Synthesis And Characterization Of Novel Photoluminescent Nanoparticles

In recent years, photoluminescent nanomaterials have attracted great attentions due to their wide applications as fluorescent probes in chemical and biological sensors, and in optical elements. Compared with traditional fluorescent dyes, photoluminescent nanomaterials have not only strong fluorescence and good resistance to light bleaching, but also the unique advantages of nanomaterials, such as quantum effects and small size effects, so they can eliminate the shortcomings of traditional fluorescent dyes and bring new development opportunity for the fields including chemistry, physics, biology and medicine. At present, the studies of photoluminescent nanomaterials focus on semiconductor quantum dots and carbon nanodots. Semiconductor quantum dots are extremely popular for their strong fluorescence, small sizes and excellent photostability. Therefore, the research on novel synthetic methods and surface modification protocols of quantum dots has a vital significance. However, the heavy metal ions such as Cd, Pb and Hg in the inorganic quantum dots might be a source of toxicity, development of novel photoluminescent nanomaterials without heavy metals has become a new trend. Therefore, many researchers devote to the exploration of carbon nanodots and organic polymeric photoluminescent nanomaterials owing to their low toxicity and stable chemical property. In this dissertation, novel methods of synthesis, characterization and application of four kinds of photoluminescent nanomaterials were presented. Water soluble alloyed CdTe(S) quantum dots with high quantum yields and surface modified CdTe(S) quantum dots with polymers were successfully prepared via one-step photochemical route. Meanwhile, pure polymeric photoluminescent nanoparticles were synthesized by a single-step sol-thermal method. Carbon nanodots with high quantum yields were prepared by modifying carbon black in a hydrothermal method.The dissertation consists of five chapters.Chapter1:The concept of nanomaterials was introduced. The background of development, methods of synthesis, protocols of surface modification and application of nanomaterials were summarized briefly.Chapter2:A successful synthesis of water soluble CdTe(S) quantum dots with high quantum yields via a mild photochemical route in one step with thioglycolic acid as the stabilizer and sulfur source was described in this chapter. The precursor solution of mixed cadmium chloride, freshly prepared sodium hydrogen telluride and thioglycolic acid was subjected directly to the UV irradiation using a500W high-pressure mercury lamp under the protection of N2. Alloyed CdTeS quantum dots with a smaller particle size (2.2nm) and a high photoluminescence quantum yield (up to80%at room temperature) were formed within25min. The proposed one-step photochemical synthesis is simple and efficient, might be a potential way for the large scale preparation of CdTe(S) quantum dots.Chapter3:Facile one-step photochemical synthesis of surface modified CdTe(S) quantum dots with polymer was developed in this chapter. The grafting and polymerization of monomers was incorporated with the forming of nanocrystals. The modified CdTe(S) quantum dots with high photoluminescence quantum yield (>74%) were synthesized in30min. CdTe(S) quantum dots with colorful photoluminescence from green and yellow to orange and red can be prepared by adjusting the reaction condition. This chapter includes two sections. Quantum dots coated with N-[3-(Dimethylamino) propyl] methacrylamide (DPMA) polymer and polyacrylate were prepared through one-step photochemical methods. MTT assay and E coli assay reveal that surface modified quantum dots are less toxic than pristine quantum dots. Quantum dots modified with DPMA polymer show a sensitive response to pH, implying their application in the pH measurement. Quantum dots coated with polyacrylate were proved to attach to cell membranes of HTB-95637through cell imaging.Chapter4:Pure polymeric nanoparticles with high photoluminescence were synthesized by reaction of melamine and dialdehyde based on Schiff base chemistry. This chapter includes two sections. In the first section, near white-light-emitting polymeric nanoparticles with photoluminescence quantum yield of22%were prepared via reaction of melamine and glyoxal. The polymeric nanoparticles show excitation-tunable emission color, that is, the fluorescence varied from white, green, yellow, to red when excitation wavelength shifted from300nm to530nm. The second section describes another polymeric nanomaterial with green photoluminescence through reaction of melamine and glutaraldehyde.Chapter5:Carbon nanodots with photoluminescence quantum yield of25%were prepared via an economical and mild hydrothermal method using commercial carbon black as the carbon source, nitric acid as the oxidant and glycol as the surface passivation agent. Blue, green, yellow, orange and red fluorescence were observed with the increase of the excitation wavelengths. Carbon dots synthesized in this way could be endocytosed into cell nucleus through cell walls, cell membranes and nuclear membranes readily due to their smaller sizes (2～3nm) and could be used to stain cell nucleus.