Ag2S silver sulfide nanoparticles and colloidal solutions: Synthesis and properties

Powders of silver sulfide Ag2S have been synthesized by hydrochemical bath deposition from aqueous solutions of silver nitrate and sodium sulfide in the presence of sodium citrate or EDTA-H2Na2. Colloidal non-toxic solutions of Ag2S nanoparticles have been prepared by chemical condensation method from the same aqueous solutions. The size of silver sulfide particles in deposited powders and colloidal solutions has been estimated with the use of X-ray diffraction, dynamic light scattering, transmission electron microscopy and Brunauer–Emmett–Teller techniques. By varying the ratio between the concentrations of reagents in the initial reaction mixtures it is possible to deposit Ag2S nanoparticles with pre-assigned average size ranging in the interval from about 500 nm down to about 40 nm. The average size of silver sulfide Ag2S nanoparticles in stable colloidal solutions is equal 10–20 nm. Special attention has been devoted to investigation of stability of synthesized colloidal solutions on the duration of their storage. The UV–Vis absorption spectra of colloidal solutions and optical reflectance of nanopowders of silver sulfide have been studied. Decreasing of average size of Ag2S nanoparticles from ∼500 nm down to ∼60 nm leads to increasing of energy band gap E g from 0.88 to 1.21 eV. Studied colloidal solutions and nanopowders of silver sulfide possess the potential antibacterial activity.