Humidity Effects According to the Type of Carbon Nanotubes

Abstract

As a new type of one-dimensional nanomaterial, carbon nanotubes (CNTs) have been used as a chemical sensing material due to their excellent electrical, mechanical and chemical properties. Several recent studies have attempted to obtain an electrochemical sensor based on CNTs, and CNT-based humidity sensors have potential applications in industrial, agricultural and medical fields and in smart wearable electronic devices. Although various CNT-based humidity sensors have been reported, in this work, we investigated the humidity effects in depth and the underlying mechanisms according to CNT type, i.e., semiconducting (s-CNT) and metallic (m-CNT) CNTs, which is determined by the chiral vector during CNT growth. For this purpose, we fabricated CNT-based humidity sensors with highly purified, solutionprocessed 99% single-walled s-CNT and m-CNT network films bridged by palladium (Pd) electrodes. The fabricated sensors exhibited completely different humidity responses, as denoted by the film resistance as a function of the relative humidity (RH), according to the CNT type. In the s-CNT-based sensor, the resistance tended to decrease as the RH increased, while the m-CNT-based sensor showed the opposite tendency. Based on these results, a humidity sensing mechanism according to the CNT type was proposed in this work. We believe that our findings can serve as design guidelines for CNT-based humidity sensors.

Silver Nanoparticles Anchored on Single-Walled Carbon Nanotubes via a Conjugated Polymer for Enhanced Sensing Applications

“…Figure shows that the Ag–PFBPy/SWCNT device had an approximately 5-time increase in response compared to the device without silver, where only 1% response was observed when the RH decreased from 50 to 41.7%. This value is consistent with the results reported for semiconducting carbon nanotube devices in which the difference in the sensing response between 40 and 50% RH air was ∼2%. Our results indicated an apparent enhancement of the sensing response by introducing silver into this composite.…”

“…To check the advantage of this type of silver-doped SWCNT composite for sensing applications, the humidity sensing behavior of a Ag–PFBPy/SWCNT chemiresistor at ∼50% RH was compared with that of a control device , comprised of the same composite material but without silver. Figure compares their response curves to an air pulse sequence with lower RHs (48.1, 46.3, 44.6, 43.1, and 41.7%).…”

Aerosol‐Synthesized Surfactant‐Free Single‐Walled Carbon Nanotube‐Based NO2 Sensors: Unprecedentedly High Sensitivity and Fast Recovery

“…This is because water vapor in the air acts as a reducing agent for CNTs. [ 88 ] Charge transfer occurs when CNTs interact with water molecules. This interaction reduces the carrier concentration of the CNTs, thereby diminishing electrical conductivity and causes baseline drift (Figure S17B, Supporting Information).…”

Coupled Multiphysics Modelling of Sensors for Chemical, Biomedical, and Environmental Applications with Focus on Smart Materials and Low-Dimensional Nanostructures

“…Continuing with the environmental domain, we also note many innovative designs of humidity sensors that have been proposed on the basis of CNTs, utilizing their excellent properties (electrical, mechanical, chemical). Such sensors have been analyzed recently in [ 289 ], based on the underlying mechanisms and types of CNTs (e.g., semiconducting s-CNTs, metallic m-CNTs, depending on the chiral vector during CNT growth). Markedly, the implications of this work go well beyond environmental sciences and include industrial, agricultural, and medical applications, along with the creation of smart wearable electronic devices.…”