No Reducing Agent Needed AND Suspended in Water

"Hole-Doped Single-Walled Carbon Nanotubes: Ornamenting with Gold Nanoparticles in Water"

Kim, D. S.; Lee, T.; Geckeler, K. E. Angew. Chem. Int. Ed. 2006, 45, 104-107.

10.1002/anie.200500234

Points:

Frontier orbital theory - hole doping of SWNTs

Done in surfactant solution, thus with small quantities

Materials: Au-SWNT

Synthesis:

• 1 mg SWNT was suspended in Tween-80 (0.1 wt%, 10mL) with ultrasonication and subject to high-speed centrifugation (80,000 g, 3h). Supernatant conc was determined to be ~48 mg/L. 0.3 mg KAuCl4 was then added to 1.2 mL of the above solution.
• The "optimized procedure" for TEM was 60 C, 1h.

Characterization:

TEM

EDX

Raman:

• Decays in RBM and G-band "is a strong indication ofthe removal of electrons from the conduction band of carbon nanotubes following the reduction of metal ions at the surface of nanotubes"
• "the peak of the tangential G-band shifted to a higher frequency" "as a stiffening of thegraphene mode, caused by the introduction of holes into the conduction band of nanotubes as a result of the charge transfer interaction".

Properties:

• 2.94(+-0.75) nm
• When increasing the salt conc to 3.5 mM, Au particle was found to be ~9 nm.
  

No Reducing Agent Needed

"Spontaneous Reduction of Metal Ions on the Sidewalls of Carbon Nanotubes"
Choi, H. C.; Shim, M.; Bansaruntip, S.; Dai, H. J. Am. Chem. Soc. 2002, 124, 9058-9059.
10.1021/ja026824t

Point:
Direct redox reactions between metal ions and nanotubes.

Materials: Au-SWNT, Pt-SWNT

Synthesis:
SWNT grown on SiO2 substrates (from CVD) was immersed in 5mM salt solutions (in 1:1 water:ethanol) for "varying periods of time".

Characterization:

AFM:

• Au particles from HAuCl4
• formed "selectively" on SWNTs, not on SiO2 substrates
• formed within 30 s of immersion (7 nm)
• increased in sizes (up to 16 nm) when increasing immersion time, but did not increase coverage density, indicating fast (<30s)>
• similar for in the dark, under room light, halogen lamp and UV light
• same for Pd particles from Na2PtCl4
• deposition from Ag+, Ni2+, Cu2+ were not "selective" - found particles on substrates.

Device-level conductance monitoring:

• hole injection from metal ions to SWNTs should induce the increase of conductance
• huge conductance improvement (from 100 nA to 700 nA) upon the immersion of device in the metal ion solution, and reach plateau in ~40 s

Speculated Applications:

• Sensors
• Catalysts
• Forming metal wires by removing carbon template