Effect of Humidity on Light-Activated NO and NO2 Gas Sensing by Hybrid Materials

Delafossite CuGaO2-Based Chemiresistive Sensor for Sensitive and Selective Detection of Dimethyl Disulfide

Dimethyl disulfide (DMDS) is a common odor pollutant with an extremely low olfactory threshold. Highly sensitive and selective detection of DMDS in ambient humid air background, by metal oxide semiconductor (MOS) sensors, is highly desirable to address the increased public concern for health risk. However, it has still been a critical challenge up to now. Herein, p-type delafossite CuGaO2 has been proposed as a promising DMDS sensing material owing to its striking hydrophobicity (revealed by water contact angle measurement) and excellent partial catalytic oxidation properties (indicated by mass spectroscopy). The present CuGaO2 sensor shows a selective DMDS response, with satisfied humidity resistance performance and long-term stability at a relatively low operation temperature of 140 °C. An ultrahigh response of 100 to 10 ppm DMDS and a low limit of detection of 3.3 ppb could be achieved via a pulsed temperature modulation strategy. A smart sensing system based on a CuGaO2 sensor has been developed, which could precisely monitor DMDS vapor in ambient humid air, even with the presence of multiple interfering gases, demonstrating the practical application capability of MOS sensors for environmental odor monitoring.

Overall perspective of electrospun semiconductor metal oxides as high-performance gas sensor materials for NOx detection

Gas sensors based on nanostructured semiconductor metal oxide (SMO) materials have been extensively investigated as key components due to their advantages over other materials, namely, high sensitivity, stability, affordability, rapid response and simplicity. However, the difficulty of working at high temperatures, response in lower concentration and their selectivity are huge challenges of SMO materials for detecting gases. Therefore, researchers have not stopped their quest to develop new gas sensors based on SMOs with higher performance. This paper begins by highlighting the importance of nitrogen monoxide (NO) and nitrogen dioxide (NO2) detection for human health and addresses the challenges associated with existing methods in effectively detecting them. Subsequently, the mechanism of SMO gas sensors, analysis of their structure and fabrication techniques focusing on electrospinning technique, as well as their advantages, difficulties, and structural design challenges are discussed. Research on enhancing the sensing performance through tuning the fabrication parameters are summarized as well. Finally, the problems and potential of SMO based gas sensors to detect NOx are revealed, and the future possibilities are stated.

Transducer-Aware Hydroxy-Rich-Surface Indium Oxide Gas Sensor for Low-Power and High-Sensitivity NO2 Gas Sensing

Low-power metal oxide (MOX)-based gas sensors are widely applied in edge devices. To reduce power consumption, nanostructured MOX-based sensors that detect gas at low temperatures have been reported. However, the fabrication process of these sensors is difficult for mass production, and these sensors are lack uniformity and reliability. On the other hand, MOX film-based gas sensors have been commercialized but operate at high temperatures and exhibit low sensitivity. Herein, commercially advantageous highly sensitive, film-based indium oxide sensors operating at low temperatures are reported. Ar and O₂ gases are simultaneously injected during the sputtering process to form a hydroxy-rich-surface In₂O₃ film. Conventional indium oxide (In₂O₃) films (A0) and hydroxy-rich indium oxide films (A1) are compared using several analytical techniques. A1 exhibits a work function of 4.92 eV, larger than that of A0 (4.42 eV). A1 exhibits a Debye length 3.7 times longer than that of A0. A1 is advantageous for gas sensing when using field effect transistors (FETs) and resistors as transducers. Because of the hydroxy groups present on the surface of A1, A1 can react with NO₂ gas at a lower temperature (∼100 °C) than A0 (180 °C). Operando diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) shows that NO₂ gas is adsorbed to A1 as nitrite (NO₂^-) at 100 °C and nitrite and nitrate (NO₃^-) at 200 °C. After NO₂ is adsorbed as nitrate, the sensitivity of the A1 sensor decreases and its low-temperature operability is compromised. On the other hand, when NO₂ is adsorbed only as nitrite, the performance of the sensor is maintained. The reliable hydroxy-rich FET-type gas sensor shows the best performance compared to that of the existing film-based NO₂ gas sensors, with a 2460% response to 500 ppb NO₂ gas at a power consumption of 1.03 mW.

The Effect of Rare Earths on the Response of Photo UV-Activate ZnO Gas Sensors

In this work, ZnO nanoparticle resistive sensors decorated with rare earths (REs; including Er, Tb, Eu and Dy) were used at room temperature to detect atmospheric pollutant gases (NO₂, CO and CH₄). Sensitive films were prepared by drop casting from aqueous solutions of ZnO nanoparticles (NPs) and trivalent RE ions. The sensors were continuously illuminated by ultraviolet light during the detection processes. The effect of photoactivation of the sensitive films was studied, as well as the influence of humidity on the response of the sensors to polluting gases. Comparative studies on the detection properties of the sensors showed how the presence of REs increased the response to the gases detected. Low concentrations of pollutant gases (50 ppb NO₂, 1 ppm CO and 3 ppm CH₄) were detected at room temperature. The detection mechanisms were then discussed in terms of the possible oxidation-reduction (redox) reaction in both dry and humid air atmospheres.

Heterobimetallic Ru(II)/M (M = Ag+, Cu2+, Pb2+) Complexes as Photosensitizers for Room-Temperature Gas Sensing

This work is devoted to the investigation of heterobimetallic Ru(II) complexes as photosensitizers for room-temperature photoactivated In2O3-based gas sensors. Nanocrystalline In2O3 was synthesized by the chemical precipitation method. The obtained In2O3 matrix has a single-phase bixbyite structure with an average grain size of 13-14 nm and a specific surface area of 72 ± 3 m2/g. The synthesis of new ditope ligands with different coordination centers, their ruthenium complexes, and the preparation of heterobimetallic complexes with various cations of heavy and transition metals (Ag+, Pb2+, or Cu2+) is reported. The heterobimetallic Ru(II) complexes were deposited onto the surface of the In2O3 matrix by impregnation. The obtained hybrid materials were characterized by X-ray fluorescent analysis, FTIR spectroscopy, and optical absorption spectroscopy. The elemental distribution on the hybrids was characterized by energy-dispersive X-ray spectroscopy (EDS) mapping. The gas sensor properties were investigated toward NO2, NO, and NH3 at room temperature under periodic blue LED irradiation. It was identified that the nature of the second binding cation in Ru(II) heterobimetallic complexes can influence the selectivity toward different gases. Thus, the maximum sensor signal for oxidizing gases (NO2, NO) was obtained for hybrids containing Ag+ or Pb2+ cations while the presence of Cu2+ cation results in the highest and reversible sensor response toward ammonia. This may be due to the specific adsorption of NH3 molecules on Cu2+ cations. On the other hand, Cu2+ ions are proposed to be active sites for the reduction of nitrogen oxides to N2. This fact leads to a significant decrease in the sensor response toward NO2 and NO gases.

Potential sensing of toxic chemical warfare agents (CWAs) by twisted nanographenes: A first principle approach

The toxic chemical warfare agents (CWAs) are extremely harmful to the living organisms. Their efficient detection and removal in a limited time span are essential for the human health and environmental security. Twisted nanographenes have great applications in the fields of energy storage and optoelectronics, but their use as sensors is rarely described. Therefore, we have explored the sensitivity and selectivity of twisted nanographene analogues (C₃₂H₁₆, C₆₄H₃₂) towards selected toxic CWAs, including phosgene, thiophosgene and formaldehyde. The interaction between CWAs and twisted nanographenes is mainly interpreted by considering the optimized geometries, adsorption energies, natural bond orbital (NBO), frontier molecular orbital (FMO), non-covalent interaction (NCI) and quantum theory of atoms in molecules (QTAIM) analyses. The structural geometries show that the central octagon of twisted nanographenes is the most favorable site of interaction. The interaction energies reveal the physisorption of selected CWAs on tNGs surface. The average energy gap change (%E_H-L^a) and % sensitivity are quantitatively determined to evaluate the sensing capability of the twisted nanographenes. Among the selected CWAs molecules, the sensitivity of tNG analogues (C₃₂H₁₆ and C₆₄H₃₂) is superior towards thiophosgene (ThP), which is revealed by the high interaction energies of -8.19 and - 12.17 kcal/mol, respectively. This theoretical study will help experimentalists to devise novel sensors based on twisted nanographenes for the detection of toxic CWAs which may also work efficiently under the humid conditions.

In2O3 Based Hybrid Materials: Interplay between Microstructure, Photoelectrical and Light Activated NO2 Sensor Properties

In this work, organic–inorganic hybrids based on nanocrystalline indium oxide and ruthenium (II) heteroleptic complexes were used as sensitive materials for room temperature light-activated NO2 detection. In2O3 was obtained by chemical precipitation method and then annealed at three different temperatures (T = 300, 500, 700 °C) in order to investigate the influence of the microstructure of indium oxide on sensor characteristics of hybrid materials and on kinetics of the rise and fall of photoconductivity. The results of the X-ray phase analysis demonstrated that the obtained materials are single-phase with a cubic bixbyite structure. The Ru (II) heteroleptic complex, which was used as a photosensitizer, made it possible to shift the optical sensitivity range of the hybrids to the low energy region of the spectrum and to use a low-power LED (λmax = 470 nm) source for the photoactivation process. The sensor properties were investigated toward NO2 at sub-ppm range at room temperature. It was found that for pure oxides, the sensor signal correlates with a specific surface area, while for hybrid materials, both the sensor signal and photoresponse increase with increasing the matrix crystallinity. In this case, the main role is played by traps of nonequilibrium charge carriers, which are structural defects in the matrix.