Preparationand Fluorescent Properties Of Carbon Nanodots

Carbon nanodots (C-dots) is a new type of carbon nanomaterials, and is consideredto be one of the most promising fluorescent material due to its low toxicity, goodbiocompatibility, stable fluorescence and so on. However, the existing preparationmethods of C-dots always have low yield, complex operation and the obtained C-dotshave poor uniformity, low fluorescence quantum yield, which seriously restrict thepractical application of C-dots. In this thesis, C-dots were firstly prepared by liquidphase plasma discharge treatment. The effects of voltage and discharge time on thestructure, morphology and fluorescent properties were studied, and the effects of C-dotsconcentration, solution pH and the variety of solvent on the fluorescent properties ofC-dots were also studied. Besides, C-dots were modified by acidificating and oxidecombined treatment, and we investigated the effects of modification on the structure,morphology and fluorescent properties of C-dots.Carbon nanomaterials were prepared by liquid phase plasma discharge treatment,and the results of serial characterization (IR, XPS, Raman, HRTEM, XRD and PL)show that as-prepared carbon nanomaterials are spherical and uniform in size which isless than10nm, the surface of particles contains large numbers of containing oxygengroups, the structure contains a small amount of graphite structure, under the excitationbetween340nm and420nm, the C-dots perform good fluorescent properties. By theabove characterization results, we concluded that C-dots were firstly prepared by liquidplasma discharge treatment. The research on effects of voltage and discharge time onstructure and morphology of C-dots shows that the voltage has a greater influence onstructure of C-dots, whose crystalline and particle size increases with the increase ofvoltage, while the discharge time has little influence on C-dots.The optical properties of as-prepared C-dots were studied, results show theobtained C-dots have wide excitation wavelength (325~450nm) and good fluorescentstability under glare continued radiation. The effects of voltage and discharge time onthe fluorescent properties of C-dots were investigated, and the results show that voltagehas a greater influence, and different voltages show different fluorescent properties, thefluorescent quantum yield of the C-dots can reach about4%at550V, which is4timesof450V, while the discharge time has little influence. By the examination of effects ofC-dots concentration, solution pH and the type of solvent on fluorescent properties ofC-dots, we obtained the applicable scope of C-dots. Finally, we stated briefly themechanism of fluorescence of C-dots, and we thought the fluorescence of as-preparedC-dots come mainly from the trapping of excited electrons by the surface defects.Acidification treatment in advance was used to improve C-dots’ dispersivity in DMF, and the results show acidification treatment can increase the amount of oxygengroups on the surface of C-dots, increase the uniformity in size distribution and reducethe crystalline of C-dots, but have little effects on the fluorescent properties, besides,acidification treatment also can weaken the influence from the loss ofoxygen-containing groups during pyrolysis stage when the preparation and fluorescentproperties of C-dots combined with metal oxide were studied. C-dots combined withzinc oxide and titanium oxide were prepared by sol-gel method. The results show thatthe C-dots after combined with zinc oxide and titanium oxide have higher fluorescencequantum yield than pure C-dots,12%and6.8%, witch is3and1.7times of C-dots,respectively.