Flower-like NiO hierarchical microspheres self-assembled with nanosheets: Surfactant-free solvothermal synthesis and their gas sensing properties

Flower-like NiO hierarchical microspheres self-assembled with thin nanosheets were successfully synthesized by surfactant-free solvothermal method. The obtained product was characterized by means of X-ray diffraction, scanning electron microscopy, and ultraviolet–visible spectroscopy. The results showed that flower-like NiO hierarchical microspheres with a cubic structure were assembled by a number of thin nanosheets with a thickness of about 10 nm. Reaction time was an important parameter for the synthesis of perfect flower-like microspheres. The band gap energy of NiO hierarchical microspheres was estimated to be 3.68 eV. The gas sensing properties showed that the sensor exhibited the highest sensitivity of 3.2 for 100 ppm ethanol at an operating temperature of 250 °C. The reversible response to ethanol at various operating temperatures and gas concentrations and good selectivity were obtained, implying a potential application for the fabrication of high performance ethanol sensors.