Oxidizing Properties of the Polysulfide Surfaces of Patronite VS4 and NbS3 Induced by (S2)2- Groups: Unusual Formation of Ag2S Nanoparticles

Similarly to transition metal dichalcogenides akin to MoS2, transition metal polysulfides like tri- and tetrachalcogenide materials are nowadays incorporated into catalysts and composites used for energy conversion and storage, etc. However, polysulfide structures feature -S-S- units, which make them strikingly different from the widely known MoS2 and other dichalcogenides. At the same time, their surface chemistry and its relation to properties are very little studied. Reported here is one of the first observations on the oxidizing properties of disulfide bridges (-S-S-)(2-) forming surfaces in polysulfide crystals. Upon interaction with silver salts or silver nanoparticles, MoS2 acts as most supports, that is, it stabilizes metallic Ag at its surface; in contrast, curiously, patronite VS4 and NbS3 stabilize Ag2S nanoparticles under identical reducing conditions. The Ag/MoS2, Ag2S/NbS3, and Ag2S/VS4 samples are characterized with X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Apparently, the unexpected formation of Ag2S is due to complex redox processes involving disulfide fragments -S-S- of nanorods VS4 or nanoribbons NbS3, which are absent in MoS2 nanosheets. This result is important for fundamental understanding of the properties of sulfur-rich surfaces and also for contributing to the number of available synthetic paths toward Ag2S nanoparticles.