Preparation And Properties Of Fluorescent Carbon Dots And Its Composites

Carbon dots(CDs) has attracted many researchers because of its good water solubility, fluorescent stability, excellent resistance to bleach, and the advantages of easy functionalization. At present, the applications of carbon dots mainly included the ion detection, preparation of optical devices, biological imaging and tracer, photocatalyst etc. However, in addition to the applications of biological imaging and tracer, other applications are not directly using carbon particles of the quantum dots or its solution. So if we can obtain the carbon dots and polymers composite which maintained the optical properties of carbon dots and the molding ability, certain mechanical properties of polymers, it will be further expanded applications of carbon dots. This paper use citric acid as carbon source and ethylenediamine or 3-aminopropyltriethoxysilane as a surface modifying agent to prepare the high fluorescence carbon dots and its composites. And the factors affecting the optical properties of carbon dots were also explored, details are as follows:1. Citric acid monohydrate and ethylenediamine were used as a raw material, and the carbon dots were prepared by a hydrothermal method. Atomic Force Microscope(AFM) image showed that the carbon dots particles have spherical shape, uniform size, good dispersion and the particle size were between 1 to 5 nm. Through the Raman spectra and X-ray diffraction(XDR), we consider that the particles’ nuclear was composed of sp2-hybridized carbon atoms and the outer layer was sp3-hybridized carbon atoms. The absorption spectra and photoluminescence(PL) emission spectra of carbon dots indicated that the absorption peak was focused on 400 nm and the fluorescence peak was focused on 475 nm. The fluorescence intensity got maximum value when the excitation wavelength at 360 nm and fluorescence peak didn’t have excitation-dependent PL behavior.2. PVA was modified by acrylic acid(AA) through free radical grafting, and the product with carbon dots form CDs/PVA composite by solution blended process. The electrostatic interaction makes carbon dots dispersed in PVA matrix uniformly. Because of the electrostatic interaction between NH2, NH- and –COOH, carbon dots can dispersed in PVA matrix uniformly. CDs/PVA solution and CDs/PVA membrane’s absorption spectra and PL emission spectra indicated that they have similar optical properties with CDs. It meant that CDs/PVA composites not only had excellent optical performance, also had the characteristics of polymer such as molding.3. Using cheap anhydrous citric acid and 3-aminopropyltriethoxysilane by oil bath heating step that can obtain the carbon dots with surface passivation. AFM indicated that carbon dots is spherical, the particle diameter was around 1 nm and good dispersion. The exploration of factors influent the optical properties indicated that with the increase of reaction temperature, the intensity of absorption spectra and PL spectra were enhance corresponding, and the quantum yield enhanced as well. Solvent on the optical properties of the carbon dots has a certain influence, lewis acid kind of solvent can weaken the absorption, and fluorescence peak position must be moving at the same time. The pH of the solution on carbon dots of fluorescence spectra also has a certain influence, with the increase of solution’s p H, fluorescence intensity increased gradually.