Dong-Bo Cao

Structures and energetics of H2O adsorption on the Fe3O4(111)surface

Water adsorption on the Fe(subscript tet1)-terminated and Fe(subscript oct2)-terminated surfaces of Fe3O4 (111) has been calculated at the level of density functional theory (GGA/PBE). On the Fe(subscript tet1)-terminated surface at 1/5 monolayer (ML), the molecular adsorption mode with a hydrogen bond and the heterolytically dissociative mode show the highest stability, whereas the hydronium-ion-like structure OH3(superscript +)-OH becomes possible at 2/5 ML, followed by the hydrogen-bonded water aggregate. These results agree well with the available experimental observations. For Fe(subscript oct2)-terminated surface, the molecular water prefers to adsorb on the surface Fe(subscript oct2) atom at 1/6 ML, whereas other adsorption modes become possible and may coexist at 1/3 ML. The Fe(subscript tet1)-terminated surface is more favorable than the Fe(subscript oct2)-terminated surface for water adsorption. The adsorption mechanism has been analyzed on the basis of the calculated local density of state.

Insight into the structure and energy of Mo27SxOy clusters

Oxygen incorporated molybdenum sulfide (MoS2) nanoparticles are highly promising materials in hydrodesulfurization catalysis, mechanical, electric, and optical applications. We report a systematic theoretical study of the successive oxidation reactions of the Mo27SxOy nanoparticles and the reaction network, along with the electronic structure changes caused by the oxygen substitution. The replacement of surface sulfur by oxygen atoms is thermodynamically favorable. Our results indicate that the oxidation on the S edge with 100% and 50% coverage is more favored than on the Mo edge. Meanwhile, it is found that the oxidation on the S edge with 100% coverage has similar replacement ability by oxygen as on the S edge with 50% coverage. Thus, sulfur coverage does not play an important role in the oxidation on the S edge. Further comparison shows that the oxidation on corner sites is more favorable than on edge sites. In addition, the replacement of the bulky sulfur on the Mo edge is equally as favored as those of sulfur on the S edge. This work provides important information on the thermodynamics of the Mo27SxOy nanoparticles, and gives new insights into the mechanism of the oxidation of MoS2 and the sulfidation of MoO3.