Reporting their work in the journal Nanotechnology, scientists from Colorado School of Mines, East China University of Science and Technology, and South-Central University of Nationalities, have synthesized gold/mesoporous silica nanocomposites with gold nanoparticles intercalated in the walls of mesoporous silica, which display useful characteristics.

Thanks to the use of the gold co-ordinating agent bis[3-(triethoxysilyl)propyl]-tetrasulfide (TESPTS), the tetrasulfide structure (-S-S-S-S-) in the centre forms strong bonds with the precursor gold species while the –Si-O-C2H5 structure at two ends, which is the same as that of the silica precursor (tetraethyl orthosilicate, TEOS), can easily condense with TEOS and form mesoporous silica (SBA-15) with the gold precursor trapped in the forming matrix. On calcination, the gold atoms form nanoparticles while the thioether decomposes.

This synthesis method yields gold nanoparticles intercalated in the wall of SBA-15 instead of on the pore wall, as has been verified by transmission electron microscopy (TEM), N2M adsoption-desorption, X-ray diffraction (XRD) and UV-visible spectroscopy (UV-vis).

In addition to the novel structure, this catalyst also exhibits excellent catalytic activity compared with the traditional gold catalysts. To the researchers surprise, this novel catalyst almost has no loss of catalytic activity after recycling three times and shows excellent stability after exposure to elevated temperatures (up to 750 °C without aggregation), thus making it possible for this system to be used as a robust and reusable catalyst in green chemistry (the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances).

Optimizing performance

The team examined the effect of various amounts of gold co-ordinating agent (TESPTS) and found that more TESPTS would co-ordinate more gold, but disrupts the regular mesoporous structure resulting in materials ranging from partially mesoporous to foam-like.

The researchers presented their results in a special issue of the journal Nanotechnology focused on Green Chemistry.