Effect of catalyst preparation on the yield of carbon nanotube growth

MARIANO ESCOBAR; GERARDO H. RUBIOLO; ROBERTO J. CANDAL; SILVIA GOYANES

PHYSICA B - CONDENSED MATTER

ELSEVIER SCIENCE BV

Año: 2009 vol. 404 p. 2795 - 2798

0921-4526

Multiwall carbón nanotubes (MWCNTs) were synthesized by catalytic chemical vapor deposition (CVD) on catalytic iron nanoparticles dispersed in a silica matrix,prepared by sol gel method. In this contribution,variation of gelation conditionon catalyst structure and it s influence on the yield of carbon nanotubes growth was studied. The precursor utilized were tetraethyl-orthosilicate and iron nitrate. The sols were dried at two different temperature sin air (25or80 1C) and then treated at 450 1C for 10h.The xero gels were introduced into the chamber and reduced in a hydrogen/nitrogen(10%v/v) atmosphere at 600 C. MWCNTs were formed by deposition of carbon atoms from decomposition of acetylene at 700 C. The system gelled at RT shows a yield of 100% respect to initial catalyst mass whereas the yield of that gelled at 80C was lower than10%. Different crystalline phases are observed for both catalysts in each step of the process. Moreover, TPR analysis shows that iron oxide can be efficiently reduced to metallic iron only in the system gelled at room temperature. Carbon nanotubes display a diameter of about 25–40 nm and several micronlengths. The growth mechanism of MWCNTs  is base growth mode for both catalysts