Room-Temperature NO2 Gas Sensors Based on Granulated Carbon Nanofiber Material

Abstract

Room-temperature gas sensors based on granulated carbon nanofiber material were investigated for the detection of NO2. The granulated material consisting of intertwined carbon nanofibers was synthesized by the decomposition of CH4 over the Ni/Al2O3 catalyst in a vibro-fluidized bed reactor. Carbon material was investigated using transmission electron microscopy, Raman spectroscopy, low-temperature nitrogen adsorption, and X-ray photoelectron spectroscopy. Investigation of the gas sensors towards NO2 at room temperature (25 ± 2 °C) was carried out in a dynamic flow-through setup in the range from 1 to 500 ppm. A comparison of the sensitivity gas sensor to NH3 and CH4 was also given. The sensor based on non-treated carbon nanofiber material showed the response ΔR/R0 of 5.1 % to 10 ppm of NO2. It was found that the sensor response to NO2 decreased when increasing the relative humidity. The effect of the relative humidity was more pronounced for low concentrations of nitrogen dioxide and decreases with a further increase in them.

Carbon Nanofibers Synthesized at Different Pressures for Detection of NO2 at Room Temperature

“…The enthalpy of adsorption increased for the set from CNFs-1 to CNFs-5 samples. Previously, we have found that the granulated carbon nanofiber material, synthesized over Ni/Al 2 O 3 catalyst obtained by coprecipitation technique and synthesized at 1 atm and 550 • C, has also shown the physical nature of NO 2 adsorption [34]. However, the enthalpy of adsorption in [34] was 2-5 times of magnitude higher compared to CNFs studied in this paper.…”

“…Previously, we have found that the granulated carbon nanofiber material, synthesized over Ni/Al 2 O 3 catalyst obtained by coprecipitation technique and synthesized at 1 atm and 550 • C, has also shown the physical nature of NO 2 adsorption [34]. However, the enthalpy of adsorption in [34] was 2-5 times of magnitude higher compared to CNFs studied in this paper. Apparently, this is caused by the higher disorder degree of CNFs investigated in this paper (according to Raman spectroscopy I(D)/I(G) was 1.69-2.0 compared to 0.98 for granulated CNF in [34]).…”

“…Special attention is paid to carbon nanomaterials because of the great variety of modifications [25][26][27][28]. In particular, carbon nanomaterials, such as single-walled carbon nanotubes (SWCNTs) [29,30], multiwalled carbon nanotubes (MWCNTs) [31,32], double-walled carbon nanotubes (DWCNTs) [33], as well as carbon nanofibers (CNFs) [34][35][36][37] are already investigated for NO 2 detection.…”

“…Carbon nanofibers, being a by-product of catalytic decomposition of methane (or other hydrocarbons) for hydrogen synthesis, are of greater interest for applications in sensing due to their relatively low cost, higher yield compared to SWCNTs and MWCNTs, almost no need for purification [34], and easier process of production [38,39]. This material can be produced both in the form of powder and granules, which is determined by the content of the active components (nanoparticles of transition metals) of the catalyst and type of reactor (fluidized bed, vibrofluidized bed, and fixed bed) [40,41].…”

“…At the same time, there is no data reported on the application of CVD-grown CNFs, synthesized at pressures above 1 bar, for gas sensing. There is only one paper devoted to the creation of NO 2 gas sensors based on granulated carbon nanofibers synthesized at atmospheric pressure [34]. For the synthesis of CNFs, it is important to control the synthesis parameters (e.g., temperature and pressure inside the reactor) since changes in parameters will make it possible to obtain carbon material with different disorder degree, texture characteristics (specific surface area, pore size, nanofiber length, etc.).…”