Ab Initio Study of SOF2 and SO2F2 Adsorption on Co-MoS2

Advances in 2D Materials Based Gas Sensors for Industrial Machine Olfactory Applications

The escalating development and improvement of gas sensing ability in industrial equipment, or "machine olfactory", propels the evolution of gas sensors toward enhanced sensitivity, selectivity, stability, power efficiency, cost-effectiveness, and longevity. Two-dimensional (2D) materials, distinguished by their atomic-thin profile, expansive specific surface area, remarkable mechanical strength, and surface tunability, hold significant potential for addressing the intricate challenges in gas sensing. However, a comprehensive review of 2D materials-based gas sensors for specific industrial applications is absent. This review delves into the recent advances in this field and highlights the potential applications in industrial machine olfaction. The main content encompasses industrial scenario characteristics, fundamental classification, enhancement methods, underlying mechanisms, and diverse gas sensing applications. Additionally, the challenges associated with transitioning 2D material gas sensors from laboratory development to industrialization and commercialization are addressed, and future-looking viewpoints on the evolution of next-generation intelligent gas sensory systems in the industrial sector are prospected.

Detection of SO2F2 Using a Photoacoustic Two-Chamber Approach

The wide use of sulfuryl difluoride (SO2F2) for termite control in buildings, warehouses and shipping containers requires the implementation of suitable sensors for reliable detection. SO2F2 is highly toxic to humans and the environment, and moreover, it is a potent greenhouse gas. We developed two photoacoustic two-chamber sensors with the aim to detect two different concentration ranges, 0-1 vol.-% SO2F2 and 0-100 ppm SO2F2, so that different applications can be targeted: the sensor for high concentrations for the effective treatment of buildings, containers, etc., and the sensor for low concentrations as personal safety device. Photoacoustic detectors were designed, fabricated, and then filled with either pure SO2F2 or pure substituent gas, the refrigerant R227ea, to detect SO2F2. Absorption cells with optical path lengths of 50 mm and 1.6 m were built for both concentration ranges. The sensitivity to SO2F2 as well as cross-sensitivities to CO2 and H2O were measured. The results show that concentrations below 1 ppm SO2F2 can be reliably detected, and possible cross-sensitivities can be effectively compensated.

Theoretical Study on Adsorption Behavior of SF6 Decomposition Components on Mg-MOF-74

SF₆ gas is an arc extinguishing medium that is widely used in gas insulated switchgear (GIS). When insulation failure occurs in GIS, it leads to the decomposition of SF₆ in partial discharge (PD) and other environments. The detection of the main decomposition components of SF₆ is an effective method to diagnose the type and degree of discharge fault. In this paper, Mg-MOF-74 is proposed as a gas sensing nanomaterial for detecting the main decomposition components of SF₆. The adsorption of SF₆, CF₄, CS₂, H₂S, SO₂, SO₂F₂ and SOF₂ on Mg-MOF-74 was calculated by Gaussian16 simulation software based on density functional theory. The analysis includes parameters of the adsorption process such as binding energy, charge transfer, and adsorption distance, as well as the change in bond length, bond angle, density of states, and frontier orbital of the gas molecules. The results show that Mg-MOF-74 has different degrees of adsorption for seven gases, and chemical adsorption will lead to changes in the conductivity of the system; therefore, it can be used as a gas sensing material for the preparation of SF6 decomposition component gas sensors.

Towards a Miniaturized Photoacoustic Detector for the Infrared Spectroscopic Analysis of SO2F2 and Refrigerants

Sulfuryl fluoride (SO₂F₂) is a toxic and potent greenhouse gas that is currently widely used as a fumigant insecticide in houses, food, and shipping containers. Though it poses a major hazard to humans, its detection is still carried out manually and only on a random basis. In this paper, we present a two-chamber photoacoustic approach for continuous SO₂F₂ sensing. Because of the high toxicity of SO₂F₂, the concept is to use a non-toxic substituent gas with similar absorption characteristics in the photoacoustic detector chamber, i.e., to measure SO₂F₂ indirectly. The refrigerants R227ea, R125, R134a, and propene were identified as possible substituents using a Fourier-transform infrared (FTIR) spectroscopic analysis. The resulting infrared spectra were used to simulate the sensitivity of the substituents of a photoacoustic sensor to SO₂F₂ in different concentration ranges and at different optical path lengths. The simulations showed that R227ea has the highest sensitivity to SO₂F₂ among the substituents and is therefore a promising substituent detector gas. Simulations concerning the possible cross-sensitivity of the photoacoustic detectors to H₂O and CO₂ were also performed. These results are the first step towards the development of a miniaturized, sensitive, and cost-effective photoacoustic sensor system for SO₂F₂.

First-Principles Calculations for Adsorption of HF, COF2, and CS2 on Pt-Doped Single-Walled Carbon Nanotubes

HF, CS₂, and COF₂ are three important decomposition components of the SF₆ gas insulation medium. In this paper, the gas sensitivity of Pt doped on (8, 0) single-walled carbon nanotube (SWCNT) to HF, CS₂, and COF₂ is investigated based on density functional theory. The binding energy, charge transfer, density of states, and frontier molecular orbital theory are discussed. It is found that all processes of HF, CS₂, and COF₂ adsorbed on Pt-SWCNT are exothermic. Pt-SWCNT donated 0.182 electrons to CS₂ molecules during the interaction process but acts as an electron acceptor during adsorption of HF and COF₂ on it. After comprehensive consideration of binding energy and charge transfer, the response of Pt- SWCNT to CS₂ may be the best, and those to HF and COF₂ are almost the same. In addition, after the adsorption of the three kinds of gases on Pt-SWCNT, the order of the conductivity of the Pt-SWCNT material is CS₂ > COF₂ ≈ HF via frontier molecular orbital theory analysis. The Pt-SWCNT material is probably more suitable as a gas sensor for the detection of CS₂ in the application of gas-insulated equipment.

First-Principle Insight into Ga-Doped MoS2 for Sensing SO2, SOF2 and SO2F2

First-principle calculations were carried out to simulate the three decomposition gases (SO2, SOF2, and SO2F2) of sulfur hexafluoride (SF6) on Ga-doped MoS2 (Ga-MoS2) monolayer. Based on density functional theory (DFT), pure MoS2 and multiple gas molecules (SF6, SO2, SOF2, and SO2F2) were built and optimized to the most stable structure. Four types of Ga-doped positions were considered and it was found that Ga dopant preferred to be adsorbed by the top of Mo atom (TMo). For the best adsorption effect, two ways of SO2, SOF2, and SO2F2 to approach the doping model were compared and the most favorable mode was selected. The adsorption parameters of Ga-MoS2 and intrinsic MoS2 were calculated to analyze adsorption properties of Ga-MoS2 towards three gases. These analyses suggested that Ga-MoS2 could be a good gas-sensing material for SO2 and SO2F2, while it was not suitable for SOF2 sensing due to its weak adsorption. This work provides a theoretical basis for the development of Ga-MoS2 materials with the hope that it can be used as a good gas-sensing material for electrical equipment.

Pt Cluster Modified h-BN for Gas Sensing and Adsorption of Dissolved Gases in Transformer Oil: A Density Functional Theory Study

Hexagonal-Boron nitride nanotubes (h-BN) decorated with transition metals have been widely studied due to their enhanced physicochemical properties. In this paper, Pt cluster-modified h-BN is proposed as a sensitive material for a novel gas sensor for the online malfunction monitoring of oil-immersed transformers. The inner oil is ultimately decomposed to various gases during the long-term use of oil-immersed transformers. Exposure to excessively high temperatures produces the alkanes CH₄ and C₂H₆, whereas different degrees of discharge generate H₂ and C₂H₂. Therefore, the identification of H₂, CH_4, and C₂H₂ gas efficiently measures the quality of transformers. Based on the density functional theory, the most stable h-BN doped with 1-4 Pt atoms is employed to simulate its adsorption performance and response behavior to these typical gases. The adsorption energy, charge transfer, total density of states, projected density of states, and orbital theory of these adsorption systems are analyzed and the results show high consistency. The adsorption ability for these decomposition components are ordered as follows: C₂H₂ > H₂ > CH₄. Pt cluster-modified h-BN shows good sensitivity to C₂H₂, H₂, with decreasing conductivity in each system, but is insensitive to CH₄ due to its weak physical sorption. The conductivity change of Pt_n-h-BN is considerably larger upon H₂ than that upon C₂H₂, but is negligible upon CH₄. Our calculations suggest that Pt cluster modified h-BN can be employed in transformers to estimate their operation status.