Preparation Of Fluorescent CdTe@SiO₂ Microsphere For Detection Heavy Metals In Aqueous Solutions

Polymer microspheres have gained increasing attention due to their unique size and morphology. Nowadays, the preparation of polymer microspheres was relatively mature, and the particle size can be synthesized from a few nanometers to several hundred microns. The preparing methods of fluorescent microsphere included physical methods and chemical methods. The polymer microspheres were used in many fields such as cell separation, DNA detection, protein detection, bio-labeling, drug screening, et al. According to different classification standars, polymer microspheres can be divided into various categories. Among them, many scholars pay more attention to fluorescent microspheres due to their monodispersity, uiform particle and photochemical stability. According to the carrier microspheres and fluorescent material, fluorescent microspheres can be divided into three categories, and nanocrystals@silica materials attracted many researchers by their advantages.In this paper, the remodeled sol-gel process was used to hydrolyze MPTMS and prepare monodisperse silica particles with micrometer length at low temperature. Then the effects on the amount of MPTMS, the string rate, the amount of ammonia and the amount of electrolyte on the particle size and the dispersion were also discussed. The results show that as the concentration of MPTMS increases, the particle diameter increases gradually, the amount of MPTMS are 100 μL and 300 μL, highly monodisperse silica particles are obtained. Then the size of particle tends to increase depending on the increase of stiring rate, when the stirring rate is 500 rpm, the silica has narrow size distribution. With the increasing concentration of ammonia,the particle size decreases, and there is no noticeable change in diapersion when the amount of ammonia are 50 μL and 100 μL. The particle size decresses when the concentration of KCl increases.The aqueous CdTe QDs capped with 3-mercaptopropionic acid(MPA) and 3-Mercaptopropyl trimethoxysilane(MPTMS) were used as organosilane to synthesis fluorescent microspheres, and the ligand exchange of MPA and MPTMS is beneficial to improve the fluorescent intensity and stability of fluorescent CdTe@SiO2microsphere. CdTe QDs were mixed with ethanol, when the ratio of ethanol to QDs is 3:7, highly monodisperse fluorescent microspheres were obtained. Based on this research, we explored the impact of reaction temperature and stiring rate on the result of the experiment. With the increasing of the reaction temperature, particles size of microspheres decrease. When the stirring rate increase, the particle size increase firstly, however, there is no obvious change when we continue to increase string speed. Fluorescence spectrum(PL), X-ray diffraction(XRD), high resolution transmission electron microscopy(HRTEM), energy spectrum analysis(EDS) were utilized to prove that CdTe QDs are encapsulated into silica sphere, what’s more, raman analysis and FTIR analysis were used to found that there are so many thiol groups on the surface of CdTe@SiO2 microsphere.Fluorescent CdTe@SiO2 microspheres were used to adsorb heavy metals, the adsorption kinetics were discussed firstly, the results show that the fluorescent CdTe@SiO2 microsphere could adsorb Ag(I), Pb(II), Cu(II) quickly, and the equilibrium are reached in a short time. With the addition of metal ions(Ag(I), Pb(II), Cu(II)), the fluorescence intensity decreased. When the concentration of heavy metals reaches a certain value, fluorescence intensity has not noticeably altered, which suggested that CdTe@SiO2 fluorescent microsphere reach maximum adsorption for heavy metals. In addition, the fluorescence intensity decreased linearly in low concentrations of metal ions. The saturated adsorption capacity(Qmax) of fluorescent CdTe@SiO2 microsphere of Ag(I), Pb(II), Cu(II) are different, and the saturated adsorption capacity(Qmax) of Ag(I) is high.