Study On The Synthesis And Optical Properties Of Functionalized Carbon Dots

Semiconductor quantum dots?QDs?are known for their unique optical properties.In recent years,carbon nanomaterials of surface and/or structural defects have been found to exhibit similar properties after functionalization in various schemes.Among these carbon-based QDs are carbon quantum dots?carbon dots?,which are generally defined as small carbon nanoparticles with surface passivation.In fact,carbon dots now represent a rapidly advancing and expanding research field.As measured by the optical properties of carbon dots,the most effective passivation has been the surface functionalization of carbon nanoparticles with organic or polymeric molecules,corresponding to much brighter fluorescence emissions across the visible spectrum and extending into the near-IR.Therefore,carbon dots have been pursued extensively for potential bioimaging and other biomedical applications.The mechanistic framework for carbon dots included photoinduced redox processes,similar to those found in conventional semiconductor QDs.As a result,carbon dots have also been pursued for their photocatalytic functions.In this article on surface-functionalized carbon dots and their derived particles,their representative syntheses and demonstrated properties and their potential uses are highlighted as follows:1.Oxidized carbon dots were synthesized through a ultrasonication assisted oxidation process at low temperature using graphite as precursor.The oxidation degree on the carbon dots is correlated with the ultrasonication power.Further investigation found that the emission of carbon dots exhibited red-shifted behavior with the increasing of the oxidation degree,thus the optical properties of carbon dots can be controlled by modulating their oxidation degree.2.Polyethyleneimine functionalized carbon dots?CDots?were prepared by thermally induced functionalization of pre-processed and selected carbon nanoparticles.This method combines advantages of carbonization method and deliberated chemical functionalization method,yielding carbon dots with similar optical absorption and fluorescence properties to those from deliberated chemical functionalization.The similarity in the photoexcited state is also reflected in the observed visible light-activated bactericidal functions of the PEI-carbon dots.3.A simple yet consequential modification was made to the popular carbonization processing of citric acid-polyethylenimine precursor mixtures to produce carbon dots.The modification was primarily on pushing the carbonization processing a little harder at a higher temperature.The CDots thus produce are in accord with the definition of carbon dots.Equally significant is the finding that the modified processing method could yield CDots of record-setting fluorescence performance,approaching the upper limit of being quantitatively fluorescent.4.The red/near-IR emissive dye nile blue?NB?was selected as the guest,and NB@CDots were prepared in a microwave assisted one-pot thermal carbonization synthesis with polyethylene glycols as the precursor and also surface passivation species in the resulting host-guest dots.The NB@CDots exhibited unique and favorable characteristics,including especially the bright red/near-IR fluorescence emissions,with the observed fluorescence quantum yield due to the guest nile blue species more than an order of magnitude higher than that of free nile blue molecules,all in aqueous solutions.The higher fluorescence intensities were coupled with a longer fluorescence lifetime,and also accompanied by excellent photochemical stability,making the NB@CDots high-performance fluorescence probes for bioimaging of live stem cells.5.The carbon/Fe₃O₄ hybrid dots with oligomeric polyethylene glycol or polyethylenimine for surface functionalization and passivation were prepared in a facile thermal carbonization synthesis with microwave energy,coupled with magnetic separation,building upon the basic structural configuration of carbon dots,iron oxide was introduced for both magnetic and fluorescence properties in the resulting hybrid dots,thus more capabilities beyond those of neat carbon dots.The dots structures,compositions and optical properties were investigated for a view of the configurations in the hybrid dots.