Dispersion Stability of MWCNTs Decorated with Ag Nanoparticles through Pulse-Reversed Current Electrodeposition Using a Deep Eutectic Solvent

Abstract

Carbon nanotubes (CNTs) represent a unique class of nanomaterials with remarkable properties with a wide variety of applications in diverse scientific and technical domains. However, one of the many challenges still requiring improvement is undoubtedly their dispersion stability. The control of the dispersion stability of CNTs is a challenge due to the strong van der Waals forces that lead to their aggregation. Metallic nanoparticles (NPs), such as silver (AgNPs), in the presence of a capping agent, e.g., poly(N-vinyl pyrrolidone) (PVP 10), are recognized as having a key role in the increase of the stability of NP dispersions, and if incorporated in multi-walled CNTs (MWCNTs), may help surpass the MWCNTs’ aggregation problem. The present work reports the enhancement of the stability of MWCNTs upon decoration by AgNPs, using an electrochemical method to generate the silver ions and promote the electrodeposition of silver. To validate the increase in stability of the Ag-decorated MWCNTs, two solvents were used, water and glyceline, a eutectic mixture of choline chloride and glycerol. The time stability of bare MWCNT and AgMWCNT nanofluids was characterized through dynamic light scattering (DLS) and ultraviolet–visible (UV–Vis) spectrophotometry. Compared to commercial MWCNTs, MWCNTs decorated with AgNPs presented a significant stability enhancement, in both water and glyceline. Glyceline also presented higher stability over time, with a retention of UV–Vis absorbance up to 97%, compared to 50% for water media. The DLS and turbidity experiments showed the same trend of MWCNTs’ stability in water and glyceline. In both cases, the use of AgMWCNT materials improved the stability of the dispersions 25× in glyceline and 2.5× in water, when compared to the stability of bare MWCNT dispersions.