Rapid sonochemical water-based synthesis of functionalized zinc sulfide quantum dots: Study of capping agent effect on photocatalytic activity

This study presents a rapid water-based chemical precipitation method for synthesis of zinc sulfide (ZnS) quantum dots (QDs), under the ultrasonic radiation, using two capping agents; including 2-mercaptoethanol and l-cysteine. It is demonstrated that by applying ultrasonic radiation, the synthesis time can be significantly decreased. The effect of capping agent type on the color specifications (using colorimetry), absorption spectra (using ultraviolet-visible absorption spectroscopy) and ZnS structure (using X-ray diffraction) are investigated. The results of the research indicate that the as-synthesized QDs were cubic structures with dimensions less than 10 nm. After characterization, the QDs samples were performed as nano-scaled photoatalysts, through a UV-driven photodegradation process for the degradation of crystalline violet (CV) as a pollutant dye. Moreover, the present study assesses the effect of operating conditions including the pH of the dye solution, UV-irradiation time, ionic strength, type and dosage of nanophotocatalyst on degradation efficiency. Experimental results of the research demonstrate the QDs can be reused for at-least five times, without a significant decrease in their photocatalytic properties. The maximum photodegradation efficiency for the CV solution adjusted at pH 11, in the presence of a low amount of QDs (i.e. 5 mg) was observed after 90 min irradiation time. Finally, the probable mechanism and kinetics of degradation reaction are proposed in the study. From the kinetic data, the acceptable regression coefficient values (> 0.98) for the pseudo first-order kinetic model was obtained for expression the present QD-based photodegradation approach.