Enhancement Sensitivity and Selectivity of Ammonium Hydroxide Using Nitrogen-Doped Double-Walled Carbon Nanotubes

Nitrogen-doped double-walled carbon nanotubes (N-DWCNTs) were synthesized by floating catalytic chemical vapor deposition (FCCVD) at 1300 °C using ethanol and urea as carbon and nitrogen sources. For comparison, the undoped double-walled carbon nanotubes (DWCNTs) were synthesized by FCCVD using ethanol as carbon source. Synthesized DWCNTs and N-DWCNTs were separately dispersed in ethanol and separately dropped onto printed circuit board substrate. The fabricated sensors were detected to ammonium hydroxide (NH4OH), acetone and ethanol vapors at part per million level. The sensor response results show that N-DWCNTs are highly sensitive to NH4OH. In the case of volatile organic compounds detection, DWCNTs and N-DWCNTs exhibit similar response to acetone and ethanol. The fabricated sensor from N-DWCNTs to NH4OH vapor was 4-fold higher than that of fabricated sensor from undoped DWCNTs. The sensing mechanism of N-DWCNTs can be attributed to the charge transfer between N-DWCNTs and NH4OH molecule. Nitrogen site has a higher response, resulting in an enhancement the selectivity and sensitivity to NH4OH. The total atomic percentage of N-DWCNTs is approximately 0.90 at%. The results suggest that the heteroatom-doping of nitrogen is a promising approach for improving the sensitivity and selectivity for NH4OH detection. HIGHLIGHTS N-DWCNTs were synthesized by FCCVD method using ethanol and urea Nitrogen site in N-DWCNTs is highly sensitive and selective to NH4OH N-DWCNTs enabled 4-fold improved NH4OH compared with undoped DWCNTs GRAPHICAL ABSTRACT