Sonochemical Synthesis Of Oxides And Graphene-based Nanomaterials And Their Applications

Several kinds of metal oxides and graphene-based nanomaterials with different morphologies have been synthesized via sonochemical method in this thesis,including twinned ZnO hollow ellipses(ZiO HEs),Cu2O-reduced graphene oxide composites(Cu2O-rGO),graphene sheets,MnO2 and so on.The morphologies of the products were controlled by adjusting reaction conditions.Techniques such as powder X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),high resolution transmission electron microscopy(HRTEM),selected area electron diffraction(SAED),X-ray photoelectron spectra(XPS),Raman spectrum and Fourier transform infrared spectrum(FT-IR)were used to characterize the crystal structures,compositions,morphologies and dimensions of the products.Furthermore,the formation mechanisms of the products are discussed.The obtained products were applied in the electrochemical sensing and photocatalysis and so on.The main results were summarized as follows:1.Sonochemical Fabrication of Twinned ZnO Hollow Ellipses for Electrochemical BiosensingTwinned ZnO hollow ellipses(ZnO HEs)have been successfully fabricated by a one-step template-free sonochemical route.The products were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results showed that the ZnO HEs had a hexagonal wurtzite structure,the wall of which was composed of ZnO nanorods.A possible growth mechanism for the formation of ZnO HEs was proposed,in which sonication played a crucial role.The highly efficient H2O2 electrochemical biosensor was fabricated using the film immobilized with hemoglobin,ZnO HEs and chitosan on glassy carbon electrode.The biosensor showed high stability and excellent electrocatalytic activity toward H2O2 with a linear range from 0.5 to 250 ?M and a detection limit of 0.15 uM.2.One-step simple sonochemical fabrication and photocatalytic properties of Cu2O-rGO compositesAn easy,one-step synthesis of Cu2O-reduced graphene composites(Cu2O-rGO)was developed using a simple sonochemical route without any surfactants or templates.The morphology and structure of the Cu2O-rGO composites were characterised using techniques such as scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),Fourier transform infrared(FT-IR)spectroscopy,Raman spectroscopy and X-ray photoelectron spectroscopy(XPS).The results indicated that the Cu2O sphere is approximately 200 nm in diameter and composed of small Cu2O particles approximately 20nm in diameter.The morphology and composition of the Cu2O-rGO composites could be well controlled by simply changing the mole ratio of the reactants under ultrasonic irradiation.The Cu2O-rGO composites displayed better photocatalytic performance for the degradation of methyl orange(MO)than pure Cu2O spheres,which may have potential applications in water treatment,sensors,and energy storage.3.Ultrasound assisted reduction of graphene oxide to graphene in L-ascorbic acid aqueous solutions:kinetics and effects of various factors on the rates of graphene formationThe reduction of graphene oxide(GO)to graphene(rGO)was achieved by using 20 kHz ultrasound in L-ascorbic acid(L-AA,reducing agent)aqueous solutions under various experimental conditions.The effects of ultrasound power,ultrasound pulse mode,reaction temperature,pH value and L-AA amount on the rates of rGO formation from GO reduction were investigated.The rates of rGO formation were found to be enhanced under the following conditions:high ultrasound power,long pulse mode,high temperature,high pH value and large amount of L-AA.It was also found that the rGO formation under ultrasound treatment was accelerated in comparison with a conventional mechanical mixing treatment.The pseudo rate and pseudo activation energy(Ea)of rGO formation were determined to discuss the reaction kinetics under both treatment.The Ea value of rGO formation under ultrasound treatment was clearly lower than that obtained under mechanical mixing treatment at the same condition.We proposed that physical effects such as shear forces,microjets and shock waves during acoustic cavitation enhanced mass transfer and reaction of L-AA with GO to form rGO as well as the change in the surface morphology of GO.In addition,the rates of rGO formation were suggested to be affected by local high temperatures of cavitation bubbles.4.Synthesis of MnO2 nanoparticles from sonochemical reduction of MnO4-in water under different pH conditionsMnO2 was synthesized by sonochemical reduction of MnO4-in water under Ar atmosphere at 200C,where the effects of solution pH on the reduction of MnO4-were investigated.The obtained XRD results showed that poor crystallinity 8-MnO2 were formed at pH 2.2,6.0 and 9.3.When solution pH was increased from 2.2 to 9.3,the morphologies of ?-MnO2 changed from nanosheets to spherical nanoparticles and finally to cubic or polyhedron nanoparticles.After further irradiation,MnO2 was readily reduced to Mn2+.It was confirmed that H2O2 and H atoms formed in the sonolysis of water acted as reductants for both reduction for MnO4-to MnO2 and MnO2 to Mn2+.The optimum irradiation time for the effective synthesis of MnO2 was 13 min at pH2.2,9 min at pH6.0,8 min at pH9.3,respectively.Taking into account the colloidal stability and size of the formed MnO2 nanoparticles,pH6.0 was considered to be the appropriate pH condition for the synthesis of MnO2 particles in our irradiation system.