Preparation Of Oxygen Sensing Carbon Dots And Their Application In Vacuum Packaging And Information Encryption

Since 2006,carbon dots(CDs),as a unique class of fluorescent nanomaterial,have attracted increasing interest owing to their excellent properties.With low cytotoxicity,high stability,harmless to environment,low cost and excellent fluorescence property,CDs have showed a diversity of applications in areas such as fluorescence sensing,biological imaging,drug delivery,and photo electrochemistry.At present,a series of CDs have been applied to detect various metal ions,small molecules or biomarkers.However,no CDs has been reported for oxygen detection.At this stage,the field of optical oxygen sensing is occupied by noble-metal phosphorescent materials,However,the shortcomings of these phosphorescent materials are obvious,such as complex preparation processes and expensive raw materials.Thus,developing novel,convenient,economical,and environmentally friendly materials for oxygen sensing is highly desired.This work is aimed at the direction of new oxygen sensing materials.We start from the internal structure of phenylenediamine CDs and aim to develop fluorescent carbon dots with different oxygen sensing modes.The contents are as follows.1.Preparation of fluorescence-switchable carbon dot and the application in vacuum packaging and information encryptionBased on the polymerization of p-phenylenediamine,red-emitting carbon dots(RCDs)with stable fluorescence properties were prepared by solvation thermal method in this chapter.Combined with the related reports of phenylenediamine carbon dots,it is known that phenazine structure exists in RCDs.It has revealed that the phenazine intermediates might be the photoluminescence center of the phenylenediamine derived CDs.Considering the oxidation-reduction properties of phenazine intermediates,the fluorescence of CDs has the potential to be regulated by oxidizing and reducing substances like oxygen gas.Based on the principles,RCDs can be reduced to oxygen sensitive CDs(OCDs)in fluorescence quenching state by reducing agent(Na2S2O4),and reversible detection of oxygen can be realized by OCDs.The response speed of OCDS to oxygen was only 12 s.Based on the reversible process,the fluorescence intensity of RCDs remained above 90%after 7 cycles of reducing agent and oxygen.In addition,it can also be quickly prepared as oxygen sensing test strips,which is convenient to carry and detect.This is the first time to discover the fluorescence emission phenomenon of CDs triggered by molecular oxygen.Compared to the previous "turn off" luminescent detection materials including coordination polymers,nanoclusters and metal-organic framework,the preparation process of CDs used in this work is simple and convenient with the high repetition rate and cheap raw material.What's more attractive is that the fluorescence "turn on"oxygen detection sensor is more benefit for visualization.As a means of rapidly sensing oxygen,this method can be applied in the fields of anaerobic packaging,anaerobic workshop,etc.2.Preparation of ratiometric fluorescent carbon dot and the application in vacuum packaging and information encryptionIn order to develop a new model of oxygen-sensing CDs,the research target is placed on other phenylenediamine carbon dots according to relevant reports.Using ophenylenediamine as the precursor,two kinds of fluorescent CDs are synthesized at the same time through the regulation of reaction conditions.They are the fluorescenceswitchable oxygen sensing CDs and the ratiometric fluorescent oxygen sensing carbon dots.The fluorescence emission position of the two CDs are similar.However,under the action of reducing agent Na2S2O4,the fluorescence changes differently.The fluorescence emission peak at 560 nm of the fluorescence-switchable oxygen sensing CDs disappears directly.The fluorescence emission peak of ratiometric fluorescent CDs is shifted from 555 nm to 480 nm,and the ratio of the fluorescence intensity at 480 nm to that at 555 nm is used to achieve the purpose of ratiometric oxygen sensing.The reduced CDs all have a rapid and reversible response to oxygen.According to this feature,the two CDs can not only be used for anaerobic packaging,but also for encryption and decryption of complex information.