Water solubility, photoluminescence and photocatalytic activity of ZnS quantum dot-sulfonated polystyrene composite

A composite of sulfonated polystyrene with zinc sulfide quantum dot (ZnS QD) was prepared directly in aqueous medium. The partially sulfonated polystyrene (PSS) of sulfonation level, f = 30% hydrogelate in aqueous solution of zinc ions and generate ZnS particles for the formation of PSS-ZnS QD composite. The sulfonated polystyrene (SPS) of sulfonation level, f > 75% behaves as a polyelectrolyte. In aqueous solution, SPS stabilized ZnS particles are synthesized and ultimately form the SPS-ZnS QD composite. PSS-ZnS QD composite is water insoluble and SPS-ZnS QD composite is water soluble. HRTEM images, UV-vis absorption and luminescence of the composites confirm the quantum confinement in ZnS particles. The photoluminescence of the composites predominates in defect state emission relative to band edge emission. Photocatalytic activity of water insoluble PSS-ZnS QD composite in degrading an organic dye is demonstrated. The composite is efficient enough to degrade 84% of methylene blue in 6 h of ultraviolet (UV) illumination. Though water solubility of SPS-ZnS QD limits it use as a photocatalyst, only a limited number of water soluble polymer composites were reported in literature.

Automated summary

In this study, a composite material of sulfonated polystyrene and zinc sulfide quantum dot (ZnS QD) was synthesized directly in an aqueous medium. Partially sulfonated polystyrene (PSS) forms PSS-ZnS QD composite by gelatinizing in an aqueous solution of zinc ions and generating ZnS particles. Fully sulfonated polystyrene (SPS) behaves as a polyelectrolyte and stabilizes ZnS particles, forming the SPS-ZnS QD composite. The PSS-ZnS QD composite is water insoluble and exhibits efficient photocatalytic activity, degrading 84% of methylene blue in 6 hours under ultraviolet illumination. The water solubility of SPS-ZnS QD limits its application as a photocatalyst, but few water-soluble polymer composites have been reported in literature.