Photoelectrochemical Sensor For The Detection Of Heavy Metal Ions

The heavy mental contaminant has been one of the most serious environmental issues due to high toxicity and accumulation.For instance,Pb²⁺has a serious hazard to the health of human,as reflected in intelligence development,skeletal development,indigestion,endocrine disorders,anemia,hypertension,arrhythmia and so on.Hg²⁺can harm the heart,brain,kidney,stomach,and nervous system.Therefore,it is impressively significant to establish a simple and rapid method for the determination of heavy metal ions in environmental surveillance,food security and biological analysis.In recent years,the photoelectrochemical sensors for detection of heavy metal ions were extensively studied and rapidly developed due to its high sensitivity,simple experimental process and easy miniaturization.Quantum dots?QDs?are used as photoelectric active materials because of simple fabrication,low cost,good stability and unique optical properties.In the first part of this thesis,the electrochemical deposition method was compared with ion exchange method for the analytical properties of Pb²⁺.Firstly,thioglycolic acid?TGA?wrapped ZnS QDs were synthesized.Then,TGA-ZnS QDs were self-assembled on the transparent indium tin oxide?ITO?glass through electrostatic interaction between poly dimethyl diallyl ammonium chloride?PDDA?and TGA-ZnS QDs.Pb²⁺was determined by ion exchange method and electrochemical deposition method.Electrochemical deposition method is that sodium thiosulfate?Na₂S₂O₃?was reduced to Sulfur ion(S^2-)by cyclic voltammetry,then PbS nanoparticles deposited on the surface of ITO/ZnS electrode through reaction between S^2-and Pb²⁺.Photocurrent enhanced with the increasing of Pb²⁺concentration.Ion exchange method is that the ITO/ZnS electrode incubated in the buffer solution certain containing of Pb²⁺for a period of time,PbS nanoparticles formed through Pb²⁺reaction with ZnS which deposited on the surface of the electrode to introduce the increase of photocurrent.Comparison of two approaches,we found that the reaction rate of electrochemical deposition method is relatively fast resulting in instability of PbS and the generated PbS is firmly immobilisated on the electrode surface through ion exchange method.Therefore,ion exchange method was used to determine Pb²⁺.In the second part of this thesis,photoelectrochemical sensor based on ion exchange reaction was used to detect low concentration of Hg²⁺through optimizing applied potential,time,temperature,pH,and so on.The photocurrent is linear with the logarithm of mercury ions concentration.The calibration equations were I=11.61+3.87lgC?0.01–30nM?,with a correlation coefficient of 0.9936,and I=112.7+68.95lgC?100–1000nM?,with a correlation coefficient of 0.9917.The detection limit?S/N=3?was estimated to be 2 pM.This sensor has high sensitivity and low detection performance compared with other methods.