Humidity-Tolerant Room-Temperature Selective Dual Sensing and Discrimination of NH₃ and NO Using a WS₂/MWCNT Composite

Abstract

Continuous detection of toxic and hazardous gases like nitric oxide (NO) and ammonia (NH3) is needed for environmental management and noninvasive diagnosis of various diseases. However, to the best of our knowledge, dual detection of these two gases has not been previously reported. To address the challenge, we demonstrate the design and fabrication of low-cost NH3 and NO dual gas sensors using tungsten disulfide/multiwall carbon nanotube (WS2/MWCNT) nanocomposites as sensing channels which maintained their performance in a humid environment. The composite-based device has shown successful dual detection at temperatures down to 18 °C and relative humidity of 90%. For 0.1 ppm ammonia, it exhibited a p-type conduction with response and recovery times of 102 and 261 s, respectively; on the other hand, with NO (10 ppb, n-type), these times were 285 and 198 s, respectively. The device with 5 mg MWCNTs possesses a superior selectivity along with a relative response of ≈7% (5 ppb) and ≈5% (0.1 ppm) for NO and NH3, respectively, at 18 °C. The response is less affected by relative humidity, and this is attributed to the presence of MWCNTs that are hydrophobic in nature. Upon simultaneous exposure to NO (5–10 ppb) and NH3 (0.1–5 ppm), the response was dominated by NO, implying clear discrimination to the simultaneous presence of these two gases. We propose a sensing mechanism based on adsorption/desportion and accompanied charge transfer between the adsorbed gas molecules and sensing surface. The results suggest that an optimized weight ratio of WS2 and MWCNTs could govern favorable sensing conditions for a particular gas molecule.

Ultrasensitive Room-Temperature NO2 Detection Using SnS2/MWCNT Composites and Accelerated Recovery Kinetics by UV Activation

“…Hence, the addition of MWCNTs enhances electron charge transfer and has proven to be beneficial for improved gas sensing. MWCNTs possess high adsorption ability and provide a different electronic environment when used as a NO 2 sensing devices. ,− Their strong mechanical properties and high thermal stability may improve device usability. MWCNTs are p-type semiconductors with a much higher hole density than electron density .…”

“…For gaseous components, a desired volume of the gas was injected into the test chamber using a high-precision syringe. For these gases, the concentration of gas molecules inside the test chamber was calculated using eq , where C c is the required concentration in the test chamber, V is the volume of the test chamber (1 L), and C p (1000 ppm) and V s are the known concentration of gas in the purchased cylinder and the volume of the gas taken in a syringe, respectively. , For ethanol, acetone, formaldehyde, and DMF, eq S1 (Supporting Information) was used to calculate the concentration in ppm. UV irradiation (2.3 mW/1 cm × 0.5 cm) was carried out over the sensor device and applied as needed.…”

“…For gaseous components, a desired volume of the gas was injected into the test chamber using a high-precision syringe. For these gases, the concentration of gas molecules inside the test chamber was calculated using eq 3 12,56…”

“…The positions and intensity ratios of the D and G bands (I D /I G ) (Table S1) indicate that the composites primarily incorporate amorphous carbon with minor graphitic crystallites. 56 Scanning electron microscopy (SEM) was used to examine the morphology and microstructure of the as-synthesized SnS 2 and composite samples. Figure S3 panel (a) shows the SEM image of MWCNTs.…”

Heterojunctions on Ta2O5@MWCNT for Ultrasensitive Ethanol Sensing at Room Temperature

“…Because of their structural properties, they will cause cardiovascular diseases, respiratory tract infections, cancers, and so on. 3−5 In addition, together with several hazardous and toxic gases such as nitrogen oxides 6 (NO x ), sulfur oxide (SO x ), ammonia 7−9 (NH 3 ), chlorine (Cl 2 ), and carbon oxides (CO x ), VOCs are also the major source of environmental pollution. 10−13 The discharge of these poisonous and harmful gases will cause many serious consequences such as acid rain and damage to the ecological environment.…”