Preparation Of Carbon-based Composites For Electrochemical Detection Of Heavy Metal Ions

Environmental pollution by heavy metal ions(HMIs)is a major problem worldwide.Except for a few heavy metal ions(iron,zinc,etc.)that play a vital role in the balance of the human metabolic system,the rest threaten human health.Therefore,finding a fast,high-sensitivity,trace,and economical method for detecting heavy metal ions has attracted the attention of researchers.The electrochemical analysis method has become a hot research because of its simple operation,fast analysis speed,high sensitivity,and cheap equipment.But the bare electrode can only produce limited sensitivity,and the detection performance of the working electrode can be improved by modifying the electrode.This article aims to find a high-performance modification material to achieve the purpose of detecting heavy metal ions in trace amounts.Good electrode performance requires characteristics such as large specific surface area(multiple active sites),excellent electrical conductivity(fast electron transport speed),and high stability(acid,alkali,and corrosion resistance).Therefore,this thesis selects cheap and readily available carbon materials as the research object of this subject.The following aspects of the work are mainly focused on carbon-based materials:1.The applications of carbon-based materials in HMIs for electrochemical detection in recent years are reviewed.The clear ways to obtain high detection performance are:(1)Find new materials or new methods to control the synthesis of new topographic materials;(2)Optimize the detection limit and sensitivity of existing sensors.A new development direction is proposed:enhancing the practicality of electrochemical detection sensors for HMIs,such as developing flexible or wearable sensors that can detect HMIs in human fluids in real time.2.A new and simple method for synthesizing carbon nanospheres was proposed.A monodispersed phenolic resin sphere was synthesized using a hydrothermal method without templates and catalysts,and the corresponding carbon spheres were obtained by high-temperature carbonization.The morphology of carbon spheres was observed by SEM.It was concluded that the newly prepared carbon nanospheres were monodispersed,uniform in particle size and smooth in surface.The average particle diameter of the carbon spheres obtained by this method is about 485 nm.The non-ionic surfactant OP 30 was introduced to reduce the size of carbon spheres,and the diameter of carbon spheres was successfully controlled at 259 nm.The prepared carbon sphere-modified glassy carbon electrode showed good detectability for Cu²⁺and Hg²⁺,and the detection limits were 4.8n M and 12.3 nM,respectively.3.Good chelating agents such as sulfhydryl groups play an important role in the synthesis of gold nanoparticles(Au NPs)or Au-doped carbon nanocomposites.Stable and monodispersed Au NPs embedded in the mesoporous carbon framework were synthesized by the simultaneous carbonization reduction method.Among them,phenolic resin,thiol and HAuCl₄ were used as carbon source,complexing agent and gold source,respectively.The effects of thiol chain length on the particle size and distribution of Au NPs and the size and pore structure of mesoporous carbon materials were systematically studied.By changing the alkyl chain length of the mercapto group,the size of Au NPs(3.71-12.86 nm)was controlled.With the increase of the thiol chain length,the specific surface area of the obtained gold-doped mesoporous carbon material(Au NPs@MPC)was from 1440 m²·g^-1increased to 1603 m²·g^-1.The square wave stripping voltammetry(SWASV)test performed on a typical MPTMS-Au NPs@MPC/GCE modified electrode shows that it has a good detection response to Pb²⁺and the limit detection is as low as 1.96 nM.