Preparation Of Graphene Quantum Dots And The Preliminary Investigation Of Its Application In Electrochemical Sensing

In recent years,environmental pollution has become one of the serious social problems.Among them,the development and establishment of accurate,sensitive and rapid analytical methods for the detection of harmful substances in environmental samples has become one of the key issues in this field.On the other hand,the morden electrochemical sensing techniques based on nano materials chemically modified electrodes have been widely studied and applied in the environmental analysis due to its unique features including high sensitivity,good selectivity,as well as low cost.Moreover,as a new type of carbon nano materials,graphene quantum dots?GQDs?have attracted more and more attention in electrochemical sensing field because of the excellent properties,such as good water solubility,low toxicity,environmental friendly,good biological compatibility,rich surface activity,as well as ease to functionization.In this paper,the preparation methods,characterization techniques,as well as the application of graphene quantum dots in the electrochemical sensing had been firstly reviewd carefully.Based on this,a new method for preparing graphene quantum dots was established by using the graphene oxide as carbon source and hydrogen peroxide as an etchant,respectively.Furthermore,several kinds of chemically modified electrodes based on graphene quantum dots were fabricated through the electrostatic assembly and electrochemical co-deposition techniques.These as-prepared modified electrodes had also been used for the detection of hydrogen peroxide,sulfite,as well as hydrazine in environmental samples.The details are as follows:1.Graphene quantum dots?GQDs?was prepared by simple refluxing method with graphene oxide as carbon source and hydrogen peroxide?H₂O₂?as etchant.It was characterized by fluorescence spectroscopy and transmission electron microscopy?TEM?.The effects of reaction time,H₂O₂ concentration and other experimental conditions on its properties were studied in detail.The results showed that this method had some attractive features such as simple,enevironmental friendly,as well as the ease for the separation and purification.2.The gold nanoparticles-graphene quantum dot-multiwalled carbon nanotubes composite?Au NPs-GQDs-PDDA-MWCNTs?was prepared by the electrostatic assembly and in-situ chemical reduction method.Futhermore,a chemically modified glassy carbon electrode with this composite modified glassy carbon electrode was prepared by dropping method.On the basis of optimizing the preparation conditions,the electrochemical properties and the electrocatalytic activity for H₂O₂ on this modified electrode were studied carefully.The results showed that this modified electrode exhibited strong electrocatalytic activity for H₂O₂ with the synergistic effect of Au NPs,GQDs and MWCNTs.Under the optimized condition,the linear range for the determination of H₂O₂ by amperometry was2.0×10-8 1.5×10-3 mol·L-1,with a detection limit of 8.0×10-9 mol·L-1?3sb?.The sensitivity was 61.6 ?A·m M–1.Compared to other sensors reported previously,the resulting modified electrode exhibited some attractive analytical features such as the wide linear range,low detection limit,as well as the high sensitivity.3.A gold nanoparticles-graphene quantum dots modified glassy carbon electrode?Au NPs-GQDs/GCE?was fabricated by electrochemical co-deposition technique.The surface morphology and the electrochemical behavior of this modified electrode were characterized by scanning electron microscopy?SEM?and electrochemical methods.Furthermore,the electrocatalytic oxidation activity of this modified electrode for sulfite(SO₃^2-)was studied carefully.The results showed that the gold nanoparticles prepared by electrochemical deposition have small size and good dispersibility in the presence of GQDs.With the synergistic action of GQDs and Au NPs,the modified electrode had high catalytic activity for the oxidation of SO₃^2-.Under the optimized conditions,the linear range for the determination of SO₃^2-by amperometry at 0.40 V vs.SCE in B-R buffer?p H4.56?was 2.0 × 10-7 1.4 × 10-3 mol·L-1,with a detection limit of 8.0 × 10-8 mol·L-1?3sb?.The sensitivity was 61.46 ?A·m M–1.The as-prepared Au NPs-GQDs/GCE was used for the determination of SO₃^2-in the local water with the recovery range of 97.6% to 103%.4.A palladium nanoparticles-graphene quantum dots modified glassy carbon electrode?Pd NPs-GQDs/GCE?was fabricated by electrochemical co-deposition technique.The electrochemical properties and the electrocatalytic activity of hydrazine?N₂H₄?on the modified electrode were studied carefully.The results showed that the modified electrode had high electrocatalytic activity for N₂H₄ under the synergistic effect of GQDs and Pd NPs.The linear range for the determination of N₂H₄ by amperometry was 5.0 × 10-8 ¹.8 × 10-3 mol·L-1,with a detection limit of 2.0 × 10-8 mol·L-1?3sb?.The sensitivity was128.3 ?A·m M–1.The modified electrode had the wide linear range,low detection limit and high sensitivity comparing to the sensors reported previously.5.A silver nanoparticles-graphene quantum dots modified glassy carbon electrode?Ag NPs-GQDs/GCE?was prepared by electrochemical co-deposition technique.The electrochemical properties of the modified electrode and its catalytic activity for H₂O₂ were also investigated carefully.The results showed that the modified electrode had high electrocatalytic activity for the reduction of H₂O₂ with the synergistic effect of GQDs and Ag NPs.Under the optimized conditions,the linear range for the determination of H₂O₂ by amperometry was 2.0 × 10-6 2.4 × 10-3 mol·L-1,with a detection limit of 8.0 × 10-7mol·L-1?3sb?and the sensitivity was 114.4 ?A·m M–1,respectively.