Fluorescence Properties Between Novel Water-soluble Cadmium Sulfide Quantum Dots And Copper Ions

Semiconductor quantum dots(QDs)have unique optical and electronic properties,such as the size-dependent bandgap energy,broad excitation spectra,narrow symmetric and tunable emission spectra.CdS is a typical semiconductor of the IIB-VIA semiconductor,and belongs to direct transition semiconductor with a band gap of 2.42 eV at room temperature with an exciton Bohr radius of 2.4 nm.In recent years,it has been widely studied in the detection of heavy metal ions and biological small molecules due to its high quantum yield,easy functionalization and excellent fluorescence performance.However,the problem of itself toxicity of CdS QDs has cast doubts on its practical use in fluorescence sensors.One promising solution to this problem is that QDs can be capped with non-toxic surfactant to reduce toxicity.First,respectively citric acid,L-cysteine,N-acetyl-L-cysteine and cysteamine hydrochloride as surface modification agent,via hydrothermal method to prepare water soluble CdS QDs with low toxicity.Then,the structure,morphology and surface functional groups of the obtained CdS QDs are characterized by XRD,Raman.AFM,TEM.XPS and FTIR.Results show that four kinds of CdS QDs have been synthesized via a simple hydrothermal method.The four CdS QDs are cubic structure with clearly lattice fringe,and the dispersion of cysteamine hydrochloride modified CdS QDs is outstanding.UV-visible absorption spectrum,fluorescence spectrum and CIE color coordinates are used to characterize the optical properties of four CdS QDs.The study found that cysteamine hydrochloride modified CdS QDs exhibit good stability with a high quantum yield of 34.31%.Next,the CdS QDs demonstrated as a selective fluorescence probes for Cu2+detection in water based on fluorescence quenching.As a Result,cysteamine hydrochloride modified CdS QDs as fluorescence probes for Cu2+ possessing many advantages,such as high selectivity,strong anti-interference,good linear relationship and extensive detection range.Under optimal conditions,a linear relationship between the fluorescence response and the concentration of Cu2+ was established in the range of 0.01-50 ?M,the limit of detection of Cu2+ was found to be 8.3 nM.In addition,the feasibility of the proposed sensor for determining Cu2+ real water samples was also studied,and satisfactory results were obtained.Lastly,XPS?TEM?UV-vis absorption spectra and the fluorescence lifetime decay curve are used to analyze the mechanism between CdS QDs and Cu2+.