Green Capped ZnS Quantum Dots: Structural, Optical, Photocatalytic Dye Degradation, and Antimicrobial Studies

ABSTRACT ZnS quantum dots (QDs) and green tea extract–encapsulated ZnS QDs have been synthesized by a simple chemical coprecipitation method. The QDs have been characterized by Fourier transform infrared spectroscopy (FTIR), PXRD, dynamic light scattering (DLS), high resolution transmission electron microscopy (HR‐TEM), scanning electron microscopy (SEM), UV–vis absorption, and luminescence spectroscopic techniques; all these methods confirm a successful encapsulation of the ZnS QDs by green tea extract. PXRD experiment reveals a cubic structure of capped ZnS QD nanocrystals. TEM measurement exhibits that the grain size of bare and encapsulated ZnS QDs are 36.49 and 7.83 nm, respectively. Zeta potential, as determined from DLS experiment, is found to be −10.2 and −16.4 mV for uncapped and capped QDs, respectively, confirming the higher stability of encapsulated ZnS QDs. Sizes of the encapsulated ZnS QDs particles determined by PXRD, DLS, HR‐TEM, and UV–vis electronic spectroscopic methods are found to be 1.54, 439.4, 7.83, and 3.02 nm, respectively. Variation of size determined by different methods has been explained. Overall, 91% photocatalytic degradation of bromocresol green dye has been achieved in 1 h by green tea extract–capped ZnS QDs under solar irradiation. Capped QDs have antibacterial activities toward Staphylococcus aureus and Escherichia coli bacterial strains, and the antibacterial efficiency increases enormously on capping the QDs towards both the bacterial strains.