| Graphene has lead to a study upsurge since its discovery all over the world, it has attracted great attention in the field of physics, chemistry, material science, energy, and so on due to its unique structure and remarkable properties. Graphene was easily obtained via one-step ultrasonic exfoliation of graphite powder by selecting N-methyl-2-pyrrolidone (NMP) as the solvent in this thesis. The electrochemical sensing property of NMP-exfoliated graphene was studied in detail, and the functionalization, electrochemical enhancement mechanism of the obtained graphene nanosheets (GS) was further investigated. Thereafter, the response mechanism of the remarkably enhanced electrochemical signal was deeply explained, and a highly sensitive electrochemical method was newly developed for the detection of small biological molecules, environmental endocrine, food colourings and so on. The research work of this thesis mainly contains the following five parts:(1) GO was prepared from the natural graphite powder by chemical oxidation method, and RGO was obtained via chemical reduction of GO by NaBH4. The electrochemical behavior of clenbuterol (CLB) and ractopamine (RAC) was studied, and it was found that GO owned more superior signal enhancement ability than RGO toward the oxidation of CLB and RAC. The signal enhancement mechanism of GO was deeply discussed under the help of scanning electron microscopy (SEM), size analysis, fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectra (XPS), the results showed that the higher electrochemical activity of GO mainly resulted from its abundant oxygen-containing functional group on its surface. Based on the remarkable signal enhancement effect of GO, a novel electrochemical method was fabricated for the highly sensitive detection of CLB and RAC, and the detection limits were17and15μg L"1, respectively. At last, this newly developed method was used for the analysis of real pork samples and the recovery was over the range from90.1%to98.6%. (2) Graphene nanosheets (GS) was easily obtained via one-step ultrasonic exfoliation of graphite powder in N-methyl-2-pyrrolidone (NMP), and the effect of exfoliation time on the graphene was discussed. SEM, TEM, Raman and particle size measurements indicated that the particle size decreased, the exfoliation efficiency and the surface defects of the produced graphene increased as ultrasonic time extended. Compared with RGO, the NMP-exfoliated showed stronger signal enhancement effect toward the oxidation of ascorbic acid (AA), dopamine (DA), uric acid (UA), xanthine (XA), hypoxanthine (HXA), bisphenol A (BPA), ponceau4R, and sunset yellow. Moreover, the electrochemical activity of GS was improved with the prolonged ultrasonic time. Based on the strong signal amplification ability of the NMP-exfoliated GS, a novel and sensitive electrochemical sensing platform was fabricated.(3) The above-mentioned NMP-exfoliated GS was re-dispersed into N,N-dimethylformamide (DMF), a kind of volatile solvent with lower boiling point, and GS modified glassy carbon electrode (GS/GCE) was then prepared by solvent evaporation. The electrochemical behavious of AC, G and A were studied, the results showed that GS owned stronger signal enhancement ability relative to RGO and bare GCE. Electrochemical impedance spectroscopy (EIS) characterization demonstrated the stronger electrochemical activity of GS was resulted from its higher electron transfer rate and larger electrode area. Therefor, a new electrochemical method with high sensitivity was developed for the simultaneous detection of AC, G and A, and the detection limits were2.5nM,10nM and10nM, respectively. At last, the method was applied in the detection of tablet and herring sperm DNA samples, and the detection result was satisfactory.(4) NMP-exfoliated GS was combined with porous Fe2O3microspheres that synthesized by hydrothermal method, and then a functional sensing interface was developed (GS-Fe2O3). SEM, TEM and XRD tests confirmed that GS were successfully composited with porous Fe2O3microspheres, and the three-dimensional structure of GS-Fe2O3hybrid was larger. The electrochemical response behaviour of BPA indicated that GS-Fe2O3owned remarkable synergetic signal amplification ability toward the oxidation of BPA. Moreover, the signal enhancement effect was further increased after addition of hexadecyltrimethylammonium bromide (CTAB). Based on the synergetic signal amplification of GS-Fe2O3hybrid and CTAB, a novel electroanalytical method with high sensitivity was developed for BPA, and the limit of detection was as low as2.5nM.(5) NMP-exfoliated GS was functionalized by anode oxidation. Compared with the widely used GO, the NMP-exfoliated GS exhibited apparently better electrochemical activity toward the oxidation of a series of phenols like hydroquinone, catechol,4-chlorophenol and4-nitrophenol. More importantly, the electrochemical activity of GS toward these phenols was further enhanced by simply anodizing at1.8V for2min. Characterizations by techniques like XPS, Raman, AFM and EIS demonstrated that the increase of oxygen-containing groups, edge-plane defects, surface roughness and electron transfer rate were responsible for the further enhanced activity of anodized GS. Therefor, a simple electrochemical method for the highly sensitive detection of phenols was established using the electrochemically functionalized GS as the sensing material and the detection limits were0.012μM,0.015μM,0.01μM and0.04μM for hydroquinone, catechol,4-chlorophenol and4-nitrophenol, respectively. |
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