Growth Control And Spectral Properties Of Gold Nanocrystals

Gold nanocrystals can be widely used in the fields of biology, environmental monitoring, medical diagnostics, photocatalysis and so on. Due to the biocompatibility, gold nanocrystals have been attracting more and more attention in DNA testing, medical diagnostics, anticancer research, which are closely related to their optical properties. Interestingly, the reported molar extinction coefficients of gold nanocrystals in literature works are significantly different from each other. Furthermore, the conversion rate during the preparation of gold nanocrystals is crucial to the calculation of the extinction coefficients, but has not been involved therein.In this thesis, our efforts are focused on the calculation of the extinction coefficient of gold atoms in spherical nanocrystals. The growth control of gold nanocrystals protected by PVP is achieved, in which sodium borohydride and ascorbic acid are used as the reducing agents in preparing seeds and controlling the growth, respectively. X-ray absorption near edge structure (XANES) spectroscopy shows that, under the studied conditions, almost all the gold precursors can be reduced to Au0. Raman spectra and the transmission electron microscopy suggest that the PVP protector efficiently prevents the synthesized gold nanocrystals from aggregation. In combination with UV-Vis spectra, the molar extinction coefficient of gold atoms in nanocrystals can be calculated. It is found that the size of gold nanocrystals can influence the position and intensity of the absorption peak. In our study, the molar extinction coefficient of gold atoms in nanocrystals ranges from2×103to4×103L-mol-1·cm-1...