In this study, zinc sulfide nanoparticles (ZnS NPs) and zinc sulfide @ Silver sulfide core-shells (ZnS@Ag2S NPs) were prepared using the green method with mint leaf extract as a reducing and coating agent, at varying concentrations of silver nitrate (AgNO3) (0.005, 0.01, and 0.02 M). X-ray diffraction analysis (XRD) results showed the formation of a cubic phase of ZnS NPs and a monoclinic phase of Ag2S with increasing silver nitrate concentration. The average crystalline size of ZnS NPs was calculated to be 2.01 nm and (2.78, 2.65, and 2.13 nm) after Ag2S formation, while the shell (Ag2S) was found to be (7.47, 5.89, and 3.83 nm). Transmission Electron Microscopy (TEM) analysis revealed the formation of an Ag2S shell around ZnS, with the shell becoming more uniform at the silver nitrate concentration (0.01 M). Energy Dispersive X-Ray (EDX) analysis showed the presence of the core’s main elements, zinc and sulfur, and an increase in silver (Ag) content with increasing silver nitrate concentration in the core-shells. Fourier Transform Infrared Analysis (FTIR) results showed vibrational frequencies belonging to the organic compounds of the plant extract, in addition to the appearance of zinc-sulfur bonds and peaks between 450 and 900 cm−1 indicating S-Ag-related vibrations. Finally, UV-Visible results showed an improvement in UV absorption capacity with increasing silver nitrate concentration. The optical energy gap of ZnS NPs was approximately 3.77 eV, while it was 3.61, 3.72, and 3.74 eV for ZnS@Ag2S NPs at different concentrations of silver nitrate (0.005, 0.01, and 0.02 M), respectively.
Ulwali et al. (Thu,) studied this question.