Synthesis and Gas-Sensing Properties of ZnO Porous Microflowers

Abstract

Three-dimensional (3D) porous nanomaterials with large surface area and abundant surface defects have promis- ing potential in gas sensing due to the following merits: (i) large contact area of gaseous species with the materials, and more adsorption sites on the highly defective surface, (ii) good accessibility to gaseous species of the 3D open structure, (iii) fast electron transport among the 3D network. Rational design and controlled synthesis of the 3D porous nanomaterials with spe- cific morphology and microstructure are essential for improving the performance of gas sensing. In this work, 3D ZnO po- rous microflowers were prepared by directly calcining the zinc-based flowerlike precursor at 400 ℃ in air. The precursor was preformed through a simple coprecipitation method, i.e., by refluxing the aqueous solution of zinc nitrate and co-precipitators of hexamethylenetetramine and oxalic acid at 90 ℃ for 4 h. The unique ZnO porous microflowers were composed of porous nanosheets of 10~50 nanometers in thickness and 1~2 micrometers in width, which inherited from the zinc-based precursor except for the randomly distributed pores on the nanosheet "petals". The 3D porous microstructures endowed ZnO with large specific surface area of 31.3 m 2 •g -1 and abundant surface defects. ZnO porous microflowers were used as active materials to fabricate gas sensors, which exhibited low working temperature, high sensitivity and fast response (recovery) characteristic against ethanol vapor, at the advanced level in comparison with the reported ZnO-based gas sensors for ethanol. The superior performance of the gas sensors could be attributed to the unique microstructures of the ZnO porous nanomaterials. In addition, the sensitivity of the gas sensors showed an exponential relationship with the concentration of ethanol vapor, indicating their capability of quantitative detection within the ethanol volume ratio of 1×10 -6 ~500×10 -6 .