Morphology-controlled Synthesis Of Fe₂O₃-expanded Graphite Composites For Electrochemical Sensing Application

Iron oxide(Fe₂O₃)has attracted much attention due to the advantages of high catalytic activity,high stability,low cost,easy access,environmental friendliness and easy regulation of morphology and structure.However,the poor conductivity and the easy agglomeration of Fe₂O₃ nanoparticles greatly limit the superior performance and its application in electrochemical sensing.Expanded graphite(EG)possesses many advantages,such as large specific surface area,good conductivity,high surface activity,high chemical stability and simple preparation,but it is seldom used in electrochemical sensing.In this work,we focused on the preparation of the composites of Fe₂O₃with different morphologies and EG,the influence of the morphology on the sensing performance and then the electrochemical sensing performance toward organic pollutants.The research work of this thesis mainly contains the following three parts:(1)Organic pollutants are highly biological toxicity to public health and environments.Their sensitive detection is highly required.Herein,a new electrochemical interface for sensitive and selective minoring of tetrabromobisphenol A(TBBPA),sunset yellow(SY),and tartrazine(Tr)is then developed with the composite of Fe₂O₃ nanomaterials and expanded graphite(EG)as the sensing materials.Three Fe₂O₃ nanomaterials,synthesized via a hydrothermal method,feature the morphologies of nanoplate,nanorod,and a three-dimensional flower-like(f-Fe₂O₃)structure.Electrochemical activity of these nanocomposites is found to be dependent on the morphology of synthesized Fe₂O₃ nanomaterials.The composite of f-Fe₂O₃/EG displays the biggest electrochemical active area and the lowest electron transfer resistance towards redox probes,due to a 3D porous hierarchical structure of f-Fe₂O₃ and a high conductivity of EG.The best sensing performance of three pollutants was thus achieved on this composite coated electrode with a limit of detection of 1.23,0.89 and 2.17 n M for TBBPA,SY,and Tr,respectively(2)Using FeCl₃ as the Fe source and EG as the carbon substrate,EG supported with Fe₂O₃cubes with different sizes(20 nm,50 nm and 80 nm,)were readily prepared by changing the concentration of FeCl₃ via hydrothermal reaction.The composites were denoted as 20-Fe₂O₃/EG,50-Fe₂O₃/EG and 80-Fe₂O₃/EG,respectively.The electrochemical behaviors of hydroquinone(HQ),catechol(CC)and resorcin(RC)were studied on these EG and Fe₂O₃/EG composites modified electrodes.Electrochemical study showed that the three dihydroxybenzene isomers can be catalytically oxidized and discriminated simultaneously on these electrodes.Owing to the integrated superior conductivity and excellent catalytic property of Fe₂O₃/EG composites,the electrochemical reactivity of the prepared Fe₂O₃/EG composites toward the oxidation of HQ,CC and RC were enhanced compared with that of EG.The 50-Fe₂O₃/EG were more sensitive for the oxidation of HQ,CC and RC,and significantly enhanced the oxidation signals of HQ,CC and RC.The differences of electron transfer rate and accumulation efficiency were the dominant reason for different signal enhancement abilities of Fe₂O₃/EG.Thereafter,an electrochemical platform was established for the simultaneous detection of HQ,CC and RC based on 50-Fe₂O₃/EG/GCE,with the detection limits of 25 nmol/L,11 nmol/L and 340 nmol/L,respectively.The detection of them in water samples were also successfully performed and good recovery was obtained.(3)It is essential to develop a simple,fast,sensitive and accurate method for the detection and quantitative analysis of 2,4-dichlorophenol(2,4-DCP)due to its high toxicity and wide existence in the environment.In this work,a novel 2,4-DCP electrochemical sensor was fabricated based on a50-Fe₂O₃/EG composite modified glassy carbon electrode.It was found that50-Fe₂O₃/EG composite exhibited excellent electrocatalytic activity towards the oxidation of 2,4-DCP.The signal enhancement mechanism for 2,4-DCP was studied using chronocoulometry revealing that the prepared 50-Fe₂O₃/EG effectively improve the surface adsorption efficiency of 2,4-DCP.The influences of p H value,amount of Fe₂O₃ nanocube/EG composite and accumulation time were examined.Under the optimum conditions,the peak current of 2,4-DCP was proportional to its concentration at the range of 0.08to 20?mol/L with a detection limit 27 nmol/L.The newly developed method was successfully applied for the determination of 2,4-DCP in different water samples,and the recovery was over the range from 97.70%to 102.88%.