Characteristics of copper sulfide nanoparticles obtained in the copper sulfate–sodium thiosulfate system

Abstract

Stable hydrosols of copper sulfide nanoparticles are synthesized by heating aqueous solutions with different ratios of sodium thiosulfate and copper sulfate in the presence of polyvinylpyrrolidone and studied by a number of physicochemical methods in situ (optical spectroscopy, dynamic light scattering) and ex situ (transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy). The main product is CuS covellite nanoparticles with some impurities of other phases (Cu₂S, Cu_1,8S, Cu₇S₄). With an increase in the initial molar ratio S₂O ²⁻₃ / Cu from 0.2 to 5 the nanoparticle size increases from 1-5 nm to 30-50 nm and then decreases to 4 nm at a ratio of 10. A substantial increase in the intensity of plasmon absorption within 800-1500 nm is observed during the formation of planar nanoparticles with a lateral size of about 30 nm at S₂O ²⁻₃:Cu = 5. A band gap obtained from both direct and indirect optical absorption spectra of sulfides (2.6 eV and 1.7 eV respectively) remains constant for all particles.