Core–Shell Nanostructures of Tungsten Oxide and Hydrogen Titanate for H₂ Gas Adsorption

Abstract

Nanostructured tungsten oxide is a promising material for sensing reducing gases such as hydrogen. However, this material exhibits limitations due to a poor response toward sensing at room temperature, incomplete recovery to the initial state, long response time, and a low response factor, which is not desired for explosive gases like hydrogen. In this work, we, for the first time, demonstrate that these limitations can be significantly overcome using the core–shell structure of tungsten oxide (WO3) nanorods and hydrogen titanate (H2Ti3O7) nanotubes developed and suitably defect-engineered by low-energy ion irradiation. The sensor based on the pristine core–shell heterostructure of tungsten oxide nanorods and hydrogen titanate nanotubes exhibits excellent response and selectivity to different concentrations of H2 ranging from 10 to 500 ppm. However, it requires a quite high temperature of 300 °C with response and recovery times of about 38 and 99.8 s, respectively. After irradiation, the hybrid form shows a similar level of response and selectivity, however, at a much lower temperature of about 120 °C with significantly faster response and recovery times of about 16 and 18 s, respectively. Such an ion beam-modified structure addresses critical issues of developing a gas-sensing device, such as the effects of moisture and power consumption. The experimental observations are very well in agreement with the predictions of the state-of-the-art Monte Carlo-based TRI3DYN ion-solid interaction simulation, and the gas-sensing mechanism was explained using first principles-based calculation. The study reveals that low-energy ion-induced defect engineering yields better charge transport, better binding of the gas with the surface, as well as the superior moisture-repelling ability of the surface, leading to better sensing performance than the pristine core-shell structure. This heterostructure between two nanomaterials carries complementary advantages in various aspects, such as the surface area, conductivity, and sensitivity toward a wide range and mixture of gases. Additionally, the wrapping yields good mechanical strength and flexibility, making it possible to use as a flexible sensing device made through a bottom-up fabrication technique.

Water-repelling behavior of the 1-D hematite nano-network

“…It is evident that a greater number of oxygen atoms is sputtered out from the nanorod surface because of preferential sputtering due to higher stoichiometry ratio and the lower atomic mass of oxygen compared with iron. 17,19 The TRI3DYN simulations also confirmed the ion beam mixing, which is much more prominent at the junction point and plays a crucial role in the formation of welded homo-junctions between the hematite nanorods.…”

“…Ar + ions were chosen because of their inertness and the higher capacity for creating cascade-collision-induced defect states because of their higher atomic mass. Previous studies on Ar + ion irradiation have shown remarkable enhancements in properties, such as gas sensing, 16 optical detection, 17 energy storage, 18 hydrogen adsorbtion, 19 nano-device fabrication 20,21 etc., owing to changes in the surface defects and morphological modifications. 22,23 Other important aspects of 1D hematite are its application in sensing, catalysis, and energy devices.…”

Defect-Engineered 3D Nanostructured MoS2 for Detection of Ammonia Gas at Room Temperature

“…In this static gas sensing system, sensing data were obtained by measuring resistance using a two-probe method. The sensing unit has a 250 CC testing chamber, where heating-cum-mounting platform of the samples, electrodes to connect Keithley probes, gas inlet, and outlets are housed . The ammonia detection technique relies on gas adsorption and desorption processes on the surface of the sensing material.…”

“…The sensing unit has a 250 CC testing chamber, where heating-cum-mounting platform of the samples, electrodes to connect Keithley probes, gas inlet, and outlets are housed. 29 The ammonia detection technique relies on gas adsorption and desorption processes on the surface of the sensing material. The sensor was placed in this sealed small chamber at room temperature (25 ± 2 °C) and relative humidity (RH) (50 ± 5%).…”

Fast response/recovery and sub-ppm ammonia gas sensors based on a novel V2CTx@MoS2 composite

“…Its bandgap is between 1.2 and 1.8 eV. 18,19 The heterostructures of MoS 2 /MXene nanocomposites renowned for their tunable bandgaps hold great potential in the elds of catalysis [20][21][22] and ion batteries. 23,24 The highly accessible surface and excellent electron-conducting properties of MoS 2 make it promising for efficient NH 3 detection at RT.…”