Luminescent properties of colloidal Ag$_2$S quantum dots for photocatalytic applications

The structural and optical properties of colloidal Ag$_2$S quantum dots in various environments are investigated. With the help of transmission electron microscopy, X-ray diffraction and X-ray energy dispersion analysis, the formation of colloidal Ag$_2$S quantum dots with an average size of 2–3 nm with a monoclinic crystal lattice, and Ag$_2$S/SiO$_2$ core-shell systems based on them, has been established. The change in the luminescence quantum yield of quantum dots with the change of the surface environment state is shown. The decoration of TiO$_2$ nanoparticles of 10–15 nm in size with Ag$_2$S quantum dots was performed and the influence of the structure of the interfaces of quantum dots and their environment (2-mercaptopropionic acid, water, ethylene glycol, SiO$_2$ dielectric shell with a thickness of 0.6 nm and 2.0 nm) on the formation of TiO$_2$-Ag$_2$S heterosystems was analyzed. For Ag$_2$S quantum dots passivated with 2-mercaptopropionic acid, signs of charge phototransfer after adsorption on TiO$_2$ nanoparticles surface have been established. Signs of reactive oxygen species appearance due to charge phototransfer in heterosystem are enstablished, based on methylene blue photobleaching under excitation of heterosystem outside of TiO$_2$ fundamental absorption region,