Preparation And Photocatalytic Properties Of Carbon Quantum Dots And Their Silver Composites

Due to their pronounced quantum confinement and edge effects, zero-dimensional carbon nanomaterials, named as carbon dots（CDs）, possess numerous novel chemical/physical properties, making them promising in photocatalysis 。 Treatment with strong oxidizing agents has been employed to exfoliate CQDs from coal. However, the major limiting factor preventing industrial scale production of high quality CQDs using this approach has been the inherent difficulty in thoroughly removing both the excess oxidizing agents and the inorganic salts that form during the neutralization phase via the addition of bases. Consequently, in order for the successful large scale production of these CQDs to come to fruition, it is essential that green and facile CQD production strategies are developed.Besides, the UV light absorption generally takes place for carbon quantum dots（CDs）, their application in the field of photocatalysis was limited. However, the enhancement of the absorption of CDs in the visible light region could be promising through in-situ composited with Ag nanoparticles. Not only can it promote rapid charge separation upon light excitation,but also broaden and shift absorption transition due to the effects of surface plasmon resonance. In this dissertation,several works have been done as follows:1, CQDs was successfully prepared through selective oxidation of coal by H₂O₂. And scanning electron microscopy（SEM）, transverse electric and magnetic field（TEM）, FT-IR spectrophotometer, X-ray photoelectron spectroscopy（XPS）, fluorescence spectrophotometer and ultraviolet spectrophotometer（UV） were employed to analyze the size, structure, element,functional groups, and properties of the composites. The results indicate that CQDs was synthesized through selective oxidation of organic carbon in coal by H₂O₂, it shows sphere morphology in 1-3 nm. CQDs are mainly coposed of C and O, consist of C-O, C-C, C=O,-COOH and-OH bands. The yield of as-prepared CQDs is higher than methods reported ever, and this method is suitable for the preparation of CQDs in a large scale. The photocatalytic activity is higher than that of commercialized P25 photocatalyst. Thus,we have find a way to prepare an efficient photocatalyst in a large scale.2, According to the disadvantage of CQDs in photocatalysis, such as low absorption in visible light region and low photocatalytic activity, Ag was applied to modified CQDs. The theory consist of following aspects: firstly, the photo absorption of CQDs can improved in visible light rigion when composed with Ag nanoparticles due to the effects of surface plasmon resonance. Then the synthetic method was designed, a photoreduction approach was employed to prepare Ag/CQDs composite with visible light irradiation due to the Upconversion photoluminescence. Finally, based on the theory of Thermodynamics of nucleation, we investigate the nucleation of Ag on the surface of CQDs.3, Based on the the theory of in-situ synthesis of Ag/CQDs nanoparticle, two kind of CQDs was used in the experiment, The result confirmed the composites between carbon dots and silver nanostructure. The small-sized particles showed the plasmon resonance absorption, exhibited stronger light absorption and higher abilities of methylene blue degradation. After that, we studied the influence on the photoreduction preparation of Ag/CQDs composite, and found the key factor on the absorption of as-prepared samples in the visible light region, which could be taken as the refrence of noble metal-based photocatalyst in a photoreduction method.