Preparation And Characterization Of Quantum Dot Films And (Graphene/TiO_x)n Films

Thin films of nanomaterials are called "the most promising materials in21century" due to its unique optical, mechanical, electromagnetic and gas sensitive properties. Along with the research progress, the research focus has shifted from the uniform film to the gradient film, from the pure film with a single component to the composite film with multiply components. In recent years, quantum dots (QDs) with the significant quantum confinement effect, graphene with the strong electron mobility and TiO2with the superior photocatalytic property have become research hotspots in nanomaterials. So it is meaningful to assemble them into gradient nanofilms or composite nanofilms.In this thesis, gradient CdTe QD films and graphene/TiO2composite films have been prepared and characterized. The photocatalytic property of graphene/TiO2composite films was investigated. Before fabricating the gradient quantum dot films, the uniform QD films were deposited and the factors affecting electrophoretic deposition (EPD) process in aqueous media were investigated in order to find out the optimum conditions. The detailed research works are shown as follows:1. The uniform CdTe QD films were deposited on ITO-coated glass by EPD in the mercaptoacetic acid-stabilized CdTe QDs aqueous suspension. The factors affecting EPD process in aqueous media, such as the choice of electrodes, the addition of antioxidant, the pH values and the range of applied voltage were investigated. The optimum conditions for forming the uniform QD films were obtained by taking a full consideration in all the factors:an ITO-coated glass was used as the anode and a zinc plate was used as the cathode; addition of ascorbic acid as antioxidant; pH values between9.0and11.5; a potential range of2.5-3.2volts.2. Under the optimum conditions for forming the uniform QD films described above, the thickness-gradient CdTe QD films were deposited onto the ITO-coated glass by applying different potentials to the two ends of the anode. The gradient films were characterized by UV-visible absorption and fluorescence emission spectroscopies, atomic force microscopy (AFM) and scanning electron microscopy (SEM). All the results indicated that the CdTe QD films with a gradient in thickness were successfully obtained. The colour of the film, the absorbance of UV-visible spectra and the relative intensity of fluorescence emission spectra all varied linearly along the lateral length of the ITO anode. In addition, the individual CdTe QDs in gradient films keep their identities because the mercaptoacetate groups covered on the surfaces of QDs can hinder the growth of small QDs to big ones.3. Graphene oxide (GO) and TiCl4ethanol-toluene solution were assembled into multilayer (GO/TiOx)n films via surface sol-gel process. Under UV irradiation, the (G/TiOx)n composite films were obtained due to the photocatalytic activity of TiOx which caused a photoreduction reaction. The composite films were characterized by UV-visible absorption spectroscopy. Raman spectroscopy, AFM and SEM. The photocatalytic activity of the composite films under visible light were investigated. The results indicated that TiOx was amorphous form in the (G/TiOx)n composite films and the methylene blue can be strongly adsorped and be decolorized under the visible light irradiation in the presence of (G/TiOx)n films as the photocatalyst. The photocatalytic activity of (G/TiOx)n composite films were greatly improved compared with pure (TiOx)n films due to the big specific surface area and strong electron mobility of graphene.