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Transition metal dichalcogenides (TMDs) have attracted enormous attention in diverse research fields. Especially, gas sensors are considered in a promising application exploiting TMDs. However, the studies are confined to only major TMDs such as MoS 2 and WS 2 . Particularly, the chemoresistive sensing properties of two-dimensional (2D) NbS 2 have never been explored. For the first time, we report room temperature NO 2 sensing characteristics of 2D NbS 2 nanosheets and the sensing mechanisms using first-principles calculations based on density functional theory. The results demonstrate that the NbS 2 edges possessing different configurations depending on synthetic conditions differ in the sensing ability of the TMD nanosheets. This study not only broadens the potential of 2D NbS 2 for gas sensing applications, but also presents the important role of edge configuration of TMDs depending on synthetic conditions for further studies.

Besides developing a large number of catalysts for hydrogen evolution reaction (HER) in alkaline electrolytes, its conversion efficiency remained low. Herein, we have developed mixed-dimensional heterostructures of niobium disulfide (NbS 2) with graphene foam grown on nickel foam (NbS 2 -Gr-NF). The strong lateral fusion results in activating the catalytic sites of NbS 2 , the three-dimensional substrate provides easy access of electrolyte to active sites and increased electrochemically active surface area, while enhanced conductivity provides faster transfer of electrons to and from active sites. Therefore, NbS 2 -Gr-NF heterostructures resulted in an exceptionally high current density of 500 mA cm−2 at a very low overpotential of 306 mV in 1 M KOH solution and even can achieve the current density values of 914 mAcm−2 at 338 mV only at a slight increase in overpotential (32 mV). Moreover, a Tafel value of ~72 mV dec−1 confirms that as-developed heterostructure provides fast reaction kinetics where the reaction is mainly controlled by the Volmer step. Achieving such high current density at a faster rate with high stability makes NbS 2 -Gr-NF heterostructures a potential candidate for water-splitting, especially in alkaline electrolytes. [Display omitted] • Synthesis of heterostructures of NbS 2 -graphene as a working electrocatalyst. • An exceptionally high current density ~500 mAcm−2 at a low overpotential ~306 mV. • A current density 914 mAcm−2 at 338 mV only at a slight increase in overpotential. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis of niobium disulfide 3D nanaosheets and nanoflake in liquid phase method. • P and Se co-doping strategy is proposed to enhance the HER activity of NbS 2 3D nanosheets. • P doping can activate the adjacent original inert Nb sites and Se doping can stabilize the catalytic activity. • P and Se co-doped NbS 2 3D nanosheets exhibit significantly enhanced HER activity and stability. Promoting the intrinsic activity and accessibility of basal plane sites in transition metal dichalcogenides (TMDs) is an important way to optimize their catalytic performance for energy conversion and storage. Here, a simple liquid-phase phosphating selenization pyrolysis method is developed to prepare P and Se co-doped niobium disulfide (NbS 2) 3D nanosheets with active basal plane for efficient catalyzing hydrogen evolution reaction (HER). Experimental results indicate that the P and Se co-doped NbS 2 3D nanosheets exhibit significantly enhanced HER activity and stability compared to their undoped counterparts. It realizes 165 mV decreased overpotential at 10 mA cm−2 and a stable durability over 40 h continuous operation at 14 mA cm−2 without observable fading. Density functional theory (DFT) studies suggest that the P dopant is to activate the adjacent original inert Nb sites, where both S and Nb sites in P, Se co-doped NbS 2 monolayer can together act as the active sites for HER. Furthermore, the addition of selenium can stabilize the catalytic activity. Our work provides a promising approach and theoretical framework for improving the electrocatalytic HER performance of NbS 2 , and may have general guidelines for other transition metal disulfides. [ABSTRACT FROM AUTHOR]

• We have developed a novel sensor based on niobium disulfide high perfect performance. • The maximum value of SPR sensitivities approached to 193°∕RIU achieved by coating the NbS 2 nanosheets in simulation calculation. • These sensors were used to detect mercy and the value of sensitivity is 13.55°∕μM, and detection limit approach 1 pM. Mercury ion (Hg2+) can affect the quality of water and cause damage to human health. Therefore, the detection of Hg2+ in water, especially trace Hg2+, is very important. However, the detection limit (approximately 200 pM) of conventional Hg2+ sensors is far lower than the detection limit (7.5 pM) proposed by the US Environmental Protection Agency for measuring Hg2+. Here, we have developed a novel sensor based on niobium disulfide (NbS 2)'s high perfect performance. The maximum value of SPR sensitivities approached to 193°∕RIU achieved by coating the NbS 2 nanosheets in simulation calculation, which had increased by 38.1% compared with the case without NbS 2 overlayer. More importantly, this work also detected the ultra-low concentration of Hg2+ and describes the sensing mechanism of NbS 2 based SPR sensors. Surprisingly, these sensors were used to detect mercury and the value of sensitivity is 13.55°∕μM, and detection limit approach 1 pM. NbS 2 nanosheets based SPR sensors provided innovative design ideas for the development of ultra-sensitive detection technology. [ABSTRACT FROM AUTHOR]