Study On The Preparation, Separationand Structure-activity Of Fluorescent Carbon Dots Produced By Microwave Assisted Synthesis

As a new type of fluorescent carbon nanomaterial, Fluorescent carbon dots(C-dots)possesses a series of excellent properties, such as stable fluorescence property, no lightflicker and no photobleaching, low toxicity, good water solubility and biocompatibility,excitation wavelength (λex) dependent photoluminescence (PL) behavior, This may lead toC-dots replace Quantum Dots(QDs) to play an important role in the biomedical sciences. Somany approaches for synthesizing C-dots have been developed to make preparation of C-dots,however, using expensive carbon source materials, such as carbon nanotubes or graphene, orexpensive equipment, such as laser pulse instrument, or even surface modified C-dots, suchas doped with metal and surface passivation of PEG, all above can obtain higher fluorescencequantum yield of C-dots. However, the preparation process is tedious, the cost is expensive,leading to restrict the synthesis of fluorescent carbon dots to large scale production. Inaddition to utilize glucose, polyethylene glycol as the precursor, microwave assistedsynthesis in strong acid or ultrasonic decomposition, with the occurrence of deputy reactionis complex, and this lead to a cumbersome and time-consuming separate process, get a lowfluorescent quantum yield, therefore limited the method. In this paper, we have preparedC-dots by microwave assisted synthesis, glycerol and tributyl phosphate have been used asthe precursor to produce C-dots respectively. The obtained C-dots performance thefluorescence excitation wavelength dependent, thus provide a better and emerging materialfor the study of the mechanism of luminescence and structure of C-dots.In this paper, we used glycerol and tributyl phosphate as the precursor to produce C-dotsby microwave assisted synthesis method respectively. By this way, we have obtained C-dotssuccessfully. In the following step, ultrafiltration and column chromatography have beenused for further separation and purification. The results show that the latter is more suitablefor the separation of obtained C-dots. Two different types of C-dots separated by columnchromatography, possess an average size of0.5~1.5nm and0.5~1.8nm, the best excitationwavelength was380nm and340nm, the maximum emission wavelength were484nm and406nm, the quantum yields were1.5%and3.63%, Zeta potential was-8.66mV and-5.79mV,302nm under UV light excitation were yellow and blue respectively.Taking into account of the morphology and diameter, structure of surface and opticalproperties, for the structure of the C-dots (glycerol and tributyl phosphate as the precursors respectively), the results show that, the former contains more oxygen than the latter (thecontent ratio of carbon and oxygen), Infrared spectrum and Zeta potential has also confirmedthat the former is richer than the latter for the oxygen groups of surface. But, the element of Pappeared to the surface of latter, this maybe one of reasons caused the reduce of thefluorescence quantum yield. The mechanism of luminescence of carbon dots obtained by thismethod is attribute to the emission of the surface state. The separated carbon dots and largenanoparticles based on column chromatography, formed by two different mechanisms. Thereis a dehydration reaction occurred for glycerol present in the concentrated sulfuric acid, afterthat, a carbonization nucleation occurred in the process of microwave. In different withglycerol, tributyl phosphate prefer an hydrolysis reaction to be happened first, in thefollowing step is an dehydration reaction, finally a carbonization nucleation occurred in theprocess of microwave.