Preparation Of Bismuth Modified Microgrid Electrode For Electrochemical Determination Of Heavy Metal Ions

With the rapid development of industry,the induced heavy metal pollution has attracted more and more attention.The in-situ on-site monitoring of heavy metal pollution in water bodies is imperative to ensure the safety of the organisms around water body and the health of human beings.At present,it is routine to take water sample and transport to the laboratory for heavy metals analysis,which have disadvantages of high cost,complicated operation and challenges to detect trace level of heavy metals.In comparison,the electrochemical detection of heavy metals has the advantages of simple operation,high sensitivity and good selectivity,but the size of conventional electrode is difficult to be integrated in small portable devices so that it is difficult to be incorporated to portable electrochemical sensors for in-situ detection of heavy metals.Microlectrodes have been widely used in electrochemical detection because of its fast mass transfer rate,large current density,small time constant,and low iR.The microelectrode array is consisted of a lot of microelectrodes operating in parallel,which is a common type of microelectrode that has been applied in electrochemical.It not only has the electrochemical characteristics of the microelectrodes but also possesses the characteristics of large current signals.However,its application was hindered by the drawbacks of time consuming fabrication process and high processing costs in processing including lithography,etching etc.In this thesis we explored how to simplify the processing steps and reduce the cost while ensuring the excellent detection charactrristic of the microelectrode array for use in portable elecchemical sensors.A conductive film with flat surface was prepared on a PET substrate,a conventional disk electrode system and a microgrid electrode system was fabricated on the conductive film by mechanical engraving technique,and then the electrode array was applied for electrochemical detection of heavy metal ions.The reseach work and major conclusions in this thesis are summarized as follows:1.Carbon materials such as carbon aerogel,conductive graphite powder,carbon black,and acetylene black were used as precursor materials to prepare conductive carbon film by spin-coating on PET plates.Conductive graphite paste and Bi@C material were mixed to prepare conductive film consisting of Bi-doped biomass derived carbon on PET plates,and the properties and performance of the two types of conductive films were characterized.2.Two conventional disk electrode systems were seperatively prepared by mechanical engraving technology on PET substrate covered with two types of conductive films.Cyclic voltammetry and electrochemical impedance experiments were used to evalaate the electrochemical performance of the electrodes prepared from the two conductive films.It showed that Bi-doped biomass carbon material conductive film was more suitable for preparing electrode for electrochemical detection.3.Anodic stripping voltammetry was used for the determination of heavy metals Pb²⁺and Cd²⁺with Bi-doped biomass carbon modified disk electrode.The optimal condition of electrochemical detection was obtained with pH of 4.5,stirring rate of 200 r min^–1,deposition voltage of–1.0 V,and deposition time of 120 s.The detection sensitivity and detection limit of Pb²⁺and Cd²⁺were 0.26?A?g^–11 L,2.03 ppb,and 0.14?A?g^–11 L,3.20ppb respectively,which were detected under optimal detection condition.When two heavy metal ions Pb²⁺and Cd²⁺were simultaneously detected,their detection sensitivity and detection limit were 0.49?A?g^–11 L,2.55 ppb,and 0.16?A?g^–11 L,and 7.29 ppb,respectively.The results showed that the disk electrode prepared from conductive film that is composed of Bi@C material and conductive graphite paste had good detection performance in the detection of heavy metal ions.Meanwhile,the conductive film can be used further for the preparation of microelectrode to detect heavy metal ions with elecchemical method.4.Fabrication of the microgrid electrode with a width of 300?m on PET substrate covered with Bi-doped biomass carbon conductive film was conducted by mechanical micro-engraving technology.Anodic stripping voltammetry was used to detect heavy metal ions Pb²⁺and Cd²⁺in the concentration range of 0–10 ppb.The sensitivity and detection limit of Pb²⁺and Cd²⁺were 0.43?A?g^–11 L,0.927 ppb and 0.07?A?g^–11 L,1.42 ppb,respectively.When these two types of heavy metal ions were detected simultaneously,the detection sensitivity and detection limit of Pb²⁺and Cd²⁺were 0.79?A?g^–11 L,0.992 ppb and 0.17?A?g^–11 L,1.71 ppb,respectively.Compared to the disk electrode,the microgrid electrode demonstrated significantly improved detection performance for Pb²⁺sensing,and it seems a promising detection method for sensing heavy metal ions.Through the research described in this thesis,the preparation process of conductive film was optimized,the preparation process of microelectrode was explored using micro-mechanical engraving technology.This work will shed light on the application of microelectrode in the detection of electrochemical heavy metals,and provide a certain guidance for the in-situ detection of heavy metal in aqueous environment.