Preparation Of Carbon Quantum Dots And Their Applications In Fluorescent Materials And Ion Detection

Carbon quantum dot?CQD?is one of inspiring luminescent nanomaterial and has been widely used in biomedicine,bio-imaging,photoelectricity,sensors and photocatalysts and other fields due to the properties of nontoxic,water-soluble,simple preparation,and easy functionalization.In this work,carbon quantum dot was prepared by L-cystine though normal microwave reactor and single-mode microwave reactor.The effects of various factors in prepration on the fluorescence properties of CQD were investigated,the obtained CQD showed high fluorescence intensity and good stability and thus were employed as fluorescent materials to dye cotton fiber,to dope silicone rubber,to make invisible fluorescent inks,as well as to detect Fe³⁺ ions.The main research conclusions were as follows:?1?The fluorescent CQD prepared by microwave reactors showed good dispersibility in the aqueous solution.The size of spherical dots is not uniform with an average size of around 2-6 nm.The color of CQD in water under day light is slight yellow,while green fluorescence under UV lamp;the maximum exciting wavelength is 420 nm and the maximum emission wavelength is 505 nm;the fluorescence quantum yield was 24% in the water solution.The color of CQD after being extracted into organic phase is colorless under day-light and shows a blue fluorescence under UV lamp;The best excitation and emission wavelengths are 365 nm and 430 nm,respectively;The average fluorescence quantum yield is 86% in chloroform and dichloromethane.The emission wavelength of CQD dis invariable with the excitation wavelength change either in water phase or in organic phase.?2?Carbon quantum dots can be stored for a long time in water phase at a 4 oC environment and in organic phase at room temperature.The fluorescence intensity of the preprared CQD is first enhanced and then weakened as expanding the reaction time,and increasing the conentration of sodium hydroxide.For a concentration of 10% cystine,the optimized temperature is 135-140 °C,and the optimized concentration of sodium hydroxide is 0.7-0.9 mol/L.The CQD in water phase shows fluorescent property over a wide p H range,and the fluorescence intensity decreases with pH decreasing.?3?The prepared CQD as a fluorescent material could dye cotton fiber,dope the silicone rubber,and to make fluorescent inks.The fluorescence of cotton fiber dyed by CQD in water phase is not stable and that of cotton fiber dyed by CQD in chloroform phase is better.The silicone rubber doped with CQD in water phase shows pale yellow,and opaque,and strong blue-green fluorescence under UV light,while the silicone rubber doped by CQD in organic phase shows colorless,transparent and blue fluorescence under the UV lamp.The fluorescent ink of CQD can be used in writing and inkjet printing,and this invisible ink can only be seen under UV lamp.?4?The quenching effect of a variety of metal cations and partial anions on the fluorescent CQD shows that some ions have no obvious quenching effect,but Fe³⁺,Fe2+ and Cu2+ have a strong response on the fluorescent quenching of CQD in hexane.The response of fluorescent quenching in water and organic phase to Fe³⁺ is very fast,the fluorescence quenching have a clear linear relationship with the concentration of Fe³⁺ at lower than 100 ?mol/L in water and between 10 and 200 ?mol/L in hexane.