A Novel Photoelectrochemical Sensor for Hg2+Detection Based on In-situ Formation of p-n Junction

KeyWord:CdS quantum dots£¨QDs£©  photoelectrochemical sensor  mercury£¨¢ò£© ion  p-n junction

Abstract:

      Water-soluble thioglycollic acid capped CdS quantum dots£¨QDs£© were prepared using a simple method.CdS QDs were assembled on the surface of tin indium oxide£¨ITO£© electrode through the electrostatic interaction between negatively charged thioglycollic acid on the surface of CdS and positively charged poly dimethyl diallyl ammonium£¨PDDA£©.The CdS QDs modified ITO electrode showed a stable anodic photocurrent in the presence of triethanolamine£¨TEA£© as an electron donor£¨or hole scavenger£©.When the CdS QDs modified ITO electrode was immersed in Hg2+solution,an obviously enhanced photocurrent of CdS QDs was observed.The in-situ formation of HgS,a p-type semiconductor,on the surface of n-type CdS semiconductor led to the formation of a p-n junction,which facilitated the charge carrier transport and promoted electron-hole separation,triggered an obviously enhanced anodic photocurrent of CdS QDs.Effects of synthetic conditions such as molar ratio of Cd/S,pH value of reaction solution and reflux time on photoelectrochemical response of CdS QDs to Hg2+were investigated.Effects of pH value of the supporting electrolyte,applied potential and reaction time between CdS and Hg2+on photocurrent enhancement£¨I/I0£© of CdS QDs by Hg2+were also investigated.Based on this,a sensitive Hg2+photoelectrochemical sensor was developed.The sensor showed a linear response to Hg2+in the concentration range of 4.0¡Á10-8-2.0¡Á10-5 mol/L,with a detection limit of 2.4¡Á10-8 mol/L.The method was applied in the detection of Hg2+in lake water samples with recoveries of 98.3%¨C103.5%.