Nanofluids Containing MWCNTs Coated with Nitrogen‐Rich Plasma Polymer Films for CO 2 Absorption in Aqueous Medium

Amine‐functionalized multi‐walled carbon nanotubes (MWCNTs) dispersed in water are investigated as CO 2 absorbents. MWCNTs grown by chemical vapor deposition on stainless steel meshes form open forests that can be coated via a RF capacitively coupled glow discharge. When treating the MWCNTs in an atmosphere containing either pure ammonia or mixtures of ammonia and ethylene for 5 min, grafting of nitrogen functional groups or deposition of a nitrogen‐rich plasma polymer layer occurs. In particular, for a 1:1 mixture, a 10 nm thick plasma polymer layer coats the MWCNTs. This layer contains about 19 N at%, and 12% of these nitrogen atoms are nucleophilic sites (such as amines) that may react with CO 2 . These functional groups not only enhance the absorption of CO 2 , but also increase the hydrophilic character of the MWCNTs, allowing them to stay suspended in water for at least three months at room temperature. The CO 2 absorption capacity of this nanofluid is 36% higher than that of water, with a MWCNT concentration of about 40 mg L −1 .