CdS quantum dots capped with hyperbranched graft copolymers: Role of hyperbranched shell in fluorescence and selective mercury-sensing

摘要

A series of hyperbranched graft copolymers with hyperbranched polyethylenimine (HPEI) as core and hyperbranched polyglycerol (HPG) as shell (HPEI-g-HPG) were used as nanoreactors and stabilizers for the synthesis of CdS quantum dots (QDs). The preparation conditions were optimized to obtain CdS QDs with a stronger fluorescence. Stable CdS QDs could be prepared by using HPEI-g-HPGs or HPEI homopolymer, but not HPG homopolymer. The CdS QDs capped by HPEI-g-HPGs emitted stronger than those capped by HPEI. Moreover, the photoluminescence intensity increased pronouncedly with increasing the HPG shell content of HPEI-g-HPG stabilizer. The measurements of UV-vis spectroscopy, transmission electron microscopy and dynamic light scattering further verified the formation of CdS QDs. Compared with the CdS QDs capped by HPEI, those capped by HPEI-g-HPGs showed a better storing stability in solution at 4℃ The as-prepared CdS QDs were only stable in the pH range of 7.0-9.0. It was found that increasing the HPG shell content of HPEI-g-HPG stabilizer could effectively raise the selectivity of the as-prepared CdS QDs towards Hg~(2+). As the ratiometric fluorescence sensors, CdS QDs capped by HPEI-g-HPGs were most sensitive to Hg~(2+) and the limit of detection was ca. 1.5 × 10~(-8) M.