Low-Temperature Ethanol Sensor via Defective Multiwalled Carbon Nanotubes

Abstract

This paper focuses on the fabrication of defective-induced nanotubes via the catalytic chemical vapor deposition method and the investigation of their properties toward gas sensing. We have developed defective multi-walled carbon nanotubes with porous and crystalline structures. The catalyst layer used in CNTs’ growth here was based on 18 and 24 nm of Ni, and 5 nm of Cr deposited by the dc-sputtering technique. The CNTs’ defects were characterized by observing the low graphite peak (G-band) and higher defect peaks (D-band) in the Raman spectrum. The defectives sites are the main source of the sensitivity of materials toward different gases. Thus, the current product was used for sensing devices. The device was subjected to various gases such as NO, NO2, CO, acetone, and ethanol at a low operating temperature of 30 °C and a concentration of 50 ppm. The sensor was observed to be less sensitive to most gas while showing the highest response towards ethanol gas. The sensor showed the highest response of 8.8% toward ethanol at 30 °C of 50 ppm, and a low response of 2.8% at 5 ppm, which was investigated here. The signal repeatability of the present sensor showed its capability to detect ethanol at much lower concentrations and at very low operating temperatures, resulting in reliability and saving power consumption. The gas sensing mechanism of direct interaction between the gas molecules and nanotube surface was considered the main. We have also proposed a sensing mechanism based on Coulomb dipole interaction for the physical adsorption of gas molecules on the surface.

Sensitive Detection of a Gaseous Analyte with Low‐Power Metal–Organic Framework Functionalized Carbon Nanotube Transistors

“…[2] The sensor is also competitive to other types of ethanol sensors as shown in the comparison Table 3. Sensors based on pristine CNTFETs show only a weak response to ethanol, [28][29][30][31] and therefore only CNT-based sensors are listed where their response was enhanced by decoration with other materials or defect formation. Also not listed are MOF ethanol sensors that are based on capacitive and optical readout, [32,33] since those sensors appeared to be slow compared to an electrical readout of FET-type devices.…”

“…However, we can nevertheless consider in more detail the dynamics of the device. The sensor responds to charge accumulation and hence to the charging of adsorption sites at the Al 2 O 3 /MOF interface, which in turn depends on the diffusion of ethanol molecules through the MoS 2 /ZnO 30 s@500 ppm 220°500 ppm [39] Fe 2 O 3 /SnO 2 9 s@100 ppm 320°2 ppm [40] ZnO/SnO 2 1 s@30 ppm 225°0.5 ppm [41] Pt-Pd/MWCNTs Not specified 25°3 ppm [42] ZnO/MWCNTs 4 s@300 ppm 260°1 ppm [43] SnO 2 /MWCNTs 150 s@not specified 350°not specified [44] Defective MWCNTs 92 s@50 ppm 30°5 ppm [30] Defective SWCNTs 60 s@500 ppm 22°Not specified [31] Carbon nanobuds 60 s@50 ppm 22°50 ppm [31] GrO/aniline 0.03 s@500 ppm 25°500 ppm [45] Gr/ZnO NWs Not specified 125°1 ppm [46] MOF/graphene 5 s@100 ppm 25°100 ppm [2] MOF/CNT 10 s@10 ppm 25°≪ 1 ppb this work MOF layer. At the Al 2 O 3 /MOF interface, the ethanol molecules are then catalytically split into H + and alkoxy − , which eventually leads to a charging of the adsorption sites as discussed above.…”

Gases in Food Production and Monitoring: Recent Advances in Target Chemiresistive Gas Sensors

“…Thus, C 2 H 5 OH sensors are considered as important for the detection of spoilage of stored food. Thus, an ultra-sensitive C 2 H 5 OH sensor was developed based on highly defected CNTs [107]. The CNTs were fabricated by the PECVD method, as shown in Figure 4a.…”

Fabrication and characterization of a bifunctional zinc oxide/multiwalled carbon nanotube/ poly(3,4-ethylenedioxythiophene): Polystyrene sulfonate composite thin film

“…Shalaan et al showed that when in an ethanol sensor MWCNTs were used to detect 50 ppm of the target gas, upon the exposure of reducing molecules, electrons were injected at the effective sites of CNTs' surface, then the electrons were released back when the gas was switched off. This caused first an increase and then a decrease in the measured resistance, showing the p-type behavior of CNTs [43]. Forming ZnO/CNT composite structure can increase the response dramatically and lower the optimum operating temperature for certain gasses [44].…”