Preferential adsorption of NH3 gas molecules on MWCNT defect sites probed using in situ Raman spectroscopy

George Chimowa (1, 2) , Boitumelo Matsoso (3) , Neil J. Coville (3) , Suprakas Sinha Ray (1, 4) , Emmanuel Flahaut (2) , Teresa Hungría (5) , Lucien Datas (2, 5) , Bonex W. Mwakikunga (1)

1 University of Pretoria [South Africa]
2 CIRIMAT - Centre interuniversitaire de recherche et d'ingenierie des matériaux
3 WITS - University of the Witwatersrand [Johannesburg]
4 UJ - University of Johannesburg [South Africa]
5 Centre Castaing - Centre de microcaractérisation Raimond Castaing

The preferential adsorption of NH3 gas molecules on multiwalled carbon nanotubes (MWCNTs) was studied using in situ Raman spectroscopy. It was observed that the full widths at half maximum of the G band and the intensity ratio I2D/IG of the MWCNTs decreased significantly during NH3 gas adsorption at elevated temperatures. These observations were explained in terms of suppressed second-order-defect associated Raman vibrations resulting in a lower disorder Raman band due to ammonia adsorption on the defect sites. Another corresponding effect was a temporary increase in electron doping levels due to ammonia adsorption. This behaviour was accompanied by a drop of ca. 2% in the resistance of the MWCNTs corresponding to the occupancy of most of the defect sites. We suggest preferential adsorption of ammonia gas molecules on the thermally activated defect sites of MWCNTs as an appropriate gas sensing mechanism. This knowledge can be used to design and tune the selectivity of ammonia gas sensors

Mots clés: Carbon nanotubes; Gas sensing; Adsorption; Raman spectroscopy

Domaines: Matériaux; Chimie théorique et/ou physique

George Chimowa, Boitumelo Matsoso, Neil J. Coville, Suprakas Sinha Ray, Emmanuel Flahaut, et al.. Preferential adsorption of NH3 gas molecules on MWCNT defect sites probed using in situ Raman spectroscopy. physica status solidi (a), 2017, 214 (10), pp.1-7. ⟨10.1002/pssa.201600930⟩. ⟨hal-01687165⟩