Acid-base properties of N-doped carbon nanotubes : a combined temperature-programmed desorption, X-ray photoelectron spectroscopy, and 2-propanol reaction investigation

Ortega, KF, Arrigo, R ORCID: https://orcid.org/0000-0002-2877-8733, Frank, B, Schlögl, R and Trunschke, A 2016, 'Acid-base properties of N-doped carbon nanotubes : a combined temperature-programmed desorption, X-ray photoelectron spectroscopy, and 2-propanol reaction investigation' , Chemistry of Materials, 28 (19) , pp. 6826-6839.

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Abstract

Chemical and electronic properties of N-doped multiwalled carbon nanotubes (NCNTs) synthesized by NH₃ treatment of preoxidized CNTs at 300, 500, and 700°C have been investigated by a set of surface sensitive techniques. Temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) were applied to characterize the nature, thermal stability, and binding state of N and/or O containing surface functional groups. Acid–base properties in aqueous phase were analyzed by potentiometric pH titration, while the catalytic reaction of 2-propanol probed the acid–base behavior of the materials in the gas phase. NH₃ treatment at 300°C leads to an acid–base bifunctional surface, predominantly decorated with imide species. Contrarily, pyrrolic N is the most abundant moiety present on the sample modified at 500°C. Here, only small fractions of lactam groups and pyridinic species are present. The incorporation of N at 700°C leads to a carbon nanotube (CNT) surface with a well-defined basicity due to pyridinic N, which serves as a Lewis basic site converting 2-propanol into acetone. Furthermore, the oxidative stability of NCNTs strongly depends on the nature of N-containing species. Regarding the oxidative stability, NCNTs obtained at 700°C behave similar to the pristine CNTs, whereas the lower NH₃ treatment temperatures are detrimental for this property. The combination of dedicated techniques reveals links between structural and functional properties of surface species that change dynamically with temperature.

Item Type:	Article
Schools:	Schools > School of Environment and Life Sciences
Journal or Publication Title:	Chemistry of Materials
Publisher:	ACS Publications
ISSN:	0897-4756
Depositing User:	Dr R Arrigo
Date Deposited:	04 Dec 2018 12:42
Last Modified:	16 Feb 2022 18:54
URI:	https://usir.salford.ac.uk/id/eprint/49119

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