Nanofluids Containing MWCNTs Coated with Nitrogen-Rich Plasma Polymer Films for CO2 Absorption in Aqueous Medium

Amine-functionalized multi-walled carbon nanotubes (MWCNTs) dispersed in water are investigated as CO2 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 CO2. These functional groups not only enhance the absorption of CO2, 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 CO2 absorption capacity of this nanofluid is 36% higher than that of water, with a MWCNT concentration of about 40 m gL(-1).