Adsorption of NO2, SO2, H2S, and NH3 on Os-Doped WSe2 Monolayers: A First-Principles Study.

In this study, DFT calculations are used to analyze the adsorption of industrial waste gases (NO2, SO2, H2S, and NH3) on WSe2 monolayers. The adsorption energy, energy band, density of states, charge transfer, and recovery time of the adsorption structures between the target gas molecules and the Os-doped WSe2 are studied. Compared with pure WSe2 monolayer, Os surface bonding doping WSe2 (Os-modified WSe2) and Os doping with Se vacancy of WSe2 (Os-embedded WSe2) exhibit improved gas molecule adsorption ability. Among them, the adsorption energy of the Os-modified WSe2 monolayer on NO2, SO2, H2S, and NH3 is greater than that of the WSe2 monolayer. At the same time, it is proved that the Os-embedded WSe2 can be used as a gas sensor for H2S and NH3 gas molecules at a high temperature.

Adsorption and Sensing of NO2, SO2, and NH3 on a Janus MoSeTe Monolayer Decorated with Transition Metals (Fe, Co, and Ni): A First-Principles Study.

This paper reports the adsorption of toxic gases (NO2, SO2, and NH3) on a MoSeTe structure based on first principles. It was found that the gas (NO2, SO2, and NH3) adsorption on a pure MoSeTe monolayer was weak; however, the adsorption performance of these gas molecules on transition-metal-atom-supported MoSeTe monolayers (TM-MoSeTe) was better than that on pure MoSeTe monolayers. In addition, there was more charge transfer between gas molecules and TM-MoSeTe. By comparing the adsorption energy and charge transfer values, the trend of adsorption energy and charge transfer in the adsorption of NO2 and SO2 was determined to be Fe-MoSeTe > Co-MoSeTe > Ni-MoSeTe. For the adsorption of NH3, the effect trend was as follows: Co-MoSeTe > Ni-MoSeTe > Fe-MoSeTe. Finally, by comparing their response times, the better gas sensor was selected. The Ni-MoSeTe system is suitable for NO2 gas sensors, and the Fe-MoSeTe and Co-MoSeTe systems are suitable for SO2 gas sensors. The Fe-MoSeTe, Co-MoSeTe, and Ni-MoSeTe systems are all suitable for NH3 gas sensors. Janus transition-metal dichalcogenides have the potential to be used as gas-sensing and scavenging materials.

Different Doping of VSe2 Monolayers as Adsorbent and Gas Sensing Material for Scavenging and Detecting SF6 Decomposed Species.

The application of intrinsic and transition metals (TM)-doped VSe2 monolayers for the detection of faulty gases in SF6 electrical insulated equipment is investigated based on first-principles calculations. The electron density difference, density of state, and adsorption energy are analyzed to further clarify the reaction mechanism. The results show that the intrinsic VSe2 monolayer has weak adsorption performance for SO2 and SOF2 molecules, but the adsorption properties of the system are significantly improved after doping TM atoms. Among them, the TM-doped VSe2 monolayer has better sensing performance for SO2 than for SOF2 molecules. Furthermore, the modulating effect of biaxial strain on the gas-sensitive properties of TM-doped VSe2 system is also analyzed. Finally, the recovery time of the gas molecules on the solid adsorbent is evaluated. The results confirm that the TM-doped VSe2 monolayer can be used as a novel sensing material or scavenger to ensure the normal operation of SF6 electrical insulated equipment. This will provide a prospective insight for experimenters to implement VSe2-based sensing materials or scavengers.

Adsorption of CO and H2S on pristine and metal (Ni, Pd, Pt, Cu, Ag, and Au)-mediated SnS monolayers: a first-principles study.

A SnS monolayer is a new two-dimensional material with a black phosphorous structure, with high carrier mobility and a large surface-to-volume ratio, and is an ideal candidate material for gas sensors. The adsorption and sensing behaviors between the SnS monolayer and gas molecules are enhanced under the action of TM atoms with high catalytic performance. The adsorption behavior of CO and H2S on intrinsic and transition metal atom modified SnS monolayers is investigated based on the first principles calculations. The adsorption structure, adsorption energy, electron transfer, density of states, electron local density, work function, and desorption properties are discussed to evaluate the potential applications of SnS monolayers as scavengers and gas sensors for CO and H2S molecules. The results show that Ni, Pd, Pt and Cu atoms tend to be adsorbed on TH sites, while Ag and Au atoms are more easily captured by TS sites. Further studies have shown that all TM atoms can significantly enhance the sensing behavior between the SnS monolayer and the gas molecules. The adsorption performance of the CO molecule on the TM-mediated SnS (TM-SnS) monolayer is obviously better than that of the H2S molecule. Furthermore, the effects of electric field and biaxial strain on the sensing properties of gas molecules on Ni-SnS monolayers are also investigated. Finally, the desorption time of gas molecules from the TM-SnS monolayer is estimated. This will provide experimenters with theoretical guidance for the application of SnS-based sensing materials, and our work is of great significance for predicting new monochalcogenide sensing materials.

First-principles study on CO oxidation on CuO(111) surface prefers the Eley-Rideal or Langmuir-Hinshelwood pathway.

Using the first-principles approach, we investigated the electronic and chemical properties of cupric oxide CuO (110) and CuO (111) and substantiated their catalytic activity toward CO oxidation. It is found that CuO (111) surface is more stable than the CuO (110) surface. We firstly study that adsorption of CO and O2on perfect, oxygen vacancies and Cu-anchored CuO (111) surface. It is found that adsorption of CO and O2molecules are chemical. Then we selected the most stable adsorption structure of CO/O2to investigated the CO oxidation mechanism on different surface, here we choose to study the Langmuir-Hinshelwood (LH) mechanism and Eley-Rideal (ER) mechanism. The results show that perfect and OvacancyCuO (111) surface is more inclined to LH mechanism, while the Cu-anchored CuO (111) surface is more inclined to ER mechanism. The results show that CuO catalyst is very effective for CO oxidation. Our work provides a deep understanding for the search of economical and reasonable CO oxidation catalysts.

Ferromagnetism and optical properties of SnS2 doped with two impurities: first-principles calculations.

Based on the first principles of the GGA method, the magnetic and optical properties of intrinsic SnS2; Fe, Cr mono-doped SnS2; and (Fe, Cr) co-doped SnS2 are studied. The results show that the ground states of Fe, Cr mono-doped SnS2 are spin polarized, and the magnetic moments caused are 1.99 µB and 3.00 µB, respectively. The magnetic moment of Fe mono-doped SnS2 is mainly produced by Fe:3d orbitals, and the magnetic moment of Cr mono-doped SnS2 is mainly produced by Cr:3d and Sn:4d orbitals. We calculate that in the (Fe, Cr) co-doped SnS2 system, Fe, Cr and the adjacent S atoms form a strong hybrid, that is, the closest S atom between Fe and Cr atoms mediates the spin polarization and ferromagnetic (FM) coupling. This promotes the formation of a Fe:3d-S:3p-Cr:3d coupling chain, so that (Fe, Cr) co-doped SnS2 obtains FM stability. In addition, with the introduction of Fe and Cr atoms, the absorption coefficient is the largest in the long-wavelength infrared region of 0.23-1.63 eV. This shows that Fe and Cr doping can make up for the lack of absorption of intrinsic materials in the infrared region. In summary, Fe, Cr doped SnS2 dilute magnetic semiconductors may be a good candidate in the field of spintronic devices.

Electron energy loss spectroscopy and first-principles study of GaN via Zn doping.

The electronic structure of GaN and GaN:Zn was investigated by electron energy loss spectroscopy and first-principles calculations. In the low-loss spectrum, the interband transitions are assigned to the observed energy loss peaks. After Zn doping, impurity levels are introduced to the density of states and hybrid orbitals of N 2p and Zn 3d are formed around the Fermi level. In the nitrogen K-edge, an additional peak was observed due to the formation of donor defect states. A core-hole effect is believed to be significant for simulation of the N K-edge for both GaN and GaN:Zn.

Adsorption of gas molecules of CH4, CO and H2O on the vanadium dioxide monolayer: Computational method and model.

Inspired by the recent use of two-dimensional nanomaterials as gas sensors, we used density functional theory calculations to study the adsorption of gas molecules (CH$_4$, CO and H$_2$O) on sandwich vanadium dioxide tablets. The results showed that of all these gases, only the CH$_4$ gas molecule was the electron acceptor with significant charge transfer on the VO$_2$ sheet. The adsorption energies of CH$_4$, CO and H$_2$O are -229.5 meV, -239.1 meV and -388.3 meV, respectively. We have also compared the adsorption energy of three different gas molecules on the VO$_2$ surface, our calculation results show that when the three kinds of gases are adsorbed on the VO$_2$ surface, the order of the surface adsorption energy is H$_2$O$>$ CO$>$ CH$_4$. It is also found that after adsorption of CH$_4$, CO and H$_2$O molecules, the electronic properties of VO$_2$ sheet changed obviously. However, due to the strong adsorption of H$_2$O molecule on VO$_2$ sheet, it is difficult to desorption, which hinders its application in gas molecular sensors. The optical properties of VO$_2$ sheet are further calculated. The absorption of CH$_4$, CO and H$_2$O molecules is introduced to red-shift the dielectric function of the thin film, which indicates that the optical properties of the thin film have changed significantly. According to the change of optical properties of VO$_2$ sheet before and after molecular adsorption, VO$_2$ can be used as a highly selective optical gas sensor for CH$_4$, CO and H$_2$O detection. These results provide a new approach for the potential application of VO$_2$ based optical gas sensors.

Surface Roughening of Nickel Cobalt Phosphide Nanowire Arrays/Ni Foam for Enhanced Hydrogen Evolution Activity.

Development of earth-abundant, efficient, and stable electrocatalysts for hydrogen evolution reactions (HER) in alkaline or even neutral pH electrolyte is very important for hydrogen production from water splitting. Construction of bimetal phosphides via tuning the bonding strength to hydrogen and increasing effective active sites through nanostructuring and surface engineering should lead to high HER activity. Here, ternary NiCoP nanowires (NWs) decorated by homogeneous nanoparticles have been obtained on Ni foam for a highly efficient HER property via long-term cyclic voltammetric (CV) sweeping. The electron density transfer between the positively charged Ni and Co and negatively charged P atoms, one-dimensional electron transfer channel of the NWs, and abundant active sites supplied by the nanoparticles and NWs endow the catalyst with low overpotentials of 43 and 118 mV to achieve the respective current densities of 10 and 100 mA cm-2 together with long durability for at least 33 h in 1 M KOH. A cycled anodic dissolution-redeposition mechanism is disclosed for the formation of the NiCoP nanoparticles during the CV sweeping process. Such a surface roughening method is found to be adaptable to enhance the HER property of other phosphides, including Ni2P nanoplates/NF, NiCoP nanoparticles/NF, and CoP NW/NF.