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The present study concerns the enhancement of methanol selectivity of three dimensional (3D) nanoflowers (NFs) of ZnO by dispersing nickel oxide (NiO) and palladium oxide (PdO) nanoparticles on the surface of the nanoflowers to form localized hybrid nano-junctions. The nanoflowers were fabricated through a liquid phase deposition technique and the modification was achieved by addition of NiCl and PdCl2 solutions. In addition to the detailed structural (like X-ray diffraction (XRD), electron dispersive spectroscopy (EDS), X-ray mapping, XPS) and morphological characterization (by field emission scanning electron microscopy (FESEM)), the existence of different defect states (viz. oxygen vacancy) was also confirmed by photoluminescence (PL) spectroscopy. The sensing properties of the pristine and metal oxide nanoparticle (NiO/PdO)-ZnO NF hybrid sensor structures, towards different alcohol vapors (methanol, ethanol, 2-propanol) were investigated in the concentration range of 0.5-700 ppm at 100-350 °C. Methanol selectivity study against other interfering species, viz. ethanol, 2-propanol, acetone, benzene, xylene and toluene was also investigated. It was found that the PdO-ZnO NF hybrid system offered enhanced selectivity towards methanol at low temperature (150 °C) compared to the NiO-ZnO NF and pristine ZnO NF counterparts. The underlying mechanism for such improvement has been discussed with respective energy band diagram and preferential dissociation of target species on such 3D hybrid structures. The corresponding improvement in transient characteristics has also been co-related with the proposed model.

Although predicted to be stable under ambient conditions, the experimental synthesis of silicenethe twodimensional silicon analogue of graphenehas been a great challenge. Here, we report the preparation of scalable quantities of crystalline nanosheets of two-dimensional silicon by simple topochemical exfoliation of layered Zintl phases. The simple process leads to the formation of stacked layers of 2D Si nanosheets which are arbitrarily surface terminated with oxygen, hydrogen, hydroxide, and other ligands. The nanosheets exhibit strong room-temperature photoluminescence, and their overall spectroscopic characteristics closely resemble other forms of silicon nanocrystals. Remarkably, the pelletized nanosheets exhibit significantly high Hall mobility even in the absence of any doping or surface treatment, which is better than the reported values of doped Si nanosystems. Such ensembles of two-dimensional nanosheets of silicon bear the signature of exotic electronic properties and represent important building blocks in two-dimensional electronics along with potential applications in solar cells, next-generation thermoelectric materials, and sensors.

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