微波法制备纳米碳点反应机制与发光机理

摘要

为探讨微波法制备纳米碳点发光性质的影响规律与本质,采用微波加热法通过控制微波功率、反应时间以及pH值合成了一系列纳米碳点,并利用荧光激发光谱与发射光谱测试对纳米碳点的发光性质进行了表征,结合紫外吸收光谱与傅立叶红外光谱对反应产物官能团变化分析,最终揭示了微波加热过程中葡萄糖向纳米碳点转变的机制与发光机理.结果表明,采用微波法制备纳米碳点,当微波功率为560 W,反应时间为2.5 min时,获得纳米碳点发光性能最佳.当采用波长370 nm紫外光激发时,对应451 nm的蓝光发射强度最高.伴随纳米碳点溶液pH值从酸性变为碱性,纳米碳点最强发光峰的激发光波长由350 nm显著向高波长方向移动,且发光峰强度显著升高.紫外吸收光谱与傅立叶红外光谱显示反应过程中形成了多环芳香族碳氢化合物,表明微波加热过程中是葡萄糖单糖向多糖聚合并最终发生碳化的过程.不同pH值下纳米碳点发光性质的差异,源于对纳米碳点中C=C键与C=O键比例的调整,从而实现对纳米碳点的光学带隙宽度及激子束缚能等的综合调控.%In order to explore their luminescence properties, a series of carbon nanodots were prepared by microwave heating by controlling the microwave power, reaction time, and pH value. The luminescence properties of carbon nanodots were characterized by their fluorescence excitation spectrum and emission spectrum. We present the transformation mechanism of glucose into carbon nanodots during the microwave heating process and the corresponding luminescence mechanism together with the analysis of functional group changes during the reaction as monitored with ultraviolet (UV) absorption and Fourier Transform Infrared (FT-IR) spectra. The results show that the optimal luminescence properties of carbon nanodots were obtained when the glucose was heated under a microwave heating power of 560 W for 2.5 min. When the carbon nanodots were excited with UV radiation with a wavelength of 370 nm, the strongest luminescence appeared at 451 nm. The wavelength of the strongest luminescence peak moved from 350 nm to higher wavelengths significantly, when the pH value was modified from acidic to alkaline, and was accompanied with a significant rise in luminescence peak intensity. We show that polycyclic aromatic hydrocarbons form in the reaction process,as evidenced by UV absorption and FTIR monitoring, indicating that microwave synthesis of carbon nanodots proceeds via polymerization and final carbonization of glucose. Carbon nanodots formed under different pH values exhibit a change in the ratio of carbon-to-carbon double bonds to carbon-to- oxygen double bonds. The optical bandgap and exciton binding energy of the carbon nanodots were also investigated co mprehensively.