Temperature dependent evolution of the local electronic structure of atmospheric plasma treated carbon nanotubes: Near edge x-ray absorption fine structure study

Abstract

Near edge x-ray absorption fine structure ͑NEXAFS͒ spectroscopy has been employed to obtain the temperature dependent evolution of the electronic structure of acid treated carbon nanotubes, which were further modified by dielectric barrier discharge plasma processing in an ammonia atmosphere. The NEXAFS studies were performed from room temperature up to 900°C. The presence of oxygen and nitrogen containing functional groups was observed in C K edge, N K edge, and O K edge NEXAFS spectra of the multiwalled carbon nanotubes. The N K edge spectra revealed three types of * features, the source of which was decisively identified by their temperature dependent evolution. It was established that these features are attributed to pyridinelike, NO, and graphitelike structures, respectively. The O K edge indicated that both carbonyl ͑C v O͒, * ͑CO͒, and ether CO -C, * ͑CO͒, functionalities were present. Upon heating in a vacuum to 900°C the * ͑CO͒ resonances disappeared while the * ͑CO͒ resonances were still present confirming their higher thermal stability. Heating did not produce a significant change in the * feature of the C K edge spectrum indicating that the tabular structure of the nanotubes is essentially preserved following the thermal decomposition of the functional groups on the nanotube surface.

Activity and active sites of nitrogen-doped carbon nanotubes for oxygen reduction reaction

“…Second, nitrogen functional groups doped in the carbon matrix are believed to be active for the ORR. The transition metals do not take part in the ORR, but the addition of transition metal in the catalyst synthesis facilitates the incorporation of nitrogen into the carbon matrix, which can increase the ORR active site density on the catalysts [25][26][27][28][29].…”

“…It is also reported that a heat treatment induce to the formation of more stable nitrogen functional groups [27,28]. Stanczyk et al [28] and Pel et al [29] showed that pyrrolic structures are transformed into pyridinic structures and vice versa via dynamic surface rearrangements during low temperature treatments.…”

One-dimensional nitrogen-containing carbon nanostructures

“…NCNTs were also formed by dielectric barrier discharge plasma processing of acid treated CNTs in an NH 3 atmosphere [256]. The exposure of SWCNTs to microwave-generated N 2 plasma [257] was found to lead to SWNCNTs.…”

Role of nitrogen–oxygen plasma functionalization of carbon nanotubes in epoxy nanocomposites

“…CNTs functionalized with nitrogen nanocomposites can accelerate the cure and promote the wrapping of polymer molecules on them, which can act as a protective layer to prevent reagglomeration of dispersed CNTs . However, the use of plasma as a tool to insert nitrogen into CNTs still presents some difficulties, such as the low nitrogen molecule dissociation rate , the easy recombination of the nitrogen atoms , and the high instability of the nitrogenous groups . These difficulties are highlighted at Abrar et al work.…”