Engineered multi-stage chemical modification of carbon nanotubes: From oxidation and reduction to silane coupling for optimal dispersion

The dispersion of carbon nanotubes (CNTs) remains a critical challenge for their application in nanocomposites and advanced functional materials. This study proposes a systematic surface modification strategy involving sequential acid oxidation, reduction, and silane coupling agent (SCA) grafting to enhance CNT dispersibility. The effects of oxidation time, reduction time, and SCA concentration on CNT surface chemistry, structure, and dispersion were comprehensively evaluated using XPS, FTIR, Raman, and TGA. Results indicated that an optimal oxidation time of 8 h maximized the introduction of oxygen-containing functional groups while maintaining CNT structural stability, whereas a 5 h reduction time effectively converted carbonyl and carboxyl groups (−CO, –COOH) into hydroxyl (–CH₂OH), enhancing reactivity for subsequent functionalization. A grafting concentration of 5 wt% SCA achieved effective surface coverage and dispersion. The resulting functionalized CNTs exhibited superior dispersion stability in polar solvents, confirmed by SEM, sedimentation, contact angle, and zeta potential analyses. Improved surface polarity, electrostatic repulsion, and steric hindrance were identified as key contributors. This work provides a comprehensive approach to CNT surface modification, offering valuable insights into tailoring CNT dispersibility for improved interfacial compatibility in polymer nanocomposites, coatings, and functional materials.