Simultaneous improvement of nanofluid stability and CO₂ absorption by chitosan-grafted multi-walled carbon nanotubes dispersed in MDEA-based nanofluid

Due to the growing concern over limiting carbon dioxide (CO₂) emissions and combating climate change, the need for innovative measures to mitigate carbon dioxide emissions has become increasingly significant. For the first time, the proposed research affirms the decent functionality of the polymer grafting method in simultaneously prolonging stability and enhancing gas removal capacity. To achieve this, the surface of acid-treated Multi-Walled Carbon Nanotubes was modified using a 1,3-Diaminopropane solution. A straightforward and novel synthesis procedure was utilized to produce chitosan-grafted Multi-Walled Carbon Nanotubes. 10 wt% aqueous MDEA-based nanofluids were prepared, incorporating both chitosan-grafted Multi-Walled Carbon Nanotubes and amine-functionalized Multi-Walled Carbon Nanotubes, to compare CO₂ absorption performance and kinetics at various particle concentrations. Results revealed significant enhancements in CO₂ removal efficiency, absorption rates, and nanofluid stability when chitosan-grafted Multi-Walled Carbon Nanotubes were employed, in contrast to amine-functionalized Multi-Walled Carbon Nanotubes and a neat amine solution. The main focus of this paper was to enhance nanofluid stability, which is one of the key properties of nanofluids in their application for CO₂ absorption. The agglomeration and sedimentation formation in nanofluids containing amine-functionalized MWCNTs was resolved by adding surfactants. This was a short-term solution, while Zeta potential measurements and sediment photography over one month demonstrated long-lasting stability attributed to the incorporation of chitosan chains on the surface of amine-functionalized MWCNTs. Moreover, the addition of chitosan-grafted Multi-Walled Carbon Nanotubes resulted in a 12 and 20% improvement in CO₂ capture capacity compared to amine-functionalized Multi-Walled Carbon Nanotubes and a fresh solvent, respectively.