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Abstract In this work, hollow MoO 3 microcages were triumphantly synthesized using a facile hydrothermal method without any template, and a possible growth mechanism of this microstructure arising from the co-effect of inside-out Ostward-ripening mechanism and the acidic etching was speculated. Subsequently, gas sensor based on such MoO 3 with hollow characteristic was fabricated to investigate the gas-sensing properties for ethanol as compared to solid MoO 3 polyhedrons. It was found that the hollow cages exhibited lager ethanol gas response than that of solid polyhedrons. The enhanced sensing behavior may originate from its unique hollow structures, leading to sufficient sensing reaction on the surface as well as abundant gas diffusion. Graphical abstract The hollow MoO 3 microcages were successfully synthesized via a simple hydrothermal method without any template. Such hollow structure based sensor presented enhanced gas response to ethanol than that of solid MoO 3 polyhedrons based sensor. The hollow nature led to sufficient sensing reaction on the surface as well as abundant gas diffusion. Image 1 Highlights • Hollow MoO 3 microcages were successfully synthesized. • The gas sensor based on the MoO 3 presented enhanced gas response to ethanol. • The hollow structure of the MoO 3 cages enhanced surface sensing reaction. [ABSTRACT FROM AUTHOR]

Hollow spheres are usually fabricated by hard template methods or soft template methods with soft surfactants, which is quiet tedious and time-consuming. In this paper, NiO hollow spheres with fluffy surface were successfully synthesized by a facile hydrothermal method and subsequent calcination, where bubbles acted as the template. NiO hollow spheres exhibited excellent gas sensing performances, which results from its hollow structure and high specific surface area. In addition, a possible evolution mechanism of NiO hollow spheres was proposed based on experimental results. [ABSTRACT FROM AUTHOR]

We successfully synthesized MoO 3 hierarchical structures assembled with nanofibers and nanosheets via a hydrothermal method assisted with hexadecyl trimethyl ammonium bromide (CTAB) and polyvinyl pyrrolidone (PVP), respectively. Then, we characterized the structure and morphology of the as-synthesized samples by X-ray diffraction and scanning electron microscopy. We analyzed the formation process of the two structures and verified the effects of different dimensionality assembly units on their gas-sensing properties through gas sensing experiments. Remarkably, nanosheet-assembled hierarchical MoO 3 structures, which possess abundant semi-closed microreaction spaces, exhibited an enhanced gas response. The gas response (the ratio of test voltage in the air to test voltage in the target gas) of a nanosheet-assembled MoO 3 based-sensor to 400 ppm ethanol reached 32 at an operating temperature of 300 °C. While nanofiber-assembled hierarchical structures showed a shorter response (3.2s) and recovery time (2.4s), which was due to the faster gas and electronic diffusion rate of the nanofibers. MoO 3 hierarchical structures assembled by nanofibers and nanosheets have been synthesized under hydrothermal conditions assisted with CTAB and PVP, respectively. Nanofiber-assembled hierarchical MoO 3 structures demonstrate less response and recovery time than the other. However, sensors based on nanosheet-assembled structures exhibit a higher gas response. The differences in the above properties can be attributed to their different dimensionality assembly units. Image 1 [ABSTRACT FROM AUTHOR]

Cu 2 O microspheres with hollow and solid features were successfully prepared via a convenient liquid phase reducing method. Interestingly, we found that the discrepancy in morphology arose from a simply changing on the adding sequence of aqueous sodium dodecyl sulfate (SDS) and CuCl 2 with other conditions unchanged. Based on experimental results, the feasible formation mechanisms of both morphologies were deduced, where the relative concentration of SDS and CuCl 2 was a crucial factor that effect the resultant morphologies. In comparison with the solid microspheres, the hollow Cu 2 O exhibited superior gas sensing performance. The significant performance might ascribe to its unique hollow structure, contributing to plenty of active sites existed on both the inner and outer surface and unrestricted gas diffusion in the hollow microspheres. In this work, hollow and solid cuprous oxide microspheres were successfully synthesized by liquid phase reducing method and the gas sensing performance of the samples was investigated. In addition, we also explore the effect of the adding sequence of aqueous sodium dodecyl sulfate (SDS) and CuCl 2 on the resultant morphologies of Cu 2 O and propose the growth formation mechanism. Image 1 • Cu 2 O microspheres with hollow and solid features were successfully prepared. • The hollow structure exhibited superior gas sensing performance than the solid microspheres. • The adding sequence played a vital role on the morphology of materials. [ABSTRACT FROM AUTHOR]