Outstanding Room-Temperature Hydrogen Gas Detection by Plasma-Assisted and Graphene-Functionalized Core-Shell Assembly of SnO2 Nanoburflower

Rahman SF, Mohd Yusoff MF, Hamzah A. Hydrogen gas sensing performance of a carbon-doped boron nitride nanoribbon at elevated temperatures

In this study, computational simulations were used to investigate the performance of a carbon-doped boron nitride nanoribbon (BC2NNR) for hydrogen (H2) gas sensing at elevated temperatures. The adsorption energy and charge transfer were calculated when H2 was simultaneously attached to carbon, boron, and both boron and nitrogen atoms. The sensing ability was further analyzed considering the variations in current-voltage (I-V) characteristics. The simulation results indicated that the energy bandgap of H2 on carbon, boron, and both boron and nitrogen exhibited a marginal effect during temperature variations. However, significant differences were observed in terms of adsorption energy at a temperature of 500 K, wherein the adsorption energy was increased by 99.62% of that observed at 298 K. Additionally, the evaluation of charge transfer indicated that the strongest binding site was achieved at high adsorption energies with high charge transfers. Analysis of the I-V characteristics verified that the currents were considerably affected, particularly when a certain concentration of H2 molecules was added at the highest sensitivity of 15.02% with a bias voltage of 3 V. The sensitivity at 298 K was lower than those observed at 500 and 1000 K. The study findings can form the basis for further experimental investigations on BC2NNR as a hydrogen sensor.

A Cr2O3-doped graphene sensor for early diagnosis of liver cirrhosis: a first-principles study

Liver cirrhosis is among the leading causes of death worldwide. Because of its asymptomatic evolution, timely diagnosis of liver cirrhosis via non-invasive techniques is currently under investigation. Among the diagnostic methods employing volatile organic compounds directly detectable from breath, sensing of limonene (C₁₀H₁₆) represents one of the most promising strategies for diagnosing alcohol liver diseases, including cirrhosis. In the present work, by means of state-of-the-art Density Functional Theory calculations including the U correction, we present an investigation on the sensing capabilities of a chromium-oxide-doped graphene (i.e., Cr₂O₃-graphene) structure toward limonene detection. In contrast with other structures such as g-triazobenzol (g-C₆N₆) monolayers and germanane, which revealed their usefulness in detecting limonene via physisorption, the proposed Cr₂O₃-graphene heterostructure is capable of undergoing chemisorption upon molecular approaching of limonene over its surface. In fact, a high adsorption energy is recorded (∼-1.6 eV). Besides, a positive Moss-Burstein effect is observed upon adsorption of limomene on the Cr₂O₃-graphene heterostructure, resulting in a net increase of the bandgap (∼50%), along with a sizeable shift of the Fermi level toward the conduction band. These findings pave the way toward the experimental validation of such predictions and the employment of Cr₂O₃-graphene heterostructures as sensors of key liver cirrhosis biomarkers.

Ultralow detection limit and ultrafast response/recovery of the H2 gas sensor based on Pd-doped rGO/ZnO-SnO2 from hydrothermal synthesis

Hydrogen (H₂) sensors are of great significance in hydrogen energy development and hydrogen safety monitoring. However, achieving fast and effective detection of low concentrations of hydrogen is a key problem to be solved in hydrogen sensing. In this work, we combined the excellent gas sensing properties of tin(IV) oxide (SnO₂) and zinc oxide (ZnO) with the outstanding electrical properties of reduced graphene oxide (rGO) and prepared palladium (Pd)-doped rGO/ZnO-SnO₂ nanocomposites by a hydrothermal method. The crystal structure, structural morphology, and elemental composition of the material were characterized by FE-SEM, TEM, XRD, XPS, Raman spectroscopy, and N₂ adsorption-desorption. The results showed that the Pd-doped ZnO-SnO₂ composites were successfully synthesized and uniformly coated on the surface of the rGO. The hydrogen gas sensing performance of the sensor prepared in this work was investigated, and the results showed that, compared with the pure Pd-doped ZnO-SnO₂ sensor, the Pd-doped rGO/ZnO-SnO₂ sensor modified with 3 wt% rGO had better hydrogen (H₂)-sensing response of 9.4-100 ppm H₂ at 380 °C. In addition, this sensor had extremely low time parameters (the response time and recovery time for 100 ppm H₂ at 380 °C were 4 s and 8 s, respectively) and an extremely low detection limit (50 ppb). Moreover, the sensor exhibited outstanding repeatability and restoration. According to the analysis of the sensing mechanism of this nanocomposite, the enhanced sensing performance of the Pd-doped rGO/ZnO-SnO₂ sensor is mainly due to the heterostructure of rGO, ZnO, and SnO₂, the excellent electrical and physical properties of rGO and the synergy between rGO and Pd.

Electronic Nose Based on Temperature Modulation of MOS Sensors for Recognition of Excessive Methanol in Liquors

An electronic nose based on metal oxide semiconductor (MOS) sensors has been used to identify liquors with excessive methanol. The technique for a square wave temperature modulated MOS sensor was applied to generate the response patterns and a back-propagation neural network was used for pattern recognition. The parameters of temperature modulation were optimized according to the difference in response features of target gases (methanol and ethanol). Liquors with excessive methanol were qualitatively and quantitatively identified by the neural network. The results showed that our electronic nose system could well identify the liquors with excessive methanol with more than 92% accuracy. This electronic nose based on temperature modulation is a promising portable adjunct to other available techniques for quality assurance of liquors and other alcoholic beverages.

The role of surface stoichiometry in NO2 gas sensing using single and multiple nanobelts of tin oxide

Typically used semiconducting metal oxides (SMOs) consist of several varying factors that affect gas sensor response, including film thickness, grain size, and notably the grain-grain junctions within the active device volume, which complicates the analysis and optimisation of sensor response. In comparison, devices containing a single nanostructured element do not present grain-grain junctions, and therefore present an excellent platform to comprehend the correlation between nanostructure surface stoichiometry and sensor response to the depletion layer (Debye length, LD) variation after the analyte gas adsorption/chemisorption. In this work, nanofabricated devices containing SnO2 and Sn3O4 individual nanobelts of different thicknesses were used to estimate their LD after NO2 exposure. In the presence of 40 ppm of NO2 at 150 °C, LD of 12 nm and 8 nm were obtained for SnO2 and Sn3O4, respectively. These values were associated to the sensor signals measured using multiple nanobelts onto interdigitated electrodes, outlining that the higher sensor signal of the Sn4+ surface (up to 708 for 100 ppm NO2 at 150°) in comparison with the Sn2+ (up to 185) can be explained based on a less depleted initial state and a lower surface electron affinity caused by the Lewis acid/base interactions with oxygen species from the baseline gas. To support the proposed mechanisms, we investigated the gas sensor response of SnO2 nanobelts with a higher quantity of oxygen vacancies and correlated the results to the SnO system.

Underpinning the Interaction between NO2 and CuO Nanoplatelets at Room Temperature by Tailoring Synthesis Reaction Base and Time

An approach to tailor the morphology and sensing characteristics of CuO nanoplatelets for selective detection of NO₂ gas is of great significance and an important step toward achieving the challenge of improving air quality and in assuring the safety of mining operations. As a result, in this study, we report on the NO₂ room temperature gas-sensing characteristics of CuO nanoplatelets and the underlying mechanism toward the gas-sensing performance by altering the synthesis reaction base and time. High sensitivity of ∼40 ppm^-1 to NO₂ gas at room temperature has been realized for gas sensors fabricated from CuO nanoplatelets, using NaOH as base for reaction times of 45 and 60 min, respectively at 75 °C. In both cases, the crystallite size, surface area, and hole concentration of the respective materials influenced the selectivity and sensitivity of the NO₂ gas sensors. The mechanism underpinning the superior NO₂ gas sensing are thoroughly discussed in terms of the crystallite size, hole concentration, and surface area as active sites for gas adsorption.