A review on recent advances of CNTs as gas sensors

Abstract

Purpose This review paper aims to focus on recent advances of carbon nanotubes (CNTs) to produce gas sensors. Gas sensors are widely used for monitoring hazardous gas leakages and emissions in the industry, households and other areas. For better safety and a healthy environment, it is highly desirable to have gas sensors with higher accuracy and enhanced sensing features. Design/methodology/approach In this review, the authors focus on recent contributions of CNTs to the technology for developing different types of gas sensors. The design, fabrication process and sensing mechanism of each gas sensor are summarized, together with their advantages and disadvantages. Findings Nowadays, CNTs are well-known materials which have attracted a significant amount of attention owing to their excellent electrical, electronic and mechanical properties. On exposure to various gases, their properties allow the detection of gases using different methods. Therefore, over recent years, researchers have developed several different types of gas sensors along with other types of sensors for temperature, strain, pressure, etc. Originality/value The main purpose of this review is to introduce CNTs as candidates for future research in the field of gas sensing applications and to focus on current technical challenges associated with CNT-based gas sensors.

Highly Sensitive Detection of NO2 by Au and TiO2 Nanoparticles Decorated SWCNTs Sensors

“…Moreover, there is a little difference in the results obtained in dry and humid environments, showing a very slight sensitivity to humidity. This result is in accordance with the theoretical studies [9], which predict a small sensitivity for water; this latter is also accompanied by a small charge transfer (which can be positive or negative depending on the tube chirality). In the tested material, water increases the conductivity, which indicates a negative charge transfer (acceptor behavior), in contrast with what happens with the most part of metal oxides.…”

“…As expected, on the basis of previous experimental works and from theoretical studies [9], the response to NO 2 is the one observed in other p-type semiconductors in all the tested conditions. In detail, the adsorbed molecule behaves as an acceptor that, by trapping free electrons [9], creates additional holes available for the conduction, so that the exposure to NO 2 causes an increase of the tube conductivity.…”

“…Hence, the effect of deposing a dose of NPs is not simply that of contributing with a new film in parallel with the first one. The pure material is expected to behave as a p-type semiconductor, owing to intrinsic acceptor-type defects; therefore, an increased conductivity is expected in air, with respect to the one measured in nitrogen, because oxygen adsorption is accompanied by negative charge transfer (extrinsic acceptor state creation) [9]. In accordance with the expected behavior, it can be seen from the results (Figure 4a) that the presence of oxygen causes an increase of the baseline conductance.…”

“…The research shows that CNTs with semiconductor behavior can be employed as gas sensing materials, exploiting the influence that the adsorption of gases from the environment has on their electronic conductivity. In fact, it was shown that adsorbates can donate or accept free carriers, moreover, they can increase the electronic scattering [8][9][10]. The very high surface to volume ratio and the structural characteristics make CNTs-based materials particularly appealing for gas-sensing applications.…”

Synthesis of carbon nanofibers by thermal conversion of the molecular precursor 5,6;11,12-di-o-phenylenetetracene and its application in a chemiresistive gas sensor

“…Our interest in that area stems from the fact that carbon based nanomaterials, e.g. CNTs, [24][25][26] CNFs 27-30 and graphene 31,32 have proven to be effective alternatives to well-established metal oxide based gas sensors. Key features of these materials compared to metal oxides are operating temperatures as low as room temperature and an increased sensitivity and high versatility introduced by the ease of functionalization of these materials.…”