Preparation Of Graphene-based Nanocomposites And Their Application In Electroanalytical Chemistry

In this thesis, graphene oxide was used as the original material to prepare several graphene-based nanocomposites. The X-ray diffraction (XRD), transmission electron microscopy (TEM) and a variety of analytical methods were used to characterize these nanocomposites. Then the nanocomposites were used as modified electrode materials for the fabrication of electrochemical sensors. Their applications in pharmaceutical analysis and hydrogen peroxide detection were investigated. The contents of this thesis were described as follows:1. An electrochemical sensor based on CdSe nanoparticles (NPs) decorated poly(diallyldimethylammonium chloride)(PDDA) functionalized graphene (CdSe-PDDA-G) nanocomposite was fabricated for sensitive detection of esculetin. The nanocomposite was characterized by XRD, Ultraviolet/visible spectra (UV/vis) and TEM. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to investigate the electrochemical behaviors of esculetin on CdSe-PDDA-G composite film modified glassy carbon electrode (GCE). The experimental results indicated that the incorporation of CdSe NPs with PDDA-G greatly enhanced the electrochemical response of esculetin. This electrochemical sensor displayed satisfactory analytical performance for esculetin detection over a range from1.0×10-8to5.0×10-5mol L-1with a detection limit of4.0×10-9mol L-1(S/N=3). Moreover, the sensor also exhibited good reproducibility and stability, and could be used for the detection of esculetin in real samples.2. An electrochemical sensor based on Fe3O4nanoparticles (NPs)-coated PDDA-functionalized graphene (Fe3O4-PDDA-G) nanocomposite was fabricated for sensitive detection of acetaminophen. The nanocomposite was characterized by XRD, TEM and vibrating sample magnetometer (VSM). The electrochemical behaviors of acetaminophen on Fe3O4-PDDA-G composite film modified GCE were investigated by CV and DPV. The experimental results indicated that the incorporation of Fe3O4NPs with PDDA-G greatly enhanced the electrochemical response of acetaminophen. This fabricated sensor displayed excellent analytical performance for acetaminophen detection over a range from0.1to100μmol L-1with a detection limit of3.7×10-8mol L-1(S/N=3). The redox peaks of acetaminophen, dopamine (DA) and ascorbic acid (AA) can be well separated on the Fe3O4-PDDA-G/GCE. Moreover, the proposed electrochemical sensor also exhibited good reproducibility and stability, and has been used to detect acetaminophen in tablets.3. β-cyclodextrin functionalized reduced graphene oxide hybrid nanosheets (β-CD-RGO) were successfully prepared by using L-ascorbic acid (L-AA) as the reducing agent under a mild condition and used as enhanced material for sensitivity determination of diethylstilbestrol (DES). In0.1M PBS (pH7.0), the redox peak currents of DES increased significantly on P-CD-RGO/GCE, suggesting that the composite film not only shows excellent electronic properties of RGO sheets but also exhibits high supramolecular recognition capability of β-CD. The experimental conditions were optimized and the kinetic parameters were investigated. Under the optimal conditions, the reduction peak current of DES increased linearly with increasing the concentration in the range from0.01to13μM with the detection limit of4nM (S/N=3). The developed electrochemical sensor exhibited high selectivity, good stability and reproducibility, and also successfully determined DES in milk samples with satisfactory results.4. PtAu bimetallic NPs were successfully synthesized on graphene sheets-multi walled carbon nanotubes (G-CNTs) hybrid nanomaterials via a simple one-step chemical co-reduction method in ethylene glycol (EG)-water system. The nanocomposites (PtAu/G-CNTs) were characterized by XRD, TEM and X-ray photoelectron spectroscopy (XPS). Then a sensitive nonenzymatic hydrogen peroxide (H2O2) sensor was fabricated based on PtAu/G-CNTs nanocomposites modified GCE. The results of electrochemical experiments demonstrated that the sensor exhibited excellent electrocatalytic activity to the reduction of H2O2. The sensor displayed a fast amperometric response time of less than4s with linear detection range from2.0to8561μM and a relatively low detection limit of0.6μM (S/N=3). In addition, the sensor also showed good selectivity for H2O2detection, long-term stability and reproducibility.5. PDDA-functionalized graphene sheets-multi walled carbon nanotubes (G-CNTs) hybrid materials (PDDA-G-CNTs) were successfully synthesized. Then, an electrochemical sensor based on PDDA-G-CNTs/β-CD was fabricated for the sensitive determination of luteolin. In0.2M HAc-NaAc buffer solution (pH5.0), the redox peak currents of luteolin increased significantly on PDDA-G-CNTs/β-CD modified GCE, suggesting that the composite film not only showed excellent electronic properties of PDDA-G-CNTs but also exhibited high molecular recognition capability of β-CD. The chronocoulometry investigation demonstrated that the composite could effectively increase the electrochemical active surface. Under the optimal conditions, the oxidation peak current of luteolin increased linearly with increasing the concentration in the range from0.05to60μM with the detection limit of0.02μM (S/N=3). The developed electrochemical sensor exhibited high selectivity, good stability and reproducibility, and also successfully determined luteolin in drug samples.