The synthesis of hybrid nanostructures of gold nanoparticles and carbon nanotubes and their transformation to solid carbon nanorods

Hybrid nanostructures composed of gold nanoparticles and multiwall carbon nanotubes (AuNPs@MWCNT) were prepared by the so called solvated metal atom dispersion method (SMAD), combined with chemical vapor deposition (CVD). In the SMAD procedure, bulk gold and an organic solvent are co-evaporated and later condensed into a frozen matrix at liquid nitrogen temperature. After warming up this matrix to room temperature, a colloid with very small and highly reactive gold clusters is obtained. These clusters react in the same vessel with MWCNTs, previously synthesized by CVD, by anchoring themselves to the sidewalls of the tubes. The resulting hybrids are very stable at temperatures up to 400 °C since the AuNPs get coated in this process by a thin layer of amorphous carbon. At temperatures beyond 600 °C the hybrid structures separate into CNTs and aggregated clusters of AuNPs. Further heating induces a severe transformation of the CNTs, due mainly to the catalytic activity of the AuNPs. The long MWCNTs are transformed into sub-micrometric solid carbon nanorods, comparable in diameter to the final size of the sintered AuNPs. The description of the synthesis products have been based on transmission electron microscopy and thermogravimetric analysis.