Tuning the Physical and Chemical Properties of 2D InSe with Interstitial Boron Doping: A First-Principles Study

InSe monolayer is a new two-dimensional (2D) material with unique geometric configuration. Its crystal structure has a large atom interval, significantly different from those of graphene and MoS₂, two typical 2D materials. This structural characteristic may facilitate interstitial doping, which is obviously impossible in graphene and MoS₂. In this work, first-principles calculations are employed to study the effects of interstitial doping of boron atoms on the electronic and magnetic properties of InSe monolayer. For comparison, substitutional doping is also studied with In replaced by boron. It is found that interstitial doping can induce spin-polarized state and nonzero local magnetic moments. In order to investigate the effects of doping contents on electronic structures and magnetism, three dopant concentrations (6.25%, 12.5%, 25%) are taken into account. For interstitial doping, with increasing the B contents, the local magnetic moments first emerge and then disappear, corresponding to the nonmonotonic doping-content dependence. For substitutional doping, no local magnetic moments are observed with any doping contents. These results show that B-doping-induced magnetism strongly depends on the doping methods and doping contents in the InSe monolayer. The reasons leading to the doping behaviors are discussed in detail. This work opens up an alternative way for tuning the physical and chemical properties of 2D InSe material, and would be helpful for future InSe-based spintronics devices

From the Surface Reaction Control to Gas-Diffusion Control: The Synthesis of Hierarchical Porous SnO₂ Microspheres and Their Gas-Sensing Mechanism

A series of hierarchical porous SnO₂ microspheres (SnO₂-Ms) with same sizes of nanoparticles were fabricated through increasing the reaction time of the one-step hydrothermal method. Especially, these SnO₂-Ms also have the different specific surface areas and pores sizes. When they are applied in sintering type thick film gas sensors, through comparing the gas-sensing property of the as-prepared SnO₂-Ms, it can clearly demonstrate that the surface chemical reaction (SCR) control of the sensing properties of sensors is gradually replaced by gas diffusion control with the increasing operation temperature (<i>T</i>_o). For the first time, this dual control is discovered through contrast experiments. According to the testing results, the sensing mechanism of sensors can be explained by many factors, such as the reaction rate constant of the SCR, the Knudsen diffusion coefficient of the target gas, the <i>T</i>_o, the specific surface area, the pore size, and the change of the H₂O, etc. A pore canal model and a hollow sphere model are introduced, which can effectively explain the sensing mechanism of gas sensors. This discovery can make up for the inadequacy of the surface-control and the diffusion-control theory, and expound their interrelationship. This discovery also provides a novel strategy for studying the sensing mechanism of sensors, which is expected to open up exciting opportunities for improving the sensing properties of the gas-sensing materials and studying some gas–solid catalytic phenomena

Homogeneous Ni Single-Atom Sites in the NiZn Intermetallic Nanostructure for Efficient Semihydrogenation of Acetylene

Catalytic semihydrogenation of acetylene is crucial for ethylene purification but still faces a grand challenge in circumventing deep hydrogenation and oligomerization so far, especially for the cost-effective catalysts. Herein, two Ni-based intermetallic nanocatalysts with different atomic arrangements were subtly constructed via controlling the reduction temperature of ZnO-supported NiO particles. The one reduced at 400 °C is L12-type intermetallic Ni3Zn with separated Ni3 trimers (denoted as Ni/ZnO-R400 or Ni3Zn/ZnO); another reduced at 600 °C is L10-type intermetallic NiZn with the homogeneous Ni single atoms completely isolated by Zn atoms (denoted as Ni/ZnO-R600 or NiZn/ZnO). The systematical evaluations validate NiZn/ZnO as an outstanding noble metal-free catalyst for acetylene semihydrogenation, showing a significantly enhanced selectivity toward ethylene relative to Ni3Zn/ZnO (87.5 vs −275.4% at 200 °C) through suppressing not only the unselective hydrogenation to ethane but also carbon deposition. According to catalytic evaluations with or without ethylene, microcalorimetry, and density functional theory calculations, the superior selectivity of NiZn/ZnO stems from the noncompetitive adsorption between the moderately σ-bonded acetylene over two neighboring Ni single atoms and weakly π-bonded ethylene on Ni single-atom sites due to its unique Ni–Zn–Ni ensemble