Photoluminescent Carbon Dots Fabrication And Application

Carbon dots,as an emerging "environment-friendly" nanomaterials,have aroused profound interest due to their low toxicity,excellent optical performance,high light stability and environmental friendliness,which is widely used in chemical sensor,biological imaging,photochemical catalysis,document security,light emitting devices and so on.So far,most of reported carbon dots only mainly limited to the short-wave region(blue and green),and it is hard to prepare long-wavelength(i.e.yellow and red regions)emitting carbon dots.Meanwhile,most of reported focus only on the fluorescence properties of carbon dots.Therefore,it is urgent to develop long-wavelength(yellow,red,and near-infrared)carbon dots and synthesize carbon dots with phosphorescent properties.In view of the above problems,four kinds of multifunctional carbon dots with excellent fluorescence and RTP properties were prepared.After the analysis of their properties,they were applied to the detection of metal ion,amino acid and information security.The details are as follows:Chapter 1: The structure,luminescence properties and synthesis methods of carbon dots are reviewed.The luminescence mechanism and luminescence property control of carbon dots are summarized.Firstly,we the structure,luminescence properties and synthesis methods of carbon dots.We outlined application of carbon dots in metal ion,biological small molecule detection and optical anti-counterfeiting luminescence.Chapter 2: Carbon dots(CDs)were prepared by one step hydrothermal treatment of phenylenediamine and phosphoric acid.The as-prepared CDs exhibit not only exceedingly optical stability,but also excellent biocompatibility and biolabeling potentials.The fluorescence of CDs can be extinguished dramatically with Cr(VI).After the addition of Cys,the fluorescence of CDs was restored due to the complexation between Cr(VI)and Cys that leads Cr(VI)to escape from the surface of CDs.The probe displayed high selectivity and sensitivity toward Cr(VI)and Cys over other analytes with a low detection limit of 0.26 ?M and 0.14 ?M,respectively.Simultaneously,the color of the CDs solution was changed(red-purple-yellow)along with the fluorescence signal of the CDs and CDs can be used as a dual response signal sensor.An "AND" logic gate for red-emitting CDs has been constructed.The dual-mode detection of CDs are more reliable than the single-mode detection results,and the red fluorescence emission is more advantageous than the short-wave detection in the biological field.Chapter 3: Nitrogen-doped carbon dots(NCDs)were prepared by oil bath heated of glucose and L-aspartic acid.The synthesized NCDs can realize room temperature phosphorescence(RTP)without any matrix.The NCDs are composed of a core and hydrophilic surface of polyaspartic acid chains arising from high-temperature polymerization.By further observation,it was found that more nitrogen doping was beneficial to RTP.The obtained NCDs have an ultralong phosphorescence lifetime of 747 ms and a high quantum yield of 35% under 320 nm excitation in air.In addition,RTP quenching will occur when NCDs are in aqueous solution.Based on this feature,a novel strategy is designed for information security.This result expands the application of carbon dots in optical anti-counterfeiting.Chapter 4: The CDs of were synthesized from diethylene triamine pentaacetic acid by one-step hydrothermal treatment diethylenetriaminepentaacetic acid.The synthesized CDs have URTP lifetime of 1.51 s which is a relatively long life RTP lifetime ever reported.Furthermore,it is revealed that the dense core of CDs,the formation of long-chain polymers on the surface,and the presence of hydrogen bond skeleton play a crucial role in the production of URTP.Also,the introduction of the N element is a critical factor in the URTP synthesis as it promotes the n–?* transition and facilitates intersystem crossing(ISC)such that the triplet state is filled with effective excitons.Notably,the CDs demonstrate URTP properties under the excitation of 365 UV light and exhibit URTP under the excitation of visible light.This is first report of visible-light-excited URTP based on CDs.Considering this excellent property,URTP CDs may be applied in the field of anticounterfeiting.Chapter 5: A strategy was presented that effectively promotes the presence of RTP of CDs in aqueous solutions by utilizing CDs and melamine to construct hydrogen-bonded networks to form a polymer(M-CDs).The obtained M-CDs not only enjoy an ultralong phosphorescence lifetime of 664 ms,but also relatively high quantum yield of 25%.This is also first example of achieving RTP of CDs with a solid state in an aqueous environment.Further investigations reveal that the hydrogen-bonded networks are critical to the implementation of RTP in an aqueous environment.The existence of covalent bonds in CDs and melamine further stabilizes the hydrogen-bond skeleton and triplet state.Furthermore,the bound water formed inside the M-CDs also plays an indispensable role in stabilizing the RTP in the aqueous solution.Given the feature,the M-CDs are used to effectively implement double data encryption and decryption.In addition,this strategy is universal for most phosphorescence materials.This novel strategy provides a new idea for the synthesis of RTP materials.