Synthesis And Surface Modification Of Water-souble ZnS:Mn Nanoparticles As Fluorescent Sensor For Heavy Metal Ions

Since the time of industrial revolution, the heavy metal elements exist in thenature in various forms with the development of industry and urban construction.Although some of the heavy metal elements are the trace elements that are necessaryto life, when the content of heavy metal exceed a certain limit, they can produceserious harm to our human life. With the development of industry, the harm of heavymetal pollution to the environment was paid much attention, and it is becoming a hotissue which is concerned by the world. For the heavy metal ions in waterenvironment, the detection methods can be summarized as the following, atomicabsorption spectrometry, electrochemical analysis, inductively coupled plasma massspectrometry, liquid chromatography, etc. But in general all these methods exist thedrawback of expensive cost, large equipment for support, complex detection stepsand low detection limit.Comparing with the traditional organic dyes the quantum dots have someunique advantages on fluorescent properties, such as the narrow and symmetricalemission spectrum, higher quantum yield. These properties of the QDs had beentaken much attention on the applications in chemical analysis, biological medicine,and solar cell. Reports of the application on heavy metal detection are also becomingmore and more. But the first important question that we met is the fluorescentstability and colloid stability. If we can choose a proper coating on the quantum dots,it will improve the detection of heavy metal ions in the complex water environment.And if the QDs are modified with different functional ligand, it may be selective todifferent heavy metal ions. The common way of modify are the shell coating andfunctionalized macromolecule. The shell coating on the QDs usually have higherband gap. This method can improve the quantum yield and the stability of the fluorescence. With the modification of functional polymer, the QDs might have gooddispersion performance and biocompatibility. In our investigation, we prepared theZnS:Mn QDs with robust and inert SiO2coating, and then a electronegative PVPcoating was introduced. The two types of nanoparticals were used in the detection ofCu2+and Pb2+in sea water respectively.The main results of this paper are as following:1) A type of monodisperse ZnS:Mn/SiO2nanoparticles which contain a ZnS:Mncore inside were prepared. The ZnS:Mn/SiO2nanoparticles have s good stability insea water. Then some factors that may influence the Cu2+detection in sea water wereinvestigated. After that the fluorescence quenching of the emission peak at585nm ofZnS:Mn/SiO2was used to detect the concentration of Cu2+in sea water. Thedetection limit is as low as6*10-8mol/L, thus affording a very sensitive fluorescentsensor for the Cu2+detection in sea water. Then the detection mechanism isdiscussed.2) A type of nanoparticle which is coating with PVP was prepared, basing onthe ZnS:Mn/SiO2synthesized in the first step. The IR, TEM and PL are used tocharacterize the morphology and fluorescence properties of the ZnS:Mn/SiO2/PVP.The products have a good fluorescent and colloid stability in sea water. After that thefluorescence quenching of the emission peak at585nm of ZnS:Mn/SiO2/PVP wasused to detect the concentration of Pb2+in sea water. The detection limit is as low as2*10-7mol/L, thus affording a very sensitive fluorescent sensor for the Pb2+detection in sea water. Then the possible detection mechanism is discussed.