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In recent years, bimetallic nanocrystals have attracted great interest from many researchers. Bimetallic nanocrystals are expected to exhibit improved physical and chemical properties due to the synergistic effect between the two metals, not just a combination of two monometallic properties. More importantly, the properties of bimetallic nanocrystals are significantly affected by their morphology, structure, and atomic arrangement. Reasonable regulation of these parameters of nanocrystals can effectively control their properties and enhance their practicality in a given application. This review summarizes some recent research progress in the controlled synthesis of shape, composition and structure, as well as some important applications of bimetallic nanocrystals. We first give a brief introduction to the development of bimetals, followed by the architectural diversity of bimetallic nanocrystals. The most commonly used and typical synthesis methods are also summarized, and the possible morphologies under different conditions are also discussed. Finally, we discuss the composition-dependent and shape-dependent properties of bimetals in terms of highlighting applications such as catalysis, energy conversion, gas sensing and bio-detection applications. [ABSTRACT FROM AUTHOR]

Great expectations have been held for the electrochemical splitting of water for producing hydrogen as a significant carbon-neutral technology aimed at solving the global energy crisis and greenhouse gas issues. However, the oxygen evolution reaction (OER) process must be energetically catalyzed over a long period at high output, leading to challenges for efficient and stable processing of electrodes for practical purposes. Here, we first prepared Fe-MOF nanosheet arrays on nickel foam via rare-earth erbium doping (Er0.4 Fe-MOF/NF) and applied them as OER electrocatalysts. The Er0.4 Fe-MOF/NF exhibited wonderful OER performance and could yield a 100 mA cm−2 current density at an overpotential of 248 mV with outstanding long-term electrochemical durability for at least 100 h. At large current densities of 500 and 1000 mA cm−2, overpotentials of only 297 mV and 326 mV were achieved, respectively, revealing its potential in industrial applications. The enhancement was attributed to the synergistic effects of the Fe and Er sites, with Er playing a supporting role in the engineering of the electronic states of the Fe sites to endow them with enhanced OER activity. Such a strategy of engineering the OER activity of Fe-MOF via rare-earth ion doping paves a new avenue to design other MOF catalysts for industrial OER applications. [ABSTRACT FROM AUTHOR]

As an insulating medium, sulfur hexafluoride (SF6) is extensively applied to electrical insulation equipment to ensure its normal operation. However, both partial discharge and overheating may cause SF6 to decompose, and then the insulation strength of electrical equipment will be reduced. The adsorption properties and sensing mechanisms of four SF6 decomposed components (HF, SO2, SOF2 and SO2F2) upon an Au-modified InN (Au-InN) monolayer were studied in this work based on first-principles theory. Meanwhile, the adsorption energy (Ead), charge transfer (QT), deformation charge density (DCD), density of states (DOS), frontier molecular orbital and recovery property were calculated. It can be observed that the structures of the SO2, SOF2 and SO2F2 molecules changed significantly after being adsorbed. Meanwhile, the Ead and QT of these three adsorption systems are relatively large, while that of the HF adsorption system is the opposite. These phenomena indicate that Au-InN monolayer has strong adsorption capacity for SO2, SOF2 and SO2F2, and the adsorption can be identified as chemisorption. In addition, through the analysis of frontier molecular orbital, it is found that the conductivity of Au-InN changed significantly after adsorbing SO2, SOF2 and SO2F2. Combined with the analysis of the recovery properties, since the recovery time of SO2 and SO2F2 removal from Au-InN monolayer is still very long at 418 K, Au-InN is more suitable as a scavenger for these two gases rather than as a gas sensor. Since the recovery time of the SOF2 adsorption system is short at 418 K, and the conductivity of the system before and after adsorption changes significantly, Au-InN is an ideal SOF2 gas-sensing material. These results show that Au-InN has broad application prospects as an SO2, SOF2 and SO2F2 scavenger and as a resistive SOF2 sensor, which is of extraordinary meaning to ensure the safe operation of power systems. Our calculations can offer a theoretical basis for further exploration of gas adsorbent and resistive sensors prepared by Au-InN. [ABSTRACT FROM AUTHOR]

The adsorption and sensing behavior of three typical industrial toxic gases NO, NO2 and SO2 by the Pd modified C3N monolayer were studied in this work on the basic first principles theory. Meanwhile, the feasibility of using the Pd doped C3N monolayer (Pd-C3N) as a sensor and adsorbent for industrial toxic gases was discussed. First, the binding energies of two doping systems were compared when Pd was doped in the N-vacancy and C-vacancy sites of C3N to choose the more stable doping structure. The result shows that the doping system is more stable when Pd is doped in the N-vacancy site. Then, on the basis of the more stable doping model, the adsorption process of NO, NO2 and SO2 by the Pd-C3N monolayer was simulated. Observing the three gases adsorption systems, it can be found that the gas molecules are all deformed, the adsorption energy (Ead) and charge transfer (QT) of three adsorption systems are relatively large, especially in the NO2 adsorption system. This result suggests that the adsorption of the three gases on Pd-C3N belongs to chemisorption. The above conclusions can be further confirmed by subsequent deformable charge density (DCD) and density of state (DOS) analysis. Besides, through analyzing the band structure, the change in electrical conductivity of Pd-C3N after gas adsorption was studied, and the sensing mechanism of the resistive Pd-C3N toxic gas sensor was obtained. The favorable adsorption properties and sensing mechanism indicate that the toxic gas sensor and adsorbent prepared by Pd-C3N have great application potential. Our work may provide some guidance for the application of a new resistive sensor and gas adsorbent Pd-C3N in the field of toxic gas monitoring and adsorption. [ABSTRACT FROM AUTHOR]

Epoxy resin–polyhedral oligomeric silsesquioxane (EP-POSS) has excellent mechanical properties and hydrophobic properties. In order to adapt for application in sensor and photovoltaic fields, graphene, nano-SiO2 and nano-ZnO were used to modify EP-POSS. FTIR was used to characterize changes on the surface structure after introducing nanoparticles. The change of hydrophobicity was measured using a contact angle test. TEM test results showed that nanoparticles were successfully inserted between the graphene sheets. However, the content of Si on the surface was low, as the cage structure of POSS in the molecular chain was coated by epoxy groups. XRD tests indicated that nanoparticles facilitated the dispersion of graphene in EP-POSS. XPS characterized the chemical state and content of the elements, confirming that the addition of graphene can induce the enrichment of Si on the surface of EP-POSS, which had a shielding effect on the main chain and improved the hydrophobicity. Wear resistance and adhesion tests showed that, after the introduction of nanoparticles, the EP-POSS coating film met the requirements of graphene materials. [ABSTRACT FROM AUTHOR]

The metal oxides/graphene nanocomposites have great application prospects in the fields of electrochemical energy storage and gas sensing detection. However, rational synthesis of such materials with good conductivity and electrochemical activity is the topical challenge for high-performance devices. Here, SnO2/graphene nanocomposite is taken as a typical example and develops a universal synthesis method that overcome these challenges and prepares the oxygen-deficient SnO2 hollow nanospheres/graphene (r-SnO2/GN) nanocomposite with excellent performance for supercapacitors and gas sensors. The electrode r-SnO2/GN exhibits specific capacitance of 947.4 F g−1 at a current density of 2 mA cm−2 and of 640.0 F g−1 even at 20 mA cm−2, showing remarkable rate capability. For gas-sensing application, the sensor r-SnO2/GN showed good sensitivity (~13.8 under 500 ppm) and short response/recovering time toward methane gas. These performance features make r-SnO2/GN nanocomposite a promising candidate for high-performance energy storage devices and gas sensors. [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 order to find an excellent sensing material for dissolved gases in transformer oil, the adsorption structures of intrinsic graphene (IG), Ge-doped graphene (GeG), and Cr-doped graphene (CrG) to H2 and C2H2 gas molecules were built. It was found that the doping site right above C atom (T) was the most stable structure by studying three potential doping positions of the Ge and Cr atom on the graphene surface. Then, the structural parameters, density of states, and difference state density of these adsorption systems were calculated and analyzed based on the density functional calculations. The results show that the adsorption properties of GeG and CrG systems for H2 and C2H2 are obviously better than the IG system. Furthermore, by comparing the two doping systems, CrG system exhibits more outstanding adsorption performances to H2 and C2H2, especially for C2H2 gas. Finally, the highest adsorption energy (−1.436 eV) and the shortest adsorption distance (1.981 Å) indicate that Cr-doped graphene is promising in the field of C2H2 gas-sensing detection. [ABSTRACT FROM AUTHOR]

The long-term stability and the extension of the use time of gas sensors are one of the current concerns. Lowering the working temperature is one of the most effective methods to delay aging. In this paper, pure MoS2 and ZnO-MoS2 nanocomposites were successfully prepared by the hydrothermal method, and the morphological characteristics were featured by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Pure MoS2 and ZnO-MoS2 nanocomposites, as a comparison, were used to study the aging characteristic. The sensing properties of the fabricated gas sensors with an optimal molar ratio ZnO-MoS2 (Zn:Mo = 1:2) were recorded, and the results exhibit a high gas-sensing response and good repeatability to the acetylene detection. The working temperature was significantly lower than for pure MoS2. After aging for 40 days, all the gas-sensing response was relatively attenuated, and pure MoS2 exhibits a faster decay rate and lower gas-sensing response than nanocomposites. The better gas-sensing characteristic of nanocomposites after aging was possibly attributed to the active interaction between ZnO and MoS2. [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]

In this study, we reported a successful synthesis of a nanocomposite based on SnO2 nanoneedles anchored to NiO microsphere by a simple two-step hydrothermal route. The results show that the SnO2/NiO nanocomposite-based sensor exhibits more prominent performances than the pristine NiO microsphere to NO2 such as larger responses and more outstanding repeatability. The improved properties are mainly attributed to the p–n heterojunctions formed at the SnO2–NiO interface, leading to the change of potential barrier height and the enlargement of the depletion layer. Besides, the novel and unique nanostructure provides large and effective areas for the surface reaction. In addition, a plausible growth mechanism and the enhanced sensing mechanism were proposed to further discuss the special nanostructure which will benefit the exploration of high-performance sensors. [ABSTRACT FROM AUTHOR]