Reversible changes in the electronic structure of carbon nanotube-hybrids upon NO₂ exposure under ambient conditions

Abstract

The properties of single-walled carbon nanotubes provide them with enormous potential as gas sensors but true effectiveness can really be expected if their interaction with sensing targets can be controlled and their recovery is granted. It is shown here how metallicity-sorted tubes filled with nickel(II) acetylacetonate in the molecular form, and also subsequently transformed into metal clusters encapsulated in the hollow core, are able to unfold two major challenges: tuning the gas-tube interaction and achieving the desorption of NO 2 at ambient temperature. Aiming at the control of the sensitivity of the nanotubes to NO 2 at room temperature, by making use of time resolved photoemission we observed that in semiconducting nanotubes the chemical potential is pinned inside their energy gap shifted to the onset of the conduction band when filled with nanoclusters. This shows that cluster filling is a key to high sensitivity, opening the possibility for a very high desorption at ambient temperature. Fig. 3 (a) Shift of the main peak of the C 1s core level signal in XPS of the semiconducting (blue) vs. metallic (red) hosts with different fillings at the stages listed in Table 1. (b) C 1s shift resulting from a time resolved experiment by exposing the Ni-nc@SC-SWCNTs to NO 2 .This journal is Fig. 4 C 1s core level spectra of Ni-acc@SC-SWCNTs (a) and Ni-acac@M-SWCNTs (b). The spectra correspondingly below (c and d) were recorded after exposure to 80 L of NO 2 . The bottom spectra correspond to Ni-nc@SC-SWCNTs (e) and Ni-nc@M-SWCNTs (f) exposed to 80 L of NO 2 . Molecular models are shown as the inset of each plot. 9756 | J. Mater. Chem. A, 2020, 8, 9753-9759 This journal is

Applications of Filled Single-Walled Carbon Nanotubes: Progress, Challenges, and Perspectives

“…The light green stripes mark the first 3 min of the recovery period, after which the recovery is mostly completed. Figure 4e,f is sketches of the Fermi-level shifts in the density of states for semiconducting and metallic SWCNTs filled with Ni clusters, respectively [179]. It can be seen that the SWCNT gas sensor is capable of recovery after exposure at ambient temperature.…”

“…A multiplexed nanotube sensor array was used to detect both species in a mixture of these molecules at once. Authors of Reference [179] demonstrated the viability of the concept of a SWCNTbased specific gas sensor for NO 2 , which is a relevant and highly toxic air pollutant. Metallicity-sorted semiconducting and metallic SWCNTs were filled with nickel (II) acetylacetonate molecules.…”

Metallocene-Filled Single-Walled Carbon Nanotube Hybrids

“…The authors of Ref. [ 173 ] demonstrated the application potential of SWCNTs in a sensor for NO2, which is a well-known highly toxic air pollutant, capable of recovering at ambient temperature. Metallicity-sorted semiconducting and metallic SWCNTs filled with nickel (II) acetylacetonate molecules as well as nickel clusters obtained by heating at 500 °C were tested.…”

“…Metallicity-sorted semiconducting and metallic SWCNTs filled with nickel (II) acetylacetonate molecules as well as nickel clusters obtained by heating at 500 °C were tested. In the case of Ni cluster-filled SWCNT, the system even fully recovered at room temperature [ 173 ].…”

“…Sixthly, applications of metallocene-filled SWCNTs attract interest. Among them, applications in electrochemistry [ 172 ], thermoelectric power generation [ 3 ], chemical sensors [ 173 ], and magnetic recording [ 174 , 175 , 176 , 177 ] are considered to be promising. For these applications, carbon nanotubes with homogeneous properties are needed.…”