Enhanced Dispersion and Functionalization of Multiwalled Carbon Nanotubes via Mild Mixed Acid Sonication Treatment

Abstract

Multi-walled carbon nanotubes (MWCNTs) have excellent characteristics, including mechanical strength and durability, as well as electrical and thermal conductivity, which make them desirable for materials science, sensing, and nanotechnology applications. MWCNTs are hydrophobic and chemical inert materials, therefore causing considerable agglomeration and poor dispersion when they are to be dispersed in a polar liquid. This study investigated the effectiveness of the MWCNT surface modification via functionalization (adding functional groups to the surface of MWCNTs) and dispersion properties of MWCNTs after mild-acid sonication with either mixed-acid (6 M Nitric Acid and Sulfuric Acid) or single acid (6 M Nitric Acid). The functionalization and dispersion properties were characterized by using FTIR, Raman, XRD, and SEM. FTIR analysis confirmed the formation of oxygen-containing functional groups, with a characteristic C=O peak at ~1720 cm-1. Raman analysis showed that functional groups formed covalent bonds and that there was no significant structural degradation. SEM analyses indicated that there is a large difference between pristine MWCNTs, as agglomerated (pristine) and functionalized and dispersed (uniformly dispersed). It was determined that although the mixed-acid sonication approach produced more stable dispersions than single-acid sonication did, there was no difference in MWCNT structures (functional group formation relative to preservation of MWCNT structural integrity). The optimal sonication duration time to achieve the best balance of MWCNT functional group incorporation and MWCNT structural integrity was 2-4 hours. Based on the results of this study, it can be concluded that functionalizing and dispersing MWCNTs using a mild mixed-acid sonication treatment is an effective and simple way to achieve those goals.