Fabrication of ZnO nanorod-assembled multishelled hollow spheres and enhanced performance in gas sensor

In this work, ZnO multishelled hollow spheres with an average diameter of 5 mu m were prepared by a facile solvothermal process in a ternary solvent system including water, ethanol and ethylene, and assynthesized products were constructed by highly directional interactions of anisotropic single-crystalline ZnO nanorods. A two-step assembly process followed symmetric Ostwald ripening process is proposed to explain the formation mechanism of obtained products, which highlights the driving force of the solvents in promoting the nanorod aggregation and the solid evacuation of final products. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy were used to characterize the structure of synthesized products. The investigation of the gas-sensing properties indicated that control of the shape-defined building units and their assembled structure provides ZnO with high performance in gas sensing, and the double-wall hollow structures exhibit the highest sensitivity to formaldehyde gas than the nanorods and hollow spheres, which is contributed to their high donor-related and the low acceptor-related intrinsic defects in ZnO crystals.