Synthesis Of Luminescent Carbon Dots Via Micro-Emulsion Method And Coating With Polymer

In recent years,luminescent carbon dots have been drawn widely attention as a new nanoscale luminescent material.Luminescent carbon dots have excellent luminescent property and also show excellent properties such as satisfactory fluorescent performance,low cytotoxicity,biocompatibility and cheap manufacturing cost,compared with the traditional fluorescent material such as organic dyes,inorganic semiconductor quantum dots and rare earth oxide.At present,researchers mainly focused on the preparation of luminescent carbon dots.The luminescent principle of carbon dots was related to the surface defects caused by the heteroatom.In this paper,luminescent carbon dots were synthesized by micro-emulsion method and doped with heteroatom.At present,using polymer to coat luminescent carbon dots was rarely reported.In this paper coating-luminescent carbon dots was also carried out by using two kinds of polymer via a variety of methods.Through the nitrogen source selecting experiment,the urea was selected as the nitrogen source and the citric acid was selected as the carbon source to synthesize luminescent carbon dots.Based on the exploration on the effects of the reaction temperature,surface active agent and the oil phase,the optimum reaction conditions were determined:SP-60 was selected as surfactant,cyclohexane was selected as oil phase,the reaction temperature was 180?,and the reaction time was 1.5 h.The luminescent properties of carbon dots were studied: fluorescent property,p H sensitivity,time stability,the durability of fluorescence.Through the research on their basic fluorescent property,it was found that they had a wide excitation band and the emission wavelength was around 450 nm under the different excitation light sources.By studying its p H sensitivity,the luminescent carbon dots were found to have a high sensitivity to p H in the acidic region.With calculating the fluorescence quantum yield,the maximum fluorescence quantum yield was 70.0%.Meanwhile,we could know that it was a kind of stable carbon dots from studying their time scan spectra.Through the UV illumination durability experiment,the half-life of luminescent carbon dots was 1600 min,suggesting that the fluorescent durability of luminescent carbon dots was very outstanding.In this paper,luminescent composite microspheres were also synthesized according to in-situ polymerization method in order to increase the stability and dispersion of carbon dots.In this case,styrene was selected as monomers,potassium sulfate was selected as the initiator,and the size of luminescent composite microspheres with core-shell structures were about 1.3 ?m.00 However,fluorescence quenching occurred in the composite microspheres.On the other hand,the polyacrylic acid was purified by vacuum distillation to coat carbon dots for synthesizing luminescent composite microspheres,with potassium sulfate as the initiator.The average particle size of the microspheres with core-shell structures was 1.5 ?m.Compared with luminescent carbon dots,the emission wavelength had a red shift and the fluorescent intensity also decreased,showing a much better coating than that of polystyrene.