Preparation Of Graphene-based Nanocomposite And Its Construction For Heavy Metal Electrochemical Sensor

A series of environmental pollution problems have emerged with the rapid development of industry and agriculture.Among them,the heavy metal ions pollution is particularly prominent because it is not biodegradable in the environment and even trace concentrations of heavy metal ions can cause detrimental risk to human health.Therefore,it is important to find a simple,fast,and efficient analytical method for heavy metal ions monitoring.Up to now,many strategies have been developed for the analysis of heavy metal ions.Among them,electrochemical method is widely used because of its low cost and simple analytical procedure,high sensitivity and selectivity,and fast analytical speed.Due to its unique structure and morphology,large surface area and special chemical and physical characteristics,graphene（GR）and its derivative are favorable in many fields.Investigation has shown that GR and its derivative have potential in electrochemical determination heavy metal ions because of their excellent electrochemical property when they used as electrode modified material.However,GR and its derivative such as graphene oxide（GO）and reduced graphene oxide（rGO）have some limitations when they used for electrochemical determination heavy metal ions.First,GR and rGO are easily aggregation due to the strongπ-πforce between individual sheets,which was greatly shorten the surface area and conductivity.Although GO contains many oxygen-functional groups which can prevent the aggregation in a certain extent.However,the introduction of oxygen functional groups in GO destroyed some of the conjugated structure in GR and then decreased the conductivity.Whereas the decreased conductivity can sluggish the electron transfer rate during electrochemical determination and weaken the sensitivity.Second,there are none/little functional groups which can form complex with heavy metal ions in GR and rGO,thus the preconcentration of heavy metal ions during electrochemical determination is greatly shortened.Therefore,these two shortages are greatly hidden the performance of GO and rGO when they used for electrochemical determination of heavy metal ions.In order to solve these problems,this paper chose GO and rGO as the starting material to form composite with other materials for heavy metal ions sening,which was not only effectively prevent the aggregation of graphene sheet but also introduce the adsorption and complexation site for graphene-based composite.Specific contents are as follows:（1）Poly（3,4-ethylenedioxythiophene）/graphene oxide（PEDOT/GO）nanocomposite has been prepared via a simple liquid–liquid interfacial polymerization approach.Scanning electron microscopy（SEM）and transmission electron microscope（TEM）were employed to characterize the morphology and structure of the as-prepared PEDOT/GO.The results revealed that PEDOT with a nanorods-like structure anchored on the surface of GO nanosheets,which could enhance the electro-active sites of the nanocomposite.Differential pulse anodic stripping voltammetry（DPASV）was applied to determine low concentrations of Hg²⁺on PEDOT/GO/GCE.Experimental conditions,including deposition time,pH values and deposition potential were optimized.In optimal conditions,a good linear relationship was found between peak currents and the concentration of Hg²⁺in 10.0nM-3.0μM range.The detection limit was estimated to be 2.78 nM at a signal-to-noise ratio of 3.Finally,the applicability for Hg²⁺determination in tap water samples was successfully demonstrated.（2）Co₃O₄/reduced graphene oxide（Co₃O₄/rGO）nanocomposite was synthesized through in situ growth of Co₃O₄ nanoparticles（NPs）on graphene（GO）and subsequent hydrazine reduction process.Scanning electron microscopy（SEM）and transmission electron microscopy（TEM）show that Co₃O₄ NPs with a diameter of around 100 nm are attached on reduced graphene oxide（rGO）sheets.The structures and compositions of Co₃O₄/rGO were further characterized by X-ray photoelectron spectroscopy（XPS）and X-ray diffraction（XRD）.Many experimental parameters,such as pH value,deposition time and deposition potential were optimized.Under optimal conditions,the calibration plot for Pb²⁺,with data acquired at-0.556 V（vs.SCE）is linear in the concentration range from 1.0 to 200.0 nM.Combining the good conductivity and high surface area of rGO,strong Pb²⁺adsorption ability of Co₃O₄NPs,and excellent Pb²⁺complex-forming ability of chitosan,the nanocompsite provides a sensitive Pb²⁺senor with a detection limit of 0.35 nM（S/N=3）.Moreover,the positively charged chitosan can interact with the negatively charged rGO to increase the stability of Co₃O₄/rGO nanocomposite.The hybrid nanocomposite Pb²⁺electrochemical senor provides a new opportunity for vegetable analysis.（3）A green and facile method was used to prepared multi-walled carbon nanotubes/graphene oxide（MWCNTs/GO）,and then polyaniline（PANI）was synthesized via an in situ chemical oxidative polymerization.It is found that the PANI/MWCNT/GO nanocomposite exhibited a good synergetic effect on the electrochemical signal from Pb²⁺,which is more efficient than that of electrodes modified with the individual materials such as PANI or MWCNT/GO.Experimental parameters including the pH value of acetate buffer,the deposition time and deposition potential were optimized.Under the optimal conditions,a good linear relationship between the stripping peak currents and the concentration of Pb²⁺was obtained in the range of 4.0 to 1400.0 nM with a correlation coefficient of 0.9963 and detection limit of 1.3 nM（S/N=3）.Benefiting from the excellent conductivity and good catalytical activity of MWCNT,the large surface area and oxygen functional groups of GO,and the nitrogen-containing groups of PANI,the PANI/MWCNT/GO modified glassy carbon electrode exhibit a sensitive platform for Pb²⁺sensing.The proposed method was also used to electroanalysis of Pb²⁺in lake water with accepted results.