-ErGO modified electrodes were investigated by cyclic voltammetry and second-order derivative linear scan voltammetry,respectively.The detection conditions?including pH value,accumulation potential,and accumulation time?were optimized systematically.The results show that Cu₂O-ErGO nanocomposites increased the electrochemical active area and improved the electrochemical oxidation reaction rate significantly.Under the optimum detection conditions,the peak current is found to be linear with sunset yellow concentration in the range of 2.0×10^-82.0×10^-55 mol/L with a detection limit of 6.0×10^-99 mol/L?S/N=3?.This modified electrode had advantages such as easy fabrication,high sensitivity and wide detection range.It was successfully applied to detect the sunset yellow in soft drink.3.Detection of tartrazine by TiO₂-ErGO/GCETiO₂ and reduced graphene co-modified glassy carbon electrode?TiO₂-ErG O/GCE?was prepared by electrochemical reduction and it was used to detect the tartrazine.The as prepared material was characterized by transmission electron microscopy and X-ray diffraction.Cyclic voltammetry and second-order derivative linear scan voltammetry were performed for analyzing the electrochemical sensing of tartrazine on different electrode.The detection conditions?including pH value,accumulation potential,and accumulation time?were optimized systematically.The results show that TiO₂-ErGO composites increased the electrochemical active area and improved the electrochemical oxidation reaction rate of tartrazine significantly.Under the optimum detection conditions,the peak current is found to be linear with tartrazine concentration in the range of 2.0×10^-82.0×10^-5 mol/L with the detection limit of 8.0×10^-9 mol/L?S/N=3?.Satisfactory results are obtained in the analysis of soft drink using the modified electrode.