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Abstract: Well-defined polyhedral hollow structures (PHSs) Cu2O with hollow interior and high geometrical symmetry are successfully prepared via a novel in situ oxidative etching method at room temperature. X-ray power diffraction (XRD), field-emission scanning electron microscope (FESEM), and high-resolution transmission electron microscopy (HRTEM) techniques were employed to elaborately characterize the structure and morphology of the as-prepared samples. These PHSs Cu2O with hollow interiors and open “window” show effective-applied and good-diffusion structure for the gas-sensing application, which will exhibit short good response, response/recovery times and good reproducibility to ethanol. It is found that type-I nanocages Cu2O have a response of 8.6–50ppm ethanol at the optimal operating temperature of 210°C and the response time is within 23.7s. [Copyright &y& Elsevier]

Graphical abstract Highlights • Rational assembly of hierarchical SnO 2 hollow cubes with well-aligned ultrathin primary nanorods. • Well-aligned nanorod-assembled cubic structure maintains highly porous and activated surfaces. • Ultrathin primary nanorods and less-agglomerated configuration promote n-butanol sensing characteristics. Abstract A new type of nonspherical hollow nanocubes functionalized with well-aligned rodlike building blocks have been successfully prepared via a facile one-pot hydrothermal approach in case of SnO 2. The structural and morphological characterization reveals that the dense rodlike SnO 2 subunits are vertically distributed on all of the six equivalent facets of cubic structure. The rodlike primary building blocks with a uniform diameter of about 5 nm exhibit a single-crystalline rutile structure. A two-step sequential growth model is proposed based on observation from a time-dependent evolution process, revealing that the initially formed of well-defined ZnSn(OH) 6 solid cubes can serve as sacrifice self-template for the interior hollowing and vertical growth of SnO 2 nanorods. Moreover, gas sensor based on SnO 2 nanocages exhibits the enhanced sensing performances to n-butanol. The significant decrease in response-recovery time can be attributed not only to the interior cavities combined with permeable shells for fast transfer of gas molecules, but also to these high-activated rodlike subunits with ultrathin diameter. [ABSTRACT FROM AUTHOR]

The designed preparation of pure and Au-loaded SnO 2 hollow multilayered nanosheets for CO detection has been realized via a rational combination of different purposeful multi-step synthetic route. The synthetic step-dependent shape and structure evolution has been investigated and the formation mechanism for the unique hollow nanosheets is also discussed. The characterized results confirm that flowerlike SnO 2 nanosheets with a polycrystalline rutile structure are assembled from hexagonal mesoporous and multilayered walls, which can further be subdivided into SnO 2 nanoparticles as structural subunits. Furthermore, gas sensors based on the as-prepared pure and Au-loaded SnO 2 have also been fabricated. The Au-loaded SnO 2 hollow nanosheets show significantly lower working temperature, faster response-recovery and improved selectivity to CO in comparison with that of pure SnO 2 . Besides structural merits including hollow and easily penetrated multilayered walls, which facilitate the transport rate and augment the adsorption quantity of gas molecule, the significant improvement of the sensing properties is also attributed to the catalytic effect of Au. [ABSTRACT FROM AUTHOR]

ZnSnO3 hollow microspheres with a hierarchical structure composed of small nanorods as building blocks are synthesized by a facile one-pot hydrothermal method at 160°C. The individual hierarchical ZnSnO3 microsphere ranges from 600 to 900nm in diameter. The time-dependent hollowing evolution of ZnSnO3 microspheres reveals that the preferential formation of solid ZnSnO3 microspheres and the subsequent dissolution of the interiors to form hollow architectures are performed via Ostwald ripening. Moreover, ZnSnO3 spheres with hollow interiors and permeable surfaces are exploited as gas sensors, exhibiting improved sensing performances to ethanol. The response-recovery times of sensor based on these ZnSnO3 hollow microspheres are 0.9 and 2.2s when the sensor is exposed in ethanol at the optimal operating temperature of 270°C. The significant decrease in response-recovery times are attributed not only to the surface accessibility obtained by the hierarchical hollow architectures, but also to these rodlike building blocks with ultra-thin diameters. [ABSTRACT FROM AUTHOR]

Abstract: A microstructure sensor based on hierarchically porous ZnO nanosheet (NS) thin films has been achieved by using a facile two-step solution phase method. The transparent ZnO seed-layer covered on both the conducting electrodes and the insulating SiO2 spacer regions acts as lattice-matched template, on which the assembly of ZnO NS thin films has been subsequently completed via a facile solvothermal process. The phase purity, morphology, and structure of the as-prepared NSs are investigated, and the results reveal that ZnO NSs, grown vertically on the substrate, exhibit hierarchically porous nanostructure with subunits of nanoparticles. The gas-sensing properties exhibit not only high response to CO with the response time of 25s, but also low cross response to common interference gases at the operating temperature of 300°C. [Copyright &y& Elsevier]

Abstract: We report the synthesis of flowerlike ZnO nanostructure using a facile hydrothermal process, and the investigation on the ammonia (NH3)-sensing properties of the pure and palladium (Pd)-sensitized flowerlike ZnO nanostructure. The phase purity, morphology, and structure of the pure and Pd-sensitized ZnO nanostructure are investigated. The characterized results reveal that the flowerlike ZnO has a wurtzite structure and is composed of numerous aggregated single-crystalline ZnO nanorods with a diameter of about 60nm. Having fabricated gas sensors based on the pure and Pd-sensitized flowerlike ZnO, we find that the Pd-sensitized sensor exhibits a response of 45.7–50ppm NH3 at 210°C, which is about 8 times higher than that of pure ZnO at the optimal operating temperature of 350°C. The enhanced NH3-sensing performance demonstrates that the significant decrease in optimal operating temperature and the distinct increase in response are attributed to the sensitization effect of Pd. [Copyright &y& Elsevier]