Acid Treatment in Alkyl-Functionalized Carbon Nanotubes: Soft Functionalization Techniques with Lower Environmental Footprint

Carbon nanotubes (CNTs) are a promising material for sensors and composites, where the addition of chemical functional groups enables selective binding or dispersion. Common functionalization processes often require refluxing in nitric acid (HNO3), resulting in poor control while adding safety, cost, and environmental burdens. Using CNTs grown from acetylene, methylacetylene, or vinylacetylene, we examined a vapor-based functionalization technique with hydrochloric acid (HCl), aiming to reduce morphological damage and material and energy consumption. HNO3 enabled increased oxygen addition via liquid versus vapor treatments (1.6-2.2% vs 0.88-1.0%), while HCl preferably added chlorine via vapor treatments (0.05-0.1% vs 0.02-0.03%). Interestingly, liquid HCl treatments yielded 1.2-2.2% oxygen, and for vinylacetylene-derived CNTs, the oxygen addition was greater than a HNO3-treated sample (2.2 ± 1.5 vs 1.6 ± 0.4%), providing important mechanistic insights for the growth of CNTs and subsequent oxygen addition reaction pathways at defect loci. Life cycle impact assessment demonstrated that using HCl reduced global warming potential and ecotoxicity (98 and 92% reductions, respectively) compared to HNO3. Vapor treatments offered additional improvements, primarily via elimination of electric heating required for reflux. These results demonstrate the importance of structure in CNT substitution and the potential for HCl- and vapor-based treatments for soft CNT functionalization with reduced environmental impact.

Duke Scholars

Author Leanne Gilbertson Civil and Environmental Engineering