Sonchemical Synthesis And Characterization Of MnnWO₄ Nanocrystals And CNT-CeO₂ Nanocomposites

Different from the routine methods, the new ultrasonic-induced synthesis approach has many advantages, such as low reaction temperature, short reaction time, and mild reaction conditions. In this thesis, MnWO4 nanocrystals and CNT-CeO2 nanocomposites have been successfully achieved by the ultrasonic technique. Their properties and applications have also been studied in our work.MnWO4 nanostructures with different morphologies have been prepared using inorganic salts as precursors via sonochemical process. In this work, the influence of the different surfactants on the morphology-control of MnWO4 nanostructures was investigated. The as-prepared MnWO4 nanocrystals were characterized by X-ray diffraction(XRD), scanning election microscopy(SEM), energy dispersive spectroscopy (EDS), fourier transform infrared(FT-IR), UV-vis spectroscopy and other techniques. Because of its good photocatalytic property, the as-synthesized MnWO4 had been introduced for the photodegradation of rhodamine B (RhB). The results indicated that MnWO4 had excellent photocatalytic property for the degradation of RhB and it had potential applications in the organic dyestuff and water treatment region. The electrochemical property of MnWO4 nanocrystals had also been studied. It is indicated that the glass carbon electrode (GCE) moditied with MnWO4 nanocrystals and CHIT could enhance electron transfer for its heme Fe(III) to Fe(II) redox couple. The MnWO4/CHIT/GCE electrode was further used as efficient supports for the immobilization of hemoglobin (Hb) to fabricate a novel biosensor. The biosensor showed an excellent bioelectrocatalytic activity towards H2O2 with a linear range from 5.0×10-6 to 4.5×10-4 M, and the detection limit of the sensor was 1.0×10-6 M at 3σ.CNT-CeO2 nanocomposites has been achieved by a cheap and simple ultrasonic technique using (NH4)2Ce(NO3)6 as precursors and the ethylene glycol (EG)-assisted. The as-prepared CNT-CeO2 nanocomposites were characterized by X-ray diffraction(XRD), scanning election microscopy(SEM), Energy Dispersive Spectroscopy (EDS), fourier transform infrared(FT-IR), and other techniques. Because of the high surface area of CeO2 and the good electrical conductivity of CNTs, they were immobilized on glass carbon electrode (GCE) to fabricate CNT-CeO2 /CHIT/GCE electrode. Then the electrochemical property of this modified electrode was studied by cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical results indicated that CNT-CeO2/CHIT/GCE electrode could enhanced electron transfer for its heme Fe(III) to Fe(II) redox couple. When Hb was cast on its surface, the modified electrode showed good electrocatalytic activity towards H2O2 reduction. The catalytic reduction peak current of Hb/CNT-CeO2/CHIT/GCE film increased linearly with the concentration of H2O2 in a linear range from 5.0×10-6 to 5.0×10-4 M. Hence, CNT-CeO2 nanocomposites achieved by ultrasonic technique can be fabricated a novel biosensor to H2O2. Its detection limit was 1.0×10-6 M at 3σ.Moreover, in order to study the potential applications of these materials in fuel cell, H2PtCl6 was electrodeposited on the MnWO4/CHIT/GCE electrode and CNT-CeO2 /CHIT/GCE electrode by cyclic voltammetry to form MnWO4/CHIT film and CNT-CeO2 /CHIT film. The electrochemical oxidation of methanol on the MnWO4/CHIT film and CNT-CeO2 /CHIT film was studied by cyclic voltammetry respectively. The primary results demonstrated that these two films had a good electorcatalytic activity for the methanol oxidation reaction.