Diverse Adsorption/Desorption Abilities Originating from the Nanostructural Morphology of VOC Gas Sensing Devices Based on Molybdenum Trioxide Nanorod Arrays

Abstract

attention from researchers because of their advantages of sensitivity, rapid response, and inexpensive production. [9,10] Recently, considerable effort has been devoted to developing much simpler routes to control the shape and grain size of SMO to achieve a higher surface-to-area ratio and unique surface chemistry behavior to improve sensing performance. [11][12][13] Among the metal oxides, molybdenum trioxide (MoO 3 ) is one of the most desirable for use in gas sensors because of its indirect wide band gap of 3.5 eV. [14][15][16][17] MoO 3 -based gas analyzing devices show excellent gas sensing properties for several kinds of gas species [18][19][20][21][22][23][24] because of their special quantum size effect, surface effect, high reactivity, and the polyvalency of molybdate. In particular, MoO 3 nanostructures, such as MoO 3 nanobelts, flower-like microstructured MoO 3 , and net-like MoO 3 porous architectures synthesized by the hydrothermal route, exhibit appealing sensing properties for VOC vapors. [25][26][27] The gas sensing properties of MoO 3 thin film fabricated by radiofrequency (RF) sputtering have also been investigated. [28] These reports showed the nanostructures possessed typical sensing performance for VOC vapors; however, these nanostructures need to be processed with two or more steps, which is time consuming. For instance, these nanostructures need to be transferred or arranged on a ceramic substrate and then annealed to obtain substantial growth/adhesion on the substrate. To increase the VOC gas sensing performance of nanostructures, they needed to be loaded with noble metal particles (e.g., Au, Nanorod arrays gas sensors are attracting much scientific and engineering interest because of their excellent sensing performance arising from their unique nanostructures. In this work, large-scale random 3D networks of ultrafine single-crystal α-MoO 3 nanorod arrays are applied as gas sensors. The arrays are spontaneously grown by a simple single-step solution route. A prompt response and obvious discrimination of ethanol, methanol, isopropanol, and acetone vapors at 573 K are investigated via the modulation of the resistance of the gas sensors. The sensitivity, response time, and recovery time of the sensors strongly depend on the specific morphologies of the nanorod arrays, such as length, number, and coverage of nanorods in the 3D network. A reaction mechanism in which the 3D-network nanorod arrays adsorb and react with the target molecules more readily than the seed layer is proposed to explain the different response and recovery times of the sensors. These random 3D-network nanorod arrays with functionally tunable morphology are promising for universal application as gas sensors for detecting various vapors, and provide valuable insights for the production of fast, largescale, low-cost, and simple synthesis of sensing devices.

Tackling Humidity with Designer Ionic Liquid‐Based Gas Sensing Soft Materials

“…Moreover, our electrical and optical systems presented lower response times to VOCs when compared with other reported sensors such as metal oxide sensors [ 44,45 ] or liquid crystals. [ 46 ]…”

Systematic Study of Oxygen Vacancy Tunable Transport Properties of Few‐Layer MoO3−x Enabled by Vapor‐Based Synthesis

“…Oxygen substoichiometry introduces electronic gap states and increased electrical conductivity . These bulk tunable transport properties have shown applicability across a number of technological regimes, including as a promising electrochromic, battery cathode material, and gas sensor . Recent excitement has been driven by the high work function (6.6 eV) and hole transport properties of MoO 3– x , which have been used to meaningfully improve conversion efficiencies for solar cells and OLEDs …”

Quantitatively Discriminating Alcohol Molecules by Thermally Modulating NiO‐Based Sensor Arrays

“…Meanwhile, regarding the same Sc-Li:NiO sensor, the optimal operation temperature shifts from ≈225 °C (methanol) to 200 °C (IPA) and 175 °C (ethanol), implying a difference in the reducibility of alcohol groups with different numbers of carbon chains, which leads to differences in the rate of the redox reaction on the surfaces of sensitive materials. [30] Although the isothermal measurements of the NiO sensor arrays (Figure 2a-c demonstrated its efficiency and capability for molecule feature extraction, [22,31] as illustrated by the recognition performance comparison between temperature modulation and isothermal testing (Figure S3, Supporting Information). Because temperature plays a crucial role in the adsorption and subsequent redox reactions of adsorbed molecules with MOS surfaces, [20] appropriately selecting the temperature range for temperature modulation is critical for fully exploring the discrimination capability of an MOS sensor.…”