Determination Of Five Kinds Of Small Molecules On Nano-Material Modified Electrode

Ionic liquids (ILs) are generally defined as a compound entirely composed of organic cations and various inorganic anions, which exist in the liquid state around room temperature. It has many special physical and chemical properties such as high ionic conductivity, good solvating properties and wide electrochemical window, which can be applied in the field of electrochemical chemistry either as supporting electrolyte or the modifier for chemically modified electrode. In this thesis, IL is used as a modifier to fabricated carbon ionic liquid electrode (CILE). The nanomaterials have the effects of large surface area and small size. So the electrode modified by nanomaterials can effectively improve the conductivity of the electrode, increase the contact area of the material and the electrode. Therefore, nanomaterials have shown great potentials in the design and application of biosensors. In this thesis, ILs are used as a modifier to fabricate two kinds of carbon ionic liquid electrode (CILE). Then five kinds of chemically modified electrodes were fabricated by coalting or electrodepositing two kinds of nano-materials on the CILE, and the electrochemical behaviors of five kinds of molecules are studied in details. The thesis can be summaried as follows:1. LiCoO2nanospheres were synthesized and further immobilized on a carbon ionic liquid electrode (CILE), which was prepared by using1-hexylpyridinium hexafluorophosphate (HPPF6) as the modifier. The characteristics of LiCoO2/CILE were investigated by scanning electron microscopy (SEM) and cyclic voltammetry. Under the selected conditions LiCoO2/CILE showed better electrochemical response towards the detection of metol than the CILE. The parameters of metol electro-oxidation on LiCoO2/CILE were calculated with the values of the electron transfer coefficient (a), the number of electrons transferred (n), the apparent heterogeneous electron transfer rate constant (ks) and the diffusion coefficient (D) as0.51,0.91,0.92s-1and7.06×10-5cm2s-1, respectively. This modified electrode can be further used to detect metol content in synthetic samples. 2. A novel electrochemical oxalic acid (OA) sensor was developed by electrodepositing graphene (GR) on the surface of a carbon ionic liquid electrode (GR/CILE). The electrochemical behaviors of OA on the GR/CILE were investigated by cyclic voltammetry. The GR/CILE exhibited high electrocatalytic performances with fast voltammetric responses and notably decreased overpotential compared to the bare CILE. Under the optimal conditions, the oxidation peak current was liner to OA concentration over the range from8.0×10-6to6.0×10-3mol L-1with the detection limit estimated to be3.48×10-6mol L1(3σ).3. A voltammetric sensor was fabricated by applying a chitosan and graphene composite film on the surface of a carbon ionic liquid electrode (CTS-GR/CILE). The CILE was prepared by mixing1-butyl-3-methylimidazolium dihydrogen phosphate ([BMIM]H2PO4) with graphite powder and the electrochemical behaviors of ATP on the CTS-GR/CILE were investigated. ATP showed an irreversible adsorption-controlled oxidation reaction with enhanced electrochemical response on the modified electrode, which was due to the presence of high conductive GR on the CILE surface. The electrochemical reaction parameters of ATP on CTS-GR/CILE were calculated with the electron transfer coefficient (a) as0.329, the electron transfer number (n) as2.15, the apparent heterogeneous electron transfer rate constant (ks) as3.705×10-5s-1and the surface coverage (FT) as9.33×10-10mol cm-2. Under the optimal conditions the oxidation peak current was proportional to ATP concentration in the range from1.0×10-6to1.0×10-3mol L1with the detection limit of0.311μmol L-1(3σ). The proposed electrode showed excellent reproducibility, stability, anti-interference ability and further applied to the ATP injection samples detection successfully.4. A kind of carbon ionic liquid electrode (CILE) was constructed by mixing graphite powder with ionic liquid1-hexylpyridinium hexafluorophosphate (HPPF6). Chitosan and graphene were sequentially casted on the surface of the CILE. The electrochemical behaviors of adenine and catechol were studied on the CTS/GR/CILE, respectively. The results showed better electrochemical performances compared with CILE. The modified electrode was further applied to the determination of milk powder and synthetic wastewater samples with satisfactory results.