Preparation And Properties Of Two Kinds Of Surface Coated Carbon Dots

Since the discovery of carbon dots(CDs)from single-walled carbon nanotubes(SWCNTs)in 2004,it has great potential application value in optoelectronic devices,biomedicine,chemical detection and anti-counterfeiting security owing to its wide source of raw materials,excellent optical properties,low toxicity and bio friendliness.However,how to achieve stable luminescence of CDs in aqueous solution is still a challenge.At present,with the rapid development of science,technology and the acceleration of industrial production,there are a lot of harmful substances in wastewater and farmland,such as explosives and metal ions,which are not conducive to the sustainable development of life.Luminescent materials are widely used in the detection of metal ions and explosives due to their sensitive response to harmful substances.Therefore,it is still a challenge to realize the stable luminescence of CDs in aqueous solution and at the same time for further high-sensitivity detection.Metal free organic room temperature phosphorescent(RTP)materials have attracted more and more attention in recent years due to their advantages of easy processing,low cost and long lifetime.At present,RTP materials can be used in fields such as bioimaging,light-emitting devices,photocatalysis,and security anti-counterfeiting.There are two ways to realize RTP:(1)by enhancing the spin-orbit coupling to promote the intersystem crossing of singlet-triplet excited states;(2)inhibiting the non-radiative transition of the triplet state,thereby reducing the triplet excitons inactivated.However,the excited triplet state is easily quenched in an aerobic and water-containing environment,which limits the application of current organic RTP materials to a large extent.In this thesis,CDs are encapsulated by polymer coating and small molecule crystals to achieve stable luminescence of CDs in aqueous solution.The specific content includes:(1)The red emitting CDs derived from p-phenylenediamine were used as raw materials.Inspired by mussel,a kind of polydopamine nano coating was constructed on the CDs surface through composite oxidation,self-polymerization and assembly of dopamine monomers.The multi-color polydopamine encapsulated CDs were realized(CDs@PDA).The coating structure on CDs endows red emitting CDs with stable fluorescence properties in aqueous environment.In particular,CDs@PDA obtained in water/ethanol solvent exhibit interesting double fluorescence emission at 330 nm and640 nm when the excitation wavelength is 285 nm.This dual-fluorescence CDs system has a wide linear detection range.The detection lines of deep purple light and red light for 4-NP are 3.44?M and 7.29?M,and the detection lines for Fe³⁺are 3.75?M and5.82?M,respectively.This study not only obtained CDs with long wavelength polychromatic emission,but also broadened the stable application of red fluorescent CDs in water environment.This work provides a new idea for the further research and application of red CDs in water.(2)A one-step hydrothermal method was used to embed citric acid(CA)-derived CDs into melamine(MA)-derived crystals to construct a composite material with RTP(CACDs-MA).CACDs-MA has an ultra-long phosphorescence lifetime of 760 ms under excitation at 270 nm and a high absolute QY(11.24%).And it has strong and stable RTP emission in organic solution and p H=1 or 14 aqueous solution.Studies have shown that CACDs were embedded in MA-derived crystals through covalent cross-linking,which hinders vibration and rotation of chromophore and promotes stable emission of phosphorescence.In addition,the hydrogen bonds formed in the composite material may also play an important role in the generation of RTP.Based on this ultra-stable RTP characteristics,the prepared composite material can be successfully applied to solid and liquid anti-counterfeiting security.Therefore,the emergence of this material provides a larger development platform for expanding the application of RTP materials under harsh conditions.