To make hollow nanocrystals of molybdenum disulphide, Ken Suslick and Arul Dhas applied ultrasound to a slurry containing Mo(CO)6, S8 and nanometre-scale silica spheres in the presence of argon.

The process generated nanoparticles of molybdenum disulphide that coated the silica spheres. Treating the coated silica spheres with hydrofluoric acid etched out the silica cores to leave hollow nanospheres of molybdenum disulphide.

To prepare molybdenum oxide spheres, the team used the same technique but without the sulphur, and in an atmosphere of air rather than argon. Surprisingly, applying an anneal at 350° C to the hollow MoO3 spheres caused them to form truncated cubic nanocrystals containing spherical voids.

The team found that the hollow molybdenum disulphide nanospheres acted as an active catalyst for hydrodesulphurization of thiophene. The hollow material performed better than either nanostructured or conventional micrometre-sized molybdenum powders.

"Molybdenum disulphide is a layered material, but its catalytic activity occurs at its edges," said Suslick. "By distorting and breaking up the layers, hollow nanospheres offer increased edge-surface area, as well as access to both inner and outer shell surfaces."

The scientists believe their technique should be able to create hollow nanostructures from a range of inorganic materials.

The researchers reported their work in Journal of the American Chemical Society.