Quantitative Studies on the Oxygen and Nitrogen Functionalization of Carbon Nanotubes Performed in the Gas Phase

• Published in: Journal of physical chemistry. C Vol. 116; no. 39; pp. 20930 - 20936
• Main Authors: Li, Chuang, Zhao, Anqi, Xia, Wei, Liang, Changhai, Muhler, Martin
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 04.10.2012
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Materials science; Nanoscale materials and structures: fabrication and characterization; Nanotubes; Physics; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Temperature dependence; TDS; Carbon nanotubes; Mass loss; Surface treatments; Desorption; XRD; Carbon; Heat treatments; Nonstoichiometry; Defects; Ammonia; Chemical modification; Corrosion; Functionalization; Thermal resistance; Oxidation; Gas phase; Surface area; Nanostructured materials; X-ray photoelectron spectra
• DOI: 10.1021/jp306866q
• ISSN: 1932-7447

Gas-phase methods were applied for the oxygen and nitrogen functionalization of multiwalled carbon nanotubes (CNTs). The oxygen functionalization was performed by HNO3 vapor treatment at temperatures from 200 to 250 °C for 12 h up to 120 h. The oxygen-functionalized CNTs were used as the starting material for nitrogen functionalization through thermal treatment under NH3. The BET surface area increased after the treatment in HNO3 vapor, which also caused the weight loss due to carbon corrosion. The oxygen content increased with increasing treatment time but decreased with increasing temperature, as disclosed by elemental analysis, X-ray photoelectron spectroscopy, and temperature-programmed desorption (TPD) results. The surface acidity increased with increasing treatment time as shown by TPD using NH3 as a probe molecule. As to nitrogen functionalization, the amount of nitrogen was correlated with the oxygen amount in the starting CNTs. A higher NH3 concentration caused a lower BET surface area due to carbon corrosion. The incorporation of both oxygen and nitrogen lowered the thermal resistance of CNTs. The nitrogen-functionalized CNTs showed only a slight decrease, in contrast to a significant decrease observed for O-functionalized CNTs. The formation or removal of coordinatively unsaturated carbon like amorphous carbon or defects was found to be involved in all of the functionalization, desorption, and oxidation processes.