Selective Scission of C–O and C–C Bonds in Ethanol Using Bimetal Catalysts for the Preferential Growth of Semiconducting SWNT Arrays

For the application of single-walled carbon nanotubes (SWNTs) to electronic and optoelectronic devices, techniques to obtain semiconducting SWNT (s-SWNT) arrays are still in their infancy. We have developed herein a rational approach for the preferential growth of horizontally aligned s-SWNT arrays on a ST-cut quartz surface through the selective scission of C–O and C–C bonds of ethanol using bimetal catalysts, such as Cu/Ru, Cu/Pd, and Au/Pd. For a common carbon source, ethanol, a reforming reaction occurs on Cu or Au upon C–C bond breakage and produces C_ads and CO, while a deoxygenating reaction occurs on Ru or Pd through C–O bond breaking resulting in the production of O_ads and C₂H₄. The produced C₂H₄ by Ru or Pd can weaken the oxidative environment through decomposition and the neutralization of O_ads. When the bimetal catalysts with an appropriate ratio were used, the produced C_ads and C₂H₄ can be used as carbon source for SWNT growth, and O_ads promotes a suitable and durable oxidative environment to inhibit the formation of metallic SWNTs (m-SWNTs). Finally, we successfully obtained horizontally aligned SWNTs on a ST-cut quartz surface with a density of 4–8 tubes/μm and an s-SWNT ratio of about 93% using an Au/Pd (1:1) catalyst. The synergistic effects in bimetallic catalysts provide a new mechanism to control the growth of s-SWNTs