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In this paper, the adsorption behaviors of three gases (H2, CO, and C2H2) decomposed by the transformer oil on Pd-GaSe and Pd3-GaSe monolayers were calculated by density functional theory. Compared with Pd single-atom doping, Pd3 cluster doping changed the original structure and charge distribution to a greater extent, and more obviously improved the conductivity. According to the analysis of adsorption energy, charge transfer and deformation charge density, the results show that the two doped structures have better adsorption performance for the three gas molecules (H2, CO, and C2H2) than the intrinsic GaSe monolayer. Compared with Pd-GaSe, Pd3-GaSe showed stronger adsorption property for the three gases. Analysis of frontier molecular orbitals and recovery characteristics shows that Pd3-GaSe can be used as an ideal gas sensitive material for H2 detection because of its good desorption properties and obvious conductivity changes. Pd-GaSe can be used as a disposable resistive sensor for CO. Pd3-GaSe is a kind of sensing material suitable for disposable resistance sensors for CO and C2H2. These two doped structures have great application potential in gas adsorption and detection, and provide indications for further study on gas sensor detection by means of metal-doped GaSe monolayer. [ABSTRACT FROM AUTHOR]

Sulphide gas is an impurity that affects the quality of natural gas, which needs reasonable storage and transportation. In this work, we investigated the adsorption structure and electronic behavior of hydrogen sulfide (H2S), carbonyl sulfur (COS), and methyl mercaptan (CH3SH) on sulphide gas molecules on pure and vacant α-Fe2O3(001) surfaces by density functional theory with geometrical relaxations. The results show that H2S and CH3SH are mainly adsorbed in the form of molecules on the pure Fe2O3(001) surface. On the vacant α-Fe2O3(001) surface, they can be adsorbed on Fe atoms in molecular form and by dissociation. The absolute value of the adsorption energy of H2S and CH3SH on the vacancy defect α-Fe2O3 surface is larger, and the density of states show that the electron orbital hybridization is more significant, and the adsorption is stronger. The charge differential density and Mulliken charge population analysis show that the charge is rearranged and chemical bonds are formed. The affinity of H2S to the vacancy α-Fe2O3(001) surface is slightly higher than that of CH3SH, while COS molecules basically do not adsorb on the α-Fe2O3(001) surface, which may be related to the stable chemical properties of the molecules themselves. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this study, the adsorption performances of graphene before and after modification to H2S and CH4 molecules were studied using first principles with the density functional theory (DFT) method. The most stable adsorption configuration, the adsorption energy, the density of states, and the charge transfer are discussed to research the adsorption properties of intrinsic graphene (IG), Ni-doped graphene (Ni–G), vacancy defect graphene (DG), and graphene oxide (G–OH) for H2S and CH4. The weak adsorption and charge transfer of IG achieved different degrees of promotion by doping the Ni atom, setting a single vacancy defect, and adding oxygen-containing functional groups. It can be found that a single vacancy defect significantly enhances the strength of interaction between graphene and adsorbed molecules. DG peculiarly shows excellent adsorption performance for H2S, which is of great significance for the study of a promising sensor for H2S gas. [ABSTRACT FROM AUTHOR]

Gas sensors are the key equipment in transformer fault online monitoring systems, and developing new and efficient gas sensing materials is an important prerequisite for breaking through existing monitoring performance. Herein, the first-principles density functional theory (DFT) is employed to study the adsorption and gas-sensing performance of two metal atomic clusters (Pt 3 and Rh 3) anchored on a WTe 2 monolayer (C-WTe 2) for four typical fault characteristic gases (CO, CO 2 , H 2 , and C 2 H 2). These results suggest that four gases can stably bind to C-WTe 2 and exist in the form of chemical adsorption due to the high adsorption energy. Also, Rh 3 -WTe 2 exhibits high selectivity and repeatability towards CO and CO 2 due to its strong response and fast recovery characteristics when used in resistive sensors; Pt 3 -WTe 2 can detect and distinguish the four types of gases due to the significant and differentiated changes in work function when used in work function sensors. Therefore, both Pt 3 -WTe 2 and Rh 3 -WTe 2 monolayers are promising gas-sensing materials for the dissolved gases detection in oil. This investigation sheds light on devices of designing metal atomic cluster anchored WTe 2 -based gas sensor for improved transformer fault monitoring performances. [Display omitted] [ABSTRACT FROM AUTHOR]

Four MoO 3 samples with the Zn element doped mole ratio of 0%, 3%, 6% and 9% were prepared by applying a convenient one-step hydrothermal synthesis method, and the samples presented three-dimensional microflower-like structures assembled by nanosheets. The systematic analysis results indicate that the 6 mol% Zn-doped sample had the most amazing detection characteristics for 50 ppm CO, with a response of 31.23 (4 times of the pure MoO 3) at a lower temperature (240 °C). The large specific surface area, big pore size and tiny particle size were proved to be beneficial to the gas sensitivity, which promotes gases transfer and provides more gases landing points during the gas-sensitive reaction. Besides, based on the density functional theory (DFT), the facilitation effect of doped Zn on the adsorption ability of MoO 3 to CO molecule was verified from the perspective of electronic properties. The excellent gas-sensing performances indicate that the 6 mol% Zn-doped MoO 3 has potential to be applied as a reliable CO sensor. [ABSTRACT FROM AUTHOR]

The online detection and control of concentration for agricultural greenhouse gas SO 2 is an important technology to ensure normal agricultural production. This paper reports on a facile hydrothermal method to synthesis Pd-decorated and Pt-decorated MoSe 2 nanomaterials, i.e. multistage flower-like structures with attached nanometallic particles and nanosheets hierarchical structures. The Pd/MoSe 2 and Pt/MoSe 2 hierarchical materials were characterized for the nanostructure, microscopic morphology and elemental compositions. The gas-sensing properties results show that the Pd/MoSe 2 and Pt/MoSe 2 nanofilm sensors have good sensitivity, stability and response rate to SO 2 gas. The response values for the metal Pd and Pt decorated samples to 20 ppm SO 2 were 2.04 and 3.42 times higher than those for the intrinsic MoSe 2 samples at room temperature. The hierarchical flower-like structure proved to be beneficial in providing more adsorption drop points. In addition, based on the first-principles, the geometrical parameters and electronic properties of the metal-decorated modified structures were calculated to comparatively investigate the enhanced sensing mechanism of SO 2 by nanoflower materials. The Pt-MoSe 2 nanofilm sensor achieves a high sensitivity detection with a response value of 2.89 for low concentration (1 ppm) of SO 2 , which is confirming the promotion of charge transfer by metal decorating. This study suggests that Pd-MoSe 2 and Pt-MoSe 2 hierarchical structures may be recommended for the detection of the agricultural greenhouse gas SO 2. • On the optimal structures of SO 2 /Pd-MoSe 2 and SO 2 /Pt-MoSe 2 monolayers, the changes in conductivity, Density of States and Frontier molecular orbital before and after gas adsorption were analyzed, and the effect of metal decorating on the electron distribution of the systems was investigated from an atomic point of view. • Preparation of MoSe 2 , Pd-MoSe 2 and Pt-MoSe 2 nanoflower-like structure materials by hydrothermal method, characterization of their material properties, and preparation of planar-type sensors. • Test the gas-sensitive performance of the three materials to the harmful gas SO 2 in agricultural greenhouse, including sensitivity characteristics, temperature characteristics, concentration characteristics, response recovery time, etc. • The Pd-doped and Pt-doped MoSe 2 exhibited good adsorption performance for the agricultural greenhouse gas SO 2 , which provides some guidance for the practical application in the detection field. [ABSTRACT FROM AUTHOR]

In intelligent agriculture, the development of gas sensing technology has practical significance. In a bid to achieve fast, accurate and effective detection of noxious gases NH 3 , H 2 S and CO 2 from breeding farms, Ti 3 C 2 O 2 , an excellent gas sensing material in the MXene family, was investigated by means of density functional theory (DFT) calculations. The optimal configuration of Pt atomic catalyst doped Ti 3 C 2 O 2 sheet was obtained via the analysis of binding energy (−1.796 eV) and charge transfer (0.373 e). The adsorption energy, charge transfer, deformation charge density (DCD), density of states (DOS), average electrostatic potential, and work function of NH 3 , H 2 S and CO 2 adsorbed on Ti 3 C 2 O 2 and Pt-Ti 3 C 2 O 2 sheet were further scrutinized. From comparative analysis against Ti 3 C 2 O 2 , Pt-Ti 3 C 2 O 2 possesses excellent adsorption capacity, electron density rearrangement and electrostatic binding ability for the adsorption of NH 3 , H 2 S and CO 2 , among which the adsorption energy for NH 3 is the largest (−2.593 eV). The results verify that Pt-Ti 3 C 2 O 2 is a potential material for gas sensors, providing guidance for expanding the gas sensing application of MXene materials. [Display omitted] • The most stable structure of the Pt doped Ti 3 C 2 O 2 sheet was firstly constructed via DFT. • The Ti 3 C 2 O 2 sheet is not suitable for the NH 3 , H 2 S and CO 2 gas sensor material. • The Pt-Ti 3 C 2 O 2 sheet can be exploited as a potential NH 3 H 2 S and CO 2 gas sensing material. [ABSTRACT FROM AUTHOR]

Oxidation resistance of Mg alloys with different amounts of Ca were examined. The oxidation resistance of Mg at 515 °C was significantly improved by alloying with Ca, and Mg alloyed with 1.0 wt% Ca demonstrated the best oxidation resistance. Based on these observations, combined with Gibbs free energy and density functional theory calculations, α-Mg and Mg 2 Ca oxidation models describing the oxidation process are proposed. Oxide films formed on α-Mg are effective at improving the oxidation resistance, whereas those formed on Mg 2 Ca are unstable, and tend to peel off from the substrate, resulting in further oxidation. • The oxidation process was calculated and simulated. • The oxidation on α-Mg and Mg 2 Ca was observed and analysed. • The oxidation models on α-Mg and Mg 2 Ca were proposed. • The oxidation effect of α-Mg and Mg 2 Ca was analysed. [ABSTRACT FROM AUTHOR]