Synthesis of vertically aligned CNT arrays using liquid based precursors and their functionalization by conjugated polymers

Abstract

In the first part of this work, a new solution based catalyst precursor application method is developed for growing high quality vertically aligned carbon nanotubes arrays (VANTA) through alcohol catalyzed chemical vapor deposition (AC-CVD). For this purpose, various solution based precursor preparation routes are investigated starting from γ-Al2O3 / Fe(NO3)3.9H2O mixtures and ranging to catalyst precursors prepared by mixing aqueous aluminium and iron nitrate solutions. Application of these solutions separately layer by layer on Si(100) substrate resulted in high quality dense vertically aligned CNT arrays. By varying the metal nitrate concentration in the precursor solutions, the dependence of the density and quality of CNT arrays on the catalyst layers are investigated. The CNT array quality and density are characterized by dynamic contact angle measurements using water droplets. Higher density CNT arrays resulted in higher contact angle measurements. The chemical and structural characterizations of CNTs are also done by using TEM, SEM, EDX and Raman spectroscopy. Some of the samples are found to be super hydrophobic even after 30 minutes of exposure to water. In this effort, application of subsequent layers of aqueous aluminium nitrate and iron nitrate on oxidized Si(100) surfaces are found to be most efficient catalyst layer preparation technique resulting in the highest density of CNT arrays. In the second part of this work, functionalization of the synthesized CNT arrays is done for the purpose of achieving good dispersibility of CNTs in aqueous media. To this end, a new approach is used to ensure stability of the CNT-water solution. In this approach, conjugated polymer nanoparticles (CPNs) are successfully used to disperse CNTs through non-covalent functionalization of the sidewalls of CNTs. The attachment of CPNs to CNTs is characterized by SEM, EDX and TEM. Moreover, interactions are investigated by UV-VIS, and Raman spectroscopy. The interaction mechanism of polymer chains with side-walls of CNTs are further scrutinized by follow-up experiments where two different conjugated polymers with brominated-alkyl and bare alkyl groups in THF media are mixed with SWCNTs (commercial), MWCNTs and an-MWCNTs (synthesized in the first part of this study). The results of this investigation suggested a limited number of docking configurations of the polymers with the CNT side-walls. Also, it is found that the defect density of the CNT side-walls play an important role in the nature of the interaction. Overall, in this work a cheap and effective route for application of catalyst is developed for the synthesis of dense, super-hydrophobic CNT arrays using ACCVD. Then, well-dispersion of these CNTs is successfully achieved using CPNs. Finally, the nature of the interaction between conjugate polymers and CNTs sidewalls are investigated using experimental techniques.