Electrochemical Synthesis Of Heteroatom-doped Carbon Quantum Dots And Its Application For Metal Ions Determination

Carbon quantum dots are a kind of fluorescent carbon nanomaterials composed of carbon cores and surface groups.The functional groups can chelate with metal ions to enhance the fluorescence detection capability.The carbon quantum dots prepared by the existing method often need to be further functionalized in order to provide the carbon quantum dot with recognition groups,which complicates the detection process.Heteroatom doping as a simple modification method can introduce abundant groups and adjust band gap,thereby endowing carbon quantum dots with excellent optical and chemical properties.It is important to develop one-step strategy by combining the preparation with the introduction of heteroatoms to prepare carbon quantum dots containing functional groups for efficient fluorescent probes.However,the abundant groups also make its fluorescence susceptible to the acidity and alkalinity,which brings unstable fluorescence characteristics and limits its practical application.Therefore,the efficient preparation of heteroatom-doped carbon quantum dots with specific functional groups and fluorescence stability has attracted a lot of attention.In this paper,two kinds of heteroatom-doped carbon quantum dots with rich groups are prepared by one-step electrochemical strategy using doped porous carbon as the raw material and applied to the detection of metal ions.The specific contents and conclusions are as follows:1.The nitrogen-doped porous carbon(NC)prepared by the template method is used as the raw material,and its porous structure is conducive to the introduction of functional groups.The carbon cloth coated with NC is used as the working electrode.Nitrogen-doped carbon quantum dots(N-CQDs)are prepared by one-step electrochemical method.The N-CQDs with an average particle size of 3.18±0.20 nm emit bright blue fluorescence(QY=10.4%).XPS results show that N-CQDs are endowed with abundant groups,including hydroxyl,carboxyl,pyridine nitrogen,and nitro groups during the oxidation process of NC by hydroxyl radicals.Therefore,N-CQDs has abundant chelation sites and shows a wide linear range(10-1000?M,150?g·m L^-1)with a detection limit of 0.19?M(10?g·m L^-1)in Fe³⁺detection.The method is successfully applied to the determination of spiked tap water.The mechanism study shows that the surface groups generated during electrolysis process can significantly enhance the interaction between N-CQDs and Fe³⁺.Dynamic quenching occurs between N-CQDs and Fe³⁺accompanied with charge transfer.Furthermore,F^-reagent is found to significantly restore the fluorescence intensity of the N-CQDs/Fe³⁺system to 94%.2.The one-step electrochemical strategy was further used to prepare the iron and nitrogen co-doped carbon quantum dots(FeN_x-CQDs)successfully,and the iron and nitrogen co-doped porous carbon(Fe-N-C)prepared by the template method was used as the raw material.FeN_x-CQDs are quasi-spherical particles with an average particle size of 4.86±0.26 nm.They emit bright blue fluorescence with a QY of 7.4%.XPS results show that the surface contains hydroxyl,carboxyl,pyridine nitrogen,FeN_x and nitro groups.The binding of N and Fe endows FeN_x-CQDs with excellent pH tolerance.FeN_x-CQDs are applied to the determination of Cu²⁺with a linear range of 100-1000n M and a detection limit of 0.059?M.It is also applied to the determination of spiked tap water.The mechanism research shows that the dynamic quenching occurs between Cu²⁺and FeN_x-CQDs.The wide band gap caused by Fe doping makes the excited electrons at the LUMO level of FeN_x-CQDs easily escape and promote efficient electron transfer,which is conducive to ion detection.The LUMO level of FeN_x-CQDs is closer to the redox potential of Cu²⁺than N-CQDs,revealing the selectivity of FeN_x-CQDs for Cu²⁺.In addition,the FeN_x-CQDs/Cu²⁺system is not easily interfered by common Cu²⁺chelating reagents and has a stable fluorescence quenching effect.The research provides a new one-step strategy for preparing carbon quantum dots with specific groups and expands the design idea of pH tolerance.There is a comprehensive understanding of heteroatom-doped carbon quantum dots as efficient fluorescent probes.Moreover,the mechanism of ions detection is revealed in depth.