Carbon nanotubes/kraft lignin composite: Characterization and charge storage properties

The results of this study demonstrate the spectral, microscopic and electrochemical properties of multi-walled carbon nanotubes (CNTs) surface-functionalized with kraft lignin (KL). XPS and FT-IR spectroscopy show that the biomolecule is effectively adsorbed on the surface of CNTs, leading to an increase in oxygen content and the appearance of spectral features characteristic of highly oxidized polyphenolic compounds. The presence of KL makes CNTs easily dispersible in organic (DMSO) and aqueous (0.1 M ammonia) solutions. Microscopic analysis (SEM and AFM) confirms the effective debundling of CNTs and the presence of densely packed globular structures on the surface of individual nanotubes. Deposition of the CNT/KL composite on the surface of a gold electrode facilitates its electrochemical characterization. This reveals that the CNT-supported biomolecule exhibits persistent reversible redox behavior attributed to KL-derived quinone moieties. Therefore the reversible redox activity of the lignin adsorbate can be utilized for charge storage, providing more than a 100% increase in the capacitance of KL-modified carbon nanotubes compared with unmodified ones.