The Impact Of Surface-modification On The Optical Properties Of Carbon Dots

Carbon-based materials,carbon nanotube,graphene,graphyne and carbon dot,have found widespread potential applications in the fields of biosensing,energy and optoelectronic devices because of their unique physical,chemical and optical properties.When compared with other optical materials,carbon dots have features of excitation-dependent emission profiles and transition feasibility from fluorescence to phosphorescence upon additional treatment.These features have aroused considerable attention in the scientific community.The objective this thesis is to demonstrate the impact of surface modification on the optical properties of carbon dots and further on their applications in the fields of information storage.Part 1.Simultaneous and reversible triggering of the phase transfer and luminescence change of amidine-modified carbon dots by CO₂.The majority of the reported smart carbon dots only showed one corresponding changes in their attributes upon the stimulation of pH,temperature and light.The objective of this work is to develop dual-response carbon dots upon the stimulation of CO₂.The results show that the reaction of N,N-dimethylacetamide dimethyl acetal?DMADMA?with amino-enriched carbon dots allows the preparation of amidine-modified carbon dots.The as-prepared amidine-modified carbon dots show the simultaneous and reversible changes in phase and luminescence upon triggering of CO₂.The mechanistic studies suggest that the CO₂ bubbles not only can react with the amidine groups on the surface of the carbon dots but also lead to the increase in the acidity of the dispersion.The later factor accounts for the luminescence of the carbon dots.By making use of the carbon dots as inks,a two-dimensional covert pattern can be created,which also shows reversible luminescence change under the action of CO₂/N₂.These findings suggest the potential application of the as-modified carbon dots in the field of anti-counterfeiting.Part 2.Stabilizing the phosphorescence of carbon dots in SiO₂ through hydrothermal sintering for anti-counterfeiting.Carbon dots afforded by carbonization of organic molecules upon the use of special methods sometime show phosphorescence.However,the phosphorescence is susceptible to a lot quenchers,including molecules and heavy metal ions,limiting their applications in the fields of bioimaging and information encoding.In this work,carbon dots were first prepared a microwave-assisted method followed by SiO₂ passivation via hydrolysis of tetraethyl orthosilicate.The obtained carbon dot@SiO₂ nanocomposites were hydrothermally treated at 160 oC for 2 h.The result show that upon the hydrothermal treatment,the lifetime of the phosphorescence was prolonged from 0.680 to 1.3 s in an aqueous dispersion.More importantly,the phosphorescence was found to show high resistance to the quenching effect of Fe3+ions,as supported by the fact that the lifetime of the phosphorescence can be almost preserved in the presence of Fe³⁺at a concentration of12 mM.By compassion,a considerable quenching effect was observed for the case of untreated carbon dot@SiO₂.The observed difference can be attributed to the improved passivation effect of the resultant Si O₂ host matrices due to the addition reactions between Si-OH groups and also an enhanced fixation effect between the SiO₂ and the carbon dots as a result of reaction between Si-OH and–OH on the surface of the carbon dots.The improved optical properties allow the as-prepared carbon dot@SiO₂ nanocomposites to find application in anti-counterfeiting.