Synthesis Of CQDs, SiQDs And Studies For Their Photocatalytic Performance With TiO₂ Nanosheets Composite Photocatalysts

The environmental pollution is a bottleneck problem which restricts harmonious development of human society, so the technology via photocatalytic degradation of pollutants with the advantages of simple, high efficiency and no secondary pollution is current research hotspot. TiO2 photocatalyst which has low price, nontoxic, stable and high catalytic redox ability is one of the main photocatalysts. However, TiO2 semiconductor with wide bandgap which can only absorb less than 5% UV light of the solar spectrum total energy, so its application is limited hugely. Besides, its photocatalytic effect is low, so both of its visible light response modification and the improvement are the main research direction in the field. As is known to all, the carbon quantum dots (CQDs) and other quantum dots in IV group have many advantages, such as rich precursor, quantum size effect, excellent photoelectric properties and environment friendly. This thesis mainly studied the synthesis of CQDs and silicon quantum dots(SiQDs), and their composites with titanium dioxide nano-sheets (TNS) aiming to broaden the visible light response of TNS and improve its photocatalytic performance for degrading the dye pollutants, so as to expand the photocatalytic applications under visible light in the composite photocatalysts of (C?Si)QDs/TNS. The research contents and results are as follows:1. The CQDs are synthesized via hydrothermal treatment at 200 ? using gelatin as carbon source, then obtained the uniform dispersion particles with grain size of about 4 nm through PEG as a modified reagent which exhibit good fluorescence properties and up-conversion fluorescence properties. When it is excitated by 300 nm wavelength, it appears the strongest emission peak at 417 nm.The CQDs/TNS composite photocatalysts are synthesized by ethanol solvent reflux method, and they can combine together stable through C-O-Ti chemical bond. The range of UV-vis absorption spectra can achieve to 550 nm. The composite photocatalysts are used for the degradation of RB, and when the mass ratio of CQDs/TNS is 7.5%, it has best photocatalytic activity which has 80% degradation ratio within 4 hours. And it has good stability, the degradation percentage is over 80% after three cycles.2. The CQDs with grain size of about 4.5 nm are synthesized via hydrothermal treatment at 180 ? using citric reagent as carbon source without PEG as a modified reagent. The same as above, the CQDs/TNS composite photocatalysts with different CQDs contents are obtained by ethanol solvent refluxing methods. When the mass ratio of CQDs is 7.5%, it has best photocatalytic activity which has 95% degradation ratio within 4 hours. And it has good stability, the degradation percentage is over 70% after four cycles.3. The SiQDs are synthesized also through hydrothermal treatment at 200? for 24 hours using 3-Amino propyl triethoxy silane(APTES) as silicon source, then we can obtain the uniform dispersion particles with grain size of about 3.8 nm which has good fluorescence properties.The SiQDs/TNS composite photocatalysts are synthesized by ethanol solvent reflux method, and they will combine together stable through Si-O-Ti chemical bond. The composite photocatalysts are used for the degradation of RB, and when the mass ratio of CQDs/TNS is 7.5%, it has best photocatalytic activity which can degradate RB fully within 3.5 hours. And it has good stability, the degradation percentage is over 90% after four cycles.