Study On The Functional Modification And The Electrochemical Performance Of Graphene

Electrochemical sensor is widely applied to medical research, food safety test and environmental detection, owning to the advantages of its high-sensitivity, excellent selectivity and stability, fast and portability, and low cost. However, the sensitivity of electrochemical sensor is related to the electro-activity of sensing materials. Nanomaterials especially the materials based on carbon, are employed to the preparation of electrode for their unique optical, electronic, thermal and catalytic property.Graphene, a two-dimensional (2D) one atom thick nanomaterial consisting of sp2-hybridized carbon, was used for the preparation of electrochemical sensor due to its unique properties, including high specific area, high-speed electron mobility, excellent thermal conductivity and well electrocatalytic activity. In this paper, Different nanocomposites based on graphene, functionalized with cyclodextrin and porphyrin, were synthesized, and were used as sensing materials to construct the detection platforms for the quantitative detection of heavy metal ions and biomolecules. The main works are as follows:1. Cyclodextrin-reduced graphene oxide hybrid nanosheets for the simultaneous determination of lead (Ⅱ) and cadmium (Ⅱ). Hydroxypropyl-p-cyclodextrin-reduced graphene oxide hybrid nanosheets (HP-(3-CD-RGO) were synthesized by microwave irradiation and characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM) and thermal gravimetric analysis (TGA). The hybrid nanosheets, combining Nafion and in situ deposited bismuth film, were used as the sensing materials for the simultaneous determination of Pb2+and Cd2+for the first time. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical properties of HP-β-CD-RGO, and the results suggested that this hybrid nanosheets possessed good electrochemical catalytic activity. Compared with HP-p-CD and graphene, the stronger square wave anodic stripping voltammetric (SWASV) responses for Pb2+and Cd2+were observed on HP-β-CD-RGO modified glassy carbon electrode (GCE)(HP-β-CD-RGO/GCE), which resulted from the associated effects of HP-β-CD, RGO, Nafion and in situ deposited bismuth film. Various experimental parameters such as supporting electrolytes, pH values, concentrations of Bi3+, deposition potentials and deposition times were optimized. Under the optimal conditions, the stripping currents increased linearly with increasing concentration of Pb2+and Cd2+in the ranges of1×10-10-9×10-9M and5×10-10-9×10-9M, and the limit of detection (LOD)(S/N=3) were estimated to be9.42×10-11M for Pb2+and6.73×10-11M for Cd2+, respectively. Most importantly, this developed electrochemical sensor exhibit high sensitivity, good stability and reproducibility, and will provide a superior platform in the environmental analysis and detection.2. Water-soluble porphyrin functionalized graphene nanocomposites for the selective and sensitive detection of dopamine. A biosensor, based on water-soluble porphyrin-reduced graphene oxide (porphyrin-RGO) nanocomposite synthesized by simultaneous covalent and non-covalent strategies through aromatic π-π stacking and the formation of chemical bonds, was prepared for sensitive detection of dopamine (DA). TEM, FT-IR, Raman, TGA, Fluorescence absorption spectroscopy and XPS were used to characterize the products, and the results showed that the porphyrin was attached on RGO by covalent and non-covalent strategies. Compared with graphene or porphyrin alone, the porphyrin-RGO nanocomposite exhibited the unique advantages for the detection of DA in the presence of interfering substances such as uric acid (UA) and ascorbic acid (AA). The CV curves indicated that the porphyrin-RGO modified GCE (porphyrin-RGO/GCE) had larger active area and better electrochemical catalytic activity which could attribute to the π-π stacking and the electrostatic attraction between positive charged DA and negative charged porphyrin-RGO, which can accelerate the electron transfer and weaken the oxidation of AA/UA on the porphyrin-RGO/GCE. Differential pulse voltammetry (DPV) was used for the quantitative detection of DA. The peak currents increased linearly with the increasing concentration of DA in the range of1×10-6to7×10-5M, and the LOD (S/N=3) was estimated to be9.45×10-9M.