Studies On The Preparation Of Fluorescent Carbon Dots And Their Multiple Applications

As a new class of fluorescent nanomaterials,since 2004,carbon dots(CDs)have received great attention with the advantage of low toxicity,resistance to photobleaching and ideal biocompatibility.Up to now,a wide range of synthetic precursors and methods have been developed.To satisfy the specific demands,CDs are often obtained by choosing the suitable precursors and approaches.Besides,heteroatom doping and functional modification could improve the quantum yield(QY)and regulate the surface state of CDs,endowing CDs different applications.At present,CDs are widely applied in multiple fields such as chemistry,biology,medicine,environment and so on.Among them,environment has influence on the health and quality of life as the basic media for the human's survival.However,with the rapid development of society,environment pollution is more and more sever,which promote human to make efforts to the environmental protection including the detection and removal of pollutants.CDs play a positive role in term of the detection of environmental pollutants with the significant superiorities of high selectivity,low equipment requirements and simple operations.Meanwhile,some CDs or their composites can be used to remove environmental pollutants.Nevertheless,CDs often aim at single function,resulting in the incomplete utilization of performances.In order to reduce the cost of detection and removal of environmental pollutants,the development of"a kind of CDs with multiple applications"is one of the hotspot in the related research field.In this paper,with the purpose of detecting and removing environmental pollutants,three types of CDs were synthesized and systematic studies were conducted about the construction and multifunctional applications of CDs and related micro/nano materials.The specific contents are as follows:In the first chapter,choosing citric acid,urea and thiourea as the carbon,nitrogen and sulfur source,respectively,N,S co-doped carbon dots(N,S-CDs)with QY of 22%were obtained by hydrothermal methods.Then,the N,S-CDs were incorporated into melamine formaldehyde resin matrix to form fluorescent microspheres(MF-CDs).MF-CDs were used to detect and remove Au³⁺,which could broaden the linear range of detection to 0.05?2?M and the adsorption capacity to 1 mmol/g.And Au³⁺adsorbted on MF-CDs could be reduced to gold nanoparticles in situ and used for the catalytic degradation of 4-nitrophenol.The catalytic performance kept stable during five cycles.The experiment showed that the novel micro-nano materials(MF-CDs)could obtained by immobilizing pristine CDs on MF.As a fluorescent probe,MF-CDs could amplify the detection signal and improve the sensitivity of Au³⁺;as an adsorbent,MF-CDs could improve the adsorption capacity of Au³⁺and the adsorbed Au³⁺could recycled,embodying the"green characters"of MF-CDs.In the second chapter,N,S-CDs(QY:4.6%)were made by hydrothermal synthesis with the participation of carbon source(dopamine)and nitrogen/sulfur source(L-cystein).The N,S-CDs were resistant to photobleaching.What's more,the N,S-CDs was sensitive to p H,temperature and Cu²⁺.When the p H was 5.4?7.4,the fluorescence intensity decreased linearly with the increase of p H and R² was 0.9996.When the temperature was 20?60°C,the fluorescence intensity decreased linearly with the increase of temperature and R² was 0.9908.Moreover,when the concentration of Cu²⁺was 0.03?0.5?M,the linear equation was F/F₀=1.36C_Cu²⁺+0.9566 with R² of 0.9940and LOD of 39 n M.N,S-CDs here could detect p H?temperature and Cu²⁺by fluorescent sensing,that embodied the multiple applications of CDs.In the third chapter,N,S co-doped non-conjugated polymer dots(N,S-NCPDs)were obtained by hydroquinone and L-cystein;and N doped non-conjugated polymer dots(N-NCPDs)were synthesized by hydroquinone and polyethyleneimine(Mw1800).N,S-NCPDs and N-NCPDs could not only detect the concentration of hydroquinone,but also be sensitive to p H.With N,S-NCPDs as an example,there was existing linear relationship between the fluorescence intensity of N,S-NCPDs and the concentration of hydroquinone(0?100?M)with R² of 0.9883.With N-NCPDs as an example,at p H6?10,the fluorescence intensity increased linearly with the increase of p H and R² was0.9625.In this study,hydroquinone was converted to useful fluorescent products by mild and fast synthesis progress.Meanwhile,the concentration of hydroquinone could be determined.In the forth chapter,the experimental contents were summarizd and the deficiencies and the future research directions were pointed out.In the fifth chapter,the applications of CDs in the detection and removal of environmental pollutants in the recent three years were summarized and prospected.