Nuclear Magnetic Resonance Study of Fullerene-Like WS<SUB>2</SUB>

Abstract

Inorganic fullerene-like nanoparticles of WS2 (IF-WS2), are synthesized by a reaction of tungsten oxide with molecular hydrogen and hydrogen sulfide. The synthesized nanoparticles appear as large agglomerates (>40 microns), each one counting thousands of IF nanoparticles. 1H nuclear magnetic resonance study of these nanoparticles is reported. The measurements show that the prepared product contains water (and possibly some hydrogen) molecules that occupy the voids in the central part of the fullerene-like nanoparticles and the nanopores between the adhering IF-WS2 particles. Defects in the IF-WS2 structure, arising due to the strain release during the folding of the layers, may result in additional sites for the absorbed water. Vacuum annealing of the powder leads to substantial reduction in the amount of absorbed water molecules.

Transport properties of fullerene‐like WS2 nanoparticles

“…The time variation of the electrical resistivity in pristine IF-WS 2 material indicates that hydrogen and water are entrapped in nanopores between the agglomerated nanoparticles and within the nanoparticles themselves [15]. Preliminary 1 H NMR measurements of the annealed sample showed that the amount of entrapped water/hydrogen molecules decreased by a factor of four in comparison with the as-prepared sample at the room temperature.…”

“…Contrarily, the water molecules which were trapped within the core of the nanoparticles during the synthesis and removed by vacuum annealing would not be expected to readsorb in the ambient conditions. In fact, a recent 1 H NMR study [15] clearly indicated that water molecules were present in the pristine nanoparticles. This study shows that the free roation of the water molecules which are present inside the IF nanoparticles and in nanopores between the agglomerated nanoparticles was frozen out below 160 K. Note also that the water induced peak was appreciably smaller for the annealed (IF) as compared to the non-annealed samples.…”

“…Unfortunately, it was found that the halogen lamp was not suitable heating element because it served as a virtual thermal leak. But given the fact that hydrogen and water are a genuine part of the IF-WS 2 synthesis, it is believed that one can distinguish between two kinds of water molecules [15]. These water molecules and the hydrogen gas can be irreversibly extracted from the nanoparticles by the vacuum annealing.…”

“…A recent 1 H NMR study of the IF-WS 2 nanoparticles showed that the nanoparticles contain water molecules (and maybe some residual hydrogen molecules). The water molecules are believed to be adsorbed on the nanoparticles surfaces as well as occupy voids in the central part of the IF nanoparticle; the defects arising due to folding of the layers of IF-WS 2 and the nanopores between the agglomerated IF-WS 2 onions [15]. The water molecules which are present at the nanoparticles surface can be readsorbed upon exposure to the ambient, while the water molecules which are occluded in the nanoparticles core are not likely to be readsobed even after long exposure to the atmosphere.…”

X‐ray photoelectron spectroscopy and tribology studies of annealed fullerene‐like WS2 nanoparticles

“…in medical devices [12]. A 1 H NMR study [13] of the IF-WS 2 nanoparticles showed that the nanoparticles entrapped water molecules, or OH groups, which were obtained as a by-product during the conversion of the oxide nanoparticles into the metal sulfide (IF) and perhaps also some residual hydrogen molecules. The water molecules are believed to be located in defects arising due to the folding of the IF-WS 2 layers.…”