Study On Preparation And Photoelectric Properties Of Carbon Dots Sensitized Inverse Opal Metal-oxide Semiconductor Films

Fluorescent carbon quantum dots (CDs) are intriguing recently discovered as one of the new members of carbon based nanomaterials family due to their interesting properties, such as stable fluorescent property, non-blinking, broad absorption spectra, environmental friendly, tunable excitation and emission wavelength, low toxicity and well biocompatibility. In addition, the excellent photoelectric conversion properties of CDs have aroused people’s concern. However, there are not many related research in improving the photoelectric property of semiconductor by using CDs as sensitizer.TiO2is a kind of excellent semiconductor materials with chemical stability, high photoactivty, low-cost and environmental friendly. However, due to the large forbidden band gap (3.2eV), TiO2could only absorb ultraviolet range sunlight (about4%of the sunlight total energy) which seriously affect the sunlight utilization. Base on the all above, How to improve the optical response range and quantum efficiency of TiO2has drawn many attentions of the researchers. Bi2O3is also an important semiconductor materials, occupies an important position in the oxide semiconductor material system. The forbidden band gap of Bi2O3is2.8eV. Because of the excellent properties of refractive index, dielectric constant and conductivity, Bi2O3becomes a new generation of photocatalyst materials. As is well-known, The porous structure or sensitization by some sensitizers are most effective ways to improve the photo-catalytic activity of oxide semiconductor material. In this thesis, The CDs were firstly prepared by a simple hydrothermal method through thermal polymerization of citric acid and urea. The as-prepared CDs exhibit good fluorescence properties. Then, the CDs were utilized to sensitize inverse opal structure of TiO2and Bi2O3semiconductor film, respectively. We studied the CDs sensitization effect on the photoelectric properties of oxide semiconductors. The main content and results of the work are as follows:1. We synthesized fluorescent CDs via a simple hydrothermal method. We also studied the influences of different reaction temperatures, pH value, and urea addition on the performance of fluorescent CDs. The CDs was found to be a label free, selective and sensitive fluorescent probe for detection of Hg2+ions with a detection limit as low as0.02μM.2. A facile emulsion polymerization approach was adopted to synthesize polystyrene (PS) spheres with different sizes. The PS colloidal photonic crystal films were fabricated through a vertical deposition method. Then inverse opal structure (IOS) TiO2thin films were prepared by using PS colloidal photonic crystal film as template and titanium isopropoxide (IV) as precursor. We also investigated the influences of different sizes of photonic crystal film on IOS TiO2structure. The IOS TiO2film was sensitized with the as-prepared CDs for the first time. Uv-vis diffuse reflectance spectra indicate that the IOS TiO2/CDs exhibits good visible light absorption ability. Due to the fluorescent CDs has strong absorption in visible and near infrared region, It could effectively broaden the sunlight absorption of TiO2to improve the IOS TiO2photovoltaic performance. The photocurrent of sensitized IOS TiO2/CDs film is five times than that of IOS TiO2by. In the end, we discussed the mechanism of improving photoelectric properties of IOS TiO2by sensitization of CDs.3. We first prepared IOS Bi2O3film by using PS photonic crystals as templates and Bi2O3as precursor prepared with Bi (NO3)3·5H2O, a certain proportion of ethylene glycol, ethanol, respectively. The effects of annealing temperature on the resulting phase and structure of IOS Bi2O3were investigated. Then the IOS Bi2O3thin film was sensitized with the as-prepared CDs. Uv-vis diffuse reflectance spectra indicates that the IOS Bi2O3/CDs exhibits good visible light absorption ability. The photocurrent of the IOS Bi2O3film sensitized with CDs significantly improved compared to the unsensitized one. We also demonstrated the IOS Bi2O3/CDs film possesses self-cleaning property through the photo catalytic degradation of rhodamine B experiment.