Behavior of C-60 under hydrothermal conditions: Transformation to amorphous carbon and formation of carbon nanotubes

The behavior of fullerenes Cu under hydrothermal conditions between 200 and 800 degreesC, and under 100 MPa pressure, in the absence and in the presen ce of nickel is reported. The highest temperature of fullerene stability, i n water was 400 degreesC after a 48-h-long, treatment. Increasing the tempe rature and/or time of the hydrothermal treatment resulted in transformation of fullerene to amorphous carbon. At 700 degreesC, high-quality open-ended multiwalled carbon nanotubes were formed in the vicinity of nickel particl es. These nanotubes typically had an outer diameter of 30-40 mn and a wall thickness of 5 nm, with a graphitization level similar to that of carbon na notubes prepared by chemical vapor deposition. The potential for large-scal e synthesis of the carbon nanotubes by the hydrothermal technique is discus sed. Since the present study was conducted tinder conditions which are comm on in the geological environment, our results imply that carbon nanotubes m ay form in natural hydrothermal Systems. (C) 2001 Academic Press.