Development of graphene/bismuth nanocomposite film modified graphite electrode for voltammetric determination of heavy metals

In recent years, due to its unique chemical, physical and mechanical features, nanomaterials which are of great interest in many fields such as chemistry, physics, material science are also frequently used for the development of electrochemical nanosensors. By choosing electrodes that are modified with nanomaterials to increase their selectivity and sensitivity, successful results have been achieved in the analysis of analytes at very low concentrations. Graphene, which is a carbon-based nanomaterial and has led to the development of revolution in technology with its discovery, is at the head of the materials used for this purpose. The main difficulty with using the graphene in electrode modification is the synthesis step. According to the method used, conventional methods have drawbacks such as high cost, long synthesis time, the usage of toxic chemicals and small-scale production, so there is a need for a rapid, environmentally friendly, low-cost synthesis method for producing graphene. In the context of this thesis, development of a low-cost, green, sensitive and selective graphene-modified electrode is aimed in order to provide precise simultaneous analysis of heavy metals in water samples. As the first step of electrode development, the surface of the pencil graphite electrode was covered with graphene in one step using an electrochemical method presented in the literature. Cyclic voltammetry (CV) method has been chosen for the modification. In this method, with the application of high anodic potentials to graphite electrode, oxygen-rich graphene oxide was formed, then by applying the potential in the opposite direction oxygen groups were eliminated and graphene structures were obtained. Various modification parameters such as modification electrolyte type and concentration, number of CV cycles, CV scan rate and CV potential range are optimized in order to get the highest response for lead and cadmium. As the second step after electrode development, an electroanalytical method, square wave stripping voltammetry method, was proposed to analyze trace levels of Cd and Pb heavy metals. In this context, the electrode surface was coated with bismuth film in order to increase electrode stability and to obtain higher signals in Cd and Pb analysis. Afterward, parameters including bismuth concentration, deposition potential, deposition time, stirring speed were also optimized. In the end, a certified reference material analysis was conducted for the evaluation of the accuracy of the electrode and method. Successful results were obtained for the Cd and Pb analysis in a working range of 5-100 μg L-1 with the developed electrode. Having a low-cost, environmentally-friendly, rapid, one-step synthesis process, the developed electrode can be used for sensitive and selective trace analysis of various heavy metals in environmental and biological samples.